Lakshminarasimman, Narasimman

Narasimman Lakshminarasimman is a speaker at WEFTEC 2026.

Titles from this speaker

Description: Behavior of Perfluoroalkyl Substance (PFAS) in Sludge Processing at Nine Canadian...

Behavior of Perfluoroalkyl Substance (PFAS) in Sludge Processing at Nine Canadian Sludge Handling Facilities

Abstract

The occurrence of emerging organic contaminants such as poly- and per-fluoroalkyl substances (PFAS) has raised concerns with beneficial land application of biosolids. The purpose of this study was to examine the occurrence and removal/formation of thirteen PFAS occurring in sludge and biosolids from nine Canadian sludge treatment facilities employing alkaline stabilization (AS), pelletization (P), aerobic digestion (AE1, AE2), and anaerobic digestion (AN1 to AN5) processes. Perfluorodecanoate (PFDA) was the most frequently detected compound (>85%) in the biosolids followed by perflurorooctane sulfonate (PFOS) and perfluorododecanoate (PFDoA). The ΣPFAS-F mass flows in the raw sludge and biosolids were estimated to study the removal performance of different sludge treatment categories. There was a significant increase in mass flow of ΣPFAS-F during pelletization and alkaline stabilization. On the other hand, the mass loadings of ΣPFAS-F decreased at AE2, AN1, AN3, and AN4 by 10 ± 0.2%, 34 ± 0.2%, 10 ± 0.1%, and 38 ± 0.2% through aerobic and anaerobic digestion processes, respectively. Substantial variability in removal/formation characteristics was observed between the biological treatment systems. The findings from this study will better inform the risk assessment and management of exposure to PFAS through biosolids.

SpeakerLakshminarasimman, Narasimman

Presentation time

13:30:00

13:50:00

Session time

13:30:00

14:10:00

SessionPFAS Management in Biosolids

Session number414

TopicMicroconstituents, Research and Innovation

Author(s)

N. LakshminarasimmanS. GewurtzS. SmythW. Parker

Author(s)N. Lakshminarasimman1; S. Gewurtz2; S. Smyth2; W. Parker1;

Author affiliation(s)University of Waterloo, ON1; Science and Technology Branch, Environment and Climate Change Canada2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157406

Volume / Issue

Content sourceWEFTEC

Word count15

Description: From Seasonal to Year-round Nitrification: Performance Evaluation of North America's...

From Seasonal to Year-round Nitrification: Performance Evaluation of North America's Largest MABR Installation

Abstract

This study evaluated the performance of North America’s largest MABR installation under different operational and seasonal conditions. Total nitrogen (TN) removal improved from 40- 50% when the plant was in a conventional activated sludge configuration to 75-85% after the MABR upgrade. The MABR reduced effluent ammonia during winters and nitrate concentrations during summer to below 10 mg-N/L in both the cases. The nitrification rate in the MABR varied between 0.7-2.2 gNm-2 d -1 with lower nitrification rates observed during reduced airflow operation and winter conditions. The development of thicker biofilms limited ammonia diffusion into the biofilm that resulted in reduced nitrification rate. Increasing the flow of sparging air was able to control the biofilm thickness to improve nitrification. The denitrification rate in the MABR process was between 100-200 gNm-3 d -1 which followed a close trend with nitrification rate. The nitrification rate in the MABR was found to be the rate limiting step for TN removal in the process.

Addition of an MABR to an existing conventional activated sludge process substantially improved TN removal and reduces seasonal spikes in effluent ammonia. The improved TN removal in the plant was due to elevated levels of simultaneous nitrification and denitrification in the hybrid MABR process.

SpeakerLakshminarasimman, Narasimman

Presentation time

15:30:00

15:50:00

Session time

15:30:00

17:00:00

SessionAlternative Approaches to Intensify Secondary Treatment

Session locationRoom S404a - Level 4

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Lakshminarasimman, Narasimman

Author(s)N. Lakshminarasimman 1; D. Celmer-Repin 2 ; J. Mank 3; J. Gagnon 4; M. Reeve 5; J. Peeters 6; W.J. Parker 1; N. Lakshminarasimman 1;

Author affiliation(s)Department of Civil and Environmental Engineering, University of Waterloo, ON, Canada 1; Region of Waterloo, ON, Canada 2 ; Ontario Clean Water Agency, ON, Canada. 3; Veolia Water Technologies 4; Veolia Water Technologies 5; Veolia Water Technologies 6; Department of Civil and Environmental Engineering, University of Waterloo, ON, Canada 1; Department of Civil and Environmental Engineering, University of Waterloo, ON, Canada 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159017

