Downing, Leon

Leon Downing is a speaker at WEFTEC 2026.

Titles from this speaker

Description: Actionable Prediction of Final Clarifier Performance Using The Data You Already...

Actionable Prediction of Final Clarifier Performance Using The Data You Already Collect

Abstract

[b]BACKGROUND[/b] In order to achieve more stable and proactive operation, many WRRFs are leveraging new sensors and modelling software to increase their predictive capacity. While our near-term predictive capacity for certain metrics, such as ammonia or DO, have matured significantly, secondary clarifier (SC) performance remains challenging to predict using conventional process models. While some common models [1] [2] can capture baseline behavior, they are not sensitive to daily variations in sludge settleability and hydraulics. Research has shown that the flocculent settling coefficient (r-floc) can be used to improve model accuracy, but calibrating the r-floc traditionally required specialized testing such as the threshold of flocculation (TOF) test [3] [4]. Recently, the authors reported that calibrating r-floc against historical effluent data can enhance model accuracy, but this may require additional sampling or measurement [5]. Since traditional approaches require specialized settling tests or complex sampling and calibration processes that may not be feasible for many utilities, this study proposes a practical and scalable method of estimating settling behavior using only routine operational data for daily automatic calibration. This unlocks real-time ESS prediction, offering operators a practical soft sensor for clarifier performance. [b]METHODOLOGY[/b] A daily autocalibration framework was developed around a 1-D clarifier model built using SUMO (Dynamita SARL) using the triple exponential extension to the double exponential (DE) model [7]. Flow, mixed liquor suspended solids (MLSS), sludge volume index (SVI), clarifier underflow, and clarifier configuration were the routine inputs to the model. A python orchestrator performed automatic r-floc calibration, keeping ESS within 10% of actual values while optimizing r-floc. Applied across six facilities, this method captured variations in sludge characteristics, hydraulics, and upstream biology. When settling data was unavailable, a modified Daigger [8] correlation was used to relate SVI data to estimate Vesilind parameters of hindered settling (r-hin) and maximum settling velocity (Vo); otherwise site-specifc Vo and r-hin estimates were used. The approach is demonstrated for a 9.8 MGD Facility (Facility A) which recorded high quality operational data and strict effluent total phosphorus limits. The calibrated r-floc parameter from the 1-D clarifier was an input to a calibrated whole plant model to evaluate ESS prediction based on the biokinetic model for Facility A. To address facilities with infrequent ESS sampling, a machine learning (ML) model using extreme gradient boosting (XGBoost) predicted r-floc from input features. Heavy-tailed features were log transformed, while others remained on natural scale. The chronological input dataset was then split (80% training/20% test) to prevent look-ahead bias. Hyperparameters were tuned via Bayesian methods and performance was evaluated on test set. [b]RESULTS[/b] The daily automated calibration generated varying r-floc estimates based on clarifier performance. The Facility A whole plant model predicted ESS within ±15% of actual, per Figure 1. Comparing r-floc values to observations and model outputs validated the method and unlocked rfloc's soft-sensing capabilities, per Figure 2. Poor settling periods, marked by extreme SVI, elevated selector zone readily biodegradable chemical oxygen demand (rbCOD) or operational disturbances like toxicity lowered r-floc, while site upgrades like upgraded sludge withdrawal system increased the r-floc. The ML model, trained on input features like calibrated r-floc estimates, SVI, RAS ratio, surface overflow rate (SOR), surface loading rate (SLR), along with model outputs like selector zone rbCOD, stored poly hydroxy alkanoates (PHA) and sludge iron content showed comparative performance and feature relevance is summarized in Table 1. [b]DISCUSSION[/b] The r-floc soft sensor showed slight shifts between test and control groups in full-scale pilots at Facility B (low DO) and C (hydrocyclones). Clarifier upgrades, including sludge withdrawal mechanisms and floor baffles at Facility A, resulted in improved r-floc. Also, an industrial discharge to Facility D led to deflocculation, and poor flocculation in a three sludge BNR process at Facility E lowered the r-floc. Figure 3 demonstrates the r-floc soft sensor's sensitivity to these impacts, both biological and hydraulic, across diverse plants. Thus, producing an ML-corrected r-floc metric can both improve mechanistic model accuracy, and serve as a novel performance indicator. This may be especially valuable for plants with low-resolution effluent data collection. [b]CONCLUSION[/b] This paper demonstrates how clarifier models can be automatically calibrated using only water quality data already being collected at a WRRF, in order to achieve accurate real-time predictions of effluent solids and improve operations. Daily, ML-enabled calibrations of the model's flocculant settling coefficient (r-floc) provided early diagnostic insights and opportunities for proactive operational adjustments, all without additional lab work or instrumentation. The r-floc was sensitive to a broad range of biological and hydraulic drivers, making it a robust and predictive parameter. Overall, this framework offers a practical tool for better clarifier reliability, predictability, and plant-wide resilience.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionOptimizing Secondary Clarifier Performance using SPA, data driven modeling and intensification approaches

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Gaidhani, Chinmay, Dunlap, Patrick, Avila, Isaac, Ali, Priyanka, Leung, Kaming, Downing, Leon

Author(s)C. Gaidhani1, P. Dunlap2, I. Avila2, P. Ali3, K. Leung2, L. Downing2

Author affiliation(s)Georgia Tech, 1Black & Veatch, 2Black & Veatch, 2Rice University, 3Black & Veatch, 2Black & Veatch, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160336

Volume / Issue

Content sourceWEFTEC

Word count13

Comparing Four Innovative Technologies for Enhanced Leachate Treatment: An Evaluation of PFAS Foam Fractionation Efficacy

Abstract

Introduction: PFAS, a group of chemicals widely used in various applications due to their water and oil resistance, are persistent, toxic, and accumulate in the environment. Disposal of products containing PFAS in landfills can result in PFAS contamination in the landfill leachate that is discharged to water resource recovery facilities (WRRFs) andwhich can lead to groundwater contamination (REF1). Foam fractionation (FF) is a process that utilizes the surfactant nature of PFASs to separate them into foam, which is collected as a concentrate for further treatment (REF2). FF significantly reduces the volume of PFAS-containing waste, making it an ideal first step in a PFAS treatment process. This study evaluates four different FF technologies and provides insights for their implementation based on bench scale comparison results. Materials and methods: In this study, four technologies were evaluated for PFAS removal. The technologies and their providers are listed as TechA, TechB, TechC, and TechD in Table 1. Equalized volume samples (55 liters) were collected from an anonymous facility's EQ-tank and distributed to different technology providers for testing. Leachate wet chemistry parameters samples were determined in accordance with APHA standard methods. Table 2 lists the analyzed parameters. A total of 40 PFAS compounds were quantified using the EPA 1633 method, the Total Oxidizable Precursor, and the Total Organic Fluorine assay. Table 3 provides a complete list of these compounds and their concentrations before FF. Results and discussion PFAS Removal Efficiency: The study evaluated the removal efficiency of different PFAS into the foam phase for the four FF technology providers. The findings, depicted in Figure 1, align with previous literature: longer fluorocarbon chains and the presence of a more surface-active sulfonic acid head group result in greater PFAS removal compared to its carboxylic counterpart. The study also shows that removal efficiency improves exponentially with longer fluorocarbon chains, and chains longer than six carbons resulted in undetected levels. This supports previous research that suggests chain length has a greater impact than head group. Longer fluorocarbon chains make PFAS less soluble and more hydrophobic, enhancing its ability to adsorb onto air-water interfaces due to their superior surface properties. Impact of Process Configuration: Technology providers employed different strategies in using FF as indicated in Table 1. A notable finding from comparing these technologies is the effectiveness of cationic co-surfactants in removing PFAS. The cationic headgroup of these co-surfactants allows for binding to PFAS at the water-air interface. TechA and TechB tested a wide range of co-surfactants at 100 mg/L and found that CTAB-based surfactants are favorable in reducing the short-chain compounds up to 50% removal. The consistent observation of the use of co-surfactants showed enhanced stability and density of the foam that helps accumulate more foam and minimize the extent of interstitial liquid drainage before the foam is harvested (REF4). However, TechC experiments showed no impact of using 8 mg/L co-surfactant compared to the absence of co-surfactant. This can be attributed to reduction of additive performance due to electrostatic uptake by competing contaminants in leachate, suggesting the need for a higher dose. For TechC it was found that a 45-minute contact time is sufficient to achieve non-detection levels of long-chain PFAS in a leachate primarily dominated by PFCAs. The study also assessed the impact of the number of FF units in series, with the consensus being that using two to three treatment units is adequate to achieve the desired removal. TechD's proprietary model approach showed that increasing the treatment stages from 3 to 5 resulted in a 10% increase in the removal of short-chain PFAS, while long-chains remained non-detectable in both cases. TechC's unique two-stage method involves de-foaming the leachate from the first fractionation unit and then re-foaming the primary foamate generated over repeated primary fractionation cycles (Figure 2). This approach significantly reduces generated foam volumes, condensing the volume of foam by up to 180 times in the secondary foamate, minimizing the capital and operating costs associated with downstream destruction technologies. Conclusions 1.Findings of this work are illustrated in Figure 3. 2.Long-chain PFAS have been effectively removed to below detection limit, while short-chain PFAS require a polishing step using adsorptive media due to their low removal rate. However, this poses challenges due to the high fouling potential of the media. Therefore, the implementation of FF and modifications to its configuration strongly depend on treatment objectives and upcoming regulations. 3.For the specific leachate that was tested, a 45-minute contact time of and up to three treatment stages in series were sufficient for removing long-chain PFAS. However, these factors may vary based on the quality of the leachate water being treated. 4.FF is a highly selective method for removing surfactants without altering effluent water quality. This results in an effluent with similar water quality to the influent but significantly reduced concentrations of PFAS, VOCs, total suspended solids, and iron.

This article discusses how foam fractionation (FF) technology can effectively remove Per- and Polyfluorinated Substances (PFAS) from landfill leachate. The study found that FF is a highly selective method for removing surfactants without altering effluent water quality. These findings are crucial in addressing PFAS contamination in landfills and guiding the implementation of different FF configurations for PFAS removal.

SpeakerSabba, Fabrizio

Presentation time

13:30:00

13:50:00

Session time

13:30:00

15:00:00

SessionPFAS Removal and Destruction Using Novel Technologies

Session number605

Session locationRoom 244

TopicIndustrial Issues and Treatment Technologies, Intermediate Level, PFAS, Research and Innovation

Author(s)

Sabba, Fabrizio, Kassar, Christian, Hunter, Gary, Downing, Leon

Author(s)F. Sabba1, C. Kassar2, G.L. Hunter3, L.S. Downing4

Author affiliation(s)1Black & Veatch, NJ, 2Black & Veatch, AZ, 3Black & Veatch, SC, 4Black and Veatch, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159515

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Decoupling Carbon and Phosphorus Release During Primary Sludge Fermentation in...

Decoupling Carbon and Phosphorus Release During Primary Sludge Fermentation in Chem-P Plants

Abstract

Introduction: Many wastewater treatment plants use chemical phosphorus removal (CPR) to meet discharge limits[sup]1[/sup]. CPR commonly uses iron (Fe) to remove phosphorus (P), and though it is reliable, the chemical can be costly[sup]2[/sup]. Plants with high enough volatile fatty acid (VFA) concentrations can often use biological P removal (BPR), and additional carbon can be supplied from primary sludge (PS) fermentation. There is also opportunity to use PS fermentate to support nitrogen (N) removal in plants which are generally dependent on external carbon addition[sup]3[/sup]. During fermentation, nutrients are released in addition to VFAs and COD. N concentrations can be managed through PdNA or reoxidation after denitrification. P is also released through hydrolysis, but with CPR there is an additional release of Fe-bound P due to anaerobic Fe reduction. This can be a significant issue for plants with low P limits, such as Blue Plains. The objective of this study was to evaluate conditions for decoupling COD and P release by managing Fe reduction of Fe-P precipitation within the fermenter. Studies show that vivianite, an Fe-P mineral, may precipitate at a pH above 6[sup]4[/sup]. Therefore, it was hypothesized that pH adjustment may be able to support CPR optimization. Methods: Two 60-L fermentation pilot reactors were fed with Blue Plains PS at 5 g/L and controlled to a SRT target of 1-d. The system was operated under several scenarios including a control: mechanical treatment, low and high microaeration, and lime slurry addition (100 or 200 mg/L CaCO₃). Fe overdosing in full-scale occurred during testing but was not controlled as a scenario. Measurements were performed on influent and decant to calculate yields. A full-scale gravity thickener (GT) at Blue Plains was converted to fermenter conditions by allowing an SRT between 0.2-2 days and was operated under full-scale conditions for sludge composition and solids loading. Influent and effluent sludges were analyzed, and data was categorized by TSS: low (<3.5 g/L), medium (3.5–5 g/L), and high (>5 g/L). Yields were calculated assuming 100% elutriation in the fermenter by measuring concentration profiles. Results and Discussion: Full-scale fermenter data from 2024 and 2025 show an estimated yield of 0.0332 mg P/mg sCOD, while literature data from BPR plants show lower P yields per mg of sCOD, from 0.0046 to 0.0022 (Fig 1). It was hypothesized that all additional release at Blue Plains was a result of Fe dosing and thus could be decoupled from sCOD release. Separating the data into low (<6) and high (>6) pH scenarios show that a high pH leads to ~20% less P yield per mg sCOD, at 0.0238 mg P released per mg sCOD, compared to 0.0298 mg P/mg sCOD at a low pH (Fig 1). Several options were explored to raise fermentate pH above 6, into a range suitable for vivianite precipitation, including alkalinity dosing, Fe overdosing, and PS dilution. In pilot control scenarios, fermentation reduced sludge pH from 6.28±0.12 to 5.51±0.26, which is below the range for vivianite formation. The average control OP-P was 13.50±2.82 mg/L. Less P was found at a pH greater than 5.83, and when iron was available for removal (Fig 2). High fermentate pH was a result of either a high lime dose (200 mg/L CaCO₃), or overdosing of FeCl3 in primary treatment, which led to high levels of Fe(OH)3 in the PS. The low alkalinity scenario (100 mg/L CaCO₃) had a pH of 5.71 with 12.62 mg/L OP-P in the fermentate, while the high alkalinity scenario (200 mg/L CaCO₃) had a pH of 6.36 and 2.72 mg/L OP-P. Overall, the high lime dose effectively removed P, while the lower dose may not have achieved a high enough pH. Periods of higher background Fe also saw effective P removal, with pH values of 6.06 and 6.01, and OP-P at 4.76 ± 3.7 and 2.65 ± 2.4 mg/L. Within the GT, PS elutriation resulted in a lower incoming TSS, and lower blanket sCOD, pH, and OP-P. At a pH greater than 5.75, the average OP-P was below 17.5 mg/L, while operating at a lower pH led to an average OP-P of 47.6 mg/L. Fe concentrations followed a similar trend to OP-P, showing that the chemical Fe-P dynamics were modified with the change in pH (Fig 3). An estimate of 0.0046 mg P/mg sCOD (Fig 1) was used to calculate P released solely from hydrolysis within the GT operating at an SRT of 0.8 to 1.5 days. Additional P release, assumed to be a result of Fe reduction, was significantly different between scenarios with a pH below and above 6 (T-test, p = 0.1126) (Fig 4). This indicates that raising the pH above 6 is a viable solution for reducing excess P release. With elutriation, the GT achieved a fermentate OP-P release of less than 17.5 mg/L, and projected mainstream P was less than 0.4 mg/L. The lower P release at higher pH showed decoupling of OP-P and sCOD, however the projected mainstream P was not yet low enough to meet plant discharge limits of 0.18 mg P/L. This demonstrates that dilution is a solution to achieve target pH conditions without losing sCOD, however additional research is needed to understand changes in buffer capacity over different seasons and sludge characteristics. Conclusions: Results of full-scale GT and fermentation pilot studies demonstrate that pH management is a viable strategy for decoupling COD and P release at CPR plants. Higher pH can be achieved through alkalinity addition, Fe overdose, or PS dilution. These strategies maintain good sCOD yields while decreasing mainstream P.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

15:30:00

15:45:00

Session time

15:30:00

17:00:00

SessionAdvancing Phosphorus Removal: What We Still Have to Learn

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Hanson, Kathryn, Davis, Sophia, Avila, Isaac, Islam, Shafkat, Massoudieh, Arash, Downing, Leon, Ladipo-Obasa, Mojolaoluwa, Miranda, Miguel, Passarelli, Nicholas, Ngo, Khoa Nam, De Clippeleir, Haydee

Author(s)K. Hanson1, S. Davis1, I. Avila2, S. Islam3, A. Massoudieh4, L. Downing2, M. Ladipo-Obasa1, M. Miranda1, N. Passarelli1, K. Ngo1, H. De Clippeleir1

Author affiliation(s)DC Water, 1DC Water, GW, 1Black & Veatch, 2George Washington University, 3Catholic University of America, 4Black & Veatch, 2DC Water & Sewer Authority, 1DC Water & Sewer Authority, 1DC Water & Sewer Authority, 1DC Water, 1DC Water & Sewer Authority, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160309

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Diversifying Carbon for Phosphorus Removal: Understanding RAS Fermentation and...

