Reifsnyder, Samuel

Samuel Reifsnyder is a speaker at WEFTEC 2026.

Titles from this speaker

Description: Advanced Aeration Control in Action: Diagnosing and Resolving Infrastructure...

Advanced Aeration Control in Action: Diagnosing and Resolving Infrastructure Limitations

Abstract

[b]APPLICABILITY[/b] Advanced aeration controls play a vital role in modern wastewater treatment by enabling low dissolved oxygen (DO) operation, improving energy efficiency, and reducing greenhouse gas emissions. However, the effectiveness of these control strategies is often constrained by infrastructure limitations, including legacy blower and piping configurations, blower turndown and staging, and sensor placement and reliability. As a result, many facilities struggle to realize the benefits of advanced aeration control without first addressing system-level constraints. This presentation offers a first-of-its-kind approach to diagnosing and overcoming these challenge through a combination of innovative, state-of-the-industry modeling and monitoring approaches. Drawing on a real-world case study, this work provides a step-by-step methodology for evaluating each aspect of a complex full-scale aeration system, including physical limitations, controls, and operational process decisions. This presentation provides actionable insights for professionals looking to understand and troubleshoot aeration system performance. Attendees will gain knowledge for evaluating existing systems, improving operational reliability, and achieving tighter process control. [b]RESULTS AND OUTCOMES[/b] [i]Methodology[/i] Metro Water Recovery's Northern Treatment Plant (NTP) (Denver, CO) has a rated capacity of 28.8 MGD and features four bioreactors configured as a seven-stage Bardenpho process with step-feed (Figure 1). Aeration is supplied by six high-speed turbo blowers, serving eight individually controlled aerobic zones in each bioreactor. NTP is implementing an advanced aeration controller (AAC) and is unable to maintain setpoints under certain conditions, indicating infrastructure limitations (Figure 2). Efforts to bring additional blowers online under these conditions have resulted in surge, further complicating system performance and troubleshooting. The primary objective of this work was to conduct a comprehensive, state-of-the-industry analysis of the aeration system to identify restrictions or deficiencies preventing the system from achieving required airflow demands when employing AAC. The methodology included: 1. A review of record drawings and onsite verification of existing conditions to validate system layout, physical constraints, and component conditions. 2. Process modeling conducted in BioWin to define treatment conditions and verify the operational capacity of the aeration system (Shown exemplary in Table 1). 3. AFT Arrow modelling to simulate airflow dynamics and identify bottlenecks in the system (Figure 3). 4. Onsite, real-time off-gas testing using Carollo's I-FLOAT to confirm key aeration design assumptions like alpha factor and oxygen transfer efficiency, which are critical for validating model outputs, ensuring accurate calibration, and help identify broken pipes previously not known (Shown exemplary in Figure 4). 5. The capacity and programming of the blowers were reviewed in collaboration with the manufacturer, including assessing control logic and implementing operational constraints to identify performance limitations. This approach provided an understanding of the system's limitations, enabling the identification of actionable improvements to enhance DO control, alleviate peak flow challenges, and facilitate AAC operation. [b]Result[/b] The analysis revealed significantly elevated blower discharge pressures in nearly all scenarios during peak diurnal loadings and high air velocities within Zones 1B and 1C under specific treatment conditions (Table 2). The discharge pressures in each scenario placed the existing blower system near or beyond surge conditions (Figure 5).

To address these issues, three solutions were evaluated by the project team:
• Option A: Upsize the piping and control valves in Zones 1B and 1C, reducing the air velocities and resulting pressure drops.
• Option B: Increase the piping in Zones 1B and 1C, extending modifications back to the main aeration lateral. This approach offers more significant pressure reductions but requires greater construction effort.
• Option C: Combine Option A's piping changes with an additional drop leg and diffuser manifold in Zone 1C. While this option does not substantially reduce blower pressures, it may improve process performance under low DO conditions. NTP is currently evaluating next steps for the aeration system from a holistic perspective, balancing operational and capital approaches to address the identified challenges. In addition, a blowoff valve was installed to assist with blower staging, and multiple control strategies have been implemented, including most-open-valve and pressure-based control tied to influent flow. The project team is coordinating with the blower manufacturer to achieve greater blower turndown and operate at greater pressures, which is currently limited by the blower's 'dynamic mean speed' control logic.

[b]Conclusions/Outcomes[/b] This work provides a novel, systematic approach to troubleshooting aeration systems, with findings that can be extrapolated to improve efficiency and performance in similar facilities, allowing for the implementation of AACs. The methodology and case study outcomes offer practical solutions to identify and address airflow limitations, optimize advanced aeration control, and enhance energy efficiency across diverse wastewater treatment projects.

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

Presentation time

08:30:00

09:00:00

Session time

8:30:00

10:00:00

SessionDesigning Flexible Aeration Systems for Low Dissolved Oxygen Strategies

Session locationErnest N. Morial Convention Center

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

Author(s)

Coday, Bryan, Berlin, Jeffrey, Reifsnyder, Samuel, Morse, Thomas, Almaraz, Nohemi

Author(s)B. Coday1, J. Berlin1, S. Reifsnyder1, T. Morse2, N. Almaraz2

Author affiliation(s)Carollo Engineers, 1Carollo Engineers, 1Carollo Engineers, 1Metro Water Recovery, 2Metro Water Recovery, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160480

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Closing the Air Gap: Aeration Testing to Resolve Missing Demand and Unlock Savings...

