Latimer, Ron, Latimer

Ron leads the Wastewater Process Modeling Group for Hazen and Sawyer and provides company-wide oversight for all aspects of BioWin™ and GPS-X...

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About Latimer, Ron

Ron leads the Wastewater Process Modeling Group for Hazen and Sawyer and provides company-wide oversight for all aspects of BioWin™ and GPS-X modeling, including field testing, calibration, and application of the model for process design and optimization. He also provides firm-wide wastewater process design support. Ron's experience includes the planning, analysis, and design of municipal wastewater facilities with expertise in BNR/ENR systems, and he has designed numerous wastewater treatment plant expansions and upgrades. Ron specializes in biological and chemical process, nutrient removal and recovery, and chemical and energy optimization. He has participated in process modeling at more than 50 BNR/ENR facilities.

Latimer, Ron

Titles from this speaker

0.6 MGD Validation of a Unique Tertiary MBR Process to Provide NdN for Pure Water

Abstract

INTRODUCTION
The Los Angeles County Sanitation Districts (LACSD) and the Metropolitan Water District of Southern California (MWD) are jointly developing the Pure Water Southern California program, which would supply up to 150 million gallons per day (mgd) of potable reuse water to the region from LACSD's A.K Warren Water Resource Facility (Warren Facility). The Warren Facility is a 400-mgd capacity non-nitrifying High Purity Oxygen Activated Sludge Plant currently being evaluated for a 'Flex membrane bioreactor (MBR)' concept that would employ a modular design enabling different reactor modes as needed by the program (Figure 1; Fitzgerald et al., 2024).

One potential mode is nitrification-denitrification (NdN) tertiary MBR (tMBR) using glycerol as the carbon source. This mode would offer additional treatment barriers between wastewater and the product water but at higher operating cost. Initial design utilizing a post-anoxic configuration showed nitrite (NO2) accumulation when tested at demonstration scale (Lai-Bluml and Trussell, 2020). Later designs utilizing a pre-anoxic configuration showed no such issue at bench and pilot scale (Liu et al., 2022; Deco et al., 2023). The current work validates these findings at demonstration scale (~0.6 mgd).

METHODOLOGY
Testing was conducted at the Napolitano Center's Demonstration Plant. The process' flow diagram is illustrated in Figure 2 and was seeded with mixed liquor from a local MBR. Warren Facility secondary effluent was utilized as the feed with characteristics summarized in Table 1. The glycerol source was MicroC-2000 (EOSi, Pocasset, MA). Additional design and operational parameters are summarized in Table 2.

The study included two major phases (Table 3): Phase 1 involved constant flow operation; Phase 2 involved diurnal flow operation, corresponding to program buildout. Routine monitoring results are summarized in Table 4. 16S rRNA metagenomic analysis was performed by DNASense (Aalborg, Denmark).

RESULTS
Observations Fitting Expectations
Figure 3 summarizes MBR filtrate nutrient levels from the study. During constant flow operation (Phase 1), all metrics met the targets: ammonium (NH4) and NO2 were consistently below 1 mgN/L; nitrate (NO3) was at or below 19 mgN/L; and soluble orthophosphate (SOP) was below 1 mgP/L. During initial diurnal flow operation (Phase 2a), process instability was encountered (discussion below). After re-stabilization, diurnal flow operation was revisited with enhanced dissolved oxygen (DO) monitoring (Phase 2c) and again met the targets.

Denitrification stability was judged by anoxic NOx (NO2+NO3) residual, which can correlate with NO2 accumulation (Liu et al., 2022). Anoxic NOx remained stable and low throughout the study (Figure 4), except: (a) during the process instability event (Phase 2a); and (b) when the system was stressed for lower NO3 target (Phase 2c). Carbon demand in chemical oxygen demand (COD) added to nitrogen removed (C/N) was in the expected range of 5~6 g-COD/g-N (Figure 5).

Unexpected Observations
Biological Instability Event
Diurnal testing (Phase 2a) showed periodic NH4 bleed through (Figure 3). This issue was attributed to a faulty DO probe and under-aeration. Airflow was increased in June which addressed NH4 bleed through but led to NO2 accumulation (Figure 6) and broad process instability, including drops in mixed liquor total and volatile suspended solids (MLSS and MLVSS) (Figures 7 and 8) and increases in filtrate SOP (Figure 9), COD (Figure 10), and time-to-filter (TTF; Figure 11). Influent inhibition was ruled out as a cause as the symptoms did not appear in other nitrifying pilots operated in parallel.

The instability event significantly reduced NO2 oxidation, while minimally affected NH4 oxidation (Figure 12). 16S rRNA metagenomic analysis showed a dramatic shift in nitrite-oxidizing bacteria (NOB) population from comammox-dominated to canonical NOB (Figure 13).

Diurnal testing was revisited with enhanced DO monitoring. During this period, the instabilities did not return, suggesting under-aeration as a potential cause for the instability. Additional microbial analyses are underway.

Biomass Yield The modeled biomass yield was ~0.3 lbs-VSS/lb-CODadded, but observations showed ~0.4 lbs-VSS/lb-CODadded (Figure 14). Two hypotheses were proposed: enrichment of specialist heterotrophs and internally stored carbon (ISC), as supported by the following:
- Ordinary heterotrophic organisms (OHOs) typically have a decay rate of 0.67 d-1, while specialist organisms, like methanol utilizers, have lower decay rates near 0.05 d-1. Analysis indicated that a specialist population with a decay rate of ~0.1 d-1 could explain the higher yield observed (Figure 15).
- Microscopy with Neisser staining suggests enrichment of organisms with storage granules (Figure 16).
- Increased airflow during process instability led to a loss of MLSS (Figure 7) and a reduced MLVSS/MLSS ratio (Figure 8), possibly due to rapid ISC oxidation.

BENEFITS AND SIGNIFICANCE
This work demonstrated that pre-anoxic NdN TMBR successfully addresses NO2 accumulation previously observed and met all key performance targets. The instability event encountered may have broader program and industry implications. Most notably, comammox-dominated nitrifying and ISC-driven denitrifying systems may be created with under-aeration and destabilized with a sharp increase in aeration.

