Reifsnyder, Samuel

Dr. Sam Reifsnyder is the Northern California R&D Lead at Carollo Engineers. He has eight years of experience in the applied research of...

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About Reifsnyder, Samuel

Dr. Sam Reifsnyder is the Northern California R&D Lead at Carollo Engineers. He has eight years of experience in the applied research of wastewater technologies with a focus on aeration, energy, and greenhouse gas emissions. Sam has extensive experience in performing off-gas field testing campaigns for monitoring aeration performance and greenhouse gas emissions of activated sludge processes. Other relevant experience includes work focused on analyzing the synergistic benefits of co-locating renewable hydrogen generation systems at wastewater treatment plants.

Reifsnyder, Samuel

Titles from this speaker

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: 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

Author(s)S. Reifsnyder 1; D. Gabel 2 ; T. Rauch-Williams Tanja 2; T. Hodel 3; S. Reifsnyder 1;

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

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159173

Volume / Issue

Content sourceWEFTEC

Word count9

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