Closing the Air Gap: Aeration Testing to Resolve Missing Demand and Unlock Savings at a 0.5 MGD Biological Nitrogen Removal Demonstration Plant

Abstract

The Los Angeles County Sanitation Districts (LACSD) and the Metropolitan Water District of Southern California (MWD) have partnered to develop the Pure Water Southern California (Pure Water) program, which aims to produce up to 150 million gallons per day (MGD) of advanced treated potable reuse water from the A.K. Warren Water Resource Facility (Warren Facility). The Warren Facility is a 400-MGD capacity, non-nitrifying high-purity oxygen activated sludge (HPOAS) plant, producing secondary effluent with ammonia of approximately 40~50 mg N/L. As the product water needs to meet 2 to 4 mgN/L total inorganic nitrogen (TIN) targets for the intended applications, tertiary membrane bioreactor reactor (tMBR) is envisioned as a part of the nitrogen management strategy. To support process selection and full-scale design, MWD constructed a 0.6-MGD demonstration plant (Demo) at the Warren Facility. Between December 2023 and December 2025, the Demo was operated in nitrification-denitrification (NdN) tMBR mode with external carbon supplementation for denitrification (Fitzgerald et al., 2024). During this testing, the aeration air demand for NdN tMBR was consistently and significantly lower than the process design estimates, by approximately 20%. It was hypothesized that the tertiary biological nitrogen removal (BNR) operation resulted in improved oxygen transfer efficiency, thus lowering air demand. OBJECTIVE To evaluate whether improved aeration efficiency is behind the reduced air demand and to inform future full-scale aeration design, off-gas testing was conducted to assess aeration performance. METHODOLOGY Off-gas testing was conducted at the Demo in accordance with American Society of Civil Engineers 18-18 guidelines (ASCE, 2018) using an off-gas analyzer, a gas-capture hood connected to the analyzer, and a dissolved oxygen (DO) meter. The hood was floated on the aeration tank water surface to collect emitted gases, while off-gas and ambient air were alternately analyzed for oxygen concentration. DO was measured adjacent to the hood. These data were used to calculate oxygen transfer efficiency (OTE), alpha-fouling factor (αF), standard process-water OTE (αFSOTE), oxygen transfer rates (OTR), and oxygen uptake rates (OUR). Carollo's Inflatable Fast and Lightweight Off-gas Analysis Technology (I-FLOAT) platform was selected to accommodate the challenging Demo conditions, which included a 15-foot drop from the catwalk down to the water surface, limited available catwalk workspace, and instrumentation mounted along the handrails. The I-FLOAT's lightweight, inflatable gas-capture hood made it well suited to overcome these constraints. Testing was conducted in two campaigns: Phase 1 in November 2024 and Phase 2 in July 2025. Each phase included continuous off-gas testing for a minimum of three consecutive days in the aerobic zone (Zone #2), followed by three days in the swing zone (Zone #3) (Figures 1 and 2). At the start of Phase 2, a one-day sweep test was performed to assess spatial variabilities in aeration performance and support airflow balancing, with measurements collected across four locations spanning both the aerobic and swing zones. RESULTS Phase 1 (November 2024): Average OTE was 20.6% in Zone #2 and 9.0% in Zone #3, with corresponding αF values of 0.77 and 0.63. Average standard process-water OTE (αFSOTE) was 28.7% in Zone #2 and 16.2% in Zone #3. These results were likely influenced by imbalanced airflows between zones (0.29 vs. 1.53 scfm/diff) and, therefore, were considered non-representative of typical full-scale conditions. Phase 2 (July 2025): Airflows were rebalanced to approximate typical operating conditions (~1 scfm/diff), resulting in uniform distribution (0.83–0.87 scfm/diff). Under these conditions, OTE decreased to 9.8–10.6%, while αFSOTE (22.7-23.5) and αF (0.78–0.82) stabilized across the two zones, producing a representative spatial aeration profile. Across both phases, measured αF values ranged from 0.63 to 0.82 (Figure 3), exceeding typical mainstream conventional activated sludge values of 0.3–0.7 (Rosso et al., 2005). It is speculated the higher αF in tertiary NdN is due to HPOAS upstream of the Demo removing surfactants and inhibitory compounds. Additional details from the testing are summarized in Table 1. The improvement in oxygen transfer efficiency explains the low air demand observed during the Demo testing. Full-Scale Project Implications: Applying the validated αF of 0.8 in full-scale Pure Water aeration design, rather than the conservative 0.65 used in initial estimates, yields significant capital and O&M savings, including a 23% reduction in diffuser capital and a 24% reduction in required airflow (Table 2). For a 150-mgd tMBR NdN system, this translates to preliminary Class 5 aeration cost savings of $13-15 million. Industry Significance: To the authors' knowledge, there has been no to limited published reports of tertiary BNR aeration performance. This work addresses the data gap and shows optimization opportunities for such processes. CONCLUSION Off-gas testing confirmed that αF factors in an NdN tMBR system are substantially higher than in conventional activated sludge, demonstrating improved oxygen transfer efficiency as the cause of reduced air demand. Incorporating these validated αF values into full-scale design supports better optimized aeration strategies for tMBRs and similar tertiary BNR systems, yielding significant savings.