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

Presentation time

13:30:00

13:45:00

Session time

13:30:00

15:00:00

SessionApplications and Optimization of MBR Technology

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Liu, Michael, Fitzgerald, Colin, Danker, Bryce, Ronn, Alan, Maceiko, Shannon, Deco, Rachel, Mansell, Bruce, Tanuwidjaja, Dian, Constantine, Timothy, Latimer, Ron, Pitt, Paul, Sun, Yewei, Khunjar, Wendell

Author(s)M. Liu1, C. Fitzgerald3, B. Danker4, A. Ronn2, S. Maceiko2, R. Deco1, B. Mansell1, D. Tanuwidjaja2, T. Constantine3, R. Latimer4, P. Pitt4, Y. Sun4, W. Khunjar4

Author affiliation(s)LA County Sanitation District1, Metropolitan Water District of Southern California2, Jacobs Engineering3, Hazen and Sawyer4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159963

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Adapting to What Flows Down the Pipe: Full-scale Bio-P Optimization Following...

Adapting to What Flows Down the Pipe: Full-scale Bio-P Optimization Following Changes in the Collection System

Abstract

The F. Wayne Hill Water Resources Center (FWHWRC) is Gwinnett County’s largest and most advanced wastewater treatment facility with a capacity of 60 MGD (maximum month). The FWHWRC utilizes enhanced biological phosphorus removal (EBPR) and chemical trim to meet a stringent effluent TP limit of 0.08 mg/L. This paper will discuss details of efforts undertaken to address impacts on full-scale plant operations, primarily resulting from changes in the collection system related to odor and corrosion control chemicals, that further influenced raw wastewater characteristics.

The F. Wayne Hill WRC is Gwinnett County's largest, most advanced wastewater treatment facility with a capacity of 60 MGD. FWHWRC utilizes EBPR and chemical trim to meet a stringent effluent TP limit of 0.08 mg/L. This paper will discuss efforts undertaken to address impacts on full-scale plant operations (Bio-P, nutrient recovery), primarily resulting from changes in the collection system related to odor and corrosion control chemicals that led to changes in wastewater characteristics.

SpeakerRam Mohan, Gayathri

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionHealthy As A Horse? Assessing Bio-P Stability

Session locationRoom S403a - Level 4

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

Author(s)

Ram Mohan, Gayathri

Author(s)G. Ram Mohan 1; R. Latimer 2 ; P. Pitt 3; C. Yi 1; J. Garmon 4; R. Harris 5; G. Ram Mohan 1;

Author affiliation(s)Hazen and Sawyer, Atlanta, GA 1; Hazen and Sawyer 2 ; Hazen and Sawyer 3; Hazen and Sawyer 1; Gwinnett County Department of Water Resources 4; Gwinnett County Department of Water Resources 5; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159175

Volume / Issue

Content sourceWEFTEC

Word count17

Combining Metabolic, Kinetic and Physical Selection to Achieve Full-Scale Continuous Flow Densified Activated Sludge and Nutrient Removal at Robert W. Hite Treatment Facility

Abstract

Introduction: Metro Water Recovery's (Metro) Robert W. Hite Treatment Facility (Hite) in Denver, CO is permitted for a maximum month (MM) flow of 220 mgd and has two parallel liquids treatment trains including the North Secondary (NSEC). The NSEC utilizes a modified Ludzack Ettinger (MLE) process with a sidestream anaerobic reactor (SAR) to achieve nutrient removal. In 2018, Metro's facility plan identified a need for increased aerobic solids retention time (aSRT) to meet future potential total nitrogen (TN) and total phosphorus (TP) regulations (Colorado Regulation 31). To avoid costly expansion, Metro commissioned a full-scale demonstration train (NAB2) to trial densified activated sludge (DAS). This work documents findings from the full-scale demonstration facility and discusses how Metro is translating DAS into a full-scale solution at the RWHTF. Specifically, this paper will discuss factors that have led to the development and long-term operation of DAS with biological and physical selection, as well as provide insights into how particle size distribution (PSD) may be impacted by operational parameters and influence nutrient removal. Materials and Methods: DAS facility: The DAS demonstration facility (denoted as NAB2) consisted of an isolated, paired aeration basin and secondary clarifier from NSEC. Description of the facility is provided elsewhere (Avila et al., 2021). Metro operated NAB2 to test multiple distinct metabolic and kinetic selector configurations, with two primary configurations, Fig 1. A 'control' train was also operated without physical and biological selection. Routine influent/eff concentrations of organics, solids and nutrient content were determined using Standard Methods for the Examination of Water and Wastewater. PSD of the MLSS, hydrocyclone UF, and hydrocyclone OF were routinely characterized. Settling Column Testing: Settling column testing of bulk DAS ML was conducted on multiple occasions to determine the Vesilind equation settling coefficients (V0 & k) as well as the PSD. Additionally, settling properties for particle size fractions: <200µm, 200-600µm, and >600µm were characterized across a concentration range of approximately 1,500 mg/L to 6,000 mg/L. Activity Testing: Batch scale activity testing of bulk mixed liquor and three particle size fractions was used to evaluate nutrient removal rates of activated sludge in 5-gallon reactors. Analytes (NH4, NO3, NO2, and PO4) were measured with HACH TNT kits. Hydrocyclone Nozzle Testing: Hydrocyclone UF nozzle sizes ranging from 15 to 25 mm were individually tested at a target pressure of 30 psi. Flow measurements from the hydrocyclone feed and OF were recorded via flow meter. Total suspended solids (TSS) and PSD samples were collected from the RAS, OF, and UF. Process and Capacity Modeling - Data from NAB2 testing were used to develop, calibrate, and validate AB2 specific and a whole plant process model in BioWinTM and computational fluid dynamics (CFD) models of the NSEC secondary clarifiers. These models establish system capacity of existing infrastructure and design criteria for full-scale implementation. Results and Discussion: Impact of biological selection on densification: PSD of NAB2 biomass during configuration 1 (SAR-MLE) mode) stabilized into a uni-modal distribution, with median size increasing from 100 to 200 um respectively (Fig 2A). The average SVI30 for the NAB2 versus control basins were 102 mL/g and 153 mL/g respectively. PSD of NAB2 biomass during configuration 2 (SAR-A2O) mode reflected a bi-model distribution (Fig 2B). The average SVI30 for the test versus control basins were 81 mL/g and 173 mL/g respectively. Cumulatively, results suggest that improved settleability is observed when the mass fraction of granules (particles >212 um) in the sludge exceeds 15%. This was observed on multiple occasions when NAB2 operated in SAR-A2O mode with anaerobic food to microorganism ratio (F/M) being sustained between 1.0 and 3.0 lb sCOD/lb MLVSS-day. Impacts on PSD on Settling Performance and Biomass Activity: Settling velocity and compressibility were observed to increase as the particle size fraction increased (Table 1). Biomass activity results indicated that larger particle size fractions had lower denitrification and nitrification rates versus smaller particle size fractions while Bio-P activity was highest in particles greater than 200 um. These results indicate that minimizing particles sizes greater than 600 um may allow Metro to exploit high nitrification/denitrification/Bio-P rates and with superior settling and compressibility (Quoc et al., 2021). Influence of Physical Selective Pressures on PSD in NAB2 (Fig 3): Results indicated that mass flow through the UF could be reduced when the nozzle size decreases (Fig 2). This phenomenon can potentially be exploited to craft a wasting strategy focused on developing and keeping a target PSD. DAS impacts on Capacity: Stress testing indicated that NAB2 could be loaded at surface overflow rates (SORs) >700 gpd/sf and solids loading rates (SLRs) >60 pounds per day per square foot (ppd/sf) while still maintaining reliable blanket control and stable effluent TSS (Fig 4). Whole plant process and CFD modeling indicated that the densified scenario could allow Metro to successfully treat 2040 flows without needing to invest in additional aeration basins or secondary clarifiers, allowing for savings of $50 million dollars.