Diversifying Carbon for Phosphorus Removal: Understanding RAS Fermentation and S2EBPR

Abstract

Management of the global phosphorus cycle is crucial for long-term sustainability. Water resource recovery facilities (WRRFs) play a critical role in in the phosphorus control and balance in many watersheds throughout North America, and the discharge of soluble and other bioavailable forms of phosphorus from WRRFs has a global impact on soluble-nutrient balances in the water cycle.
Enhanced biological phosphorus removal (EBPR) is one key process applied to remove phosphorus from the liquid discharges at WRRFs. Through EBPR, phosphorus is concentrated from the wastewater into the biosolids stream, where it can be recovered in biosolids or extracted as a fertilizer product. Recycling phosphorus in this way helps close the phosphorus cycle without discharging phosphorus into waterbodies. Over the past 50 years, EBPR has evolved from an unexplained phenomenon to a widely adopted process that is simultaneously praised for its efficiency and environmental soundness and, cursed for its instability. Understanding of the process has never been complete, but recent advances in the research and interests in alternative processes at the facility mean the time has come to enhance water-sector understanding with the latest knowledge of EBPR ecology, functionality, and design. One of the key innovations for phosphorus removal has been the adoption of sidestream EBPR (S2EBPR) concepts into the design of EBPR facilities. These concepts focus on fermentative activity of phosphate accumulation organisms (PAOs) to drive EBPR, often in sidestream reactors. These sidestream reactors focus on hydrolysis of a portion of return activated sludge (RAS) or mixed liquor (ML) to select for PAOs and drive phosphorus removal. Conventional design EBPR focused on providing volatile fatty acids (VFAs) to PAOs in an influent anaerobic zone. As an alternative, RAS fermentation diverts a portion of RAS flow to a longer hydraulic retention time (HRT) sidestream reactor. In this sidestream reactor, biomass and particulate COD is fermented to generate the VFA required for PAO metabolism. In a strict RAS fermentation reactor, this results is selection of PAO metabolism without direct use of influent readily biodegradable COD (rbCOD) or VFA. In a carbon focused wastewater paradigm, this provides increased flexibility for COD diversion and capture; use of influent rbCOD for nitrogen removal; and potentially more stable phosphorus removal due to a lack of sensitivity to influent COD characteristics.
This presentation will present the most recent results from Water Research Foundation project 4975, which is focused on developing practical guidelines for fermentative phosphorus removal processes. An overview of the project and concepts will be presented, with a focus on carbon balance and carbon sources for EBPR. Three case studies will then be presented, each with a different focus: â€¢RAS fermentation and the importance of effluent nitrate (Figure 1) â€¢RAS fermentation with carbon addition and the approach to developing an EBPR carbon balance (Figure 2) â€¢Mixed liquor fermentation and impacts of low DO operation (Figure 3) Attendees will be exposed to operational experience, as well as take home messages about designing for fermentation processes in EBPR systems. Example design curves for a facility will be presented (Figure 4) with an explanation of the design approach for RAS fermentation.

Attendees will be exposed to operational experience, as well as take home messages about designing for fermentation processes in EBPR systems. Example design curves for a facility will be presented with an explanation of the design approach for RAS fermentation. More details related to RAS fermentation will be available in WRF Report 4975, set to be published in January 2023.

SpeakerDowning, Leon

Presentation time

08:35:00

08:50:00

Session time

08:30:00

10:00:00

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Downing, Leon

Author(s)Leon Downing1; Patrick Dunlap2; Eric Redmond3; James Barnard4

Author affiliation(s)Black & Veatch1; Black & Veatch2; Black & Veatch3; Black & Veatch4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158499

Volume / Issue

Content sourceWEFTEC

Word count11

Effluent Excellence: Unleashing Hybrid Model Magic at Fond du Lac

Abstract

Background and Objective:
Wastewater treatment facilities must meet stringent effluent water quality targets while managing higher flows from extreme weather conditions. They rely on activated sludge models (ASM) for design capacity evaluation (Henze et al., 2000). For smaller utilities, maintaining these models is challenging due to frequent updates, recalibration based on influent flow characteristics, input data quality issues, and manual scenario simulations. Recently, hybrid process models combining predictive machine learning (ML) for influent forecasting, automated data handling for ASM, and auto-calibrated simulations have been proposed to increase modeling tool adoption (Mannina et al., 2019; Zhao et al., 2020). Automatic data storage and processing remain challenging due to variability in lab methods, analyzer drift, non-standard naming conventions, poor data organization, and cybersecurity concerns (Demir & Szczepanek, 2017 and Newhart et al., 2019). This study explores hybrid modeling at the Fond du Lac Wastewater Treatment & Resource Recovery Facility (WTRRF) in Wisconsin. Key facts about the WTRRF (Figure 1):
- Rated for 12 mgd (~44,000 m3/day), serving a population equivalent of 60,000 people.
- Utilizes EBPR processes combined with Chem P removal for phosphorus trimming. Managed extreme flow conditions in 2024, while maintaining low effluent TSS and nutrient limits.
- By 2027, a 6-month mass load allocation equating to an average total phosphorus (Total P) concentration of 0.19 mg/L-P is anticipated. It is aimed to meet this goal while minimizing operational and maintenance costs for chemical phosphorus removal and future capital costs. Fond du Lac WTRRF collaborated with Black & Veatch and Maia Water to design and deploy a hybrid model optimizing operational decision-making around flow and load management.

Approach:
The cloud-based hybrid modeling approach for WTRRF included an ML model for primary effluent flow and load forecasting, followed by an ASM to estimate effluent quality and performance using the application package interface (API) for SUMO22 (Dynamita, France) (Figure 2). Process data was imported, supplemented with live weather data to generate a historical dataset for the ML algorithm. The dataset was used to auto-calibrate a 1-D secondary clarifier SUMO model (Figure 3) to match observed secondary effluent TSS. Next, future influent flows and concentrations were forecasted using XGBoost and input into a larger plant model (Figure 4) with calibrated parameters. The SUMO model simulations provided performance forecasting and soft sensor capabilities. The workflow's modularity enabled new optimization routines, updates, and adoption lab results at varying frequencies. It culminated in a hybrid modeling dashboard as a data-backed advisor to Fond du Lac, offering visualizations, optimization routines, sensitivity analyses, and model training options.

Findings & Significance:
Influent Forecasting: For a 7-day trend of 15-minute interval influent flow, a mean absolute percentage error (MAPE) of 26.9% was observed between forecasted and actual flows (Figure 5). A rain event far exceeded forecasts (Figure 6), impacting flow forecasting accuracy. The MAPE between forecasted annual flow relative to actual was 16.2% (Figure 7). A reasonable match was observed between influent total COD and total P forecasts. The MAPE for COD was 9.4% (Figure 8) and for TP was 7.5% (Figure 9). These forecasts indicate that operations at Fond du Lac WTRRF can be augmented with forecasts for improved decision-making. The current ML forecasting model will be optimized as more data becomes available.

Hybrid model: The forecasted secondary effluent TSS from SUMO matched well with observed data, with an MAPE of 12.58% and absolute differences within ±0.8 mg/L (Figure 10). Sensitivity analysis can demonstrate differences in forecasted effluent TSS quality with clarifiers in/out of service for maintenance planning. Forecasted effluent TSS supports improved decision-making around clarifier operations.

The hybrid model indicated better P removal from EBPR and Chem P versus observations (Figure 11). The difference underscores challenges in predictively modelling EBPR and Chem P at low OP concentrations due to relevant parameters' complexity. While the absolute error between observed and forecasted effluent OP was 0.05 mg/L-P, less than industry standard stop criteria of Â±0.5mg/L-P (IWA, 2013), a more accurate match is required. An effluent OP error correction model using XGBoost and several features from influent, operational, temporal, and model-derived data improved effluent OP forecasting. Model-derived features indicate P loading to carbon uptake ratio by polyphosphate accumulating organisms over relevant time scales. The error correction allowed for a simpler regression model factoring system loading history. Figure 12 shows testing data from this model that will be integrated with outlier detection in final deployment.

This approach unlocked soft-sensor capabilities from model results: model estimates for rbCOD in selector effluent were compared to observed settleability revealing potential correlations. Spikes in rbCOD from selector effluent led to a rise in SVI-30 (Figure 13). Further analyses are planned to reveal more correlations using soft-sensor values, opening opportunities to leverage state variables for making informed process decisions.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

16:00:00

16:15:00

Session time

15:30:00

17:00:00

SessionData in Action! Data-Driven Optimization Models

Session locationMcCormick Place, Chicago, Illinois, USA

TopicProcess Control and Modeling

Author(s)

Gaidhani, Chinmay, Coffey, Carolyn, Emaminejad, Aryan, Dunlap, Patrick, Avila, Isaac, Lesnik, Keaton, Schoepke, Cody, Downing, Leon

Author(s)C. Gaidhani1, C. Coffey1, A. Emaminejad1, P. Dunlap1, I. Avila1, K. Lesnik2, C. Schoepke3, L. Downing1

Author affiliation(s)Black & Veatch1, Maia Analytica2, Fond du Lac Wastewater Treatment and Resource Recovery Facility (WTRRF)3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159983

Volume / Issue

Content sourceWEFTEC

Word count11

Emissions, Energy, and Performance: Low Energy BNR at Full Scale

Abstract

BACKGROUND:
NEW Water will upgrade their aeration basins at their Green Bay Facility over the next decade. In preparation, NEW Water is collaborating with Black and Veatch and EnviroMix to pilot a transition from an anaerobic-oxic (AO) process to an anaerobic-anoxic-oxic (A2O) process at low dissolved oxygen (DO). This includes the addition of EnviroMix's mixing technology and aeration control strategy. The setup includes two full-scale parallel aeration basins, designated as test and control, each with its own secondary clarifier and effluent for independent evaluation (Figure 1).

OBJECTIVES:
While many facilities have demonstrated the ability to achieve nutrient removal at low DO setpoints (Water Research Foundation Project 5083 on this topic is ongoing), a side-by-side demonstration to explore not only energy and nutrients, but to understand the impacts of low DO and control strategies on nitrous oxide (N2) emissions and process stability has not previously been completed. This demonstration focuses on three objectives:
- Validate low DO energy savings and nutrient removal
- Understand control requirements and flexibility improvements
- Assess N2 production from low DO systems
APPROACH:
Over seven months, the test basin DO was systematically reduced from an initial 3 mg/L to 0.3 mg/L, followed by four months of FlexZone operation. The control basin operated at a constant DO setpoint of 3 mg/L throughout the demonstration. Table 1 details the progression of DO setpoints in the test basin's first three zones (SZ1, SZ2, SZ3). The fixed AE at the end of the basin operated at a DO between 1.5-3.0 mg/L DO during all test phases. FlexZone operation utilizes a novel aeration and mixing control strategy developed by EnviroMix to transition environments based on changing influent loading. Individual subzones can operate as aerated, unaerated/mixed, or with dynamic DO setpoints. This results in variable DO ranging from 0.2 to 0.8 mg/L.
RESULTS:
Energy savings and effluent performance: Throughout the demonstration, the difference between airflow required per load in the test basin compared to the control basin has increased. During low DO (<0.5 mg/L) and FlexZone operation, a 22-30% reduction in airflow was observed (Figure 2). Figure 3a shows higher phosphate concentrations in the test basin anaerobic zone compared to the control during low DO and FlexZone operation, suggesting more active EBPR, characterized by phosphate release during sCOD uptake. Additionally, effluent phosphorus was more stable in the test basin than the control basin (Figure 3b). A reduction of effluent nitrate in the test basin was observed as DO setpoint decreased (Figure 4). This decrease is attributed to the IMLR and to SND in the low DO zones. Figure 5 shows the calculated mass of denitrification occurring in the anaerobic and anoxic zones compared to the mass due to SND in the low DO zones. NOx removal was calculated using grab samples from each zone. Figure 5 shows an increasing trend of SND within the low DO operation period. The mass of NOx removed by SND is correlated with increasing primary effluent COD load (r2 = 0.72) and specifically, increasing sCOD load (Figure 6). To investigate the fate of dynamic COD fractionation, SND operation, and IMLR ratio, various simulations are in progress (using the newest Sumo version, v24).

Growth pressures: The impact of DO swings on biological growth pressures were assessed. Figure 7 shows preliminary modeling work assessing the impact of DO control on OHO and PAO growth, where instantaneous growth rate swings in a wider range with DO variability. This may be an indication of biological instability. This emphasizes the importance of having a well-tested and well-design low DO controls strategy with DO setpoint ranges in each zone, sensitive and flexible aeration valve control, and proper placement of sensors. The low DO operation has been going through constant testing and optimization in the past four months and improvements have been observed in process stability and effluent quality.

N2 production from low DO systems: N2 assessments in the test basin (two sensors: one in SZ1, one in SZ2) highlighted that emissions initially increased when DO levels were lowered to 0.5 mg/L but subsequently stabilized and returned to levels similar to high DO operation after the system adapted to the new conditions (Figure 8). This indicates that reduced N2 emissions at low DO can be achieved with stabilization over time. A probe failure in August temporarily halted data collection, with monitoring to resume in winter 2025 to assess the impact of low temperatures. Liquid temperature ranged from 16-26°C and SRT from 7-32d.To understand the key factors impacting N2, multiple correlations were performed (data not shown). It was evident that aeration intensity plays a major role in N2 off-gassing, highlighting the importance of stable aeration control in reducing N2 emissions (Figure 9).
CONCLUSIONS:
This study is among the few to use full-scale, side-by-side testing to evaluate low DO impacts and control strategies. Key findings include energy and nutrient removal improvements from low DO operation, such as enhanced EBPR, nitrogen removal, SND, and aeration savings. The study also underscores the necessity of maintaining stable growth conditions in DO control to achieve nutrient removal objectives and mitigation.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

08:30:00

08:40:00

Session time

08:30:00

10:00:00

SessionMicrobial Selection and Performance Under Low DO Conditions

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Gutenberger, Gretchen, Downing, Leon, Sadreddini, Sara, Biese, Tyler, Watson, Joe, Elger, Sarah, Koch, John, Jordan, Taylor

Author(s)G. Gutenberger1, L. Downing1, S. Sadreddini1, T. Biese3, J. Watson3, S. Elger5, J. Koch5, T. Jordan5

Author affiliation(s)Black & Veatch1, , New Water, Green Bay Metro Sewerage District3, City of Medford, OR4, EnviroMix5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159986

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Exploring the Carbon Balance in a Sidestream Enhanced Biological Phosphorus Removal...

Exploring the Carbon Balance in a Sidestream Enhanced Biological Phosphorus Removal (S2EBPR) Demonstration Facility

Abstract

Introduction
Conventional design of enhanced biological phosphorus removal (EBPR) focuses on providing volatile fatty acids (VFAs) to phosphate accumulating organisms (PAOs) in an influent anaerobic zone. As an alternative, sidestream EBPR (S2EBPR) diverts a portion of RAS flow to a longer hydraulic retention time (HRT) sidestream reactor. In this sidestream reactor, biomass and particulate COD is fermented to generate the VFA required for PAO metabolism. In a strict RAS fermentation reactor, this results in selection of PAO metabolism without direct use of influent readily biodegradable COD (rbCOD) or VFA. In a carbon focused wastewater paradigm, this provides increased flexibility for COD diversion and capture; use of influent rbCOD for nitrogen removal; and potentially more stable phosphorus removal due to a lack of sensitivity to influent COD characteristics. In addition, moving the PAO selection to the sidestream provides increased infrastructure flexibility for incorporation of EBPR into existing facilities. The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) began pilot testing of RAS fermentation in April 2021. The facility moved through a series of operational setpoints (Figure 1) to optimize phosphorus removal. One of the keys was the addition of a cranberry waste to provide additional carbon for RAS fermentation. By the end of the testing period, effluent total phosphorus was averaging less than 0.4 mg/L with no chemical addition (Figure 2).
Carbon Balance Exploration
To better understand why the S2EBRP configuration was working at the WRWWTP, a series of bench-scale tests were completed to explore the carbon balance for the facility. Batch RAS fermentation rate tests were completed as previously described (WRF Project UR13). The fermentation rate tests provided an indication of the amount of soluble biodegradable COD (sbCOD) produced per mass of volatile solids in the fermenter. On average, a fermentation rate of 1.5 mg sbCOD/g vss-hr was observed over the testing period (Figure 3). This is a critical piece of information, as it provides insight into how much carbon can be released from RAS fermentation. Phosphorus release and uptake rate testing (Figure 4) provided insight into the use of carbon by PAOs in the system. As EBPR was established, the sbCOD:P ratio was reduced to 13:1 (Figure 5).
This information provides insight into the ratio of carbon required by PAOs in the S2EBPR reactor. The last set of batch experiments explored the phosphorus release rate of the ecology with various external carbon sources. The full-scale system was fed a cranberry juice wastewater, with was dominated by sugars. During bench scale testing, the cranberry juice exhibited the highest release rate of the three carbon sources tested (Figure 6). This difference is likely driven by an adaption of the ecology to the carbon source, and not specifically tied to the cranberry juice. Although, cranberry juice is well noted for its overall health benefits, and the antioxidants from Wisconsin grown cranberries may provide additional benefits to PAOs. But this detail was not explored during this research. The bench scale testing provided the information to complete the carbon mass balance for an S2EBPR system (Figure 7). Using the measured rates, the sbCOD deficiency can be calculated. If a deficiency is occurring, a reduced level of effluent phosphorus removal performance would be anticipated. If the deficiency is zero, or if extra carbon is available in the RAS fermenter, effluent phosphorus concentrations should be reduced. As shown in Figure 8, the mass balance around carbon correlated to observed effluent phosphorus performance.
Benefits and Significance
This presentation will provide a detailed review of an extensive testing of S2EBPR. The following benefits will be provided to the audience: - High-level review of bench testing protocols - Value proposition for adding bench testing to operational data for EBPR and S2EBPR facilities - Outline of how to complete a carbon balance for an S2EBPR facility - Target values for fermentation and sbCOD:TP in S2EBPR facilities These results will be significant for anyone planning, designing, or operating an EBPR facility.