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

Presentation time

16:20:00

16:40:00

Session time

15:30:00

17:00:00

SessionMembrane Treatment Applications Past, Present, and Future

Session locationErnest N. Morial Convention Center

TopicClimate Change Adaptation and Metrics, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Wong, Larry, Reifsnyder, Samuel, Fitzgerald, Colin, Danker, Bryce, Liu, Michael, Mansell, Bruce, Tanuwidjaja, Dian

Author(s)L. Wong1, S. Reifsnyder2, C. Fitzgerald3, B. Danker4, M. Liu1, B. Mansell1, D. Tanuwidjaja<5/sup>

Author affiliation(s)LA County Sanitation District, 1Carollo Engineers, 2Jacobs, 3Hazen and Sawyer, 4LA County Sanitation District, 1LA County Sanitation District, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160433

Volume / Issue

Content sourceWEFTEC

Word count23

Converting HPO to Nitrogen Removal: Closing the Oxygen Gap Through Electrolysis

Abstract

APPLICABILITY Major US water recovery facilities (WRRFs) operate as High Purity Oxygen Activated Sludge (HPOAS) systems, originally built for BOD removal. Stringent nutrient limits now require lowering effluent nutrients, leading HPOAS facilities to consider expanding or upgrading for nitrification/denitrification processes (NDN). Upgrading presents challenges, including the need for extra oxygen to nitrify ammonia, requiring expansion of the existing oxygen supply system. In parallel, there has been global recognition of green hydrogen as a way to decarbonize hard-to-electrify sectors , with several facilities commissioned in the US. This study explores co-locating electrolytic green hydrogen generation at HPOAS facilities, producing green hydrogen and co-valorizing byproduct oxygen to increase oxygenation capacity. This strategy interfaces with two trends: expanding oxygen capacities of large HPOAS transitioning to NDN and decarbonizing hard-to-electrify industries through green hydrogen. Converting HPO Facilities to Nitrogen Removal and Its Implications Adapting Large High Purity Oxygen Activated Sludge (HPOAS) systems for nitrogen removal is gaining attention (Pitt et al. 2023). Coastal facilities, traditionally exempt from strict nitrogen regulations, are anticipated to upgrade their system to nutrient removal due water reuse and ocean discharge requirements. Retrofitting for nitrogen removal poses challenges in meeting increased oxygen demands, potentially surpassing existing oxygen demand by over 60%. Thorough evaluation of the oxygenation system is crucial for HPOAS upgrades to an NDN process, considering both immediate and future oxygen requirements. Energy Transition and Green Hydrogen An emerging solution for decarbonizing hard-to-electrify industries is green hydrogen production, which enables the storage of renewable energy in hydrogen form, addressing reliability issues during low renewable energy periods. Green hydrogen benefits energy storage and aids in decarbonizing sectors like long-distance transportation, industrial chemical synthesis, and various fuel applications (Davis et al., 2018; Saeedmanesh et al., 2018). The Case for Green Oxygen Recovery at HPO Plants Green hydrogen generation yields a valuable by-product: pure oxygen. In the context of Water Resource Recovery Facilities (WRRFs), this by-product oxygen, holds the potential for beneficial re-use in the bio-reactors. Given WRRFs' frequent co-location with industries (i.e., airports, ports, chemical industries, etc.) there is an opportunity to integrate renewable hydrogen generation systems at WRRFs. This enables the supply of green hydrogen for local industry decarbonization while recovering pure green oxygen for aeration. Since HPOAS systems operate at high purity oxygen levels (greater than 95%) the oxygen produced by the electrolyzer can be easily blended into the pure oxygen line of the plant. The ability to leverage the existing oxygen equipment allows to minimize the need for modification to the existing oxygenation system. Figure 1 illustrates a process schematic of an HPOAS system incorporating green oxygen from electrolysis. Case Study: City of Cedar Rapids The Cedar Rapids Water Pollution Control Facility (CRWPCF) shows the application of this approach. Operating on a UNOX configuration (45 MGD), with an oxygen generation capacity of 80-ton/day. Available renewable energy sources (RES) were assessed when developing hydrogen production curves. Figure 2 shows the specific solar power generation for the geographic coordinates of the CRWPCF (PVWatts, NREL). Various electrolyzer sizes are considered to project dynamic green oxygen generation curves. These are compared with the estimated oxygen demand from the hetero- and auto-trophic process and to assess oxygen storage needs. Overall, to supply the near-term oxygen needs of the CRWPCF approximately 35MW are required. As part of the ongoing work, this study will further explore different RES blends and assess the costs/performance/constructability/ implications of retrofitting the existing UNOX equipment to receive electrolytic oxygen. Conclusions This case study explores integrating green hydrogen production at HPOAS facilities at WRRFs. Co-valorizing oxygen enables concurrent green hydrogen production, supporting the acceleration of global decarbonization. Re-using by-product oxygen for nitrification meets NDN transition needs of HPOAS systems, expanding capacity and generating renewable fuel. This approach allows to leverage ongoing decarbonization funding opportunities, offsetting costs, and expanding oxygen supply operations at HPOAS. The City of Cedar Rapids provides practical insights on infrastructure, power, and equipment considerations, offering a sustainable solution for wastewater utilities. RELEVANCE TO AUDIENCE This research introduces an innovative approach for HPOAS plants aiming for NDN and sustainability. Valuable insights for plant operators, engineers, and decision-makers for upgrading HPOAS systems will be addressed. The study also highlights the potential synergy between wastewater treatment and green hydrogen production. The proposed co-location of electrolytic green hydrogen generation and HPOAS facilities not only addresses environmental concerns but also creates economic opportunities for nearby industrial users. This research contributes to a holistic understanding of sustainable practices at WRRF.

This study assesses the financial opportunities and barriers of co-valorizing the oxygen by-product of a renewable-powered green hydrogen facility at a High Purity Oxygen Activated Sludge (HPOAS) plant, with the intent of expand the oxygenation capacity of HPOAS transitioning to nitrification/denitrification (NDN).

SpeakerReifsnyder, Samuel

Presentation time

14:30:00

14:50:00

Session time

13:30:00

15:00:00

SessionBuilding a Hydrogen Future

Session number206

Session locationRoom 244

TopicEnergy Production, Conservation, and Management, Intermediate Level, Research and Innovation

Author(s)

Reifsnyder, Samuel, Gabel, Dale, Wolohan, Brendan, Busch, Lindsey

Author(s)S. Reifsnyder1, D. Gabel2, B. Wolohan3, L.I. Busch4

Author affiliation(s)1Carollo Engineers, CA, 2Iowa Member Account, CO, 3Carollo Engineers, Inc., 4Carollo Engineers, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159519

Volume / Issue

Content sourceWEFTEC

Word count12

Description: Dynamic Influent Load Diversion as a Demand Response Service In Systems of...