To meet future nitrogen and phosphorus regulations without constructing new infrastructure, Metro Water Recovery conducted a full-scale demonstration of densified activated sludge (DAS) at its Robert W. Hite Treatment Facility. This study evaluated the DAS system, focusing on metabolic and kinetic selector configurations, particle size distribution, and nutrient removal efficiency. Results include impacts of configurations, particle size, and nozzle size and projected capital cost savings.

SpeakerMaltos, Rudy

Presentation time

09:00:00

09:30:00

Session time

08:30:00

10:00:00

SessionFull-scale Intensification Experience

Session number510

Session locationRoom 343

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

Author(s)

Maltos, Rudy, Rauch-Williams, Tanja, Freedman, Daniel, Cavanaugh, Liam, Scopp, Anna, Priest, Ryan, Griborio, Alonso, Mayer, Alyssa, Noteboom, Haley, Latimer, Ron, Sun, Yewei, Khunjar, Wendell

Author(s)R. Maltos1, T. Rauch-Williams1, D. Freedman1, L.M. Cavanaugh1, A. Scopp2, R. Priest2, A. Griborio3, A.J. Mayer4, H. Noteboom5, R.J. Latimer6, Y. Sun7, W. Khunjar8

Author affiliation(s)1Metro Water Recovery, CO, 2Hazen and Sawyer, CO, 3Hazen & Sawyer, FL, 4Hazen & Sawyer, OH, 5Hazen & Sawyer, NY, 6Hazen and Sawyer, GA, 7Hazen and Sawyer, VA, 8Hazen & Sawyer PC, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159645

Volume / Issue

Content sourceWEFTEC

Word count24

Densification Specific Considerations for Secondary Clarifier Assessments

Abstract

Intensification is a major innovation for water resource recovery facilities (WRRFs) to realize cost-effective use and deployment of infrastructure. One of the promising technologies and approaches for process intensification is densified activated sludge (DAS). Secondary clarifiers are a key unit process to ensure retention of the solids inventory and permit compliance. The performance of clarifiers depends on several interrelated processes and factors including hydrodynamics, settling, turbulence, flocculation, sludge rheology, atmospheric conditions, tank geometry, internal features and loading conditions. Several tools and design “rules of thumb” are available from regulatory loading guidelines such as Ten State Standards, sludge specific assessment tools such as state point analysis, and calibrated, site-specific tools such as 2D and 3D computational fluid dynamics (CFD) modeling. These tools have been in use for decades with traditional sludge settling characteristics. However, the industry is still working through methods and procedures to assess the impacts of DAS settling characteristics on traditional secondary clarifier operations and loading guidelines. This paper will highlight the use of clarifier evaluation tools for DAS applications, including key considerations, observed performance, potential loading rates, and other relevant properties. Case studies are highlighted to demonstrate potential impacts at full-scale WRRF sites.

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

SpeakerMartin, Will

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionSecondary Clarification Advancements

Session locationRoom S401d - Level 4

TopicAdvanced Level, Municipal Wastewater Treatment Design

Author(s)

Martin, William

Author(s)W. Martin 1; A. Griborio 2 ; R. Latimer 3; R. Vandermeulen 4; G. Ram Mohan 5; W. Martin 1;

Author affiliation(s)Hazen and Sawyer, St. Paul, MN 1; Hazen and Sawyer, Hollywood, FL 2 ; Hazen and Sawyer, Atlanta, GA 3; Hazen and Sawyer 4; Hazen and Sawyer 5; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159196

Volume / Issue

Content sourceWEFTEC

Word count8

Hybrid MABR Technology for Nitrogen Removal in a Low Suspended Growth SRT

Abstract

This paper focuses on the hybrid MABR technology for nitrogen removal at a WRRF operating in a low suspended growth SRT (i.e., cBOD mode). To date, full-scale MABR installations have been limited to WRRFs already performing nitrogen removal, whereby the MABR is working in a complementary fashion to the existing suspended growth activated sludge.

The novel application of using MABR in a low suspended growth SRT was piloted at Central Contra Costa Sanitary District (Central San) in the San Francisco Bay Area. Under this application, the hybrid MABR biofilm exclusively performed the ammonia/total nitrogen removal (i.e., non-complementary with the low suspended growth sludge). The focus of this presentation can be broken into three areas:
1) Background, objectives, and results
2) Sumo® modeling results
3) Carbon, energy, and greenhouse gas (GHG) emissions potential benefits for this hybrid MABR in a low suspended growth SRT mode

Background, Objectives, and Results
Central San is one of the five largest wastewater treatment plans in the San Francisco Bay Area with a permitted capacity of 53.8 mgd average dry weather flow. The Bay Area recently adopted total inorganic nitrogen (TIN) load limits (40 percent baywide aggregate TIN load reduction). Transitioning from secondary treatment to nitrogen removal at Central San is challenging due to plant capacity, site contaminated soil, and a return stream from incinerator air pollution control equipment containing cyanide (a known inhibitor of nitrifiers). MABR was selected for piloting as it has the potential to remove TIN within existing tankage while addressing the other listed challenges.

At the pilot onset, Central San had not yet received permit limits. The overarching piloting goal was to evaluate whether existing tankage could be retrofit with this intensification technology in a relatively fast construction project (~1 year) with minimal modifications to the secondary process.

Central San's pilot included four core objectives:
1. Confirm ability to form an ammonia removing biofilm on the membranes (addresses cyanide concerns)
2. Evaluate ammonia and TIN removal while maintaining low suspended growth SRT
3. Determine specific ammonia removal rates to confirm ability to remove ammonia/nitrogen in existing tankage
4. Determine the optimal MABR cassette's location at Central San

MABR Pilot Setup and Results
The pilot process flow diagram is presented in Figure 1. The pilot can be fed from different locations across the plant (see Figure 2). Details for each phase are provided in Table 1.