This presentation will provide a detailed review of an extensive testing of S2EBPR. The following benefits will be provided to the audience: - High-level review of bench testing protocols - Value proposition for adding bench testing to operational data for EBPR and S2EBPR facilities - Outline of how to complete a carbon balance for an S2EBPR facility - Target values for fermentation and sbCOD:TP in S2EBPR facilities

SpeakerDowning, Leon

Presentation time

09:25:00

09:40:00

Session time

08:30:00

10:00:00

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Downing, Leon

Author(s)Ryan Giefer1; Derek Budsberg2; Stefania Marroquin3; Leon Downing4

Author affiliation(s)City of Wisconsin Rapids1; City of Wisconsin Rapids2; Black & Veatch3; Black & Veatch4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158533

Volume / Issue

Content sourceWEFTEC

Word count15

Description: Impact of carbon sources and dosing ratios on denitrification and N2O dynamics in a...

Impact of carbon sources and dosing ratios on denitrification and N2O dynamics in a low DO BNR process

Abstract

Introduction

Nitrous oxide (N2O) is a potent greenhouse gas (GHG), making its emission a critical concern. Wastewater treatment plants (WWTPs) are recognized as notable sources of N2O, particularly in a biological nutrient removal (BNR) process (Daelman et al., 2013).

Low dissolved oxygen (DO) BNR is gaining popularity due to its potential for significant energy savings with improved BNR efficiency. There exists conflicting evidence on N2O emissions in low DO BNR, which undermines its energy saving advantages. Identifying N2O production and developing mitigation strategies are crucial to fully leverage the advantages of low DO BNR.

Objective and Novelty
There is limited research on N2O production pathway across aerobic and anoxic conditions in a low-DO BNR system. This study aims to fill this gap by focusing on the following test objectives:
- N2O production in low DO aerobic zones: Investigate the trends of N2O production under low DO conditions in aerobic zones.
- Investing N2O mitigation strategies in anoxic zones: Identify impact of (a) carbon sources and (b) dosing ratios on N2O production and mitigation.

Methods
A 100 gallons sequencing batch reactor (SBR) fed with trickling filter effluent (TFE) (low C:N, ~2.5) was operated at the Hayward WPCF in Hayward, CA. The SBR cycle was 4.8 hrs long with alternating aerobic and anoxic phases. Carbon was dosed at the start of the anoxic phases. The reactor was commissioned with a an aerobic SRT of 8.3d, and then gradually dropped to 6 days and 4 days. The SBR at 4d aeSRT was operated under two distinct phases with variation in the carbon type (a) using MicroC®2000 (EOSi), and (b) synthetic fermentate (SF). The SF comprised 50% acetate, 30% propionate, and 20% butyrate, based on our previous research (Cecconi et al., 2023).

Comprehensive SBR cycle characterization and batch tests were conducted at each phase of operation. Batch tests included (a) N2O dynamics at different COD:NOx, (b) comparison of denitrification rates with different carbon sources.

Results and discussion
Anoxic N2O detected, not in low DO aerobic zones.

In a representative SBR cycle (Fig 1), we observed an increase in N2O concentration through the anoxic phase, while the N2O concentration dropped through the low DO (0.3 mg/L) aerobic phase. This suggests that anoxic N2O production was significant in our alternating anoxic-aerobic configuration. This is an important note, as it focuses our N2O mitigation efforts on anoxic operation and allows for continued optimization of aerobic operation for low DO setpoints. This low DO benefit with lack of N2O has been highlighted elsewhere (Wen et al., 2020), but this is the first detailed exploration of the interaction in anoxic and aerobic conditions. The magnitude of anoxic N2O varied with the type of carbon used- MicroC®2000 showed higher N2O (maximum 1.1 mg-N/L) compared to SF (maximum 0.27 mg-N/L) (Fig 1).

Carbon choice makes a large difference in N2O production dynamics
During our testing periods, we observed simultaneous reduction of NO3 and accumulation of NO2 at the start, followed by reduction of NO2 during denitrification (Fig 2). However, a distinct difference in the N2O dynamics were observed with different carbon sources. The denitrification with MicroC®2000 showed higher N2O during the experiment compared to denitrification with SF. More importantly, a drop in N2O concentration was only observed after the depletion of inorganic NOx when MicroC was used.

Additionally, the production, reduction, and accumulation of N2O increased with increasing COD:NOx (Fig 3). However, it should be noted that the N2O accumulation lasted only for a brief period with SF, unlike MicroC (Figure 2b). This is a crucial point to consider when using NOx-based control strategies with MicroC as carbon source. It appears that with MicroC, a complete NOx reduction, and beyond, is critical to ensure that the dissolved N2O isn't carried over to the aeration basins where they are likely to get stripped. Unlike MicroC, SF showed less risk of N2O carryover at lower NOx concentrations (Fig 2b).

Further, we observed similar denitrification rates when SF and MicroC were used with the MicroC acclimated biomass (Fig 4). However, the denitrification rate using MicroC on SF acclimated biomass was significantly lower. Our results were similar to those observed in Cherchi et al 2009 that compared MicroC and acetate as carbon sources for denitrification. Nitrite accumulation was notably significant when carbon was introduced to the ecology that had already acclimated to the respective caron type.

Benefits and Significance
This research provides a comprehensive assessment of N2O dynamics across the low DO BNR system. The data and findings from this study will enrich the audience's understanding of N2O in low DO BNR system. Significant findings include:
- Evidence that low DO does not increase N2O production.
- Anoxic zones are the highest risk for N2O production.
- Higher COD:NOx results in increased rates of production, reduction, and accumulation of N2O. Sufficient anoxic HRT is critical to prevent N2O carryover to aeration basins.
- Carbon source selection is critical for N2O mitigation strategies. Glycerol-based carbon source tend to produce more N2O than acetate-rich fermentate.
- MicroC-acclimated sludge readily utilized fermentate, while fermentate-fed sludge showed limited ability to use MicroC, highlighting the significance

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

14:30:00

14:45:00

Session time

13:30:00

15:00:00

SessionDecarbonizing Water: N2O Modeling - From Low DO to HPO

Session locationMcCormick Place, Chicago, Illinois, USA

TopicResearch

Author(s)

Downing, Leon, BHATTARAI, BISHAV, Pifer, Leah, Sabba, Fabrizio

Author(s)L. Downing1, B. BHATTARAI1, L. Pifer1, F. Sabba1

Author affiliation(s)Black & Veatch1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159977

Volume / Issue

Content sourceWEFTEC

Word count19

Description: Insights from Full-scale Primary Sludge Fermentation for Carbon Management and...

Insights from Full-scale Primary Sludge Fermentation for Carbon Management and Nutrient Removal

Abstract

Background and Objectives
Nitrogen and phosphorus removal from municipal wastewater require sufficient organic carbon in the form of readily biodegradable carbon (rbCOD) and volatile fatty acids (VFA), which are often limited in influent. Primary sludge (PS) fermentation has been applied for decades in a variety of configurations (Table 1) to produce rbCOD and VFA while also providing sludge reduction benefits1. Despite their widespread application, there is a lack of unified guidance for PS fermenter design, operation, and monitoring and limited information on tradeoffs of different elutriation mechanisms (e.g. solids vs dilute feed). While fermenters are ultimately intended to increase nutrient removal performance, unoptimized fermenters may act as internal sources of additional nitrogen and phosphorus that outweigh the benefits of increased carbon availability. This work will synthesize findings from full-scale PS fermenters (Table 2) to
1) Compare fermentation performance and key performance indicators of different types of PS fermenters and elutriation mechanisms
2) Provide guidance for monitoring PS fermenters to maximize understanding of carbon and nutrient contributions to the mainstream An example case study is provided for Eagles Point Water Resource Recovery Facility and similar analyses will be performed for the facilities in Table 2.

Eagles Point Case Study
#Eagles Point Water Resource Recovery Facility in Cottage Grove, Minnesota is operated by Metropolitan Council Environmental Services (Met Council). This facility, which utilizes biological phosphorus removal in an A2O configuration, has an average design flow of 10 MGD and a 1 mg/L total phosphorus (TP) effluent permit limit. Eagles Point has operated a PS fermenter (~90,000 gal gravity thickener with recirculating elutriation pump) since 2004. As part of a recent transition to low DO operation in the mainstream, staff collected weekly NH4, PO4, and filtered COD samples from the gravity thickener overflow (fermentate). During this period, influent BOD:TP ratios averaged 36, meeting recommended levels without the PS fermenter addition. The PS flow to the thickener and thickened sludge pumping were stable this sample collection period at 0.22 &PLUSMN; 0.03 MGD and 23 &PLUSMN; 2 gpd, respectively. Fermenter sludge blanket levels ranged from 1.5ft to over 9ft during this period with an HRT of ~0.4 d.

In recent years, staff noted that mainstream P removal performance did not seem to correlate with fermenter operation, in that effluent P concentrations did not increase during maintenance periods when the fermenter was offline. Data collected during the low DO transition provides additional context for these observations. On a mass basis, fermentate contributed 22 ± 5 lbs/day PO4-P to the anaerobic zone, while influent wastewater accounted for 166 &PLUSMN; 7 lbs/day. As expected, there was a strong positive correlation between fermentate filtered COD and fermentate PO4 at a consistent ~32:1 COD to P ratio (Figure 1). Assuming a VFA to sCOD ratio of 0.6:1 in PS fermentate2, the VFA to P ratio (19:1) in the produced fermentate is theoretically sufficient to uptake more P in the mainstream anaerobic zone than is recycled from the fermentate itself. However, fermentate P concentrations were positively correlated with effluent P (Figure 1). While effluent P was maintained at low levels regardless of the fermenter contribution, this result suggests a minimal or even net negative effect of the PS fermenter on mainstream P removal.

An additional consideration is temperature, which can have competing effects on fermenter performance and nutrient removal. Fermenter temperature was not measured, but influent wastewater temperature was positively correlated with both fermentate COD and effluent P. Higher ambient and water temperatures improve fermentation, resulting in increased COD outputs1, but also tend to favor microbes that compete with phosphate accumulating organisms (PAO) for rbCOD, leading to worse P removal3,4. Surprisingly, no relationship was found between fermentate COD and sludge blanket levels, suggesting that temperature was the main driver of fermenter productivity rather than SRT (Figure 2). Further sampling to be performed this year will provide a more complete accounting of carbon contributions from the fermenter. This case study highlights the value in routine nutrient monitoring of fermentate and demonstrates a gravity thickener PS fermenter that provided minimal or net negative effects to mainstream nutrient removal performance.

Significance for audience
PS fermenters are widely adopted and provide an 'internal' source of carbon for nutrient removal facilities. However, as demonstrated at Eagles Point, PS fermenters may introduce nutrient loadings back to the mainstream that are not neutralized by increased carbon availability. As facilities continue to meet lower effluent nutrient limits, accounting for internal nutrient recycles in addition to internal carbon recycles is critical. This presentation will use multiple case studies to evaluate the value proposition of PS fermenters, tradeoffs of PS fermenter configurations, and recommendations for monitoring strategies. We will also facilitate knowledge sharing of PS fermenter operation and monitoring through open discussion with participants.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

10:30:00

10:45:00

Session time

10:30:00

12:00:00

SessionFull-Scale Primary Sludge Fermentation

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Farmer, McKenna, Pifer, Leah, Liberzon, Jon, deBarbadillo, Christine, Prater, Trevor, Hogan, Kelsey, Pinkerton, Lee, Menniti, Adrienne, Schauer, Peter, Downing, Leon

Author(s)M. Farmer1, L. Pifer1, J. Liberzon1, C. deBarbadillo1, T. Prater2, K. Hogan2, L. Pinkerton2, A. Menniti3, P. Schauer3, L. Downing1

Author affiliation(s)Black & Veatch1, Metropolitan Council Environmental Services2, Clean Water Services3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160079

Volume / Issue

Content sourceWEFTEC

Word count13

Intensification on the Clock: How MABR Delivers

Abstract

[b]Abstract Summary[/b] Faced with rapid growth, TRA's DCRWS plant needed interim capacity before its major expansion would be completed in 2028. This presentation explores how Membrane Aerated Biofilm Reactor (MABR) technology was selected and integrated to increase treatment capacity. Specifically, challenges related to design and construction within active basins in less than 14 months' time. [b]Introduction and Background[/b] The Denton Creek Regional Wastewater System (DCRWS), operated by the Trinity River Authority (TRA), has been experiencing rapid growth. Originally designed to accommodate a flow of 11.5 million gallons per day (mgd), the plant has experienced unprecedented growth in recent years necessitating an expansion starting in 2022. In response to this growth trajectory, TRA initiated a phased expansion plan, with Phase 1 targeting a capacity increase to 16.5 mgd. Construction for this phase started in 2024, but was just underway when the plant saw a sharp rise in flows that was higher than anticipated – approximately 1 mgd in less than a 6 months. With construction of the major expansion phase not completing until 2028 concerns were focused on maintaining treatment performance and remaining within existing permitted capacity. Recent data was used to update projections and review capacity each year until construction was completed. The secondary treatment was the primary focus with increased organic loadings resulting in a significant peak flow capacity restriction, Figure 1. To mitigate this risk, TRA authorized development of a rapid solution to increase treatment capacity ahead of the major expansion project. Due to the increasing flows, the solution would have to be implemented without taking any existing treatment units offline. [b]The Solution[/b] The preliminary assessment indicated that intensification would be the quickest way to increase capacity. Intensification in the wastewater treatment realm often refers to increasing the capacity of existing infrastructure. The intensification technology selected was the membrane aerated biofilm reactor (MABR) system. MABR is an advanced biological wastewater treatment technology that integrates gas-selective membranes and attached growth biofilm processes. The biofilm develops on the outer surface of the membrane and is exposed to the bulk wastewater on one side and to oxygen on the other, enabling stratified microbial zones: (a) Aerobic/Nitrifying Zone (b) Anoxic/Denitrifying Zone. Because a portion of the biomass is retained in the biofilm and not subject to washout, the total sludge inventory in the bioreactor can be increased without increasing the mixed liquor suspended solids (MLSS) load to the clarifier. This increased biomass retention enhanced the overall treatment capacity of the secondary treatment process, Figure 2, without requiring major changes to the clarifier or aeration volumes. [b]Design, Construction, and Installation[/b] The facility consists of three aeration basins with Aeration Basins 1 and 2 being mirror images and Aeration Basin 3 double the size with a slightly different configuration. The strategic placement of MABR cassettes in Aeration Basins 1, 2, and 3 enabled enhanced biological activity without the need for extensive downtime or reconfiguration of major unit processes. The MABR system at the DCRWS Plant consists of 14 cassettes each in Aeration Basin No. 1 and 2 and 36 cassettes in Aeration Basin No. 3, making it the largest MABR installation in the US at this time. Retrofitting new treatment technologies into existing treatment trains can be difficult. The installation at the DCRWS Plant had the additional complexities of expedited timelines and the requirement of keeping the plant online without shutdowns. The MABR technology consists of cassettes similar to MBRs but are placed within the anoxic zone and provide aeration to a biofilm rather than filtration like the MBR. These cassettes typically hang into the zone, which created a significant challenge considering 10,000 lb cassettes and spans of up to 52 feet. The requirement to not shutdown any treatment trains led to a complex structural design. The team attempted to avoid this complex design by looking at alternative solutions, such as floating the cassettes or supporting cassettes in a cage from the floor. However, these alternative methods all proved to have flaws that would be prohibitive to implementation. Therefore, all structural supports had to be designed to span the basins without any intermediate supports. A significant focus will be on the special design and construction considerations for varying basin dimensions. The site included aeration basins with spans less than 20 ft (two MABR cassettes) up to 52 ft (six MABR cassettes). The longer span required significantly more structural evaluation with the end results a bridge truss type of support structure to enable installation while the basins are in service, Figure 3 and Figure 4. To meet the increasing demands the BV team, along with the manufacturer, designed and prepared bid documents in less than 3 months. This was successful due to a collaborative design between TRA, the consultant, and contractor. The MABR is currently onsite with the first cassettes scheduled to be installed in February and the final by March, Figure 5.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

16:30:00

16:45:00

Session time

15:30:00

17:00:00

SessionA Potpourri of Biofilm Technologies

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Research and Innovation

Author(s)

Redmond, Eric, Ho, Tania, Davies, Tom, Salekar, Prachi, Nash, James, Downing, Leon

Author(s)E. Redmond1, T. Ho2, T. Davies2, P. Salekar1, J. Nash1, L. Downing1

Author affiliation(s)Black & Veatch, 1Trinity River Authority of Texas, 2Black & Veatch, 1Black & Veatch, 1Black & Veatch, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160474

Volume / Issue

Content sourceWEFTEC

Word count8

Description: MABRs Are Neat, But How Do I Design Them? A Practical Design Methodology for Hybrid...