Dynamic Influent Load Diversion as a Demand Response Service In Systems of Hydraulically Connected WRRFs.

Abstract

In recent years, the global discourse concerning sustainable wastewater treatment has shifted toward the decentralization of water resource recovery facilities (WRRFs). In fact, decentralized wastewater treatment infrastructures have been implemented under various settings such as rural, peri-urban, suburban and even urban areas (Siegrist, 2017). Decentralized WRRFs that are hydraulically connected to a centralized sewer collection system are known as satellite WRRFs (Gikas and Tchobanoglous, 2009). A system where decentralized satellite facilities have been integrated within an existing centralized wastewater infrastructure is also known as a hybrid system. In parallel, the progressive introduction of renewable solar energy has resulted in the manifestation of the well-know “duck curve” phenomenon, characterized by an apparent decrease of net power demand of the electrical grid during the late afternoon hours. The challenge associated with balancing supply and demand during grid ramping hours (“neck” of the duck) has motivated energy providers to shift the user’s energy consumption, often by means of economic incentives such peak time-based rates or demand response programs (Musabandesu and Loge, 2020). To address this emerging challenge, this study proposes a new demand response strategy to lower the power required for wastewater treatment during grid ramping hours by taking advantage of the interconnected nature of a hybrid system of wastewater treatment plants. The underlying concept of such strategy relies on exploiting the hydraulic delay of sewer trunk lines for the deferral of the treatment intensity between hydraulically connected facilities during peak energy cost hours.

Satellite water resource recovery facilities have strengthened the ability to provide cheap and reliable recycled water to meet the local water demand of growing suburbs. This study provides a new conceptual framework for the dynamic management of hybrid systems comprised of both centralized and satellite wastewater treatment plants. A case-study analysis is presented showing the potential to lower greenhouse gas emissions, power demand, energy use, and costs by dynamically shifting the diurnal influent wastewater loads between hydraulically connected treatment facilities.

SpeakerReifsnyder, Samuel

Presentation time

16:00:00

16:10:00

Session time

16:00:00

17:00:00

Session21st Century Water Resource Recovery Facilities: Improving Water Quality While Becoming Carbon Neutral

Session number317

TopicEnergy Production, Conservation, and Management, Municipal Wastewater Treatment Design, Research and Innovation, Sustainability and Climate Change

Author(s)

Samuel Reifsnyder

Author(s)S.L. Reifsnyder1,2,3; F. Cecconi1,2,3; N. Melitas4; D. Rosso1,2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158061

Volume / Issue

Content sourceWEFTEC

Word count16

Energy Management at WRRFs - Is Hydrogen a Viable Alternative?