A summary for each phase (approximately 2-months each) and the corresponding results:
- Phase I (secondary clarifier influent feed): to demonstrate the hybrid MABR ammonia removal efficacy while maintaining a relatively low suspended growth SRT. The ammonia removal performance in Phase I is presented in Figure 3. Some key observations:
- Ammonia Removal occurred rapidly within initial 2 weeks with an effluent steady state of 5-10 mg N/L.
- Ammonia removal rate (approximately 2.1 g/m2/d) was similar to other full-scale installations with a longer SRT (typically 2-2.5 g/m2/d).
- TIN removal was minimal as expected due to limited available carbon at this feed location.
- Phase II (anaerobic selector feed): to verify that the hybrid MABR biofilm can effectively remove nitrogen in the presence of ambient cyanide. The ammonia and TIN removal performance are presented in Figure 4 and Figure 5, respectively. Some key observations:
- Ammonia Removal was similar to Phase I, showing robust and reliable removal.
- Up to 40% TIN removal was observed. TIN removal improved from Phase I, but it was still limited due to carbon availability.
- Phase III (blend of anaerobic selector and primary effluent): to stress the system with the highest possible cyanide, ammonia, and carbon levels. The ammonia loading and TIN removal performance were initially similar to Phase II as presented in Figure 6. Some key observations:
- Ammonia Removal was similar to Phases I and II, showing robust and reliable removal.
- Up to 50% TIN removal was observed.
- Upon increasing the loading rates, the nitrifying biomass appears to be the limiting factor as evidenced by an increase in effluent ammonia levels.

Full-Scale Hybrid MABR Modeling Results for this Low Suspended Growth SRT Mode
Sumo® was used as the modeling platform as its features lends itself to such attached growth systems. The datasets used were as follows: daily pilot grab samples, influent and effluent ammonia and nitrate online probes, daily composites from the raw influent and primary effluent samplers during the phases II and III, and diurnal sampling from July/August 2019.

A comparison of the data against the calibrated model is presented in Figure 7. Overall, the model was deemed reasonably calibrated to compare various MABR layouts and relative TIN removal performance.

The energy efficiency benefits of MABR are well documented with an emphasis on oxygen transfer efficiency (e.g., Castrillo et al., 2019) and simultaneous nitrogen removal. While attractive, how does a hybrid MABR operating in a low versus high suspended growth SRT compare in terms of cost, carbon, energy, and GHG emissions? For comparative purposes, a Modified Ludzack-Ettinger (MLE) configuration was used as a baseline while comparing the low versus high suspended growth SRT as shown in Table 2.

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

SessionLow SRT Performance of Membrane Aerated Biofilm Reactors (MABR)

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Cunningham, Michael, Goel, Nitin, Falk, Michael, Zhang, Yihan, Pitt, Paul, Latimer, Ron, Daigger, Glen

Author(s)M. Cunningham1, N. Goel1, M. Falk2, Y. Zhang2, P. Pitt4, R. Latimer4, G. Daigger5

Author affiliation(s)Central Contra Costa Sanitary District1, HDR, Inc.2, Oakland County WRC3, Hazen and Sawyer4, University of Michigan5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159971

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Leveraging Densified Activated Sludge and Partial...

Leveraging Densified Activated Sludge and Partial Nitrification/Denitrification/Anammox within an Integrated Advanced Water Treatment Facility for Large-Scale Potable Reuse

Abstract

The Los Angeles County Sanitation Districts (Districts) have been exploring options for implementing nitrogen removal at the Joint Water Pollution Control Plant (JWPCP), a 400-MGD capacity high purity oxygen activated sludge (HPOAS) facility, due to potential reuse and regulatory drivers. This paper summarizes pilot-scale demonstrations of a secondary BNR (Densified Activated Sludge, DAS) and a tertiary BNR (tertiary moving bed biofilm reactor, TMBBR). These approaches has proven successful at meeting the nitrogen removal targets and provide program enhancements, including densification and PANDA/PdNA.

The Los Angeles County Sanitation Districts are exploring nitrogen removal options at the Joint Water Pollution Control Plant (JWPCP), a 400-MGD capacity high purity oxygen activated sludge (HPOAS) facility, to address potential reuse and regulatory drivers. Two potential approaches developed were a three stage A2O configuration and a tertiary moving bed biofilm reactor. Both approaches were successfully pilot tested and demonstrated the ability to meeting nitrogen removal targets.

SpeakerSun, Yewei

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionReconsidering Biological Treatment for Water Purification: Reuse-nutrient Removal-nexus I

Session locationRoom S404c - Level 4

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients, Potable Reuse, Water Reuse and Reclamation

Author(s)

Sun, Yewei

Author(s)Y. Sun 1; B. Danker 2 ; R. Deco 3; H. Long 3; M. Liu 4; A. Laleian 5; N. Melitas 4; B. Mansell 5; P. Ackman 6; P. Pitt 7; W. Khunjar 8; R. Latimer 9; H. Noteboom 10; R.M. Deco 3; H.C. Long

Author affiliation(s)Hazen & Sawyer 1; Hazen & Sawyer 2 ; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 4; Los Angeles County Sanitation Districts, 24501 Figueroa Street, Carson, CA, 90745 5; Los Angeles County Sanitation Districts 4; Los Angeles County Sanitation Districts 5; Los Angeles County Sanitation Districts 6; Hazen & Sawyer 7; Hazen & Sawyer 8; Hazen & Sawyer 9; 10; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 3;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159099

Volume / Issue

Content sourceWEFTEC

Word count19

Leveraging Glycerol-Driven and Primary-Effluent-Driven PdNA within Advanced Wastewater Treatment Facility