MABRs Are Neat, But How Do I Design Them? A Practical Design Methodology for Hybrid MABR/AS

Abstract

Membrane Aerated Biofilm Reactors (MABR) have been applied at full-scale wastewater treatment plants since 2017 (Underwood et al., 2018) to intensify conventional activated sludge (CAS) to increase flow and/or meet stricter effluent limits. MABRs are typically installed in a pre-anoxic zone and add nitrifying biomass to increase the nitrification capacity (Houweling et al., 2017). The design of MABRs is often done using a combination of process modelling, spreadsheet mass balances, and empirical methods. The objective of this paper is to demonstrate a straightforward design methodology for MABRs that references common design practice for CAS systems.

To achieve reliable nitrification in CAS, process designers typically define a design aerobic solids retention time (aSRTdesign) by applying a safety factor (SF) to a minimum aSRT (aSRTmin) as follows.

aSRTdesign=SF x aSRTmin

Where aSRTmin is commonly defined by kinetic equations presented in Metcalf & Eddy (2014) and can be adjusted to target specific effluent ammonia concentrations across a range of design temperatures, as discussed in Chapter 1 of Houweling and Daigger (2020). Figure 1 shows representative curves for aSRTmin and aSRTdesign with a safety factor of 2 as a function of temperature for an effluent ammonia target of 1 mg/L.

In order to intensify the treatment capacity of nitrifying CAS plants, a media-supported biofilm can be added into the system to enable reliable nitrification at shorter aSRTs than would be typically used. Houweling and Daigger (2020) published a set of design curves relating the fraction of inlet ammonia treated by the biofilm, FNit,B, to aSRT and nitrification safety factor. Figure 2 shows an example of one of these curves at 15°C.

A design methodology is proposed using a combination of the theory used in Figures 1 and 2, where the designer
a) selects a safety factor and design aSRTdesign for a CAS plant to achieve their nitrification goal and,
b) correlates the aSRTdesign and safety factor to a lower aSRT (typically the aSRT available at an overloaded CAS plant, aSRTavailable) plus a fraction of influent ammonia removal by the biofilm.

Application of the design methodology is demonstrated using examples from two real-world MABR designs, with one operating MABR equipped plant and one plant that requires an upgrade using MABR.

Case Study 1
The Hespeler WWTP located in Cambridge, Ontario, Canada is a 9.32 MLD facility that was upgraded with MABR in 2022. The MABR upgrade has achieved year-round nitrification at this facility, which was previously only able to nitrify seasonally (Lakshminarasimman et al., 2023). The design criteria for the Hespeler WWTP was to achieve an effluent of 5 mg/L as ammonia nitrogen at a temperature of 10°C with as low as 4 to 5 day aSRT in the aeration tanks (Natvik et al., 2020).

Figure 3 shows the conventional nitrification curves for the Hespeler case, targeting an effluent ammonia concentration of 5 mgN/L. At 10°C the aSRTmin to achieve 5 mgN/L is 5 days, whereas the aSRTdesign with 1.5 times safety factor is 7.5 days.

Applying the design points to the biofilm safety factor curves by Houweling and Daigger as shown in Figure 4, a 7.5 day aSRT corresponds approximately to a SF of 1.5 when FNit,B = 0. To maintain the nitrification safety factor at 1.5, some removal on the biofilm is required. In this case a 5 day aSRTavailable at SF of 1.5 corresponds to an FNit,B of 0.42, meaning that 42% of the influent ammonia must be removed in the biofilm.

The Hespeler WWTP has 36 ZeeLung™ MABR cassettes by Veolia with 1,920 m2 of surface area each for a total of 69,120 m2. At an average nitrification rate of 1.7 gN/m2/d the MABR will remove 117.5 kgN/d. The influent design ammonia load is 260 kgN/d. Therefore, the MABR will remove 45% of the influent ammonia load, which approximately corresponds to the design points illustrated in Figures 3 and 4.

Case Study 2
A wastewater plant in Texas, USA is approaching design capacity and requires a biological upgrade within a short time frame. The plant has a design temperature of 20°C and is required to meet a monthly effluent ammonia limit of 1.4 mgN/L and can operate at a bulk aSRTavailable of 4.3 days. Figure 5 shows the conventional nitrification curves for the Texas case for a target effluent ammonia of 1.4 mgN/L at 20°C where aSRTmin is 2.8 days and aSRTdesign is 5.5 days with a SF of 2.

Applying a 5.5 day aSRTdesign to the biofilm safety factor curves at 20&Deg;C corresponds to a SF of ~2.25, as shown in Figure 6. In order to maintain a SF of 2.25 at an aSRTavailable of 4.3 days an FNit,B of 0.29 is required.

The influent ammonia load for the Texas WWTP is 1340 kgN/d. To achieve a 29% ammonia removal, 389 kgN/d are required to be removed by the MABR biofilm. Assuming a nitrification rate of 2.6 gN/m2/d, a surface area of ~150,000 m2 is required.

The designs in case studies 1 and 2 use different safety factors, where a less stringent ammonia limit requires a lower safety factor and vice versa. Recommendations for safety factor for ranges of effluent ammonia limits will be presented along with one or more additional case studies.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionExploring the Capability and Flexibility of MABRs

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment Technology - Secondary & Tertiary Treatment

Author(s)

Reeve, Matt, Houweling, Dwight, Downing, Leon, Redmond, Eric, Cecconi, Francesca

Author(s)M. Reeve1, D. Houweling2, L. Downing3, E. Redmond3, F. Cecconi3

Author affiliation(s)Veolia Water Tech1, Polytechnique Montreal2, Black & Veatch3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160087

Volume / Issue

Content sourceWEFTEC

Word count17

Measuring In-Situ Nitrification and Denitrification Rates at Low DO

Abstract

INTRODUCTION/BACKGROUND NEW Water is planning to upgrade the aeration basins at their Green Bay Facility over the next decade. Future permit regulations for total nitrogen (TN) may impact these capital improvement projects. In preparation, NEW Water is collaborating with Black & Veatch and EnviroMix to pilot a transition from an existing anaerobic-oxic process to an anaerobic-anoxic-oxic (A2O) process at low dissolved oxygen (DO) concentrations. The A2O test aeration basin receives an average primary effluent flow of 7 mgd and includes EnviroMix mixing technology and aeration and process control (Figure 1). The demonstration has been operational for two years. In the first year at low DO, simultaneous nitrification-denitrification (SND) was observed via grab samples collected throughout the basin. In the past year, the team has worked on understanding and optimizing SND and developing a novel SND measurement method capturing SND activity in-situ at full-scale using two ammonia and nitrate sensors installed on either side of the low DO zone. This study provides a long-term, longitudinal data set over six months and various low DO control strategies, including static 0.3 mg/L and 0.5 mg/L, and FlexZone control, a strategy to dynamically transition DO setpoints based on influent loading (Table 1). METHODOLOGY Two YSI VARiON ion-selective electrode sensors measuring ammonia (NH4) and nitrate (NO3) were installed to support continuous, in-situ rate calculations. One sensor was located at the end of the anoxic zone, and one was installed in the middle of subzone 2 (SZ2). They recorded NH4 and NO3 concentrations at one-minute intervals, providing high-resolution data. DO was monitored in each aerated zone using optical DO sensors, and biomass concentration was measured using a total suspended solids (TSS) sensor. Sensor data quality was maintained through verification with grab samples collected on a weekly to monthly basis, with matrix adjustments applied as needed. Sensor data was used to calculate in-situ nitrification and denitrification rates in SZ1 and SZ2. The rates were calculated as shown in Figure 2 based on NH4, NO3, and TSS sensor values and a measured MLVSS/MLSS ratio. RESULTS SND has been observed where bulk oxygen is limiting, less oxygen diffusion into flocs creates a thin aerobic layer over an anoxic center, and organisms with greater oxygen affinity are favored (Jimenez et al. 2025). This can result in lower effluent TN outside a designated anoxic zone (Rieger et al. 2012; Regmi et al. 2022). Here, SND was observed in the low DO zone across aeration control strategies. The in-situ nitrification and denitrification rates grouped by test phase are shown in Figure 3. In-situ rates were validated with lab-scale rate tests (results not shown). When the DO setpoint was reduced from 0.5 mg/L to 0.3 mg/L, the nitrification rate stayed the same, suggesting the biomass had fully adapted and/or acclimated to low DO. The nitrification rates are in the upper range of rates observed by Jimenez et al. 2025 across 21 water resource recovery facilities. Low secondary effluent NH4 was maintained throughout the demonstration (data not shown). Additionally, when the DO setpoint was reduced from 0.5 mg/L to 0.3 mg/L the denitrification rate increased. FlexZone operation supported the highest nitrification and denitrification rates, likely because the DO target adjusted according to load. Balancing complete nitrification while achieving denitrification benefits will drive the DO control strategy for full-scale design. The diurnal variation in nitrification and denitrification rates is shown in Figure 4 for a representative weekday (May 9, 2025) with a constant DO of 0.3 mg/L across low DO zones. The peak flow to the basin occurred at 14:00, after which the nitrification rate increased and remained high until the minimum flow occurred at 7:00. At its maximum, the nitrification rate was 32% higher than at its minimum. The denitrification rate did not vary as much, but increased from 0:00 until midday, when the flow was highest. At its maximum, the denitrification rate was 22% higher than at its minimum. Figure 5 shows the relationship between the nitrification and denitrification rate during a stable phase of operation from June 3 to August 4, 2025. The wastewater temperature during this time ranged from 21-24°C. As the nitrification rate increased above 5 mg NH4/g MLVSS-hr, the denitrification rate increased by 17-33%. The nitrate leaving the anoxic zone was consistently less than 0.6 mg/L, and therefore, nearly all nitrate available for denitrification came from nitrification in the low DO zones. CONCLUSIONS AND SIGNIFICANCE Evaluating aeration control strategies to balance nitrification and denitrification at low DO is important for facilities looking to improve TN removal while reducing energy consumption. A novel method of sensor-enabled in-situ rate measurement was advanced, allowing NEW Water to investigate long-term trends in SND. This method can provide a time-saving alternative for SND rate measurement if equipment or personnel are unavailable for lab testing, with the added benefit of live feedback on TN removal. Diurnal variability and a dependence of denitrification rate on the nitrification rate were observed.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionNitrogen Removal in Low DO Conditions

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Gutenberger, Gretchen, Downing, Leon, Sadreddini, Sara, Biese, Tyler, Watson, Joe, Koch, John, Elger, Sarah, Jordan, Taylor, Stenz, Adrienne

Author(s)G. Gutenberger1, L. Downing1, S. Sadreddini1, T. Biese2, J. Watson2, J. Koch3, S. Elger3, T. Jordan3, A. Stenz4

Author affiliation(s)Black & Veatch, 1Black & Veatch, 1Black & Veatch, 1New Water, Green Bay Metro Sewerage District, 2New Water, Green Bay Metro Sewerage District, 2EnviroMix, 3EnviroMix, 3EnviroMix, 3YSI, A Xylem Brand, 4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160436

Volume / Issue

Content sourceWEFTEC

Word count10

Membranes Vs Concrete: Defining the value and limitations of hybrid MABR retrofits

Abstract

The capability of membrane aerated biofilm reactors (MABRs) to be retrofit into existing basins provides a unique value proposition for legacy WRRFs with tightening regulations or capacity limitations. For plants seeking more nitrogen removal, MABRs allow for development of long-SRT biofilms which can both nitrify and denitrify, decoupling nitrification capacity from the aerobic SRT of the suspended biomass. This adds nitrification capacity without altering the plant's suspended biomass inventory or increasing loading on secondary clarifiers. Placement of MABRs in unaerated zones also allows this technology to be coupled with low-DO aeration controls and simultaneous nitrification-denitrification configurations that don't require mixed liquor recycles (IMLR). In combination, these intensified process configurations allow for low-energy and carbon-efficient treatment in addition to retrofittable capacity increases.

These benefits, described in the literature mainly in general terms, are now being realized with implementation of full-scale hybrid MABR retrofits. Using a combination of historical data and process modeling, this paper quantifies the benefits and identifies design best-practices for spiral-configured MABR retrofits, both for a real installation in Israel, and more generally, for a typical North American plant located in the temperate climate zone.

Roughly two years of water quality and operational data were analyzed from a hybrid, spiral MABR retrofit in the anoxic zone of the Maayan Tzvi WRRF, an A2O plant operated at low-DO setpoints (DO<0.5 mg/L) and without IMLR. Performance results, as measured by the quantity of ammonia oxidized by MABR versus suspended growth at the plant, demonstrate that MABR met or exceeded the expectations established by earlier piloting, though the impact of the MABR was somewhat variable over time (Fig. 1). Influent, effluent and operational data were used to develop SUMO models of this plant in both MABR and 'conventional' (no MABR) configurations. Using real-world data within a dynamic process model allowed for investigation of factors contributing to biofilm nitrification rates, which can serve as a measure of process efficiency and operational performance.

SUMO analysis found that, for a membrane configuration designed to nitrify 30% of influent NH4 (as is the vendor's standard,) performance improved with decreased organics loading and increased NH4 loading, but only up to a maximum of 10 g N/d*m2 (Fig. 2, 3). At higher NH4 loadings and concentrations (such as may occur in dry regions with established water conservation programs), modelled system performance diminished during diurnal periods of increasing nitrogen loading (roughly 11:00-19:00 in this dataset). This finding suggests that for certain periods of the day in these geographies, nitrification may not be substrate-limited as generally assumed, but rather limited by some other factor. Oxygen limitation is one potential contributor, as nitrification rates rebounded when modelled rates of oxygen transfer through the membrane were set well-above the data-derived values. Previous findings of similar inhibitory effects at full scale identified low ORP or high sulfur concentrations as likely factors (Uri-Carreño et al. 2023), however neither were reflected in this study's modeling results. While additional high-resolution sampling of full-scale retrofits would help to confirm these findings, they nonetheless suggest that designers consider using IMLR, equalization, increased membrane area, or other techniques for maintaining instantaneous MABR substrate loadings below a threshold value of 10 g N/d*m2 throughout the diurnal cycle to avoid inhibitory effects on performance when using these commercially available membranes.

When considering the benefits of MABR to designers, this study found that in temperate regions (design water temperature of 15°C), addition of MABRs tasked with removal of up to 30% of influent ammonia reduces the required aerobic SRT of the suspended biomass system by two full days, while maintaining a 2x nitrification safety factor (Fig. 4). This represents a 25% reduction in the required secondary clarifier capacity (achieved through reduction in MLSS), or a 14% reduction in the aerobic basin concrete volume (Fig. 5). In both cases, reducing the need to construct additional basin volume or clarifiers results in GHG emission savings above and beyond the savings in aeration energy. In warm (>30°C) climates, by contrast, this benefit is lost. By combining MABR with low-DO operation, a total energy savings of 30% can be achieved regardless of climate (Fig. 6), while also producing a small (roughly 3mg/L) improvement in effluent total nitrogen.