Abstract

APPLICABILITY Green hydrogen, that is hydrogen produced with renewable energy, is a likely energy source to decarbonize heavy transportation and other industries. The production of hydrogen through electrolysis produces pure oxygen and thermal energy as green byproducts, which can be used at Water Resources Recovery Facilities (WRRFs). Two case studies will explore the viability of integrating hydrogen production at WRRFs, the full-scale demonstration project at St Cloud, MN and the feasibility study at Cedar Rapids, IA. DEMONSTRATED RESULTS/CONCLUSIONS Co-locating hydrogen electrolyzer systems powered by renewable energy in proximity of existing WRRFs allows for the concurrent decarbonization of local industries and wastewater treatment operations. From the viewpoint of WRRFs, the byproduct green oxygen can be beneficially to oxygenate aeration tanks in an activated sludge process which would reduce the demand for grid electricity to power blowers. A second waste by-product is thermal energy resulting from cooling of the electrolyzer. The hydrogen could be used either on-site at the WRRF or off-site by local industries as a zero-carbon fuel source. For the past 10 years, several WRRFs have implemented pilot systems to evaluate the feasibility of incorporating electrolyzers into their process, primarily in Europe and Australia. The City of St. Cloud, MN will be the first United States installation of a full-scale electrolyzer system for green hydrogen production using renewable energy sources, with concurrent oxygen and heat recovery. A focus of the St. Cloud project is green hydrogen production for utilization by local industries, including a bus manufacturing company and a bus transport company. The City of Cedar Rapids, IA is conducting a feasibility study for incorporating an electrolyzer into their treatment facility as a replacement of an aging cryogenic oxygen production facility to produce the pure oxygen required by the City's WRRF. Potential revenue from the green hydrogen and beneficial use of the waste thermal energy are also being investigated. St. Cloud Demonstration Project The City of St. Cloud is striving to decarbonize its energy profile and develop additional marketable products. The City's Nutrient, Energy, and Water Recovery Facility (NEWRF) currently incorporates a significant amount of energy production and resource recovery through combined heat and power production, on-site solar production, and a waste to energy program with trucked-in high-strength wastes. The current project focuses on further decarbonizing energy production to include converting biogas to renewable natural gas for pipeline injection and construction of additional on-site solar capability as the primary energy source for the full-scale green hydrogen electrolyzer demonstration. Key objectives of the demonstration project include: (1) evaluating off-site markets and on-site uses for the produced hydrogen and oxygen gases, (2) developing strategies for the utilization of the produced oxygen within the existing NEWRF infrastructure, (3) assessing the need for storage of the renewable energy, hydrogen, and oxygen, and (4) optimizing the return on investment (ROI) using the renewable energy portfolio of the NEWRF. The full-scale demonstration project is being designed around a commercially available 1-megawatt (MW) hydrogen electrolyzer. Figure 1 presents a process flow diagram for integrating the electrolysis system into the NEWRF. As illustrated, a separate solar array will be installed for the electrolyzer with additional electrical energy provided by the existing cogeneration system and a procured Solar Garden subscription. The primary market for the green hydrogen will be for commercial sale to local transportation industries requiring compression and short-term storage facilities. Alternatives for utilization of the pure oxygen include blending it with aeration air downstream of the blowers and setting up separate zones with an independent aeration system for introduction of the pure oxygen. Excess thermal energy captured from the cooling loop of the electrolyzer will be either integrated into the existing process heating loop or used as a heating source for dedicated buildings. Cedar Rapids Feasibility Study. The City of Cedar Rapids Water Pollution Control Facility (WPCF) treats approximately 45 mgd of combined high-strength-industrial and domestic wastewaters for organic matter, solids, and ammonia removal. The heart of the secondary treatment process is a pure-oxygen UNOX system with the oxygen produced on-site by an 80-ton per day cryogenic system. The cryogenic system is nearing the end of its useful life and is being evaluated by the City for repair or replacement of the UNOX system. The feasibility study will evaluate the renewable power requirements, footprint, required equipment and facilities, required water treatment facilities, hydrogen production, and thermal energy production for an electrolyzer system capable of producing 80 tons per day of pure oxygen to replace the cryogenic production facility. A preliminary assessment indicates a 25-30 MW electrolysis system will be needed. Results The St Cloud Demonstration Project is currently in detailed design and scheduled to be completed in 2024. In addition to facilities layout, process connections, and required utilities, the four critical areas to be addressed for an electrolysis project to be successful at a WRRF include: (1) Securing renewable energy sources. The primary source of electrical energy for the electrolyzer will be a new 1 MW solar array to be constructed on-site. However, as illustrated in Figure 2, the dedicated solar array can only provide electricity for part of each day. To optimize the hydrogen and oxygen production, supplemental energy sources are needed to maintain a baseload of electricity for the electrolyzer. Maintaining a minimum level of 30% of capacity will produce nearly 2 times as much green hydrogen and green oxygen produced without this energy baseload. (2) Marketing green hydrogen. An aspect of the demonstration project is to blend some of the hydrogen produced with the natural gas feed to the cogeneration units. The target quantities and required blending equipment will be identified during the design phase in conjunction with the cogeneration system manufacturer. The primary commercial target markets for the green hydrogen will be the local bus transportation company and a bus manufacturer that is developing hydrogen-fuel cell powered buses. (3) Pure oxygen utilization. The oxygen produced will be used by the WRRF in its activated sludge process. Initially, the oxygen will be bled into the aeration header providing air to aeration basins which will increase the oxygen concentration of the air stream slightly. The pure oxygen produced by the 1 MW electrolyzer will provide approximately 5% of the total oxygen demand of the BNR treatment facility. To increase the beneficial use of the pure oxygen stream, pilot testing of aeration systems suitable for pure oxygen, such as membrane aerated biofilm reactors (MABR) and Speece cones are planned for the future. (4) Excess heat utilization. The electrolysis process produces heat that is typically removed through a water-based cooling loop and transferred via a heat exchanger to a glycol-based cooling loop and vented to the atmosphere through an outdoor air-cooled heat changer. Capturing the estimated 23,000 therms/yr of waste heat for beneficial use during the colder months of the year is an objective of the project. The Cedar Rapids feasibility study will be completed in the spring of 2024. An assessment of the existing UNOX system will be conducted to identify equipment and facilities that could be retrofitted for use with electrolyzer-produced pure oxygen. Compatibility between the existing oxygen equipment and the electrolyzer-produced oxygen will also be assessed. Recommended equipment redundancy needs will be presented. The amount of thermal energy electrolysis system will be quantified, and opportunities identified for integrating this heat energy into the WPCF heating systems. An assessment of renewable energy sources available to supply electrical energy to the electrolysis facility will be conducted including on-site solar and wind, on-site generation from WPCF produced renewable natural gas, and off-site purchased energy agreements. The feasibility study will include an assessment of potential markets for the produced hydrogen in addition to on-site use at the WPCF to include regional natural gas utilities, industrial users, transportation users. RELEVANCE The St. Cloud project is focused on the commercial production of hydrogen, whereas the Cedar Rapids study is focused on pure oxygen production. Both projects include the beneficial use of thermal energy and oxygen byproducts. These projects will provide bookends for the assessment of integrating electrolyzers into WRRFs.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerGabel, Dale

Presentation time

09:00:00

09:30:00

Session time

08:30:00

11:15:00

SessionEnergy Management: From Production to Safety

Session number25

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAlternative Energy Source, Hydrogen, Innovative Technology

Author(s)

Gabel, Dale

Author(s)D. Gabel1, T. Hodel2, J. Flamming3, S. Reifsnyder1, B. Wolohan1

Author affiliation(s)Carollo Engineers 1; City of St. Cloud 2; City of Cedar Rapids WPCF 3; Carollo Engineers 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159437

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count11

Description: Head-to-Head Continuous Aeration Performance Monitoring of Full-Scale Densified and...