Abstract

Introduction The Los Angeles County Sanitation Districts (LACSD) and Metropolitan Water District of Southern California (MWD) have collaborated to evaluate the development of the Pure Water Southern California (PWSC) Program. The PWSC Program would implement a full-scale advanced water treatment facility (AWTF) to produce up to 150 million gallons per day (mgd) for indirect and potentially direct potable reuse. One of the AWTF options considered would include a new biological nutrient removal (BNR) facility followed by RO/UV/AOP. The new BNR facility would be constructed at the existing A.K. Warren Water Resource Facility (Warren Facility), which is a 400 mgd capacity high purity oxygen activated sludge facility. The AWTF and BNR upgrades are intended to achieve a nitrate <19 mg/L, prior to the RO/UV/AOP facility. Partial nitrification/denitrification/anammox (PANDA/PdNA) was identified by the PWSC team as a promising approach to intensify BNR, by facilitating reduction of supplemental carbon needs and potentially increasing TIN removal capacity, without increasing tank volume. This work summarizes findings from an ongoing multi-year pilot effort focused on validating the PANDA/PdNA concept within a large-scale reuse program. Specifically, the objectives were to: i) demonstrate the ability to achieve nutrient targets reliably by intensifying a tertiary MBBR and IFAS configuration with PANDA/PdNA; ii) validate carbon savings that can be achieved by implementing PANDA/PdNA; and iii) investigate the feasibility of incorporating primary effluent driven partial denitrification to further reduce projected operating costs associated with the PWSC Program. Methods Tertiary MBBR: A tertiary MBBR was configured as a step-feed BNR process, consisting of alternated aerobic and anoxic cells, with zone configuration and influent feed split (Figure 1). Both primary effluent (PE) and a glycerol-based supplemental carbon source (MicroC 2000) were used for supporting denitrification in anoxic zones. This flexible configuration allowed for performing both conventional BNR and PANDA/PdNA. Tertiary IFAS: The MBBR system was modified to include clarifiers to retain flocculant biomass. Additionally, a Solitax probe (Hach) was added in the last cell of the system to monitor the mixed liquor suspended solid concentration in the system. The first aerobic zone of Tertiary MBBR was converted to anoxic because the RAS feed was able to recycle sufficient NOx load into the that zone, negating the need for nitrification in that zone. Monitoring: Composite samples (24-hr) were used to monitor influent and effluent solids, organics and nutrients. Profile samples were grabbed from different cells across the system periodically to analyze for nitrogen species and organics (Hach TNT). Operational Modes: Three different operational modes were tested: 1) Hybrid conventional BNR mode in MBBR, during which both PE and glycerol were supplied to the system to perform full denitrification; 2) PANDA/PdNA mode in MBBR, during which both PE and glycerol were supplied to the system to perform partial denitrification and anoxic ammonia removal via anammox; and 3) PANDA/PdNA mode in IFAS (on-going), during which suspended biomass is retained in the system by using a clarifier. Results and Discussion Hybrid BNR Mode: The system operated in this mode from July 2022 to April 2023. Findings were reported in Sun et al., 2023. Briefly, both the ammonia target of 1 mg/L and the NOx target of 16 mg/L were achieved during hybrid BNR mode operation, confirming that a conventional BNR option could reliably achieve nutrient targets. MBBR PANDA Mode: The MBBR system was transitioned to PANDA/PdNA mode in May 2023 and operated until October 2023. Key findings are as follows:

*The system was able to reliably achieve the effluent ammonia and NOx targets of 1 mg/L and 16 mg/L, respectively (Figure 2). It was also possible to further decrease effluent TIN as low as ~ 9 mg/L, without increasing total system volume (Figure 2).

*Carbon usage was tracked during different phases of operation (Table 1). During the hybrid BNR and PANDA phases, approximately 7 to 9% of the total flow was comprised of PE. The COD addition/N removal ratio reduced from ~3.9 lb sCOD/lb NOx during hybrid BNR phase to ~1.2 lb sCOD/lb NOx during the PANDA/PdNA phase. This reduction was due to enhanced anammox activity and represents greater than 70% savings in supplemental carbon needs.

*Investigation into PdNA activity within the system revealed that partial denitrification was likely driven by both PE (first anoxic) and glycerol (second anoxic), with PE driven PdNA accounting for 3 to 7 mgN/L anoxic ammonia removal (Figure 3) and glycerol driven PdNA accounting for up to 9.4 mgN/L anoxic ammonia removal (Table 1). Batch tests confirmed that PE and internally stored carbon could be used to successfully drive partial denitrification if sufficient control of carbon, nitrate and ammonia is provided (Figure 4). PANDA/PdNA in IFAS Mode: In November 2023, the system was transitioned to operate in IFAS PANDA/PdNA mode. The IFAS phase of operation will be completed in mid-2024, the results of which and lessons learned will be presented during the conference.

The Los Angeles County Sanitation Districts are exploring nitrogen removal options to address potential reuse and regulatory drivers. A tertiary step-feed moving bed biofilm reactor (tMBBR) configuration was evaluated as an approach. The tMBBR configuration was successfully pilot tested and demonstrated the ability to meet nitrogen removal targets. It was also found that by leveraging glycerol-driven and PE-driven PdNA, aeration energy and carbon savings can be ~28% and up to 70%, respectively.

SpeakerSun, Yewei

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionAnoxic Reactor Design for Low Energy BNR

Session number520

Session locationRoom 335

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

Author(s)

Sun, Yewei, Mansell, Bruce, Coracero, Ariana, Farrokh Shad, Mojtaba, Tsai, Raymond, Pitt, Paul, Khunjar, Wendell, Latimer, Ron, Danker, Bryce, Sun, Yian

Author(s)Y. Sun1, B.O. Mansell2, A.K. Coracero3, M. Farrokh Shad2, R. Tsai4, P.A. Pitt5, W. Khunjar6, R.J. Latimer7, B. Danker8, Y. Sun5, M. Farrokh Shad2

Author affiliation(s)1Hazen and Sawyer, VA, 2LA County Sanitation District, CA, 3Los Angeles County Sanitation Districts, CA, 4LACSD, CA, 5Hazen and Sawyer, CA, 6Hazen & Sawyer PC, VA, 7Hazen and Sawyer, GA, 8Hazen, CA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159618

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Primary Effluent- and Glycerol-Driven PdNA for Large-Scale Potable Reuse: Maximizing...

Primary Effluent- and Glycerol-Driven PdNA for Large-Scale Potable Reuse: Maximizing Benefits from MBBR to IFAS Transition

Abstract

Introduction
The Los Angeles County Sanitation Districts (LACSD) and Metropolitan Water District of Southern California (MWD) have partnered to implement a full-scale advanced water treatment facility (AWTF) for reuse. One of the AWTF options considered was a new biological nutrient removal (BNR) facility followed by RO/UV/AOP. The BNR upgrades are intended to achieve a nitrate goal of <19 mg N/L, prior to RO/UV/AOP.

A promising approach identified to intensify BNR performance is Partial Nitrification/Denitrification/Anammox (PdNA). PdNA can reduce supplemental carbon requirements and enhance Total Inorganic Nitrogen (TIN) removal capacity without increasing tank volume. The ongoing multi-year pilot study summarized here explores PdNA application for a large-scale reuse program.