This study combines modeling with fullscale data from a successful hybrid MABR retrofit to identify design factors which influence the performance of such systems under various temperature and loading regimes. This information will be useful to designers wishing to maximize the value derived from MABR retrofits of existing assets. By translating dynamic performance metrics into reductions in minimum aerobic SRT, this study also helps to define the value proposition of MABR capital investments as compared to construction of additional tankage. As understanding of this value proposition improves, MABR is likely to become a more widely adopted technology for retrofit of capacity-constrained BNR plants.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionExploring the Capability and Flexibility of MABRs

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Liberzon, Jon, Gutenberger, Gretchen, Pifer, Leah, Cecconi, Francesca, Nathan, Neri, Ben Yosef, Chever, Downing, Leon

Author(s)J. Liberzon1, G. Gutenberger1, L. Pifer1, F. Cecconi1, N. Nathan2, C. Ben Yosef2, L. Downing1

Author affiliation(s)Black & Veatch1, Fluence Corporation2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160006

Volume / Issue

Content sourceWEFTEC

Word count13

Modelling of Primary Sludge and RAS Fermentation for Carbon Management Optimization at WRRFs

Abstract

Introduction Conventional wastewater treatment plants are transitioning to integrated resource recovery and upcycling, which requires effective management of biodegradable organic carbon. This involves developing approaches to carbon diversion, such as anaerobic digestion of primary sludge and waste activated sludge for energy and fertilizer (Gavala et al 2003). Alongside the push to enhance resource recovery, many WRRFs are also under pressure to meet strict effluent nutrient (N and P) discharge targets. While new nitrogen management strategies that do not rely on carbon are emerging, the majority of nutrient removal systems still follow a conventional, optimized nitrification-denitrification pathway that relies on biodegradable organic carbon to support denitrification. Moreover, biodegradable organic carbon is crucial for biological phosphorus removal. Years of experience have demonstrated that successful biological nutrient removal depends not only on sufficient organic substrate, but also on the right type of bioavailable carbon supplied at the appropriate location and time for optimal utilization (Wu et al, 2009; Huang et al, 2018). Our research aims to determine the best way to utilize the variety of organic-carbon rich feedstocks available in a WRRF and how fermentation can be used as a platform process to manage the logistics of biodegradable organic carbon supply and demand. To address these questions, we conducted a pilot-scale assessment of the fermentation of a blend of wastewater-derived primary sludge (PS) and waste activated sludge (RAS) from two treatment plants. Plant 1, which only performs BOD removal, has a short solid retention time (SRT) of 2 days, while Plant 2 performs biological nutrient removal (both TN and TP) and has a longer SRT of 10 days. We conducted batch fermentation experiments on different blends of RAS and PS over a two-week period to analyze biomass kinetics and the products formed during fermentation. We used the SUMO simulator software to model each batch experiment, calibrate the two-week experimental data, and analyze the hydrolysis rates and influent fractionation variations based on the feedstock characteristics. Material and Methods Experimental Set-up Pilot-scale fermentation experiments were performed using a purpose built two-tank pilot system (Figure 1). Each bioreactor have a capacity of 75 L (20 gal). The temperature was controlled at 20 degrees C in each bioreactor. Each fermentation experiment was run in duplicate for 14 days. Three blend scenarios of RAS and PS were targeted, for both Plant 1 and Plant 2 feedstocks: 1)RAS only 2)50% RAS and 50% PS in VSS mass 3)100% PS Modelling Data from each batch experiment were modelled using Sumo Dynamita to validate the observed results as well as elucidate the biological processes. Full plant models were configured for Plant 1 and Plant 2 (see Figure 2) and an SBR process unit was used to represent the pilot reactor. Default influent parameters and fractionation for the full plant models were initially used and were tuned in order to match the TCOD, TSS, VSS, sCOD, NHx and OP data. After the initial conditions were matched, the kinetics and biology were calibrated until the experimental curves were fitted. The reduction factor of anaerobic hydrolysis was also tuned from the 0.5 default to the 0.05-0.15 range, as observed in the Water Research Foundation 4975 report. Results and Discussion Figure 3 shows the timeseries of the soluble COD yield, expressed as mass of sCOD produced per unit mass of VSS (mgCOD/gVSS) throughout the experiment for the different RAS and PS blends, for both short SRT combinations (left) and long SRT combinations (right). For each test, the experimental data was simulated on SUMO and the results of the calibrated models are shown in the dashed line. It can be noticed that the sCOD yield is different between the different PS and RAS blend combinations and also between the long and short SRT RAS. Overall, the highest fermentation rate is achieved around 3 days from the start of the experiment for all the tests. Higher sCOD yields are shown in the first week, while the sCOD production largely slows down in the second week of the test. Figure 4, left) shows the 3-day fermentation rate comparison for the different RAS and PS blends, for both short SRT and long SRT RAS biomass. The reduction factor of the anaerobic hydrolysis kinetic parameter was calibrated for each test and varied between the different feedstock blends (Figure 4, right), showing higher hydrolysis rates with higher fermentation rates and higher PS content, as reported by Ozyildiz et al 2023. The average 3 day fermentation rates ranged from 0.25+/-0.1 mg sCOD/gVSS/h for long RAS only to 3.1+/-0.2 mg sCOD/gVSS/h for 50% PS and 50% RAS, long SRT. Overall, the 50/50 ratio was noticed to be the optimum ratio to maximize soluble COD production, with both RAS types, however a higher fermentation rate (around 50% higher) was achieved when longer SRT RAS was combined with PS compared to the short SRT/PS blends. The fermentation performance is driven by the ratio between the concentration of hydrolysing microorganisms, mainly deriving from RAS, and the fermentable substrate, which is more available in primary sludge. Our research outcomes will be of value to utilities aiming to integrate the stringent effluent nutrient (N and P) discharge targets with energy and resource

The main objective of this pilot fermentation testing was to evaluate the most effective utilization of the range of organic-carbon rich feedstocks within a water resource recovery facility (WRRF). Experimental results suggest that a 50-50 blend of primary sludge (PS) and return activate sludge (RAS) fermentation leads to highest sCOD yield. The experiments were modelled using SUMO by calibrating the hydrolysis rate, plant influent fractionation, and the hydrogen production yield.

SpeakerCecconi, Francesca

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionEBPR Pulse: Current Trends, Full-Scale Optimization, Model for Sustainability

Session number227

Session locationRoom 243

TopicAdvanced Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Cecconi, Francesca, Pifer, Leah, Bhattarai, Bishav, Downing, Leon

Author(s)F. Cecconi1, L. Pifer1, B. Bhattarai1, L.S. Downing2

Author affiliation(s)1Black & Veatch, CA, 1, 2Black and Veatch, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159568

Volume / Issue

Content sourceWEFTEC

Word count14

Navigating Carbon Limits: Lessons Learned from Small and Full-scale S2EBPR Operation in a C-limited Facility

Abstract

Introduction Water reclamation facilities use enhanced biological phosphorus removal (EBPR) to prevent the release of phosphorus into aquatic environments. Phosphorus-accumulating organisms (PAO) drive EBPR by using rbCOD to perform phosphorus cycling. However, PAO may compete with other desirable heterotrophs and glycogen-accumulating organisms (GAO). Sidestream EBPR (S2EBPR) is designed to reduce upsets from low or unreliable rbCOD in influent wastewater. In this study, Calumet WRP conducted a small-scale and full-scale study of S2EBPR to achieve effluent P goals below 1 mgP/L. This study evaluated the performance of S2EBPR with and without external carbon dosing, compared small-scale findings to full-scale performance, and assessed the PAO and GAO community over time. Methods Small- and full-scale reactors (SSR and FSR) were operated at Calumet WRP for 1 year, in 2019 and 2021, respectively (Figure 1a and 1b; also see Sabba et al. 2023 and Farmer et al. 2023 for additional details about the FSR). The SSR was supplied with external C addition in 3 phases: 50, 25 and 0% C. The FSR was also operated with changing C dosing, 2 periods with C and 2 periods without. Composite samples of reactor effluent were collected on a daily and/or weekly basis for TP, OP NH3−N, NOx, TKN, BOD5, total and volatile suspended solids and VFA and measured with EPA and APHA standard methods. 16S rRNA gene sequencing was performed on samples collected from SSR and FSR, and metagenomic sequencing was performed on select samples from the FSR. Results SSR S2EBPR findings Batch testing was to measure P uptake on nitrate and oxygen in the SSR (Figure 2a). Oxygen-driven P uptake appeared to be the main contributor to P removal. However, the weekly average P removal observed in the reactor was significantly correlated with nitrate-driven rate, not the oxygen-driven rate, suggesting that nitrate-driven P uptake was important for overall performance (Figure 2b). Overall, these results suggest a higher proportion of PAO can denitrify than previously reported (Nielsen et al., 2019). Figure 3a and 3c shows the relative abundance of PAO and GAO population in the SSR during the three C phases. Despite the C reduction, overall, the S2EBPR shows stability of PAO population, including the canonical PAO Accumulibacter, with only a slight decrease in relative abundance of Tetrasphaera. Interestingly the decrease of C to 0% did not lead to exclusion of GAO but rather, a stable population of Ca. Competibacter and Micropruina was established. FSR S2EBPR findings Figure 3b displays the relative abundance of PAO and GAO in the FSR during the four C phases. Both PAO and GAO populations increased and established during the two phases where C was dosed. Notably, Ca. Competibacter increased during phase III (C on) and persisted during phase IV (C off). To further investigate the trends observed in the FSR with regards to PAO and GAO and connect them with denitrification-based P uptake observed in Figure 2, we next analyzed the denitrification pathway using metagenomic sequencing data with a focus on denitrifying PAO and GAO (known as DPAO and DGAO). We mapped our metagenomic reads to curated denitrifying genes from Ca. Accumulibacter, Dechloromonas, Tetraphaera, and Ca. Competibacter. We found that the complete denitrification pathway was encoded by DPAO and DGAO, but there were considerable differences in the gene abundances amongst the organisms. For example, most nitrate reductases mapped to narG from Ca. Accumulibacter, but the nitric oxide reductases mapped to nor genes from Ca. Competibacter, suggesting that the DPAO and DGAO may have been partial denitrifiers. Our metagenomic findings also point to the possibility of N2O accumulation due to incomplete denitrification, though further analysis of the denitrification pathway completeness considering other denitrifying bacteria is needed to increase our confidence. Comparison of SSR and FSR performance External C dosing had a substantial impact on P removal performance in both SSR and FSR. In the SSR, the median OP removal was 90% with the 50% C dose, compared to 83% with the 25% C dose and 50% without dosing. In the FSR, both the 50% and 25% C dosing conditions achieved less than 1mgP/L with a median effluent 0.49 and 0.40 mgP/L, respectively. The FSR exhibited similar trends; the median OP removal was 90% with C dosing (average of 3.3 L/min) compared to a median of 15% OP removal, as well as occasional net OP release, without C dosing. The median effluent OP from the FSR was 0.29 mgP/L under the high C dosing condition, also achieving the less than 1mgP/L goal. Overall, the performance was comparable between the SSR and the FSR, despite the differences in C dosing regimes and reactor configurations. Benefits and significance This presentation will highlight the successful scale-up of an S2EBPR process from a small lab-scale system to a full-scale demonstration, as well as the potential role of DPAO in combined P and N removal. For practitioners, this work will provide insights into optimizing EBPR systems at low carbon facilities, understanding how DPAO can contribute to P and N removal, and operating relevant pilot studies to inform full-scale work. For researchers, our findings on denitrification gene abundances are relevant for further study of truncated denitrification pathways in DPAO and DGAO.

This paper assesses the performance of S2EBPR at Calumet WRP in achieving effluent P goals below 1 mgP/L. It compares small-scale findings to full-scale performance, including the impact of external carbon dosing on P removal. The study highlights the potential role of denitrifying phosphorus-accumulating organisms in combined P and N removal and provides insights for optimizing EBPR systems at low-carbon facilities and operating relevant pilot studies to inform full-scale work.

SpeakerSabba, Fabrizio

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionUsing Side-Stream Enhanced Biological Phosphorus Removal to Improve EBPR Performance

Session number523

Session locationRoom 350

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Sabba, Fabrizio, Farmer, McKenna, Jia, Zhen, Wells, George, Downing, Leon

Author(s)F. Sabba1, M. Farmer2, Z. Jia2, G. Wells3, L.S. Downing4

Author affiliation(s)1Black & Veatch, NJ, 2Northwestern University, IL, 3, IL, 4Black and Veatch, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159516

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Navigating Process Challenges of Sidestream Nitrogen Removal: Insights from the Fond...

Navigating Process Challenges of Sidestream Nitrogen Removal: Insights from the Fond du Lac WRRF

Abstract

Background
As regulatory pressures and environmental stewardship drive stringent effluent quality targets across North America, wastewater utilities are forced to manage more complex nutrient removal processes. Fond du Lac Wastewater Treatment & Resource Recovery Facility (FDL) operates a low DO, anoxic-aerobic (AO) process, rated for 44,000 m3/day [~12 mgd] (Figure 1). Additionally, FDL commissioned Paques' ANAMMOX® process for sidestream nitrogen elimination in 2018 to manage dewatering centrate nitrogen loads.

ANAMMOX® is a well-established, upflow granular sludge bed process used for single-stage partial nitritation and anammox (PNA). Tilted plate settlers are used to reduce influent solids, retain biomass granules, and waste lighter floc (Figure 2). Some common process challenges associated with PNA systems in general include control of nitrite-oxidizing bacteria (NOB), temperature sensitivity of process microbiology, sufficient alkalinity for aerobic ammonia oxidizing bacteria (AOB), and retention of slow-growing anammox organisms [1].

Recently, FDL observed a drop in both nitrogen removal efficiency and the granule fraction of biomass. This presentation and paper will discuss observed process challenges, key optimization steps, and impacts on nitrogen elimination.

Operations and Timeline
In 2021, FDL upgraded their solids processing equipment, which impacted dewatering operations. With consistently higher loading and airflow to their ANAMMOX® process, FDL observed granule washout. Adding granules and a new screening process for biomass retention overcame washout concerns, but removal efficiencies unexpectedly decreased. Strategies included addition of iron, micronutrients, and caustic for pH adjustment to reduce effluent nitrate and ammonia. DO control was also optimized to control NOBs, and activity tests returned normal results. With monitoring of alkalinity and dilution water (for temperature control) and ending caustic and iron addition, FDL has mostly restored anammox activity in the system. Temperature setpoint was historically 36°C, until 2024 when the following changes were initiated (Table 1).

Observations and Discussion
Granule washout occurred in July 2021 (Figure 3), with granule counts stabilizing quickly with minimal floc accumulation. In May 2022, granule count began to decline, and Imhoff cone results reached a minimum in early 2023. Coinciding with this, flocculant biomass flourished, reaching a maximum quantity (88% of Imhoff cone) in May 2023 (Figure 3, shaded). This suggests poor granule retention and that process conditions promoted growth of light, flocculant biomass. Flocculant biomass does not support the growth structure (anoxic layer) required by anammox.

Effluent nitrogen as ammonia, nitrite, and nitrate are shown below (Figure 4). Minimum granule quantity coincided with high concentrations of effluent nitrite, suggesting there was little to no anammox activity (shaded area of Figure 4). Nitrite consumption was recovered shortly after. As granule count increased through late 2023, FDL began to see elevated effluent ammonia and nitrate from ANAMMOX®. While granule counts have rebounded, anammox activity may not be optimized despite process improvement efforts to dose iron and control the pH in the reactor. High effluent nitrate suggests poor NOB control, and high effluent ammonia suggests poor AOB performance. As effluent ammonia decreased in summer 2024, FDL decreased their DO setpoint to continue to drive out NOB.

There is a positive correlation of influent alkalinity concentration with TIN elimination (Figure 5). FDL uses heated plant effluent to control temperature in the ANAMMOX® reactor, which dilutes the influent alkalinity concentration. There was no clear correlation between dilution water flow rates and TIN elimination. There is a slight decrease in the ratio of influent alkalinity to ammonia over time.

Theoretical stoichiometry of single-stage PNA suggests a 0.1 molar ratio of nitrate produced to ammonia consumed. This can increase or decrease with the presence of other organisms, like NOB and denitrifiers, and a higher nitrate:ammonia ratio suggests the presence of NOB and can be used as a process indicator of NOB control in the ANAMMOX® process. The trend of this ratio over time was reasonably well-controlled until late 2023, following a sharp increase in floc and effluent nitrate (Figure 6). NOB may have outcompeted anammox bacteria for available nitrite, a theory also supported by high effluent nitrate concentrations (Figure 4).

FDL's ANAMMOX® biomass and nitrogen elimination performance displayed a compounded response to DO, temperature, and alkalinity changes. This presentation will discuss FDL's optimization strategies, perplexing system responses, and operational conclusions. Next steps include process modeling focused on granular and flocculant fractions observed in the field to further understand performance and guide optimization.

Relevance
- Sidestream nitrogen removal technologies are becoming more commonplace and process upsets are often still poorly understood and characterized.
- Determining which process variables are available, reliable, and important to track in specific systems is critical to informing process control decisions and evaluating system response.
- Presentation and discussion of full-scale case studies are valuable mediums for sparking innovation and conversation.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

13:30:00

14:00:00

Session time

13:30:00

14:30:00

SessionAdvanced Strategies for Optimization of Sidestream Nitrogen Removal

Session locationMcCormick Place, Chicago, Illinois, USA

TopicOptimization of Municipal Facility Operations

Author(s)

Coffey, Carolyn, Schoepke, Cody, Avila, Isaac, Downing, Leon

Author(s)C. Coffey1, C. Schoepke2, I. Avila1, L. Downing1

Author affiliation(s)Black & Veatch1, Fond du Lac Wastewater Treatment and Resource Recovery Facility (WTRRF)2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825159916

Volume / Issue

Content sourceWEFTEC

Word count15

Description: Nitrification Kinetics of a Full-scale, Low DO Activated Sludge System: Online...

Nitrification Kinetics of a Full-scale, Low DO Activated Sludge System: Online Monitoring for Process Analysis and Operational Training

Abstract

Black & Veatch (BV) in collaboration with the Trinity River Authority of Texas (TRA) at the Central Regional Wastewater System treatment plant (CRWS) developed an implementation plan of the in-tank nitrification rate (INR) reactor. Nitrification rate testing is a tool to assist with early identification of process health and identify variability in nitrification kinetics in a low dissolved oxygen (DO) activated sludge system. The TRA CRWS facility currently operates the secondary system in a low DO environment with ammonium-based airflow controls (ABAC). A low DO comammox Nitrospira nitrifying community has been documented at the facility. The INR reactor was proposed as a measure that allows TRA CRWS operation to monitor the health of the overall activated sludge bacterial community health continuously without adding the burden of monitoring and sampling on the operators.