Head-to-Head Continuous Aeration Performance Monitoring of Full-Scale Densified and Conventional Activated Systems

Abstract

[b]BACKGROUND AND OBJECTIVES[/b] Increased loads and constrained facility footprints are driving water resource recovery facilities (WRRFs) to adopt intensification strategies that increase treatment capacity without expanding tankage. Among these, densified activated sludge (DAS) is a promising and cost-effective approach that selectively wastes poorly settling floc through hydrocyclones, reducing the sludge volume index (SVI), increasing biomass inventory, and enabling higher clarifier loading rates. The benefits of DAS are well-documented, but little information is available on its aeration performance under full-scale conditions, particularly for in-process inefficiencies quantified by the alpha factor (aF). Because aeration represents the dominant energy demand at WRRFs, reliable aF values are essential for both proper design and operation of aeration systems. Metro Water Recovery's Robert W. Hite Water Treatment Facility (RWHTF) in Denver, Colorado, treats approximately 130 mgd of municipal wastewater. To evaluate process intensification strategies, a full-scale 2-MG treatment train, with a dedicated secondary clarifier and return activated sludge (RAS) was operated as a densification pilot in parallel with 11 conventional activated sludge (CAS) treatment trains. To assess aeration performance and generate representative aF values suitable for scale-up design, a continuous, side-by-side off-gas testing campaign was conducted on the DAS and CAS systems. The DAS system was configured as an anaerobic-anoxic-oxic (A2O) process in the North Aeration Basin 2 (NAB2), while the CAS train operated as a MLE process in the NAB4. In the DAS system, the IMLR can be routed to multiple upstream zones, but usually A3 (A2, A3 and A4, see Fig. 1). A4, a swing zone, was operated as anoxic during the testing. [b]TESTING METHODOLOGY[/b] Continuous off-gas testing was performed using the I-FLOAT™ system (Inflatable Fast Lightweight Off-gas Analysis Technology), enabling rapid deployment and automated, continuous monitoring of aeration performance and process emissions (see Fig. 2). Three locations per basin were monitored over 24-hour periods. Concurrent side-by-side testing was conducted using two hoods connected to a single analyzer alternating every 10 minutes, yielding one data point per zone every 20 minutes (see Fig 1). Testing followed ASCE 18-18 guidelines (ASCE, 2018). [b]RESULTS AND FINDINGS[/b] During testing, the DAS system operated at ~25% granule mass fraction, MLSS of 5,000 mg/L, and SVI₃₀ of 68 mL/g, compared to <5% granulation, 3,900 mg/L MLSS, and SVI₃₀ of 89 mL/g for CAS. Aerobic/total SRTs were approximately 11/14 days (DAS) and 6/8 days (CAS). Despite these differences, in Zone A6, DAS and CAS exhibited similar aeration performance, with average OTEs of ~8.3–8.4% and aF values of 0.42. Diurnal aF ranged from 0.32 to 0.55, highlighting substantial diurnal variability and the importance of performing continuous monitoring over spot-check testing. This zone operated at relatively high air fluxes (2.2 scfm/diffuser for DAS; 2.7 for CAS). Greater differences were observed in Zone B4, where average OTEs were 14.4 (DAS) and 22.0 (CAS), corresponding to aF values of 0.72 and 0.91. Both systems operated at lower air fluxes, with CAS exhibiting both higher aF and higher OTE (see Table 1). The lower aF observed for DAS in Zone B4 may be influenced by differences in bubble coalescence associated with higher MLSS and potential effects of microbial by-products (e.g., SMPs or EPS, Germain et al., 2007). However, these mechanisms were not confirmed, and MLSS differences alone are unlikely to fully explain the differences in aF, based on previous aF-MLSS correlation studies (Krampe & Krauth, 2003).The absence of similar discrepancies in Zone A6 suggests convergence of bubble behavior at higher air fluxes, regardless of differences in MLSS or microbial by-products. In Zone C4, DAS results were considered representative (OTE 13.4, aF 0.83), although data loss occurred over night. CAS data were excluded due to an air leakage that compromised the data. Oxygen uptake rates (OURs) were estimated via a similar approach presented in Reifsnyder et al., 2018. OURs values for CAS were approximately 15–20% higher than DAS across Zones A6 and B4. [b]CONCLUSIONS AND RELEVANCE[/b] This study presents a first-of-its-kind, continuous, full-scale, side-by-side off-gas comparison of DAS and CAS systems. Results indicate that in initial aerobic zones operating at higher air fluxes, DAS and CAS exhibit comparable aF values, supporting similar aeration sizing assumptions. However, at lower air fluxes in downstream zones, DAS systems exhibited reduced aF relative to CAS. Results imply that under low-air-flux conditions, downstream air demands in DAS systems may be approximately 15–20% higher than CAS to achieve equivalent oxygen transfer rates, which translates to larger aeration equipment sizing, increased capital costs, and higher operating expenses. These findings provide early, design-relevant insights into mechanistic differences in aeration performance of DAS and CAS systems, and provide the basis for future studies. Results reflect performance at the tested granule mass fraction. Further evaluation at higher fractions (e.g., >40%) is needed. Ongoing testing at re-balanced air fluxes will refine aF guidance for DAS systems under typical operating conditions.

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

SessionDAS Design New Frontiers

Session locationErnest N. Morial Convention Center

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

Author(s)

Reifsnyder, Samuel, Zambrano, Jorge, Berninghaus, Ashley, Marron, Brian, Maltos, Rudy, Wisdom, Blair, Rauch-Williams, Tanja

Author(s)S. Reifsnyder1, J. Zambrano2, A. Berninghaus1, B. Marron2, R. Maltos2, B. Wisdom2, T. Rauch-Williams2

Author affiliation(s)Carollo Engineers, 1Carollo Engineers, 1Metro Water Recovery, 2Metro Water Recovery, 2Metro Water Recovery, 2Metro Water Recovery, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160479

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Process Roadmaps to Low DO Operations - Lessons Learned from a North American Survey...