Volume / Issue

Content sourceWEFTEC

Word count14

Getting Control of Low DO with ABAC

Abstract

ABSTRACT: This study highlights the necessity of controls and process optimization when transitioning from conventional BNR to low energy BNR (low DO) to achieve nutrient removal objectives to allow for biological adaptation to new low DO settings. Key start-up considerations for the ABAC low DO transition include allowing time for ecological adaptation and control system fine-tuning. Although modeling validated the design, the WRRF experienced start-up challenges. Early operation showed promising EBPR and densification, but further on-site testing is needed to optimize P uptake and denitrification. RELEVENCE: The paper will focus on the lessons learned related to the process control of the ABAC Low DO process. It will give insight into other utilities implementing similar intensification projects through challenges and lessons learned. BACKGROUND: The 25 MGD Boulder WRRF recently converted the 4-stage bardenpho process to AO SND process using ABAC (Figure 1). This intensification project was one of the first of its kind to transition to low DO using ABAC with hydrocyclones and tight nitrogen and P limits (Table 1) in a cold-weather environment. The intensified low DO process was selected (1) to obtain P removal without the need of additional tankage and (2) to reduce energy consumption with no internal mixed liquor pumping and lower airflows. During the design, ABAC was selected over constant low DO since modeling showed improved performance with respect to response to ammonia fluctuations using ABAC. METHODOLOGY: This paper describes the challenges with converting the WRRF to low DO operation. Low DO conversion takes time and is especially challenging with daily maximum ammonia and nitrate limits and ongoing construction and maintenance activities. The timeline of the key activities during the upgrade is shown in Table 2. RESULTS: Figure 2 shows the process control and instrumentation for this project. Constant Low DO: To acclimate the MLSS to low DO, the aeration control in Z4-8 was changed to constant low DO in May 2025 and was operated in this mode for about three months. The effluent concentrations were examined to evaluate the SND and EBPR performance of the low DO process. Average effluent ammonia, nitrate, and TP were 0.3, 12.7, and 1.9 mg/L, respectively, during the low DO operation, as presented in Figure 3. The effluent quality is compared with before and after the upgrades and with model predictions for the low DO process. The constant low DO process achieved lower effluent TP and ammonia, but higher nitrate compared with before the upgrades. This shows the adaptation of nitrifiers to the low DO environment and occurrence of EBPR. The model underpredicted effluent TP and nitrate. DO profile for the low DO and ABAC process is presented in Figure 4. ABAC: Upgrade to the ABAC process was conducted in September 2025. The average effluent nitrate and TP concentrations with ABAC were 13.4 and 1.5 mg/L, respectively (Figure 3), exceeding the treatment targets. Table 3 shows the model results for ABAC using default kinetics (ammonia probe in Zone 7 and Zone 8). Process modeling was also conducted using adjusted kinetics for KDO AOB and NOB based on onsite rate testing (Figure 5). Compared with model predictions, the model underpredicted effluent TP and nitrate. The Z9 with supplemental carbon proved to be instrumental in meeting the daily max NO3 limit; however, it also removed SND process volume. In addition, dosing acetic acid in this zone resulted in a secondary release of P, and may interfere with the feast/famine cycle necessary for selecting granules capable of EBPR. Discussion SND: Comparing monthly average effluent NO3 (Figure 3), the NO3 was lower (< 10 mg-N/L) during constant low DO operations compared to the ABAC operation (12-14 mg-N/L). The higher NO3 values indicate that the ABAC set points are not optimal for SND. Testing of different max DO set points in a stepwise manner is underway. Fine tuning of the DO set points is expected to improve denitrification. EBPR: Figure 6 illustrates the correlation between the P uptake and P release mass rates observed. P uptake varied linearly with P release and was 105% of the P release which is lower than the 1.2-1.5:1 typical ratio. This confirms the activity of PAOs but there is opportunity for improvement for P uptake. Figure 7 compares the P release and uptake before and after the upgrade. The constant low DO and ABAC process showed P release and uptake, with higher P uptake for the constant low DO process compared with ABAC. Process optimization for EBPR is required. Process Improvement: Process improvement measures taken for optimization of the new process are presented in Table 4. Biological activity testing is underway (Table 5). Future optimization efforts will inform near-term operational adjustments for improved performance, calibrate the existing plant model, and provide the City with a stronger technical basis for future optimization of bio-P and SND. SUMMARY: While extensive process modeling validated the design, the WRRF faced challenges with start-up and adaptation to the low DO process using ABAC. Start-up and a few months of operation showed that the Low DO SND process achieved EBPR but there is substantial opportunity for improvement. The process successfully achieved densification with biological and physical selection, but onsite testing is critical for understanding P uptake and denitrification.

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

Presentation time

14:30:00

14:45:00

Session time

13:30:00

15:00:00

SessionAmmonia-Based Aeration Control in Practice – Lessons Learned

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Arabi, Sara, Regmi, Pusker, Sigmon, Cole, Marks, Christopher, Lakshminarasimman, Narasimman, Brown, Nathan, Trujillo, Shelley, Janoka, Brad

Author(s)S. Arabi1, P. Regmi1, C. Sigmon2, C. Marks2, N. Lakshminarasimman1, N. Brown1, S. Trujillo, B. Janoka2

Author affiliation(s)Stantec Inc., 1Stantec Inc., 1City of Boulder, 2City of Boulder, 2Stantec Inc., 1Stantec Inc., 1City of Boulder, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160451

Volume / Issue

Content sourceWEFTEC

Word count8

Description: Insights into emerging organic contaminants behavior in different full-scale sludge...

Insights into emerging organic contaminants behavior in different full-scale sludge treatment systems