The study objectives are: i) to demonstrate reliable nutrient target achievement by intensifying a tertiary Moving Bed Biofilm Reactor (MBBR) and Integrated Fixed-film Activated Sludge (IFAS) configuration with PdNA, ii) to validate the carbon and aeration energy savings achieved through primary effluent-driven and glycerol-driven PdNA, and iii) to assess the benefits and considerations of incorporating suspended-phase biomass and provide insights for future full-scale PdNA design in membrane bioreactor systems.

Methods
Tertiary MBBR: The tertiary MBBR was a step-feed BNR process with alternating aerobic and anoxic zones (Figure 1). Both primary effluent (PE) and glycerol (MicroC 2000) were used to support denitrification in the anoxic zones, allowing for conventional BNR and PdNA processes.

Tertiary IFAS: The MBBR system was modified to include flocculant biomass retaining clarifiers (Figure 2 and 3). The first aerobic zone was converted to an anoxic zone, with RAS recycling NOx for pre-anoxic partial denitrification. PE was the primary carbon source for Anx1, but glycerol was used when necessary. Operational periods with and without PE are labeled in Figures 4, 5, and 6.

Monitoring and System Control: 24-hour composite samples were used to monitor influent and effluent solids, organics, and nutrients, while periodic grab samples from different system cells were analyzed for nitrogen species and organics. Nitrification and aeration were monitored with NOx and DO probes in each aerobic cell. In the IFAS system, a Solitax probe tracked MLSS concentration. Control loops were used for glycerol feeding based on NOx and DO readings. The NOx/NH3 ratio was controlled by adjusting SE step feed flowrates based on NH3 and NOx probe readings.

Operational Phases:
- Hybrid NdN Mode in MBBR: Both PE and glycerol were supplied to the system for full denitrification.
- Hybrid PdNA Mode in MBBR: Both PE and glycerol were provided to perform PdN and anoxic ammonia removal via anammox.
- PdNA Mode in IFAS: Suspended biomass was retained using a clarifier, and only glycerol (no PE) was supplied to perform PdNA.
- Hybrid PdNA Mode in IFAS: Suspended biomass was retained, and both PE and glycerol were supplied to the system.

Results and Discussion
System Performance: During steady-state operation (August to October 2023), the system consistently met the effluent 1 mg/L NHx limit and the 16 mg/L TIN limit (Figure 4). The transition from MBBR to IFAS mode occurred early November 2023 to April 2024, in which suspended solids began accumulating in the system (Figure 5). Despite operational challenges, the system maintained stable effluent NH3 levels throughout this period. However, during transition, effluent TIN levels temporarily rose above 20 mg/L due to fluctuating MLSS concentrations (Figure 4). Once MLSS stabilized at 2,000 mg/L (Figure 5), effluent TIN gradually decreased to less than 16 mg/L, with effluent NH3 consistently remaining below 1 mg/L (Figure 4).

PdNA Efficiency and Anammox Activity: Anoxic ammonia removal (AAR, g/m2/d), commonly used as a proxy for anammox activity during the PdNA process, is presented in Figure 6. In Anx2, ammonia removal was solely driven by glycerol-fed PdNA, while in Anx1, it was either driven by PE or by glycerol. The AAR driven by PE increased from approximately 0.21 g/m2/d during the steady-state hybrid MBBR operation (August to October 2023) to 0.37 g/m2/d during the steady-state hybrid IFAS operation (June to July 2024). Glycerol-driven AAR rates were comparable between MBBR and IFAS steady-state operations. However, Anx2 required lower bulk NHx and NO2 concentrations to maintain similar removal rates during IFAS mode (Figure 7), due to an increased anammox activity rate, as shown in ex-situ activity tests (Table 1). The bulk NHx concentration of <0.5 mgN/L in Anx2 also eliminated the need for Aer2 in the IFAS system.

Activity Migration into Suspended Phase: IFAS differs from MBBR in the incorporation of suspended biomass, which may facilitate the denitrifier migration from the biofilm phase to the suspended phase, freeing media space for slow-growing anammox bacteria. During the IFAS transition period, elevated effluent TIN levels were observed due to unstable MLSS concentrations (Figure 4). The reduction in ARR alongside MLSS reduction from December 2023 to March 2024 (Figure 6) suggested denitrifiers migrated to the suspended phase. The rise in effluent ammonia concentration (Figure 4) and 7/29/2024 biomass loss (Figure 5) suggests nitrifiers may have also migrated to the suspended phase. This was confirmed by ex-situ batch nitrification act

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

Presentation time

09:00:00

09:30:00

Session time

08:30:00

10:00:00

SessionPdNA: Insights into Pilot and Full-scale Implementations

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment Technology - Secondary & Tertiary Treatment

Author(s)

Farrokh Shad, Mojtaba, Sun, Yewei, Mansell, Bruce, Hsia, Patricia, Danker, Bryce, Coracero, Ariana, Khunjar, Wendell, Sun, Yian, Pitt, Paul, Latimer, Ron

Author(s)M. Farrokh Shad1, Y. Sun2, B. Mansell1, P. Hsia1, B. Danker2, A. Coracero1, W. Khunjar2, Y. Sun2, P. Pitt2, R. Latimer2

Author affiliation(s)LA County Sanitation District1, Hazen and Sawyer2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825159969

Volume / Issue

Content sourceWEFTEC

Word count17

Description: Successful Full-Scale Continuous Flow Densification of Activated Sludge at Crooked...

Successful Full-Scale Continuous Flow Densification of Activated Sludge at Crooked Creek Water Reclamation Facility Without Physical Selection