Process Roadmaps to Low DO Operations - Lessons Learned from a North American Survey on Suboxic and Low DO Activated Sludge Facilities

Abstract

Facilities throughout the United States are successfully implementing low dissolved oxygen (DO) and suboxic nutrient removal (SBNR) operations using a variety of plant configurations and controls strategies to decrease energy consumption while achieve high effluent quality standards. As part of a Department of Energy project, several facilities participated in workshops to identify common operational strategies and challenges for low DO/SBNR operational. From the workshop, it was determined that successful low DO/SBNR systems can be achieved with a variety of aeration process configurations and controls strategies. Aeration demand and blower turndown were the largest obstacles in achieving low DO operations. Instrumentation is key: understanding which probes are appropriate and the importance of probe location can significantly influence process performance. In addition, Los Angeles County Sanitation Districts is implementing SBNR operations at the Pomona Water Reclamation Plant which will provide real-world guidance on SBNR execution and operations.

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

SpeakerYoung, Michelle

Presentation time

13:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionConversion of Conventional Activated Sludge to Suboxic (Low DO) Nutrient Removal

Session locationRoom S404c - Level 4

TopicEnergy Production, Conservation, and Management, Fundemental Level, Municipal Wastewater Treatment Design, Nutrients, Sustainability and Climate Change

Author(s)

Young, Michelle

Author(s)M Young 1; N. Beach 2 ; P. Ackman 3; T. Weiland 4; A. Ekster 5; S. Reifsnyder 6; T. Rauch-Williams 7;

Author affiliation(s)Carollo Engineers, Inc 1; Carollo Engineers, Inc 2 ; Los Angeles County Sanitation Districts 3; Los Angeles County Sanitation Districts 4; Ekster & Associates 5; Carollo Engineers, Inc 6; Carollo Engineers, Inc 7;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825158980

Volume / Issue

Content sourceWEFTEC

Word count23

Description: Synergistic Interaction Between Water Resource Recovery Facilities and Renewable...

Synergistic Interaction Between Water Resource Recovery Facilities and Renewable Hydrogen Generation.

Abstract

As of today, about 85% of the global energy consumption originates from non-renewable sources, such as coal, natural gas, and oil (Abdalla et al., 2018). The imperative need to mitigate climate change impacts has led to collective efforts towards the de-carbonization of the increasingly growing energy sector. The progressive implementation of renewable technologies, such as wind and solar photovoltaic, in the energy market is part of the ongoing strategies adopted by various worldwide climate action programs (Williams et al., 2012). Although renewables are virtually unlimited compared to fossil energy sources, their reliability is constrained by their intermittent and fluctuating dynamics (Colbertaldo et al., 2019). Therefore, much attention has been posed on the ability to store renewable energy in order to balance electrical grid operations and preventing energy curtailment. Power-to-gas (P2G) is currently among the most studied energy industry alternatives to store energy (Colbertaldo et al., 2019). In P2G systems, electrolyzes can be used to electrochemically split the water into oxygen and hydrogen using excess renewable energy (see Fig.1). The resulting renewable hydrogen generated (also known as green hydrogen) can be stored, and eventually used during periods characterized by lower renewable temporal availability either directly as process gas or via hydrogen fuel cell (HFC) systems to generate electrical power during periods of deficit on the electric grid. A different fate is typically reserved for the pure oxygen stream, which is usually vented to the atmosphere.

This paper introduces a novel analytical study that considers renewable oxygen generation (or green oxygen) for the aeration of the activated sludge processes. This is achieved by leveraging the operation of large-scale electrolyzer systems used for renewable energy storage. This study demonstrates the potential synergistic interaction that renewable hydrogen systems can have with local wastewater treatment plants.

SpeakerReifsnyder, Samuel

Presentation time

16:35:00

16:45:00

Session time

16:00:00

17:00:00

Session21st Century Water Resource Recovery Facilities: Improving Water Quality While Becoming Carbon Neutral

Session number317

TopicEnergy Production, Conservation, and Management, Municipal Wastewater Treatment Design, Research and Innovation, Sustainability and Climate Change

Author(s)

Samuel Reifsnyder

Author(s)S.L. Reifsnyder1,2,3; M. Arrizon Melchor1,4; L. Mastropasqua4,5; J. Brouwer1,4,5; D. Rosso1,2;

Author affiliation(s)Department of Civil and Environmental Engineering, University of California, Irvine, CA1Water-Energy Nexus Center, University of California, Irvine, CA 2Black and Veatch, Walnut Creek, CA3National Fuel Cell Research Center, University of California, Irvine –Engineering Laboratory Facility, Irvine, CA 4Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA5

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158063

Volume / Issue

Content sourceWEFTEC

Word count12

Two Birds, One Test: Off-gas Testing for Assessing Scope 1 and Scope 2 Emissions

Abstract

Background
The wastewater sector is rapidly adopting intensification technologies, driven by the need for improved process efficiency, reduced space requirements, and increased nutrient recovery. While intensification offers smaller footprint and potential operational benefits, their environmental trade-offs have not been thoroughly vetted. Technologies are likely to perform differently in terms of energy used and greenhouse gas (GHG) emissions. Bioreactor aeration is energy-intensive, contributing to most Scope 2 (indirect) emissions at water resource recovery facilities (WRRFs). Additionally, bioreactors can release nitrous oxide (N2O), a potent GHG with a global warming potential 270 times greater than carbon dioxide (CO2). While much focus has been placed on reducing Scope 2 emissions, direct Scope 1 emissions like N2O are also a significant contributor to WRRFs' overall emissions. N2O represent a significant portion of WRRFs' carbon footprint in conventional biological activated sludge processes. However, research and monitoring of N2O emissions from emerging intensification technologies is still in its infancy.