Abstract

1. Background Sludge treatment processes typically incorporate physical, chemical, and biological unit operations to reduce sludge volume, odour, vector attraction, and pathogens in the product biosolids [1]. Biosolids are regulated with respect to pathogen, nutrient, and heavy metal content if land applied [2]. However, biosolids may also carry a wide range of anthropogenic chemicals such as pharmaceuticals, personal car e products, surfactants, plasticizers, flame retardants, and water and stain resistant coatings [3], collectively called emerging organic contaminants (EOC). The presence of trace levels of EOCs has been identified as a concern associated with their land application as they could potentially mobilize into soil, infiltrate into ground water, or be uptaken by vegetation [4]. While the long-term risks of exposure to humans are relatively unknown, some of the EOCs are known to be toxic, persistent and bioaccumulative [3,4]. Hence, an understanding of the occurrence and fate of EOCs in sludge handling systems that produce biosolids will provide a basis on which risks can be quantified. Further, most studies pertaining to EOCs and wastewater solids only document the contaminant presence in the product biosolids and there is little information on their removal through sludge processing systems. Further, the relative performance of different physical, chemical and biological sludge treatment processes is also largely unknown The objective of this study was to study the behavior of five major classes of EOCs: per- and poly-fluoroalkyl substances (PFAS), polybrominated diphenyl ethers (PBDE), alkyl phenols and ethoxylate derivatives, bisphenol A (BPA), and triclosan in common sludge treatment systems. The final paper will highlight the key findings from this multi-plant study and discuss the practical implications for biosolids management practices. 2. Study Design Samples of raw sludge and the final stabilized biosolids were collected from nine sludge treatment systems that included pelletization (P), alkaline stabilization (AS), aerobic digestion (AE1 and AE2) and anaerobic digestion (AN1 to AN5) processes. Grab samples were collected in glass jars on three consecutive days within a one-month period in each of 2015 and 2016 and shipped overnight on ice to the lab for contaminant analysis. The target analytes included 13 PFAS, 21 PBDEs, 4 alkyl phenols and ethoxylate derivatives, BPA, and triclosan. All the EOC analyses were conducted by SGS AXYS International (Sidney, BC) following stringent quality control procedures. 3. Major Findings The measured concentrations were used to estimate contaminant mass flows (mg/day) in and out of the system (contaminant concentration ng/g x solids flow kg/day) to assemble contaminant mass balance through the system. Percent removal was then calculated to evaluate the relative performance of the treatment systems. An overview of five major findings from this study are subsequently presented. A detailed discussion on the influence of the contaminant and treatment plant related factors will be included in the final paper. 3.1 All types of sludge treatment lead to EOC removal: While sludge treatment systems are primarily designed to prepare biosolids for subsequent disposition, the results of this study suggest that some removal of EOCs also occurs during the process. Up to 87% removal of triclosan was observed in AE2 during aerobic digestion. Nonylphenol monoethoxylate and diethoxylates were removed in both aerobic (Mono: 59 to 86%; Di: 84 to 95%) and anaerobic digestion (Mono: 35 to 79%; Di: 69 to 96%). Alkaline stabilization, where the raw sludge was stabilized at high pH using lime and cement kiln dust, was effective in reducing Î£PBDE mass flows by 53 ±12%. During pelletization, where the raw sludge was thermally dried and compacted, there were low removals of perfluorodecanoate (PFDA) (17%) and Î£PBDE (6%) mass flows. Hence, all treatments resulted in some degree of contaminant removal but removals differed between technologies. 3.2 Contaminant formation is possible during sludge treatment: The conditions established in sludge treatment can also lead to transformation of contaminants resulting in an increase in mass flows through the systems. Such an effect was commonly observed for selected PFAS where the average mass flow of the measured compounds increased by 59%, 19%, 2%, 264%, and 13% in AS, P, AE1, AN1, and AN5, respectively (Figure 1). Further, a net increase in mass flow of 4-nonylphenol was consistently observed in all five anaerobic digestion systems. Evidence of reductive debromination of fully brominated PBDE congeners into partially brominated PBDE congeners was also seen in anaerobic digestion systems. Thus, sludge treatment systems can transform precursors to increase contaminant mass flows through treatment. 3.3 Removal is dependent on sludge feed characteristics: The raw sludge fed to sludge treatment processes can differ because of differences in the inputs of contaminants to the sewershed and in the types of wastewater treatment processes generating the sludge. EOC use and release in a given sewershed will be reflected in the contaminant loading from the sludge treatment process. For example, BPA was measured in the raw sludge in all treatment systems except AE2. Since BPA was not detected in the raw sludge at AE2, this substance was also not detected in the biosolids at this treatment system. Differences in upstream wastewater treatment processes design can also impact the EOC content in the final biosolids. For instance, the biosolids where the raw sludge was predominantly composed of primary sludge had less diversity in overall PFAS composition compared to blended raw sludge feeds (primary and waste activated sludge) where a wide variety in PFAS composition was observed. Hence, differences in raw sludge properties were found to impact the biosolids quality following treatment. 3.4 Removal is dependent on the type of sludge treatment: The target compounds behaved differently in physical, chemical and biological treatments leading to different final biosolids quality. For example, while alkaline stabilization was effective in removing PBDEs, anaerobic digestion led to an increase in PBDE mass flows. In addition, the behavior of perfluorodecanoate (PFDA) differed between treatment systems with responses ranging from moderate removal (41%) to substantial formation (-264%). Even in the studied biological processes, there were distinctions between aerobic and anaerobic sludge treatments. For example, PFOA had low levels of net removal (< 25%) during anaerobic digestion (AN3 and AN5) and contrarily a net increase in mass flow by -68% and -282% in aerobic digestion systems (AE1 and AE2 respectively). The differences in transformations was found to impact the final biosolids quality. 3.5 Removal is dependent on the plant operations: Site specific factors, especially in biological treatment systems, such as the solids retention time, staging of the treatment processes and the active microbial consortia appeared to impact contaminant fate through treatment and hence biosolids quality. For instance, BPA was removed in AN2 with an average efficiency of 75% whereas formation of BPA was seen in other anaerobic digestion processes (AN1, AN4 and AN5). In aerobic digestion, there were low levels of average removals of perfluorohexanoate (PFHxA) (28%) in plant AE1, whereas AE2 reported low average levels of formation (-11%). A detailed discussion on the site-specific factors and operating conditions that may be responsible for the observed removals and biosolids quality will be presented in the full paper. 4. Significance of the findings This study evaluated contaminant loadings and removal of five major classes of EOCs namely PFAS, PBDEs, alkyl phenol, BPA, and triclosan in different full scale sludge treatment systems. The lessons learned will benefit all stakeholders of the biosolids industry in understanding the responses of EOCs thorough sludge treatment. The removal efficiencies presented in this study will enable the treatment plant managers to appraise the performance of sludge handling systems with respect to EOCs. The contaminant loading estimates could be used to communicate the significance of biosolids quality to end users. Further, there is little information describing contaminant mass balances and overall removal through sludge treatment. This study bridged this critical knowledge gap and addressed major questions related to PFAS, PBDEs and phenolics in physical, chemical and biological sludge treatment processes.

The following conference paper was presented at Residuals and Biosolids 2021: A Virtual Event, May 11-13, 2021.