The following conference paper was presented at WEFTEC 2021, October 16-20, 2021. To read the full abstract, see "Abstract" tab below.

SpeakerDowning, Leon

Presentation time

16:45:00

17:30:00

Session time

16:00:00

17:30:00

SessionKnowledge Development Forum: Process Intensification Using Low DO Operation - Is It Possible and What Can I Control and Look For?

Session number316

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Research and Innovation

Author(s)

Leon Downing

Author(s)L. Downing1;E. Redmond2;McK. Farmer3;M. Reeves4;M. Young5;

Author affiliation(s)Black & Veatch, Madison, WI1Black & Veatch, Des Moines, IA2Black & Veatch, Chicago, IL3Trinity River Authority of Texas, Grand Prairie, TX4,5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158178

Volume / Issue

Content sourceWEFTEC

Word count19

Description: Operational Considerations for Integration of AquaNereda Reactor Expansion with an...

Operational Considerations for Integration of AquaNereda Reactor Expansion with an Existing Activated Sludge Facility

Abstract

Introduction The application of the AquaNereda® process, were aerobic granular sludge (AGS) is applied in a sequencing reactor, is often seen as a replacement for the conventional activated sludge process. AquaNereda(R) is a sequencing process that utilizes a single tank for react and settle phases, and therefore is often not compatible as a retrofit with existing activated sludge systems that utilize separate tanks for reaction (aeration basins) and settle (final clarifiers). While this can be seen as a limitation for the application of AquaNereda(R), there is an opportunity to construct an expansion of facilities with AquaNereda(R), and then integrate the AquaNereda(R) in parallel to a conventional activated sludge plant. Four Rivers Sanitation Authority (FRSA), located in Rockford, Illinois, is currently working towards this integrated overall facility. While maintaining 40 mgd of average day flow capacity in a more conventional biological nutrient removal (BNR) activated sludge facility, FRSA is adding an additional 10 mgd of average day flow capacity with a new AquaNereda(R) AGS facility. The AGS facility will be operational in 2025, with the BNR upgrades being completed in 2026. During design of the new facilities at FRSA, the largest question for integration of the processes became how to manage the waste activated granular sludge (WAGS). Given the characteristics of WAGS in terms of percent solids as well as the sequencing wasting schedule from AquaNereda(R), it was decided to send the WAGS into the activated sludge system and then to waste to solids handling (see Figure 1 for a process flow diagram). The waste activated sludge (WAS) would then contain flocs from the activated sludge process as well as WAGS. This simplified operation, but there were major questions related to the impact of WAGS on the activated sludge process. Potential oxygen demand impacts, nitrification rates, and settling rates were all of interest to FRSA to understand the impact of WAGS. While most facilities would rely solely on process modelling to assess these impacts, FRSA has access to WAGS for testing. The AquaNereda(R) demonstration facility is on site and operating with FRSA wastewater. This facility (treating 200,000 gpd) generates WAGS that can be utilized for testing. Approach and Methodology To help understand the impacts and strategies to manage WAGS from the AGS facility, a series of bench scale tests were completed using WAGS from the AquaNereda(R) demonstration facility and WAS from the existing FRSA aeration basins. Three sets of bench scale tests were completed:

*Settling rate testing to identify potential enhanced settling, as outlined by Daigger, Redmond, and Downing (2017)

*Specific oxygen uptake rate (SOUR) measurement, utilizing standard methods, to assess the oxygen demand of the WAGS. The WAGS have the potential to exert a significant oxygen demand, as past work has shown a biomethane production potential of WAGS that is similar to primary sludge (Guo et al., Digestibility of waste aerobic granular sludge from a full-scale municipal wastewater treatment system, 2020).

*Nitrification rate testing, as outlined by Melcer et al (2003), to identify any potential seeding effect from WAGS. Results and Outcomes To evaluate the effect of WAGS on the settling characteristics of the existing waste activated sludge (WAS), batch settling experiments were performed using WAS and a mixture of WAGS-WAS at various dilution ratios to generate settling curves. The WAGS-WAS mixture proportions were calculated based on the predicted WAGS flows from the new AGS facilities. Figure 2 provides the settling rate impacts. Addition of WAGS increased the settling rate of the activated sludge biomass. The effect on settling rate would increase the peak flow capacity of the activated sludge facilities from 110 mgd to 130 mgd. SOUR testing indicated that the WAGS would have a 25% higher oxygen uptake rate than WAS (Figure 3). This indicates that there will be an oxygen demand associated with either particulate COD bound in the WAGS or potentially stored carbon. This oxygen demand is considered during aeration operation in the activated sludge system. The nitrification rate of WAGS (4 mgN/gVSS-hr) was similar to the nitrification rate of WAS (3.9 mgN/gVSS-hr). This was an unexpected result, as the WAGS likely contains a high VSS content of particulate COD from the influent. The benefit is that the WAGS will be adding a significant load of nitrifiers into the activated sludge system, increasing system resilience. The outcomes from this testing highlight how construction of an AquaNereda(R) facility in parallel to an activated sludge facility can provide a net benefit to the activated sludge facility. Applicability AquaNereda(R) has been sold as the evolution of activated sludge, but the requirement for a sequencing reactor can been seen as a limitation. The work completed highlights how an AquaNereda(R) process can be constructed in parallel to an activated sludge system, with positive impacts on the activated sludge facility. Audience Appeal Anyone looking at process expansion, nutrient removal requirements, and aging infrastructure would benefit from this presentation.

Application AquaNereda®, where aerobic granular sludge (AGS) is applied in a sequencing reactor, is often seen as a replacement to conventional activated sludge. During design FRSA facilities, the largest question for integration of the processes became how to manage the waste activated granular sludge (WAGS). The decision to send WAGS into the activated sludge system was informed by bench results showing positive improvements to SVI, stored carbon diversion and no nitrification impacts.

SpeakerDowning, Leon

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionEvaluating Plantwide Impacts of AGS and DAS

Session number606

Session locationRoom 343

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Downing, Leon, Loconsole, Jennifer, Redmond, Eric

Author(s)L.S. Downing1, J.C. Loconsole2, E.D. Redmond3

Author affiliation(s)1Black and Veatch, WI, 2Black & Veatch, IL, 3Black & Veatch, IA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159637

Volume / Issue

Content sourceWEFTEC

Word count15

Optimization Strategies: Improve P-removal (TRA) Case Study

Abstract

Converting a nitrification facility to a facility that achieves nitrogen and phosphorus removal can often require a significant amount of new infrastructure for a facility. The Trinity River Authority of Texas implemented an eight-year program to understand nutrient removal at low dissolved oxygen (DO) concentrations. The result is the design and operation of a small-footprint, high performance facility.

SpeakerDowning, Leon

Presentation time

10:50:00

11:00:00

Session time

08:30:00

12:00:00

SessionStrategies to Optimize WRRFs for Nutrient Removal

Session number510

TopicNutrients, Research and Innovation

Author(s)

A. ShawL. DowningL. Downing

Author(s)A. Shaw1; L. Downing2; L. Downing2;

Author affiliation(s)Black & Veatch, TX1; Black & Veatch, WI2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157511

Volume / Issue

Content sourceWEFTEC

Word count8

Partial Denitrification and Nitrous Oxide Dynamics Across Carbon Sources

Abstract

[b]Introduction[/b] Nitrous oxide (N[sub]2[/sub]O) is a potent greenhouse gas (GHG), making its mitigation a critical priority in efforts to combat climate change. Water Reclamation Facilities are recognized as a major source of N[sub]2[/sub]O emissions, particularly during biological nutrient removal processes (Daelman et al., 2013). Effective mitigation strategies focus on reducing N[sub]2[/sub]O carryover from anoxic denitrification zones into highly aerated zones where stripping occurs. Since nitrite is a key precursor for N[sub]2[/sub]O formation, understanding the mechanisms of N[sub]2[/sub]O production during denitrification, especially partial denitrification, is essential as the industry advances toward more resource-efficient treatment processes. [b]Objective and Novelty[/b] Research on N[sub]2[/sub]O dynamics during partial denitrification, especially the role of different carbon sources, is limited. This study addresses that gap through the following objectives: •[i]N₂O production during partial denitrification[/i]: Investigate the pattern of N₂O production under partial denitrification using various carbon types. •[i]Investigation N₂O mitigation strategy[/i]: Assess the feasibility of employing alternative carbon sources to sustain denitrification while minimizing N₂O emissions. [b]Methods[/b] A 100 gallon sequencing batch reactor (SBR) was operated at the Hayward WPCF using low strength trickling filter effluent. The reactor ran with a 12 hour HRT under intermittent aeration. The aerobic SRT was gradually reduced from 8.3 to 6 to 4 days. Carbon was added at the start of each anoxic phase to support denitrification. At 4 day aeSRT, two carbon sources were tested: MicroC®2000 and a synthetic fermentate (SF) containing 50% acetate, 30% propionate, and 20% butyrate. With SF, both low and high COD:NOx conditions were evaluated. After ~3 weeks of acclimation for each carbon source, in situ denitrification batch tests were performed to assess denitrification rates and N₂O dynamics. Under high COD:NOx with SF, individual VFAs were also tested. Dissolved N₂O was measured using a Unisense sensor. [b]Results and discussion[/b] [i]Higher N₂O with MicroC[/i] Batch denitrification assays indicated partial denitrification with both MicroC and SF as carbon sources showed that nitrite accumulation increased with higher COD:NOx dosing ratios (Figure 1). It was observed that the ecology acclimated to higher COD:NOx dosing exhibited lower nitrite accumulation. However, parallel bench-scale experiments during the same period of reactor operation showed nitrite accumulation as high as 65 %, highlighting variability in the efficiency of nitrite accumulation. Figure 2 shows typical nitrate, nitrite, and N₂O profiles during denitrification testing at 4 day aeSRT with both carbon sources dosed at a COD:NOx of 6:1. While both carbon types produced partial denitrification, their N₂O patterns differed: MicroC led to continued N₂O buildup until NOx was fully depleted, whereas SF resulted in minimal, short lived N₂O accumulation, indicating simultaneous NOx and N₂O reduction. [i]VFA fractionation in fermentate impacts nitrite accumulation during denitrification[/i] Denitrification assays using SF acclimated biomass were conducted to evaluate partial denitrification efficiency with individual VFAs. NO2 accumulation differed across carbon sources (Figure 3). Propionate exhibited the least NO₂ buildup, consistent with previous findings that link PHV synthesis to reduced NO₂ compared to PHA derived from sodium acetate (Ji et al., 2025). Despite these differences in nitrite accumulation, N₂O concentrations remained largely unchanged, indicating that N[sub]2[/sub]O dynamics were not significantly influenced by the choice of VFA. [i]Switch between carbon sources[/i] Denitrification and nitrite accumulation were evaluated using MicroC and SF after biomass acclimation to the alternate carbon source. When MicroC was added to SF acclimated biomass, denitrification rates were similar, but nitrite accumulation decreased. Conversely, poor denitrification rates were observed when MicroC was added to SF acclimated biomass. These bench scale tests did not measure N[sub]2[/sub]O, but given earlier evidence of simultaneous N₂O reduction with SF, co dosing SF may help facilities relying on MicroC reduce N[sub]2[/sub]O emissions. [b]Benefits and Significance[/b] This research provides a comprehensive assessment of N[sub]2[/sub]O dynamics during anoxic denitrification, offering valuable insights for process optimization and greenhouse gas mitigation in biological nitrogen removal systems. The findings enhance understanding of N[sub]2[/sub]O behavior and inform strategies for sustainable wastewater treatment. Key contributions include: •Comparable partial denitrification efficiency was achieved using both MicroC and synthetic fermentate as carbon sources. •Carbon source selection is critical for N[sub]2[/sub]O mitigation; glycerol-based sources tend to generate higher N2O emissions compared to acetate-rich fermentate. •Partial denitrification depends on VFA composition, with propionate exhibiting lower nitrite accumulation than acetate and butyrate. •Synthetic fermentate demonstrates strong affinity for N[sub]2[/sub]O reduction, and its comparable performance in MicroC-acclimated systems highlights its potential as a co-dosing strategy to reduce N[sub]2[/sub]O emissions.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionAdvances in PdNA through Lab and Pilot Scale Research

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Bhattarai, Bishav, Pifer, Leah, Sabba, Fabrizio, Downing, Leon

Author(s)B. Bhattarai1, L. Pifer1, F. Sabba1, L. Downing1

Author affiliation(s)Black & Veatch, 1Black & Veatch, 1Black & Veatch, 1Black & Veatch, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160496

Volume / Issue

Content sourceWEFTEC

Word count10

Description: Performance, Key Operational Parameters, and Design Targets For Nitrogen Removal...

Performance, Key Operational Parameters, and Design Targets For Nitrogen Removal During Post Aerobic Digestion (PAD): Analysis From Two Full-Scale PAD Reactors Over Multiple Years of Operation

Abstract

Background
Sequential anaerobic-aerobic digestion is an under-studied, under-used process that offers potential for improved solids digestion with simultaneous nutrient removal. Previous studies have highlighted the importance of post-aerobic digestion (PAD) following anaerobic sludge digestion and reported high volatile solids removal (VSR) and chemical oxygen demand (COD) reduction along with improved sludge dewaterability (Parravicini et al. 2008, Zupancic and Ros 2008). In addition, nitrogen removal can occur via nitrification and dentrification resulting in reduced nitrogen load recycled to the head of the plant (Novak et al 2011). Limited information is available on the PAD process for full-scale systems. Thus future design and current understanding of parameters that drive this process are not well documented or understood. The PAD process has been a critical component of overall nitrogen removal at the Northern Treatment Plant (NTP) for the Metro Water Recovery in Denver and the WRRF in Boulder. Analysis of these systems is needed to help fill this critical knowledge gap.
Status These full-scale reactors have been in operation for several years. Full-scale data have been collected for multiple years at both plants during times of healthy operation and poor performance. Analysis has been conducted on this data set. The presentation and proceeds will present work on this completed study. Findings Overall, the PAD process at both Boulder and Denver resulted in substantial removal of N and reduced the returned N burden. Boulder and Denver had similar average influent ammonia concentrations of approximately 1,600 mg/L (NH4-N). Denver had a longer SRT (Table 1) than Boulder, and slightly more ammonia removal than Boulder, but both plants achieved â‰¥ 80% ammonia removal. The VSR was slightly higher at Denver than Boulder, but both were near 10% which has been observed in lab-scale studies as well (Novak 2011). Denver had very low nitrite and nitrate levels, both less than 5 mg/L, implying substantial denitrification following nitrification. Denver's 91% TIN removal is substantial in terms of minimizing nitrogen that otherwise would be returned to the head of the plant. Boulder had higher levels of nitrite, over 50 mg/L, resulting in 80% removal of TIN, and thus a major reduction in nitrogen that would be returned to the head of the plant. While the average ammonia and TIN removals were similar between the two plants, the nitrogen loading rate and the nitrogen rate of removal was much greater at Boulder. Boulder operated at a lower SRT and consequently had an ammonia loading rate to the PAD reactor that was double that of Denver. The ammonia removal rate per volume of reactor and per kg VS was nearly double in the Boulder reactor compared to the Denver reactor. These data represent the first data set on two full-scale PAD operators and indicate that PAD can operate well over a wide range of feed rates and SRT values. At both Denver and Boulder, higher removal rates occurred at SRT values below 15 days (Figure 1). All removal rates above 125 mgN/L-day (indicated by blue line) occurred at SRT values less than 15 days. Conversely, when SRT values were above 15 days, the ammonia removal rate never surpassed 124 mgN/L-day. Lab-scale experiments revealed more than 80% removal and 10% VSR at an SRT value of 5 days (Novak et al. 2011). Based on these selected healthy operational data, an SRT value of 6 to 8 days would be an appropriate operational target. Ammonia removal rate was linearly correlated to nitrogen loading rate (Figure 2). Boulder had higher ammonia removal rates and higher nitrogen loading rates than Denver. The linear relationship between nitrogen loading rate and ammonia removal rate did not taper off across the ranges used. Therefore, it's possible that nitrogen loading rate could be increased even more to achieve higher ammonia removal rates. This result is similar to the SRT results above, i.e. that SRT could be decreased even more which would result in a higher nitrogen loading rate. For the Boulder data set, 94% of ammonia removal rate variance was explained by nitrogen loading rate. Loading rate is therefore a major driver of performance. Denver had a lower, but still strong R2 value of 69%. Slow changes to operation rates could reveal how much beyond the 0.3 gN/L-day threshold the loading rate could be increased. Both treatment plants had extended periods of healthy reactor operation, as evidenced above. Both plants had periods of poor performance (Figure 3). At Denver, ammonia removal rate had a steady decline beginning Fall, 2020 and lasting through mid 2021. The Boulder PAD reactor was off-line from September, 2018 until mid-summer, 2019. The functional data from all of these periods were evaluated together to determine the impact of operational parameters (SRT, pH, temperature) on process performance based on N removal. In general, the reactors operated well at pH values lower than 7.5 (Figure 4). At higher pH values and higher ammonia concentrations, free ammonia (NH3) toxicity and inhibition of nitrification can become an issue. Other data not shown here revealed that sudden changes to multiple parameters such as dropping pH and temperature can have confounding impacts. The PAD system is fundamentally driven by biology; when the microbial community is perturbed process upset occurs, leading to a rise in pH and process failure. The complete set of functional data will be presented at WEFTEC, including aeration rates, anoxic/oxic cycling times, SRT, and alkalinity.
Significance of the Investigation This is the first report to compare multiple full-scale PAD reactors relative to design criteria. Information on PAD reactors even at the lab-scale is scarce in literature. This technology, though, can be readily applied at WRRFs that have available tanks. The data presented in this proceedings and presentation can be used to determine how much additional ammonia removal could be achieved via PAD systems. Several key design parameters to consider for PAD design: - Ammonium loading rate: volumetric removal rates of up to 300 mg/L-day and were strongly correlated to loading rate - Sludge Retention Time (SRT): higher removal rates were observed at lower SRTs. - pH: ammonium removal was achieved at a pH range of 6 to 7.5. Bicarbonate alkalinity is the larger driver, which will be discussed during the presentation. - Volatile solids reduction: the VSR was consistently 9 to 10% - Operational stability: one key area to highlight is the importance of SRT stability in PAD For the Denver facility, it can be seen that periods of time where the SRT is changed rapidly correspond to effluent ammonium stability (Figure 5). There may be a tendency to think of PAD as an equalization volume before dewatering, but SRT stability is stressed.