Abstract

Abstract: In this work, we demonstrate successful densification of activated sludge at the Crooked Creek Water Reclamation Facility, owned and operated by Gwinnett County Department of Water Resources, utilizing conventional bioreactors and secondary clarifiers. Densification was achieved through control of substrate utilization rates (kinetic selection) and use of anaerobic conditions (metabolic selection). Physical selection was not necessary to improve sludge settling characteristics. During densification, the CCWRF consistently achieved effluent NH3 and TP of less than 0.5 mg/L and 0.2 mg/L, respectively. Keywords: Intensification, Densified Activated Sludge, Granular Sludge
Introduction- Biological treatment for carbon and nutrient control is expected to remain a core process for water resource recovery facilities (WRRFs) of the future. Advancing biological technologies that allow for unlocking treatment capacity, while also minimizing capital and operating costs is therefore critical. Aerobic granular sludge (AGS) and densified activated sludge (DAS) are two approaches that seek to achieve intensification of BNR via improvements to sludge settling velocity and compaction properties, such that WRRFs can operate at elevated mixed liquor concentrations (> 5,000 mg/L) and solids loading rates (> 40 lb/ft2-day) to clarifiers. This work documents efforts to achieve full-scale densification at the Crooked Creek Water Reclamation Facility (CCWRF). Specifically, we will discuss, 1) Factors that have led to the development of DAS at CCWRF, 2) Data from start-up of new bioreactor basins and the process to achieve successful densification without physical selection and, 3) Improvement in water quality since transitioning from oxidation ditches to conventional biological reactors. The work documented in this paper will provide practitioners with insights into how to design and operate system to achieve continuous flow densification using conventional BNR technologies.
Background â€“ The 16 mgd CCWRF was originally an Orbal Oxidation ditch that was converted in late 2014 into a plug flow A/O process with diffused air (Figure 1). After the conversion, the settling properties improved significantly with SVIs averaging 60 to 70 mL/g with 99th percentile SVI values of 80 to 85 mL/g year after year (Table 1). In 2018, we identified this plant as achieving DAS and investigated the plant performance to understand key drivers for this result. At the same time, design for new bioreactors using an A2O configuration to replace the old, converted oxidation ditches was being completed. Elements of the new design for the bioreactors were included to ensure that DAS was maintained. The new bioreactors were brought online (Figure 2) in March 2021 and successfully maintained DAS as discussed below. The A/O oxidation ditch plant was removed from service at the same time.
Methods - CCWRF is designed to treat 16 mgd using an A2O configuration. The facility does not practice anaerobic digestion and has achieved effluent NH3 and TP less than 0.5 mg/L and 0.2 mg/L, respectively. Field Sampling - Field sampling was performed at the facility to identify and characterize factors leading to densification of activated sludge. - Profile sampling was performed across the bioreactors to characterize nutrients and organic carbon, - Depth profile sampling in the selector zones was performed to characterize fate of phosphorus and carbon, - DAS size distribution analyses was performed to determine how particle size changes over time, - Sludge settling velocity and compaction rates were measured via settling column tests to develop quantitative metrics of densification for use in modeling, - Microscopic analyses were performed to qualitatively characterize filaments and distribution of phosphorus (PAOs) and glycogen accumulating organisms (GAOs) - DAS extracellular polymeric substance (EPS) content was characterized to determine changes over time. - Lastly, calibration of a secondary clarifier CFD model based on stress and column testing data was completed.
Data analytics- Historical data was examined using advanced data analytics techniques executed in Python. Daily operating data were interrogated to develop multi-day lookback averages (e.g., 3-day, 7-day, 15-day, and 30-day) to best elucidate long-term trends in performance. Supervised and un-supervised learning models were developed to illustrate relationships between environmental and operating parameters and sludge settling properties.
Results and Discussion â€“ Prior to start-up of the new bioreactors (March 2021), the 50th and 99th percentile sludge volume indices at the plant were 62 and 84 mL/g respectively (2017 to March 2021). Since start-up of the new reactors the 50th and 99th percentile sludge volume indices have remained low at 60 and 80 mL/g respectively (2021; Figure 3). The current SVI 5/30 ratio of the system is 1.15. Between 30 and 50% of the biomass at CCWRF has a particle size greater than 212 um (Figure 4). Correspondingly, initial settling velocity at CCWRF was estimated to be ranging from 58 to 63 ft/hr. Floc settling parameter ranged from 0.20 to 0.35 L/g. These values indicate excellent floc characteristics, partial granulation, and excellent settling properties. Process sampling indicated that anaerobic F/M observed within the entire selector zone ranged from 0.5 to 1.0 lb sCOD/lb MLSS. The initial contact zone F/M was observed to range from 2.0 to 4.0 lb sCOD/lb MLSS. Cumulatively, these results indicate that it is possible to achieve stable densification in continuous flow applications through control of substrate utilization rates (kinetic selection) and use of anaerobic conditions (metabolic selection). Physical selection is not always necessary.
Capacity evaluations utilizing the calibrated clarifier CFD model and BioWin model have shown that it is possible to operate at MLSS concentrations up to 5,500 mg/L and peak solids loading rate in excess of 55 lb/ft2-day. Utilizing these parameters, the team has demonstrated the secondary process capacity of the facility can be increased beyond the design flow of 16 mgd without addition of new bioreactor basins. Achieving this additional treatment capacity using the existing infrastructure at the plant could facilitate significant savings if future expansion is required.

In this work, we demonstrate successful densification of activated sludge at the Crooked Creek Water Reclamation Facility utilizing conventional bioreactors and secondary clarifiers. Densification (DAS) was achieved through a combination of kinetic selection by controlling substrate utilization rates and metabolic selection using anaerobic selectors. Physical selection was not necessary to improve sludge settling characteristics.

SpeakerLatimer, Ron

Presentation time

14:30:00

14:55:00

Session time

13:30:00

15:00:00

TopicAdvanced Level, Municipal Wastewater Treatment Design

Author(s)

Latimer, Ron

Author(s)R. Latimer1; A. Griborio1; P. Pitt1; W. Khunjar1; G.R. Mohan1; M. Meyer1; H. Notebook1; R. Harris2; D. Jones2

Author affiliation(s)Hazen and Sawyer1; Gwinnett County Department of Water Resources2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158668

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Successful Full-scale Demonstration of Nitrogen Removal in a High Purity Oxygen...

Successful Full-scale Demonstration of Nitrogen Removal in a High Purity Oxygen Facility with No Infrastructure Modification

Abstract

The Los Angeles County Sanitation Districts (Districts) have been exploring options for implementing nitrogen removal at the Joint Water Pollution Control Plant (JWPCP), a 400-MGD capacity high purity oxygen activated sludge (HPOAS) facility, due to potential reuse and regulatory drivers. This paper summarizes a fullscale demonstration of a novel concept of utilizing HPOAS for nitrogen removal with no infrastructure modification. This approach has proven successful at providing robust nitrogen removal and provides a significant benefit to the JWPCP and potentially other HPOAS facilities.

The Los Angeles County Sanitation Districts are exploring nitrogen removal options at the Joint Water Pollution Control Plant (JWPCP), a 400-MGD capacity high purity oxygen activated sludge (HPOAS) facility, to address potential reuse and regulatory drivers. Through a full-scale demonstration of the high-purity oxygen Ludzack-Ettinger (HPOLE) process, robust nitrogen removal was achieve, indicating that HPOLE provides a significant benefit to the JWPCP and is scalable to other HPOAS facilities.