SpeakerLakshminarasimman, Narasimman

Presentation time

13:20:00

13:40:00

Session time

13:00:00

14:00:00

SessionPFAS and Contaminants of Concern in Biosolids

Session number1

Session locationSimu-Live

TopicBiosolids, PFAS/Emerging Contaminants, PPCPs

Author(s)

N. LakshminarasimmanS. GewurtzS. SmythW. Parker

Author(s)N. Lakshminarasimman1; S. Gewurtz2; S. Smyth3; W. Parker4

Author affiliation(s)University of Waterloo 1; Environment and Climate Change Canada 2; Environment Canada 3; University of Waterloo 4;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2021

DOI10.2175/193864718825157944

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count13

Intensifying BNR with low DO and DAS: The Start-up Story

Abstract

ABSTRACT: This paper provides startup insights from Boulder WRRF's upgrade from MLE configuration to continuous flow densified activated sludge (DAS) with low DO without the internal mixed liquor recycle (IMLR). The DAS upgrade reduced SVI30 from 223±57 to 76±12 mL/g (66% improvement) and enabled granule formation. Profiling P release and uptake across the basins showed evidence of EBPR with potential for improved P uptake. The ongoing optimization will further fine tune the ABAC and the biological selection to improve SND and EBPR. BACKGROUND: The Boulder WRRF was recently upgraded to include hydrocyclones for physical selection and tank modifications for biological selection (without IMLR). The process changes are shown in Figure 1 and the timeline of the upgrade is shown in Table 1. Hydrocyclones were installed as a mixed liquor (ML) wasting process, with the design criteria presented in Table 2. METHODOLOGY: The densification upgrade started with installation of the hydrocyclones followed by conversion of the Z1-Z3 to anaerobic (Table 1). The hydrocyclone was operated with 20 mm and 18 mm nozzles to evaluate the impact of nozzle size on sludge settleability. To acclimate the MLSS to low DO, the aeration control in Z4 to Z8 was changed to constant low DO in May 2025 followed by ABAC in Sep 2025. Performance indicators were closely monitored using inline sensors (Figure 1) and lab analysis. Sludge samples were regularly collected to characterize the PSD, granular mass fraction, and microscopic images to study the evolution of densified sludge. RESULTS Biological selection: Figure 2 shows the selector F/M ratio during and after start-up. The F/M ratio remains above the min level required for granulation. The statistical correlation between the P uptake and the P releases was developed. P uptake was 105 percent of the P release which confirms PAO activity and EBPR occurrence, though this is below typical ratios of 1.2-1.5:1, indicating substantial opportunity for improvement. Ex-situ denitrification batch testing and P release and uptake testing are conducted to measure the specific denitrification rates and PAO activities (presented in the full paper). Settleability Improvements: The changes in sludge settleability during the densification upgrades were evaluated by comparing the SSV and SVI under different operations (Figure 3 and 4). Compared to before, SVI30 after the DAS upgrade was much lower (Figure 3). Considering the 2025 data, there was a steep decline in SVI30 from 223 ± 57 to 56 ± 10 mL/g, indicating the predominance of densified sludge with the physical selector (Figure 4). When the IMLR was turned off, the process maintained similar settleability with a higher SVI30, SSV5, and SSV30 values of 76 ± 12 mL/g, 408 mL/L, and 237 mL/L, respectively. The settleability between operations with nozzle size 20 mm and 18 mm was also compared (Figure 4). The settleability performance with both physical and biological selectors are well within the range reported for densified sludge in other studies (Regmi et al., 2025). Densification: The ML PSD was evaluated over time to track the accumulation of granular biomass (Figure 5). After DAS upgrade, there is rightward shift in particle count to include a higher percent of particles over 200 µm size indicating densification. Moreover, microscopic images of the ML and underflow show the dominant presence of dense granules (Figure 6) and the overflow wasted sludge consisiting of filamentous sludge. The full paper will delve into the change in sludge characteristics by showing the temporal changes in granule mass fraction. Outlook on continued optimization work: The plant effluent concentrations were examined to evaluate the SND and EBPR performance of the low DO process. The average effluent nitrate and TP concentrations after upgrade were 13.4 mg-N/L and 1.5 mg-P/L, respectively, exceeding the targets (10 mg/L NO3 and 1 mg/L TP). Considering P uptake and release rates across different zones, we observe an increase in PAO activity over time with different upgrades (Figure 7). While the increase in PAO inventory is encouraging, the low DO process needs fine tuning. Optimization activities will address the effluent quality issue through two lines of inquiry:
• Secondary carbon dosing: The plant has acetate dosing in the post anoxic zone. It is hypothesized that carbon dosing at the end of the process may interfere with the feast/famine cycle necessary for selecting granules capable of EBPR. Hence, the acetate dosage is minimized currently to investigate its impact on granule formation and ultimately, the effluent quality.
• Fine tuning ABAC DO set points: Comparing monthly average effluent NO3 (Figure 8), the NO3 was lower (< 10 mg-N/L) during constant low DO compared to the ABAC operation (12-14 mg-N/L). The higher NO3 values indicate that the ABAC set points are not optimal for SND. Testing of different max DO set points in a stepwise manner is underway. With the fine tuning of the DO set points, the denitrification in the process is expected to improve. Significance of study: This study delivers practical startup insights for DAS retrofits, highlighting a 6–9 month acclimation period, improved settleability, granule formation trends, and optimization of integrated low-DO/DAS systems. The paper emphasizes lessons learned, including ABAC tuning, biological selector optimization, and balancing low DO with low daily ammonia limits

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

Presentation time

10:30:00

11:00:00

Session time

10:30:00

12:00:00

SessionDensified Activated Sludge: From Startup to Optimization

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Arabi, Sara, Brown, Nathan, Sigmon, Cole, Marks, Christopher, Regmi, Pusker, Lakshminarasimman, Narasimman, Trujillo, Shelley, Janoka, Brad

Author(s)S. Arabi1, N. Brown1, C. Sigmon2, C. Marks2, P. Regmi1, N. Lakshminarasimman1, S. Trujillo, B. Janoka2

Author affiliation(s)Stantec Inc., 1Stantec Inc., 1City of Boulder, 2City of Boulder, 2Stantec Inc., 1Stantec Inc., 1City of Boulder, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160421

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Phosphorus Sequestration via Calcium Chloride Dosing into Full-scale Post-Aerobic...

Phosphorus Sequestration via Calcium Chloride Dosing into Full-scale Post-Aerobic Digesters

Abstract

[b]Summary[/b] The City of Boulder Wastewater Resource Recovery Facility (WRRF) implemented a pilot for dosing calcium chloride (CaCl2) to sequester phosphorus in its Post-Aerobic Digestion (PAD) process. Since its startup in September 2025, the pilot has achieved >75% orthophosphate (OP) removal while PAD's primary function of nitrogen removal has continued unimpeded, helping mitigate sidestream impacts associated with enhanced biological phosphorus removal (EBPR). After nearly four months of pilot operation a reactor was removed from service and two forms of precipitate were discovered, grit and scale. XRD analysis of both precipitates revealed the formation of hydroxyapatite (HAP), despite its reported slow growth. Visual MINTEQ modeling performed using PAD conditions with CaCl2 addition predicts high supersaturation for HAP, aligning with observations. The full paper will include detailed discussion of ongoing testing and sampling efforts to optimize Ca:P dosing following startup completion. [b]Background[/b] Efforts to prepare the WRRF for future strict effluent nutrient limits resulted in the Phosphorus Upgrades Project (PUP) which reconfigured the WRRF's 25 MGD nitrogen removal secondary process to remove phosphorus. EBPR is known to have negative impacts on solids treatment causing increased nuisance precipitates, reduced dewaterability, and increased OP recycle. The PUP aimed to intentionally sequester OP in the sidestream as a calcium-phosphate (Ca-P) precipitate (ex., brushite), which included building a pilot facilities to deliver CaCl2 to PAD. [b]Design[/b] Excel-based analysis and process modeling were conducted during the design phase to estimate the OP removal rate in the sidestream PAD at various CaCl2 and Ca(OH)2 dosages. Figure 1 shows the predicted lime dosage requirements. Process modeling results (SUMO 21), shown in Table 1, completed during this phase showed about 90% OP removal at Ca/P molar ratio of 2. SUMO 21 also predicted higher brushite quantities with increasing Ca/P molar ratio (Figure 2). The models predicted smaller quantities of struvite with increasing Ca/P ratio. [b]Startup Results[/b] Operation of the process with EBPR began in May 2025. The upgraded PAD with CaCl2 dosing began operation in September 2025, and results from this preliminary phase include the following. [i]OP Removal:[/i] The OP concentration in the digesters increased as EBPR began operating. Once CaCl2 dosing began, OP removal across the PAD averaged about 75%, from about 225 to < 50 mg/L (Figure 3). The PAD effluent P concentration was examined as a function of the Ca applied (Figure 4) to understand the dose-response behavior of the system. The regression plot showed a slight negative trend: higher Ca dosage was associated with lower effluent PO4 concentrations. [i]Nitrogen Removal:[/i] The PAD's nitrogen removal has not been affected by the CaCl2 dosing. [i]Precipitate XRD Analysis:[/i] The City conducted XRD analyses on three precipitate samples – one collected before CaCl2 addition and two collected after about 4 months of calcium addition. The XRD results are summarized in Table 2. Both samples from the recent CaCl2-influenced precipitate show consistent results with high amorphous content. The primary crystalline phase appears to be HAP, a result of CaCl2 addition. XRD analysis did not show struvite formation, but small quantities of vivianite were present, likely due to the ferric chloride used in anaerobic digesters for hydrogen sulfide control. [i]Revised Visual MINTEQ Analysis:[/i] HAP is expected when magnesium-to-calcium ratios are less than 4-to-1 [sup]1[/sup], as is present in the Boulder PAD. The growth rate of HAP is very slow, so conversion takes a long time (one month to several years) [sup]2,3[/sup]. HAP formation is not included in process models (ex., S), has a very low precipitation rate, and is not commonly expected or reported in the literature. A previous study for this project and other similar studies [sup]4,5[/sup] excluded HAP for MINTEQ analysis. Based on the XRD results, the chemical precipitation analysis for PAD was recently completed with HAP added to the MINTEQ database. Figure 5 shows the predicted saturation index for various precipitates over three different molar ratios. [i]Revised SUMO Modeling:[/i] The model was updated with data obtained after CaCl2 dosing began. The updated SUMO results (Figure 6) indicate small amounts of ACP in PAD and 2 times higher brushite precipitation in PAD than the digesters. SUMO predicts greater than 90% OP removal, agreeing with the demonstrated ~80% removal. [b]Summary and Next Steps[/b] Since September 2025, the Boulder PAD has successfully demonstrated over 80% OP removal in a PAD through CaCl2 dosing to create a Ca-P precipitate without negatively impacting the PAD's nitrogen removal performance. Building on this first phase, an investigation with a stepwise increase in molar Ca:P ratio is underway in 2026 to evaluate and understand PAD performance. A comprehensive sampling plan accompanies the testing, and the data and results from these efforts will be part of the completed report including evaluations of the following: •Metals and alkalinity balance •Solids and dewaterability impacts •EBPR impacts on digester ferric dosing for hydrogen sulfide removal

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

Presentation time

16:00:00

16:15:00

Session time

15:30:00

17:00:00

SessionScaling Smart: Sidestream P Management for Struvite Control

Session locationErnest N. Morial Convention Center

TopicBiosolids and Residuals, Circular Water Economy, Facility Operations and Maintenance, Nutrients

Author(s)

Brown, Nathan, Arabi, Sara, Marks, Christopher, Sigmon, Cole, Janoka, Brad, Lakshminarasimman, Narasimman

Author(s)N. Brown1, S. Arabi1, C. Marks2, C. Sigmon2, B. Janoka2, N. Lakshminarasimman1

Author affiliation(s)Stantec Inc., 1Stantec Inc., 1City of Boulder, 2City of Boulder, 2City of Boulder, 2Stantec Inc., 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160371

Volume / Issue

Content sourceWEFTEC

Word count11

Retrofitting MABRs in existing treatment infrastructure: What you need to know

Abstract

[b]Background[/b] Membrane aerated biofilm reactors (MABRs) are bubbleless aeration systems where oxygen is supplied through gas-permeable membranes that also serve as biofilm media. MABRs offer several benefits such as higher oxygen transfer efficiency, reduced energy use, improved winter nitrification, simultaneous nitrification-denitrification, mitigated N₂O emissions, quick installation, and smaller footprint.¹˒² These advantages make MABRs a leading intensification technology with growing full-scale adoption worldwide. MABRs are often retrofitted into existing treatment trains to boost capacity with minimal expansion. Because every plant has unique characteristics, site specific considerations are critical for successful MABR installation. Drawing on our experience from multiple MABR projects, this abstract consolidates the key lessons learned. With two full-scale plants that were the first Canadian and first Australian MABR installations as case studies, this paper provides practical design and operational insights that can help utilities make informed decisions. [b]Study Sites[/b] The study sites are full-scale MABR facilities at Hespeler WRRF (Canada) and Elanora STP (Australia). Table 1 and Figure 1 present the site details and process flowsheets. Hespeler's upgrade was completed in Aug 2022, supported by long-term monitoring (Jan 2020–Apr 2024) to benchmark plant performance before and after the upgrade. Elanora's commissioning is scheduled for 2026 with a following performance testing. [b]Study findings[/b] Existing vs. new tanks: Retrofitting existing reactors can pose challenges. MABR cassette dimensions may create unused volume in deep tanks. At Elanora, a high clarifier-to-bioreactor ratio required a large aerobic fraction, limiting anoxic volume and cassette count. At Hespeler, existing aeration tank walls could not support cassettes, so a new 637 m³ anoxic tank was built. Despite new construction, the upgrade cost was about half that of aeration tank expansion due to MABR's compact footprint. Mixing design: MABR tank mixing needs due considerations to avoid solids settling. At Hespeler, initial jet mixers and intermittent air sparging were insufficient, causing sludge accumulation and ammonia release. Adding intermittently aerated coarse bubble diffusers resolved the issue. Elanora adopted this approach upfront. CFD modeling during design is recommended to ensure proper mixing. Biofilm thickness management: At Hespeler, an increased N loading did not boost nitrification as expected. Increasing wastewater loading also increased the carbon supply and grew thick biofilms that restricted ammonia diffusion. Thus, managing biofilm thickness appropriate scouring intensity under dynamic loading conditions is critical for optimal MABR operations. There can be spatial variations with MABR cassettes in a plug flow tank showing a longitudinal increase in biofilm thickness (Figure 3). Cassettes at the front the receives the higher carbon loading develop a thicker biofilm. This can be detrimental because the front cassettes have the highest NH4 gradient to drive the nitrification rate which is dampened by thick biofilms. Thicker biofilms could also support sulfur reducing organisms which compete with denitrification for carbon and can cause odor. Designing for higher scouring at the front could alleviate these issues. Monitoring biofilm through direct sampling or pressure decay tests can inform operations, though these methods are costly. Emerging data-driven techniques using effluent NH₃ and exhaust O₂ may offer practical alternatives.³˒⁴ Seeding effect in SRT design: MABR biofilms act as 'nitrifier nurseries' for the whole plant, reducing aerobic SRT (aSRT) required for downstream nitrification. Figure 5 shows the critical role of the MABR NH₃ removal fraction and biofilm SRT (sloughing rate) in maximizing the nitrifier seeding effect. At Elanora, these factors guided the design of MABR surface area and decreased the post-upgrade aSRT from 10 to 6 d. At Hespeler, because of the seeding effect, winter effluent NH₄ remained <10 mg/L at 4–5 d SRT and 10–12°C.² Moreover, the average NH4 removal efficiency in the downstream aeration tank increased from 52% to 71% with an increase in MABR scouring intensity (Figure 4). Hence, the overall SRT design should consider the operational airflows and scouring intensity in determining safety factor. Downstream aeration impacts: MABRs influence more than nitrification in the downstream processes. At Hespeler, MABRs removed over half the TKN and significant carbon through denitrification that the aeration tank airflow was halved (Figure 6). Even at minimum blower settings, the post upgrade DO in the aeration tank remained uniformly high (>2 mg/L) throughout as opposed to a longitudinal increasing trend before upgrade (Figure 6). These findings indicate that, i) MABR reduced the operational cost related to process air by half, ii) MABRs can offer additional aeration capacity for any increase in future loading, and iii) having appropriately variable speed blowers can help realize additional electricity savings. In conclusion, this study consolidates real-world lessons on design trade-offs, operational strategies, and site-specific considerations for retrofitting MABRs. The full paper will include additional factors to consider when integrating other intensification technologies such as MBR and hydrocyclones.

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

SessionCharting the Future of MABR Technology

Session locationErnest N. Morial Convention Center

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Lakshminarasimman, Narasimman, Astrand, Niclas, Gloag, Graham, Staib, Cameron

Author(s)N. Lakshminarasimman1, N. Astrand1, G. Gloag1, C. Staib2

Author affiliation(s)Stantec Inc., 1Stantec Inc., 1Stantec, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160308

Volume / Issue

Content sourceWEFTEC

Word count12

Description: Rumen-Inspired Anaerobic Dynamic Membrane Bioreactor Enhances Hydrolysis in Food...

Rumen-Inspired Anaerobic Dynamic Membrane Bioreactor Enhances Hydrolysis in Food Waste and Sludge Digestion

Abstract

Abstract A novel acid-phase anaerobic dynamic membrane bioreactor (AnDMBR), inspired by the stomach of ruminant animals, was operated to achieve efficient hydrolysis at a hydraulic retention time (HRT) of 12 h with minimal membrane fouling. This rumen-mimicking AnDMBR achieved volatile fatty acid (VFA) yields of 0.4 ± 0.2 g VFA/g volatile solids (VS) fed over three years of continuous operation with both mono-digestion of food waste and co-digestion of food waste and wastewater sludge. The bioreactor retained core rumen-associated microbes, such as Prevotella, Prevotella_7, and Bifidobacterium, supporting its adaptability across different feedstocks. These results highlight the rumen-AnDMBR as a robust option for producing VFAs from diverse organic waste streams, suitable for downstream methane or medium chain fatty acid production. Introduction Anaerobic digestion (AD) is widely used to convert organic wastes into renewable bioenergy and nutrient-rich digestate but faces challenges like long retention times. Anaerobic membrane bioreactors (AnMBRs) have been employed for high-rate anaerobic treatment, retaining biomass and enabling operation at high solids retention time (SRT). However, AnMBRs are challenged by membrane fouling, particularly with high-solids waste streams, which reduces flux and increases maintenance costs (Osman et al., 2023). AnDMBRs offer a cost-effective alternative by using low-cost materials to replace conventional membranes and employing energy-efficient fouling mitigation strategies, such as backwashing and relaxation (Hu et al., 2018). We developed a novel AnDMBR that simulates the rumen environment and rumination processes, such as regurgitation and mastication (Fonoll et al., 2024). In this system, the hydraulic retention time (HRT) is decoupled from the SRT by forming a dynamic membrane on a mesh that supports the growth of microbes enhancing hydrolysis and fermentation (Mason and Stuckey, 2016). By periodically breaking the biofilm, similar to regurgitation and mastication in ruminants, the system reduces the inhibitory effects of high volatile fatty acids (VFA) concentrations, creating a favorable environment for microbial activity and enhancing hydrolysis. The rumen-AnDMBR successfully produced an average VFA yield of 0.55 ± 0.12 g of VFA/g of VS during mono-digestion of food waste (FW) at an OLR of 18 ± 2 g VS/Lreactor/d (Fonoll et al., 2024). In comparison, conventional AD systems that operate acid-phase treatment of FW typically produce around 0.3--0.4 g VFA/ g VS at an organic loading rate (OLR) below 11 g VS/Lreactor/d (Jiang et al., 2013; Lim et al., 2008). FW typically has high compositional variability compared to feedstocks like animal manure or wastewater sludge leading to challenges such as poor hydrolysis and VFA accumulation in mono-digestion systems (Dalke et al., 2021). Co-digestion of FW with organic wastes such as animal manure, lignocellulosic waste, and sludge can mitigate these issues by providing alkalinity, supplemental nutrients, and diverse microbial communities (Karki et al., 2021). However, FW generally offers a higher methane yield than other organic wastes, which can decrease with co-digestion due to dilution effects (Li et al., 2020; Luo et al., 2024). Co-digestion of FW with sludge has not been previously explored in rumen-mimicking AD systems. The lack of co-digestion studies with rumen-mimicking systems motivated us to study co-digestion of FW and sludge in a rumen-inspired AnDMBR. We demonstrated the long-term (over three years) stability of the rumen-AnDMBR process under FW mono-digestion and FW and sludge co-digestion. The hydrolysis performance data were complemented with 16S rRNA gene sequencing data to understand changes in a few key rumen microbial populations in response to operational changes. Materials and Methods Liquid and solid rumen contents collected from a fistulated cow at the Michigan State University dairy farm (East Lansing, MI, USA) and first-phase digestate obtained from the Flint Water Resource Recovery Facility (WRRF) (Flint, MI, USA) were used to inoculate the rumen-AnDMBR. FW was collected from two dining halls at the University of Michigan (Ann Arbor, MI). A blend of 60% primary and 40% thickened waste activated sludge, referred to as wastewater sludge in this study, was collected from the holding tank at the Ann Arbor WRRF (Ann Arbor, MI, USA). A 6.2 L AnDMBR was operated to mimic rumen conditions (Fig. 1) where a dynamic membrane containing a cake layer of biofilm and solids was formed, broken, and reformed on a 147 Âµm pore size mesh support during a 21 h period each day. The pH in the rumen-AnDMBR was maintained between 6.2--6.3 by automatically dosing 2.5 N NaOH. The operating conditions for the rumen-AnDMBR at different periods are summarized in Table 1. The FW, wastewater sludge, bulk digestate, and permeate samples were collected twice a week for chemical analyses. Total and suspended solids concentrations (APHA, 2012) were measured to adjust SRT; while COD concentrations (Hach, Loveland, CO, USA), and VFAs (Fonoll et al., 2024) were analyzed to determine the hydrolysis rate and VFA yield observed under different operating conditions. 16S rRNA gene sequencing was performed on the digestate samples to evaluate the microbial community structure and identify key microbes responsible for hydrolysis function. DNA extraction, amplification, and sequencing procedures have been detailed in Fonoll et al. (2024). The DNA sequences were analyzed using DADA2 (Callahan et al., 2016). The hydrolysis rate constant (d-1) was calculated using a steady-state particulate COD mass-balance approach in a continuously stirred tank reactor: khyd =[(Qin x Cin) - (Qdig x Cdig + Qperm x Cperm)]/ Cdig x V , where Qin, Qdig, and Qperm represent the flow rates of feed, wasted digestate, and permeate in the rumen bioreactor, respectively. Cin, Cdig, and Cperm represent the particulate COD concentrations of feed, digestate, and permeate, respectively. V is the volume of the bioreactor. The net VFA yields, reported in this study in terms of COD, are values calculated after subtracting the concentration of the respective VFAs in the feed. Results and Discussion Rumen-AnDMBR achieved high VFA yields and microbial adaptability under varied feedstock conditions The hydrolysis rate constants were consistently maintained across both mono- and co-digestion periods, highlighting the rumen-AnDMBR's adaptability to varied feedstocks, even with the dilution effect introduced by sludge (Fig. 2). The average net VFA yields in the rumen-AnDMBR was 0.42 ± 0.18 g VFA/g VS for FW mono-digestion and 0.35 ± 0.18 g VFA/g VS for co-digestion, reaching the upper limits of the typical range. This sustained VFA yield demonstrates the rumen-AnDMBR's robustness in maintaining hydrolysis and fermentation efficiency at a higher loading rate, even when feedstock characteristics vary, positioning it as a resilient alternative to conventional systems. The relative abundance of select genera was investigated to understand the retention of known hydrolytic rumen microbial populations, originating from the rumen inoculum, in the rumen-AnDMBR (Fig. 3). The genera Prevotella, Ruminococcus, Bifidobacterium, and Fibrobacter, typically present in the rumen microbiome, are highly efficient in cellulose and hemicellulose degradation, which are critical for VFA production (Mizrahi et al., 2021). Prevotella and Bifidobacterium maintained their abundance across mono- and co-digestion periods. Prevotella, which peaked during the mono-digestion period, was replaced by Prevotella_7 as a dominant genus in the co-digestion period, reflecting the system's ability to adapt to changing feedstock conditions. The fiber-degrading genera Ruminococcus and Fibrobacter exhibited relatively low abundances, likely attributed to the low fiber content of the feedstock. However, the increase in the relative abundance of Ruminococcus during the co-digestion period indicates some potential for fiber degradation. With steady hydrolysis rates, high VFA yields at high OLRs, and adaptable microbial dynamics, the rumen-AnDMBR demonstrates strong potential as a scalable, resilient solution for sustainable waste processing across diverse waste streams. Acknowledgements We thank Steve Donajkowski, Ethan Kennedy, and Tom Yavaraski for technical assistance. Thanks also to the staff at Michigan State University dairy farm, Flint and Ann Arbor WRRFs, and the University of Michigan dining halls. We also thank Yuang Guo, Victor Luk, Jenna Kutscher, Evan Zalek, Brianna Jimenez, Olivia Sherman, Sofia Martinez Cantu, and Alisson Villarreal Hurtado for their contributions to this work. This work was funded by the Department of Energy (DE-FOA-0002203_FY20_BETO_Multi-Topic).

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerLakshminarasimman, Narasimman

Presentation time

11:25:00

11:45:00

Session time

10:45:00

11:45:00

SessionAcademic Advancements in Digestion and Fugitive Greenhouse Gas Emissions

Session number2

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Anaerobic Digestion, Biogas, Biogas Production, Energy recovery, food waste, Greenhouse Gases, Membrane bioreactor, Nitrous oxide, Resource Recovery, Sustainability And Social Responsibility

Author(s)

Karki, Renisha, Starostka, Renata, Lakshminarasimman, Narasimman, Puente, Pedro, Fairley-Wax, Timothy, Zhu, Kuang, Skerlos, Steven, Raskin, Lutgarde

Author(s)R. Karki1, R. Starostka1, N. Lakshminarasimman1, P. Puente1, T. Fairley-Wax1, K. Zhu1, S. Skerlos1, L. Raskin1

Author affiliation(s)University of Michigan, 1University of Michigan Dept of Civil & Env Eng, 1University of Michigan, 1University of Michigan, 1University of Michigan, 1University of Michigan Dept of Civil & Env Eng, 1University of Michigan, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159766

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Description: Ten Years After: The Status of Polybrominated Diphenyl Ethers (PBDE) in Canadian...

Ten Years After: The Status of Polybrominated Diphenyl Ethers (PBDE) in Canadian Biosolids and Their Fate Through Solids Treatment Processes

Abstract

Occurrence of persistent organic pollutants such as polybrominated diphenyl ether (PBDE) flame retardants in biosolids are a concern as these contaminants may be transported into the environment during land application. This study monitored the concentration of 21 PBDE congeners in raw sludge and biosolids collected from nine sludge treatment facilities across Canada that employed 4 different solids treatment processes. The overall ΣPBDE-Br concentration varied between 0.25 to 1.5 μg-Br/g dry weight. Deca-BDE (BDE-209) was the predominantly occurring congener and its concentration constituted 40-65% of the overall ΣPBDE-Br concentration in both raw sludge and biosolids samples. Tri-, hepta-, and octa- BDE made up less than 1% of the overall ΣPBDE-Br in the raw sludge and biosolids samples. Contaminant mass balances were assembled around the treatment systems and the overall fate of the PBDEs was found to depend upon the treatment technology. While there was no significant change in mass flow during pelletization, ΣPBDE-Br mass flow was reduced by approximately 30% during alkaline stabilization. The removal of PBDE was not consistent in aerobic or anaerobic digestion treatment systems.

SpeakerLakshminarasimman, Narasimman

Presentation time

14:30:00

14:50:00

Session time

13:30:00

15:30:00

SessionEmerging Topics in Microconstituents

Session number402

TopicMicroconstituents

Author(s)

N. LakshminarasimmanS. GewurtzW. ParkerS.A. Smyth

Author(s)N. Lakshminarasimman1; S. Gewurtz2; W. Parker1; S.A. Smyth2;

Author affiliation(s)Department of Civil and Environmental Engineering, University of Waterloo1; Science and Technology Branch, Environment and Climate Change Canada2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157392

Volume / Issue

Content sourceWEFTEC

Word count21