This is the first report to compare multiple full-scale PAD reactors. This technology can be readily applied at WRRFs that have available tanks. The data presented in this proceedings and presentation can be used to determine how much additional ammonia removal could be achieved via PAD systems. This work also provides a range of healthy operational values similar to what the field has for anaerobic digestion. As PAD reactors gain in their popularity, they will be designed from scratch inste

SpeakerDowning, Leon

Presentation time

13:30:00

13:55:00

Session time

13:30:00

15:00:00

TopicIntermediate Level, Biosolids and Residuals, Facility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Downing, Leon

Author(s)Leon Downing1; Patrick Dunlap1; Christopher Marks2; Patrick McNamara1; Eric Redmond1; Thomas Worley-Morse3

Author affiliation(s)Black & Veatch1; City of Boulder2; Metro Wastewater Reclamation District3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158579

Volume / Issue

Content sourceWEFTEC

Word count27

Primary Filtration Waste: How Do We Handle This High Volume Waste? Completing the Carbon Diversion PFD - SAF Pilot Results

Abstract

Introduction Intensification processes have been a focus largely for secondary and anaerobic treatment processes. These approaches have enabled utilities to increase performance, reduce footprint, and enable carbon redirection and capture. As we continue to evaluate drivers that include capacity, nutrient removal, carbon redirection, intensification, and energy reduction, enhanced primary treatment (EPT) plays a key role to whole facility integration considerations. Primary filtration technologies are increasingly evaluated as an alternative that enables high carbon redirection through >80% TSS and 50 to 70% BOD capture in a footprint that is approximately 25% of conventional primary clarification. This technology offers significant opportunity for facilities to divert carbon from liquid stream systems to anaerobic digestion, saving on aeration costs and increasing biogas production. However, full integration into existing facilities requires consideration to existing thickening facilities. Primary filter sludge is a high volume, low concentration that is 2 to 3x the volume seen with conventional primary clarifiers with a concentration of 3,000 to 5,000 mg/L. Further, the characteristics of the waste stream include a significant increase to non-settleable TSS and colloidal material that was previously not captured with conventional primary treatment. A comparison of anticipated capture efficiencies of thickening technologies (Figure 1) and footprints (Figure 2) indicates conventional gravity thickeners are significantly disadvantaged compared to other mechanical thickening technologies. Primary filter technologies are often solids limited vs. hydraulically limited (as in the case of tertiary filters). A reduction in capture efficiency of 5 to 10% has a resulting impact to filter loading rates, increasing surface area requirements by an equivalent rate. This technology review also indicated a potential opportunity for Suspended Air Flotation (SAF), offering a high hydraulic loading rate with potentially high capture efficiencies. SAF, provided by Heron Innovators, is similar to dissolved air flotation thickening but uses a surfactant to aid in solids separation and flotation. However, the technology had no primary sludge (filter or clarifier) thickening references and limited municipal waste activated sludge (WAS) case studies (with most installations to date being industrial applications). The Trinity River Authority of Texas (TRA) will soon be expanding the Denton Creek Regional Wastewater System (DCRWS) Facility. One component of the proposed expansion is the addition of primary filters. A preliminary assessment of a range of thickening technologies using economic and noneconomic factors indicated that SAF thickening could offer substantial economic benefits to TRA. Potentially, the SAF system could require the least amount of equipment, which correlates to a smaller footprint, and low chemical conditioning requirements, which translates to lower operations costs. As a result of the evaluation of technologies, SAF was selected as the basis of design for co-thickening blended (primary and waste-activated) solids. The decision to select SAF as the thickening option in this design constitutes an uncommon and innovative use of this technology. To confirm suitability of SAF for primary filter applications and to better understand the key design parameters driving SAF performance in the blended solids thickening application at DCRWS, a SAF pilot study was conducted at the Ten-Mile Creek Regional Wastewater System (TMCRWS) Facility. TRA and BV worked with Herron Innovators, Inc., providers of the SAF technology, to develop the pilot test. SAF systems are similar in concept to the older dissolved air flotation (DAF) systems in that both technologies float solids to the top of their respective tanks for thickening and removal. The key difference is that DAF systems use pressurized air dissolved in water while SAF systems instead employ a surfactant charged emulsion of air and water (also referred to as 'froth') to efficiently float solids. This allows SAF systems to achieve high solids loading rates (SLRs), which reduces equipment and space requirements. Table 1 provides a summary of key design criteria comparing DAF and SAF technologies. The SAF pilot setup explored low solids concentration, high volume feed solids conditions indicative of primary filter solids and blended solids (primary solids + WAS) thickening applications. Key questions were explored related to hydraulic and solids loading rates as well as polymer and froth dosages, to determine what targets for each of these primary design criteria are best correlated with overall thickening performance in terms of solids capture and the resulting thickened solids concentrations. The pilot was operated for a total of five weeks to test a range of loading rates and scenarios. Pilot Setup The SAF pilot study was conducted at TMCRWS from July 11th through August 18th, 2023. The study setup included a trailer-mounted pilot-scale SAF unit provided by Heron, specifically the CF125 model, which has a flow capacity of 350 gpm and a flotation area of 17 ft2. Throughout the study, TRA staff collected samples twice daily for analysis. Results The results of the pilot study which will be elaborated on in the full paper, include:

*Capture Efficiency oPrimary Solids Capture Efficiency — the primary solids thickening performance was excell

Primary filtration, increases capture efficiencies in a small footprint. However, the backwash creates challenges due to the large volume and low concentrations. Pilot study focused on Suspended Air Flotation (SAF), with primary and blended sludges. Results indicate SAF linked with primary filters is capable of high loading rates, 5 to 10x that of conventional dissolved air flotation (DAF), with capture efficiencies of 95% and 5% thickened sludge.

SpeakerRedmond, Eric

Presentation time

09:30:00

09:50:00

Session time

08:30:00

10:00:00

SessionThickening and Dewatering: Design Considerations

Session number301

Session locationRoom 354

TopicBiosolids and Residuals

Author(s)

Redmond, Eric, Knight, Greg, Ruff, Caitlin, Harness, Crystal, Downing, Leon

Author(s)E.D. Redmond1, G. Knight2, C. Ruff3, C. Harness4, L.S. Downing5

Author affiliation(s)1Black & Veatch, IA, 2Black & Veatch, GA, 3Black & Veatch, TX, 4, TX, 5Black and Veatch, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159648

Volume / Issue

Content sourceWEFTEC

Word count21

Primary Sludge Fermentation in Chem-P Plants: Decoupling P-Release from C-Release

Abstract

Introduction Many wastewater treatment plants rely on chemical phosphorus removal (CPR) to meet discharge limits. CPR commonly relies on iron (Fe) addition to remove phosphorus (P), and though it provides reliability, the chemical can be costly. Plants with high enough volatile fatty acid (VFA) concentrations are often able to use biological P removal (BPR), allowing for savings on chemical costs. Additional carbon can be supplied from primary sludge (PS) fermentation to drive BPR. There is also an opportunity to use PS fermentate to support nitrogen (N) removal in plants with low discharge limits, which are generally dependent on external carbon addition, to offset chemical costs. Despite the potential cost reduction, there are challenges with implementing PS fermentate as a carbon source. During fermentation, nutrients are released in addition to VFAs and COD. N concentrations are low compared to COD, and can be managed through PdNA or reoxidation after denitrification. P is released through hydrolysis similar to N, but in CPR plants there is an additional release of Fe-bound P due to Fe reduction under anaerobic conditions. This can be a significant issue for plants with low P limits, such as the Blue Plains AWWTP which has a 0.18 mg/L discharge limit. The objective of this study was to evaluate conditions for decoupling COD and P release by managing Fe reduction of Fe-P precipitation within the fermenter. Recent studies show that vivianite, an Fe-P mineral, may precipitate at a pH greater than 6. Therefore, it was hypothesized that pH adjustment may be a viable strategy to support optimizing CPR. In addition to elutriation, lime dosing was explored as a method for raising the pH due to its availability at Blue Plains. Materials and Methods Two 60-L fermentation pilot reactors were fed with Blue Plains PS at 5 g/L and controlled to a SRT target of 1-d. The system was operated under several test scenarios including a control: mechanical treatment, low and high microaeration, and low and high lime slurry addition (100 and 200 mg/L CaCO3). Fe overdosing in full-scale treatment also occurred during testing but was not controlled as a test scenario. Measurements were performed on influent and decant fermentate to calculate concentrations and yields. A full-scale gravity thickener (GT) at Blue Plains was converted to fermenter conditions by allowing an SRT between 0.2-2 days and was operated under full-scale conditions for sludge composition and solids loading. Influent and effluent sludges were analyzed, and data was categorized by TSS: low (<3.5 g/L), medium (3.5-5 g/L), and high (>5 g/L). Yields were calculated assuming 100% elutriation in the fermenter by measuring concentration profiles within the GT. Results and Discussion Full-scale fermenter data from spring and summer 2024 and 2025 shows an estimated yield of 0.0332 mg P/mg sCOD, while literature data from BPR plants show much lower P yields per mg of sCOD, from 0.0046 to 0.0022 (Figure 1a). It was hypothesized that all additional release at Blue Plains was a result of Fe dosing and thus could be decoupled from the sCOD release (Figure 1a). Separating the data into a low (<6) and high (>6) pH scenarios show that a high pH leads to ~20% less P yield per mg sCOD, at 0.0238 mg P released per mg sCOD, compared to 0.0298 mg P/mg sCOD at a low pH (Figure 1b). Several options were explored to raise fermentate pH above 6, into a range suitable for vivianite precipitation, including alkalinity dosing, Fe overdosing, and PS dilution. Alkalinity dosing and Fe overdosing In fermentation pilot control scenarios, PS fermentation reduced sludge pH from 6.28±0.12 to 5.51±0.26, which is below the range for vivianite formation, leaving Fe and P in their soluble forms. The average control fermentate OP-P was 13.50±2.82 mg/L (Figure 2a). Lower P levels were found at fermentate pH greater than 5.83, and when sufficient iron was available for P removal (Figure 2a, b). High fermentate pH was a result of either a high lime dose (200 mg/L CaCO2), or overdosing of FeCl3 in primary treatment, which led to high levels of Fe(OH)3 in the PS. The low alkalinity scenario (CaCO3 dose of 100 mg/L) had a pH of 5.71 with 12.62 mg/L OP-P in the fermentate, while the high alkalinity scenario (CaCO3 dose of 200 mg/L) had a pH of 6.36 and 2.72 mg/L OP-P. Overall, the 200 mg/L lime dose was effective at removing P, while the lower dose may not have achieved a high enough pH for efficient P removal. Periods of higher background Fe also saw effective P removal, with pH values of 6.06 and 6.01, and OP-P at 4.76 ± 3.7 and 2.65 ± 2.4 mg/L in the decant fermentate. PS dilution Within the GT, PS elutriation resulted in a lower incoming TSS, leading to lower blanket sCOD, higher average blanket pH, and lower OP-P (Figure 3). At a pH greater than 5.75, the average OP-P was below 17.5 mg/L, while operating at a lower pH led to an average OP-P of 47.6 mg/L (Figure 3a). Fe concentrations followed a similar trend to OP-P, showing that the chemical Fe-P dynamics were modified with the change in pH (Figure 3b). Decoupling COD and P release An estimate of 0.0046 mg P/mg sCOD (Figure 1) was used to calculate P released solely from hydrolysis within the GT operating at an SRT of 0.8 to 1.5 days. Additional P release, assumed to be a result of Fe reduction, was significantly different between scenarios with a pH below and above 6 (T-test, p = 0.1126) (Figure 4). This indicates that raising the pH above 6 is a viable solution for reducing excess P release. With elutriation, the GT achieved a fermentate OP-P release of less than 17.5 mg/L, and the projected mainstream P was less than 0.4 mg/L. The lower P release at higher pH showed decoupling of OP-P and sCOD, however the projected mainstream P was not yet low enough to meet plant discharge limits of 0.18 mg P/L. This demonstrates that dilution is a low-cost practical solution to achieve target pH conditions without losing sCOD loads, however additional research is needed to understand changes in buffer capacity over different seasons and sludge characteristics. Future work includes testing in wintertime to investigate seasonal effects. Conclusions The results of the full-scale GT and fermentation pilot studies demonstrate that pH management is a viable strategy for decoupling COD and P release at CPR plants. A higher pH can be achieved through alkalinity addition, Fe overdosing, or sludge dilution. These strategies maintain good sCOD yields while decreasing P in the mainstream.

This paper was presented at the WEF Residuals, Biosolids, and Treatment Technology Conference in Kansas City, MO, May 11-14, 2026.

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionOptimizing Sludge Fermentation: Managing P Release and Recovery

Session locationKansas City Convention Center

TopicDigestion

Author(s)

Hanson, Kathryn, Davis, Sophia, Poli, JoCo, Boulware, Mekhi, Avila, Isaac, Islam, Shafkat, Massoudieh, Arash, Downing, Leon, Ladipo-Obasa, Mojolaoluwa, Miranda, Miguel, Passarelli, Nicholas, Ngo, Khoa Nam, De Clippeleir, Haydee

Author(s)K. Hanson1, S. Davis1, J. Poli2, M. Boulware, I. Avila3, S. Islam4, A. Massoudieh5, L. Downing3, M. Ladipo-Obasa1, M. Miranda1, N. Passarelli1, K. Ngo1, H. De Clippeleir1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2026

DOI10.2175/193864718825160232

Volume / Issue

Content sourceResiduals, Biosolids and Treatment Technology Conference

Word count11

Description: Repurposing Infrastructure for Phosphorus Removal: Developing Design Guidelines for...

Repurposing Infrastructure for Phosphorus Removal: Developing Design Guidelines for S2EBPR

Abstract

Management of the global phosphorus cycle is crucial for long-term sustainability. Water resource recovery facilities (WRRFs) play a critical role in in the phosphorus control and balance in many watersheds throughout North America, and the discharge of soluble and other bioavailable forms of phosphorus from WRRFs has a global impact on soluble-nutrient balances in the water cycle. Enhanced biological phosphorus removal (EBPR) is one key process applied to remove phosphorus from the liquid discharges at WRRFs. Through EBPR, phosphorus is concentrated from the wastewater into the biosolids stream, where it can be recovered in biosolids or extracted as a fertilizer product. Recycling phosphorus in this way helps close the phosphorus cycle without discharging phosphorus into waterbodies. Over the past 50 years, EBPR has evolved from an unexplained phenomenon to a widely adopted process that is simultaneously praised for its efficiency and environmental soundness and cursed for its instability. Understanding of the process has never been complete, but recent advances in the research and interests in alternative processes at the facility mean the time has come to enhance water-sector understanding with the latest knowledge of EBPR ecology, functionality, and design. One of the key innovations for phosphorus removal has been the adoption of side stream EBPR (S2EBPR) concepts into the design of EBPR facilities. These concepts focus on fermentative activity of phosphate accumulation organisms (PAOs) to drive EBPR, often in side stream reactors. These side stream reactors focus on hydrolysis of a portion of return activated sludge (RAS) or mixed liquor (ML) to select for fermentative PAOs and drive phosphorus removal. This presentation will focus on results for the ongoing Water Research Foundation (WRF) project focused on developing practical considerations for S2EBPR design and operation (Project Number 4975). This project will yield guidelines for the design, operation, and implementation of a unique configuration to help remove phosphorus while maximizing the use of existing infrastructure. The re-purposing of existing infrastructure is a key benefit of S2EBPR configurations. When fermentative PAOs are the main driver for phosphorus removal, the selective pressure occurs in a side stream reactor typically conditioning RAS. Only 10 to 30% of the RAS is diverted to this side stream reactor, resulting in a relatively small reactor. Depending on the influent characteristics, this side stream reactor can ferment RAS, select for PAOs, and then this fermented flow is sent back to the existing aeration basins. This can result in a phosphorus removal upgrade the requires no modifications to the existing aeration basins, a smaller anaerobic side stream reactor, and often the side stream anaerobic reactor can be incorporated into existing, underutilized tankage for facilities. There are 14 full-scale demonstration facilities participating in the WRF project, and each facility has repurposed infrastructure in different ways. Some of the unique configurations being tested include:
- A Texas facility that utilized existing tanks to test ML fermentation to successfully achieve a 1 mg/L effluent limit with no new tanks (WRF Report 4827C) ###- A large midwestern facility that converted excess aeration basin capacity into a side stream reactor at a COD limited facility to achieve a 0.5 mg/L effluent limit
- A northeastern facility that utilized an abandoned gravity thickener tank to achieve a 0.3 mg/L effluent limit###- Danish facilities that utilize small RAS hydrolysis tanks with no mainstream selector zones to achieve phosphorus removal The facilities being tested, as well as past literature values, will be presented to observe trends in sizing and performance related to diversion rates of return activated sludge (RAS), hydraulic retention times of side stream reactors, and the ratio of biomass in the side stream reactor. One important concept is the idea of the fermenter biomass to total biomass in the system. This idea, first developed in Denmark, provides a design basis for S2EBPR that relates the time in the side stream anaerobic zone to the overall sludge retention time of the system. When well performing EBPR facilities are examined (effluent phosphorus below 0.75 mg/L), the generally fall above a curve developed for Danish facilities (Figure 1). Facilities that fall below this curve to not achieve consistent EBPR.