SpeakerDanker, Bryce

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionSweat Your Assets Off: BNR Optimization

Session locationRoom S403b - Level 4

TopicIntermediate Level, Nutrients

Author(s)

Danker, Bryce

Author(s)B. Danker 1; P. Pitt 2 ; R. Latimer 3; P. Hsia 4; M. Liu 4; B. Mansell 5; G. Caro 5; S. Patel 5; K. Panesar 5; W. Khunjar 6; Y. Sun 7; H. Noteboom 8; N. Melitas 4; B. Danker 1;

Author affiliation(s)Hazen & Sawyer 1; Hazen & Sawyer 2 ; Hazen & Sawyer 3; Los Angeles County Sanitation Districts 4; Los Angeles County Sanitation Districts 4; Los Angeles County Sanitation Districts 5; Los Angeles County Sanitation Districts 5; Los Angeles County Sanitation Districts 5; Los Angeles County Sanitation Districts 5; Hazen & Sawyer 6; Hazen & Sawyer 7; Hazen & Sawyer 8; Los Angeles County Sanitation Districts 4; Hazen & Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159005

Volume / Issue

Content sourceWEFTEC

Word count17

Description: Unraveling the many benefits of DAS — Insights into nitrifier enrichment...

Unraveling the many benefits of DAS — Insights into nitrifier enrichment through SRT decoupling of flocs versus granules

Abstract

Introduction:
Metro Water Recovery's (Metro) Robert W. Hite Treatment Facility (Hite) in Denver, CO serves 2.2 million people across an 805-square-mile service area. Hite is currently permitted for a maximum month (MM) flow of 220 mgd and has two parallel liquids treatment trains including the North Secondary (NSEC). The NSEC utilizes a modified Ludzack Ettinger (MLE) process with a sidestream anaerobic reactor (SAR) to achieve nutrient removal.

Metro's facility planning efforts identified a need to increase aerobic solids retention time (aSRT) to meet future potential total nitrogen (TN) and total phosphorus (TP) regulations (Colorado Regulation 31). Densified activated sludge (DAS) was identified as a means for improving sludge settleability to allow Metro to operate at aSRTs necessary for future potential nutrient removal targets. Metro has successfully demonstrated the ability to achieve DAS and operate at elevated aSRT and solids loading rates (Maltos et al., 2023).

Beyond settling benefits, DAS systems with a physical selector can provide the ability to decouple the SRT of floc versus granule fractions. It is hypothesized that aSRT decoupling may allow for operation at lower bulk aSRT while still allowing Metro to meet nutrient targets. This paper/presentation will provide insights from NAB2 investigations into SRT uncoupling effects. Specifically, testing was performed to inform the following questions:
i) What is the minimum bulk aSRT and associated granule fraction needed to sustain nitrification?
ii) At what bulk aSRT will preferential nitrifier retention on granules be observed and will there be a nitrifier enrichment factor that can be sustained?

Materials and Methods:
DAS facility: The full-scale DAS demonstration facility (denoted as NAB2) consisted of an isolated, paired aeration basin (7,700 m3 (2.05 MG) and secondary clarifier (1,200 m2 (13,270 ft2)) from the North Secondary (NSEC). Description of the facility is provided elsewhere (Avila et al., 2021). The DAS demonstration facility was equipped with eight (8) hydrocyclones (44 GPM each; HC) which were fed from the return activated sludge (RAS) line. The control reactor was operated in SAR-MLE mode without physical selection.

aSRT Operation: Starting in Q3 and continuing through the end of Q4 2024, Metro began to progressively decrease the bulk aSRT from ~5 day to a target of ~ 3 day. Effluent quality, settling properties and particle size distribution of MLSS, hydrocyclone UF, and hydrocyclone OF were monitored as described in Maltos et al., 2023. Activity testing of bulk mixed liquor (MLSS) and size fractioned MLSS was also performed.

Results and Discussion:
- The granule fraction (> 200 um) of NAB2 ranged from 18 to 38% (Figure 1) while the average SVI5 and 30 for NAB2 were 78 and 62 mL/g respectively. The Control granule floc fraction averaged less than 5% for the same period while the corresponding average SVI5 and 30 for the Control were 129 and 85 mL/g respectively.
- During this testing period, the average bulk aSRT for NAB2 was 3.6 day versus 6.9 day for the Control while the corresponding average effluent ammonia concentration were 1.1 mg NH3-N/L and 1.2 mg NH3-N/L respectively (Figure 2).
- NAB2 and Control reactors observed ammonia spikes at various points during testing.
o 10/18 event - Effluent ammonia for both systems increased to approximately 2 mg N/L but rapidly declined. Both reactors were operating at bulk aSRTs of approximately 4.5 day.
o 11/7 to 11/12 event — Effluent ammonia for the Control increased to 2.5 mg N/L while operating at a bulk aSRT of 6 day. Effluent ammonia for NAB2 increased to ~ 5 mg N/L while operating at a bulk and mass weighted bulk aSRT less than 3 day. Notably, NAB2 ammonia concentrations decreased despite continuing to operate at a bulk and mass weighted bulk aSRT of ~ 3 day.
o Cumulatively these results indicate that NAB2 did not completely lose nitrification even when operating at bulk aSRTs between 2.5 and 3 days. During these periods, the granule fraction was 25 to 30% of the MLSS while the corresponding granule aSRT was always greater than 5 days.
- Activity testing results are summarized in Figure 3.
o Measurable nitrifier activity (as quantified via nitrate production rate) was observed in all biomass fractions even when operating at low bulk aSRTs.
o Nitrifier activity in the <100 um and 200 to 600 um fractions was observed to increase as the bulk and granule aSRT increased (positive correlation).
o Nitrifier activity in the 100 to 200 um fraction was observed to decrease as the bulk and granule aSRT increased (negative correlation).
o Nitrifier activity in the > 600 um fraction did not show any correlation to bulk or granule aSRT.
o Notably nitrifier activity in all size fractions was observed to decrease as the granule composition of the MLSS increased.
o Complete activity results from denitrification and PAOs will be presented in the full-paper/presentation.

Significance of Work: This work provides evidence that it is possible to nitrify in DAS systems equipped with a physical selector at bulk aSRTs as low as 3 days provided that the granule fraction remains between 20 and 30% and the granule aSRT is greater than 5 days. Full discussion of nitrifier retention and enrichment factors will be provided in the presentation/paper.

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

Presentation time

14:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionDensified Activated Sludge (DAS) Fundamentals

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Khunjar, Wendell, Maltos, Rudy, Freedman, Daniel, Rauch-Williams, Tanja, Florence, Kelley, Sun, Yewei, Mayer, Alyssa, Latimer, Ron

Author(s)W. Khunjar2, R. Maltos1, D. Freedman1, T. Rauch-Williams1, K. Florence2, Y. Sun2, A. Mayer2, R. Latimer2

Author affiliation(s)Hazen and Sawyer2, Metro Water Recovery1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160128

Volume / Issue

Content sourceWEFTEC

Word count18

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