Off-Gas Testing as a Dual-Purpose Tool
Off-gas testing has long been employed to evaluate aeration efficiency and estimate the energy consumption of specific secondary treatment aeration zones. By measuring the air flux and making targeted assumptions, off-gas testing can estimate blower power demand through the adiabatic compression formula. When paired with data of the carbon intensity of the energy grid, Scope 2 emissions of the secondary treatment process can be also assessed. The combined ability to directly estimate oxygen transfer efficiency (OTE) and energy usage provides critical insights into the potential energy and GHG savings, which can be achieved by improving OTE or reducing air demand. Additionally, coupling this approach with GHG monitoring, such as N2O or methane release enables a comprehensive view of both Scope 1 and Scope 2 emissions. This approach offers insights into the GHG contributions from energy use versus direct emissions, proving valuable for assessing both existing conventional and new intensification technologies.

Tracking both Scope 1 and 2 emissions through off-gas testing allows utilities to observe the dynamic carbon footprint of their operations. This is important, as both direct and indirect emissions often show diurnal and seasonal variability. Understanding these fluctuations opens opportunities to develop control strategies that mitigate one or the other based on their respective impacts.

Methodology
An off-gas testing campaign including a hood and a portable analyzer was conducted at a WRRF to monitor N2O emissions and track Scope 2 emissions. The facility comprises four tanks operating in parallel, with one tank out of service for maintenance during the testing period. The reactors are configured in the Westbank configuration, with an average flow of 21.5 mgd. The hood used in this testing campaign (Figure 1), is a Carollo-developed, inflatable, self-ballasting hood designed for portability, ease of installation, and maximized sample representativeness. The hood measurements, combined with the portable analyzer measurements, enables high-frequency monitoring of airflow and gas species, allowing utilities to quickly, accurately, and cost-effectively estimate real-time GHG emissions.

Results and Discussion
The two-day off-gas testing, combined continuous measurements with sweep testing, revealed that N2O concentrations were proportional to CO2 levels and inversely proportional to O2 concentrations, reflecting the effects of gas absorption and stripping in the aerated zones (Figure 2). This highlights the interplay between diurnal OTE variation and how it correlates to N2O stripping. Continuous N2O and airflow monitoring enabled the estimation of Scope 1 and 2 emissions. Figure 3 compares blower-related electricity use emissions and N2O emissions as CO2 equivalents, showing higher N2O rates in the initial aerobic zones with higher airflow. Correlations between TKN and ammonia from daily samples yielded an N2O emission factor of 0.64% N2O-N/TKN-NPE -lower than the IPCC estimate of 1.6% but within the 0.03% to 1.29% range for secondary treatment bioreactors (Ahn et al., 2010; Kampschreur et al., 2009).

Extrapolated N2O emission represented 78% of the secondary treatment emissions due to the process' low specific energy use (530 kWh/MG). Figure 4 compares direct emissions of N2O to emissions from blower power use for a range of electricity emission factors representing various US states. It shows that the N2O emissions are larger, regardless of the carbon intensity of the electric grid, for this process configuration.

Conclusion
Intensification technologies hold promise for improving performance and capacity of WRRFs, but their N2O emissions are not yet fully understood. Direct, high-frequency monitoring of these emissions is essential for gaining an understanding of the carbon footprint associated with these technologies.
Real-time data on N2O emissions can support the development of new mitigation strategies based on assessment of Scope 1 and Scope 2 emissions. Process engineers and plant operators can use this data to fine-tune treatment processes, adjust operational parameters, and reduce energy use and GHG emissions.

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

Presentation time

08:30:00

08:45:00

Session time

08:30:00

10:00:00

SessionDecarbonizing Water: Across Space and Time - Techniques for CH4 and N2O Monitoring

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiogas & Energy Recovery

Author(s)

Reifsnyder, Samuel, Stanczak, Greg, Pruett, Maya, Zambrano, Jorge, Woodiwiss, Malachai, Young, Michelle, Brown, Jess

Author(s)S. Reifsnyder1, G. Stanczak1, M. Pruett1, J. Zambrano1, M. Woodiwiss1, M. Young1, J. Brown1

Author affiliation(s)Carollo Engineers1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160081

Volume / Issue

Content sourceWEFTEC

Word count15

WRRFs as a Hub for Green Hydrogen Production

Abstract

Due to its ability to decarbonize hard-to-electrify sectors, green hydrogen production projects are being built across the United States and several other countries. Although this technology constitutes a promising tool in the decarbonization portfolio, the high capital and operational expenses are the main obstacles in its wide-scale commercial implementation. By recovering the by-products from the electrolysis process, such as oxygen and waste heat, there is the potential to reduce the costs tied to green hydrogen production, while decarbonizing the operation of WRRFs. The City of Saint Cloud initiated a 2023 study to assess the potential to recover by-products from the hydrogen produced via electrolysis powered by renewable energy sources. Through this case study, this paper discusses the benefits of producing green hydrogen to aid in decarbonizing WRRFs and local industries; the practical considerations for capturing the waste by-products; and the challenges of cost-effectively integrating electrolyzers into existing WRRFs.

The opportunity to co-locate electrolyzer systems powered by renewable energy in proximity of existing WRRFs could allow for the concurrent decarbonization of local industries and wastewater treatment operations. The City of St. Cloud in Minnesota will be the first example in the United States to install a 1MW electrolyzer demonstration system to produce green hydrogen via onsite solar-photovoltaic, with concurrent recovery of the oxygen and heat by-products.

SpeakerReifsnyder, Samuel

Presentation time

11:00:00

11:20:00

Session time

10:30:00

12:00:00

SessionBuilding A Hydrogen Future

Session locationRoom S501a - Level 5

TopicAdvanced Level, Energy Production, Conservation, and Management, Research and Innovation, Sustainability and Climate Change

Author(s)

Reifsnyder, Samuel