The following conference paper was presented at WEFTEC 2021, October 16-20, 2021. To read the full abstract, see "Abstract" tab below.

SpeakerDowning, Leon

Presentation time

13:30:00

13:45:00

Session time

13:30:00

15:00:00

SessionBringing It All Together: Guide to Designing and Implementing S2EBPR Processes

Session number502

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Leon Downing

Author(s)L. Downing1;E. Redmond2;P. Dunlap3;J. Barnard4;

Author affiliation(s)Black & Veatch, Madison, WI1Black & Veatch, Des Moines, IA2Black & Veatch, Philadelphia, PA3Black & Veatch, Kansas City, MO4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158179

Volume / Issue

Content sourceWEFTEC

Word count11

SND: Why You Should Believe

Abstract

INNOVATION AND IMPACT Over the past two years, NEW Water, the brand of the Green Bay Metropolitan Sewerage District, completed full-scale demonstration testing of low dissolved oxygen (DO) setpoints to investigate the dynamics of simultaneous nitrification and denitrification (SND). The testing completed at NEW Water gave insight into: -SND dynamics quantified both in the field and via bench scale testing related to COD availability, DO setpoint impact, and COD type -Confirmation that SND does occur in both the field and bench scale testing -Identification of controlling parameters for SND, including COD:TN, floc size and DO setpoint -Identification of emissions risks, and the importance of SRT and aeration control to minimize emissions With the results from NEW Water, we can start to have a better prediction of the level of SND that will occur in our biological nutrient removal (BNR) designs. INTRODUCTION/BACKGROUND NEW Water is collaborating with Black & Veatch and EnviroMix (Xylem) to pilot a transition from their existing anaerobic-oxic process to an anaerobic-anoxic-oxic (A2O) process at low DO concentrations. The full-scale A2O test basin has an average primary effluent (PE) flow of 7 mgd and includes the addition of EnviroMix mixing technology and aeration and process control strategy (Figure 1). The demonstration at NEW Water has been operational for two years. Three different low DO aeration control strategies have been compared, as shown in Table 1, including static low DO setpoints of 0.3 mg/L and 0.5 mg/L, and FlexZone operation, an aeration and mixing control strategy to dynamically transition DO setpoints. METHODOLOGY Sensors: Two YSI VARiON ion-selective electrode (ISE) sensors measuring ammonia (NH4) and nitrate (NO3) were installed within the demonstration basin to support continuous, in-situ nitrification and denitrification rate calculations. One sensor was located at the end of the anoxic zone, while the second was installed in the middle of subzone 2 (SZ2), approximately one-third of the way through the low DO aeration zone. DO was monitored in each aerated zone using optical sensors, and biomass concentration was estimated using a total suspended solids (TSS) sensor. In-situ Rate Calculations: Probe data was used to calculate in-situ nitrification and denitrification rates occurring in SZ1 and SZ2 under low DO conditions. The in-situ rates were calculated based on NH4 and NO3 values from both sensors on a one-minute frequency and utilizing a TSS probe and assumed MLVSS/MLSS ratio. Bench-Top Rate Testing: The impact of DO setpoint on nitrification rate was measured using benchtop nitrification rate testing. A DO controller was used to maintain a constant DO setpoint during three-hour rate tests ranging between 0.1 mg/L and 4 mg/L. Similarly, the denitrification rate was measured on the bench top with a range of DO setpoints, carbon-to-nitrogen ratios (C/N), and carbon sources, including endogenous decay products (no external carbon), acetate, and a synthetic fermentate mixture. RESULTS Full Scale SND Simultaneous nitrification-denitrification has been observed under conditions where bulk oxygen is limiting, reduced oxygen diffusion into flocs creates a thin aerobic layer over an anoxic core, and organisms with greater oxygen affinity are favored. This has resulted in reported reductions in total effluent nitrogen in the literature (Rieger et al. 2012; Regmi et al. 2022). Here, SND was observed across low DO control strategies. Mass balance calculations indicated SND increased with decreasing DO setpoints (Figure 2). The calculated nitrification and denitrification rates grouped by test phase are shown in Figure 3, with the correlation of nitrification rate and denitrification rate show for different DO bins. Figure 4 shows how the PE COD:TKN related to denitrification rate. Dissolved nitrous oxide (N2O) was also measured throughout testing to understand emission dynamics (Figure 5). Key observations from full-scale SND measurements include: -SND was consistently quantified using overall mass balance calculations in the aerobic zones during low DO testing. -At low DO conditions (<0.5 mg/L), the denitrification rate was consistently between 2 and 2.5 mgN/gVSS-hr despite the nitrification rate ranging from 2 to 6 mgN/gVSS-hr, indicating that denitrification was likely limited by carbon availability. -At higher DO setpoints (>0.5 mg/L), the denitrification rate was strongly correlated to the nitrification rate, with the denitrification rate typically 30% of the nitrification rate. The maximum denitrification rate occurred at high nitrification rates (>6 mgN/gVSS-hr). At this high nitrification rate, the denitrification rate matched those observed at low DO setpoints (approximately 2 mgN/gVSS-hr). This indicates that nitrate availability is a critical aspect of SND at slightly higher DO setpoints. This may be associated with diffusion into flocs or possibly denitrification kinetics. -Although the lower COD:TKN data set was limited, a significant decrease in denitrification rate in the low DO zones was observed when COD:TKN was less than 6 in the PE. Denitrification rates averaged a more similar number at higher COD:TKN. -Emissions were dependent on an ecology that is stabilized for low DO operation. Benchtop Scale Testing Nitrification and denitrification kinetics were further explored with benchtop testing. Nitrification followed a similar pattern to previously reported conditions (Sabba et al. 2024, Jimenez et al. 2024) (Figure 6). Benchtop denitrification rates were also measured at low DO conditions. With no external carbon added, no denitrification was observed in the lab. The greatest denitrification rate was observed with a complex carbon source at the highest C/N ratio. Additionally, when the DO setpoint was above 0.1 mg/L, denitrification was reduced significantly (Figure 7). Key observations from bench-scale SND measurements include: -Nitrification would likely not be limiting until the DO reached 0.1 mg/L. At this DO, the nitrification rate (1.2 mgN/gVSS-hr) is less than the average denitrification rate under low DO conditions -The denitrification rate at 0.1 mg/L is significantly higher than at a 0.25 mg/L DO setpoint and is highly dependent on the availability of carbon. -Interestingly, the denitrification rate in the full-scale (2 to 2.5 mgN/gNSS-hr) at <0.5 mg/L DO is similar to the denitrification rate in benchtop experiments at 0.1 mg/L DO. This may be an indicator that the DO profiles within the aerobic zone are critical, as small pockets of lower DO (~0.1 mg/L) may be a large driver for SND rates in full-scale aeration basins. The benchtop results also highlight the criticality of floc size, as a larger floc may experience more volume at less than 0.1 mg/L and drive higher SND rates. CONCLUSIONS AND SIGNIFICANCE SND was confirmed to be occurring with full-scale data based on lab measurements and online sensors. In addition, bench scale experimentation examined dynamics related to DO concentration, COD availability, and COD type on nitrification and denitrification rates at low DO concentrations (<0.5 mg/L). The results provide insights into why SND has been variable at different sites, and why the occurrence of SND was a hotly debated topic at WEF RBITT 2025. This project provides the following key insights: -Carbon matters. Higher PE COD:TKN ratios resulted in higher rates of denitrification in the low DO zones. When a facility has a COD:TKN ratio of less than 6, it may result in decreased rates of SND. -Denitrification is highly sensitive to DO concentration. In lab tests, the denitrification rate almost disappeared at a DO of 0.25 mg/L, but was similar to the observed rate at a DO of 0.1 mg/L. This relatively small change in DO likely lead to large variations in observed SND rates, and site-specific mixing and airflow distribution likely contribute to variations in observed SND in aeration basins. Maintaining a DO of less than 0.5 mg/L also appears to be a critical control factor. -Nitrification rate influences denitrification rate under low DO conditions. When the DO is greater than 0.5 mg/L, the denitrification rate is correlated to the nitrification rate. This means that SRT and HRT will have a large impact on the SND rates in the system. -Floc size will be a critical factor. This relates to the DO and nitrification rate influences on SND rates. The smaller the floc, the more sensitive SND will be to DO concentration as the micro-gradients in the floc will play a critical role in SND. -SRT and controls matter for SND and emissions. More stable SRTs and allowing for biological adaptation were critical for both SND rates as well as N2O production rates. SND designs should consider the design SRT, control equipment, and control loops carefully to maximize the level of SND occurring in the system.

This paper was presented at the WEF Residuals, Biosolids, and Treatment Technology Conference in Kansas City, MO, May 11-14, 2026.

Presentation time

08:30:00

09:00:00

Session time

08:30:00

10:00:00

SessionSmall Particles, Big Gains: Engineering the Ingredients for Intensification

Session locationKansas City Convention Center

TopicResource & Energy Recovery

Author(s)

Gutenberger, Gretchen, Downing, Leon, Sadreddini, Sara, Biese, Tyler, Watson, Joe, Elger, Sarah, Koch, John, Jordan, Taylor

Author(s)G. Gutenberger1, L. Downing1, S. Sadreddini1, T. Biese2, J. Watson2, S. Elger3, J. Koch3, T. Jordan3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2026

DOI10.2175/193864718825160245

Volume / Issue

Content sourceResiduals, Biosolids and Treatment Technology Conference

Word count6

Description: The Media is the Message: New Primary Treatment Process Based on Synthetic Media...

The Media is the Message: New Primary Treatment Process Based on Synthetic Media Biofiltration Allows for a More Sustainable and Resilient Alternative to CEPT in a Retrofittable Package

Abstract

This paper was presented at WEFTEC 2023 in Chicago, IL.

A new deep-bed primary filter was developed in Korea and transferred to North America as a more sustainable carbon diversion strategy than traditional chemically-enhanced primary treatment. This technology has been proven at scale and adapted to new markets by employing new configurations such as a biological split bed and retrofittable design.

SpeakerLiberzon, Jon

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionPrimary Treatment Technologies: Should We Settle for Conventional Primary Sedimentation?

Session locationRoom S501a - Level 5

TopicEnergy Production, Conservation, and Management, Facility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design

Author(s)

Liberzon, Jonathan

Author(s)J. Liberzon 1; D. Rhu 2 ; M. Magruder 3; L.S. Downing 4; G.T. Daigger 5;

Author affiliation(s)Tomorrow Water 1; Tomorrow Water 2 ; Milwaukee Metropolitan Sewerage District 3; Black & Veatch 4; University of Michigan 5;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159002

Volume / Issue

Content sourceWEFTEC

Word count29

Understanding Nitrous Oxide (N2O) Impacts on Carbon Footprint When Considering the Full Footprint of Nutrient Removal

Abstract

Introduction Water resource recovery facilities (WRRFs) have adopted low dissolved oxygen (DO) operation to reduce operating costs of activated sludge processes. However, the relationship between DO levels and greenhouse gas (GHG) emissions is complex and has attracted considerable interest. This modelling study investigated the impact of low DO conditions focusing on nitrous oxide (N2O) emissions, energy consumption (expressed as carbon dioxide equivalent, CO2-eq), and the beneficial nutrient removal, which includes reduced external carbon and chemical inputs. Although low DO operation in Biological Nutrient Removal (BNR) processes may increase the risk of N2O production, the net environmental impact may be surprisingly positive. This presentation will shed light on the carbon footprint (CF) and trade-offs between N2O emissions, energy consumption, and system performance of low DO operation at WRRFs. Materials and methods: A process model was developed within SUMO v.22 simulation platform (Dynamita, France). The process model (Figure 1) was based on an existing WRRF in Texas (USA) and was calibrated and validated utilizing special sampling and historical influent as well as operational data (RAS, MLSS and WAS) obtained from the facility. Dynamic simulations were conducted over a 720-day period using historical data for low DO (0.5 mg/L) and conventional DO (2 mg/L) with two different influent characteristics (carbon rich, high C, and carbon-deficient, low C). The model outputs from the four scenarios were used to compute indirect GHG emissions stemming from electricity and chemicals. The aeration energy necessary to maintain the designated DO levels in the reactors was determined based on airflows derived from the model. Using a conversion factor of 25 scfm/hP, the total blower power requirement was estimated. This blower power was then converted to kWh and multiplied by the daily CO2-eq of consumed electricity. The chemical phosphorus removal process involved the use of alum, while methanol addition was presumed to reduce nitrates to a maximum concentration of 8 mg/L. Daily CO2-eq values for alum and methanol were employed to estimate carbon emissions from chemical consumption, contributing to the calculation of total indirect GHG emissions in a BNR system. Results and Discussion: The results presented in Figure 2 indicate that the cumulative indirect GHG emission rates were consistently lower for low DO operation across all four scenarios, regardless of the influent carbon content. The average emissions for low DO operation were 58% lower than high DO operation (red dashed lines in Figure 2). Figures 3 and 4 illustrate the total GHG emissions from non-N2O sources and reveal that high DO scenarios had a 28% higher average aeration energy, which posed denitrification challenges. To address these challenges, high DO operations required post-anoxic carbon dosing, which increased the CF. Conversely, low DO operations exhibited lower aeration energy and minimal chemical addition, with Case C requiring 98% less carbon dosing than Case A and D requiring 88% less than Case B. Based on blower energy use, external carbon, and chemical coagulant addition operating a BNR system at low DO setpoints results in a significant reduction in CF for the known emission sources. The key question the industry is facing is how much N2O is emitted from low DO setpoints, and if this N2O emission offsets the CF reduction from energy, carbon, and chemical addition. While there has been research investigating the impact of low DO operation on N2O production, the rate of N2O production for low DO system is far from an established metric. For low DO systems to have a net reduction in CF, the resulting N2O emissions would need to be less than the carbon reduction from the known parameters (energy use, chemical addition, carbon addition). If the CO2 reduction is converted to kg N2O, and related to kg N2O production per influent N, an estimation of how much N could be emitted as N2O can be made while maintaining a net CF benefit. As shown in Figure 5 an increase in the N converted to N2O of 0.4 to 0.8% would need to occur before low DO would result in a net increase in CF. Using IPCC guidelines, a typical activated sludge system emits 0.7% of the influent nitrogen as N2O. Therefore, a low DO system would only result in a net increase in CF if the N2O emissions doubled compared to a conventional DO system. Conclusions: Understanding N2O emissions is a major driver for WRRFs. While European and Australian facilities have advanced the understanding on the dynamics associated with N2O production in activated sludge, the impacts of low DO operation on the net CF of BNR facilities needs to be better understood. An important consideration when evaluating the net CF is not just the N2O emissions and energy impacts, but the potential reduction in carbon and chemical addition by moving to lower DO setpoints. The simulation work completed highlighted key aspects of N2O emissions:

*N2O emissions in a low DO system would need to double the N2O emissions from a conventional DO system to offset the carbon emissions savings from energy, carbon addition, and chemical addition savings from low DO operation

*The lower the influent COD, the larger the net carbon emission benefit of operating at low DO concentrations in a BNR basin

This paper was presented at the WEFTEC 2024 conference in New Orleans, LA October 5-9.

SpeakerDowning, Leon

Presentation time

15:30:00

15:40:00

Session time

15:30:00

17:00:00

SessionN2O Unmasked: Understanding and Taming Emissions

Session number426

Session locationRoom 253

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation