Charbonnet, Elizabeth

Elizabeth Charbonnet is a speaker at WEFTEC 2026.

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About Charbonnet, Elizabeth

Elizabeth Charbonnet is a speaker at WEFTEC 2026.

Charbonnet, Elizabeth

Elizabeth Charbonnet is a speaker at WEFTEC 2026.

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Addressing Practical Barriers to Large-Scale Co-Digestion to Improve Feasibility

Abstract

APPLICABILITY The desire to reduce greenhouse gas emissions related to food waste disposal in landfills has driven great interest in co-digestion as one way to avoid methane emissions (see Figure 1). Utilities and regulators in New York, California, and other states with climate change mitigation goals understand the promise that co-digestion holds and the opportunity to leverage excess digester capacity in furtherance of those goals (see Figure 2). However, large-scale implementation of food waste co-digestion has been hampered by practical barriers that must be addressed before the process can achieve its promise and deliver on its benefits. DEMONSTRATED RESULTS AND OUTCOMES Our identification and understanding of both benefits and barriers has grown through several co-digestion projects including: - California Co-Digestion Capacity Analysis completed in 2019 for the State Water Resources Control Board - Characterization and Contamination Testing of Source Separated Organic Feedstocks and Slurries for Co-digestion at Resource Recovery Facilities completed in 2023 for the Water Research Foundation - Food Waste Pre-Processing and Co-Digestion Evaluation completed in 2023 for the City of Oxnard, California The benefits of large-scale food waste co-digestion paired with beneficial use of biogas include GHG emissions reduction from landfills, offsets of fossil-fuel based natural gas, reduction of purchased electrical power and/or natural gas for water resource recovery facilities (WRRFs), and potential revenue generation at WRRFs through tipping fees. The environmental benefits just in California exemplify the promise of these processes. If the state were to successfully implement co-digestion and biogas utilization for 35-50% of its 6.8 million wet tons of food waste projected for disposal in 2030, it could reduce landfill emissions by approximately 2 million metric tons of carbon dioxide equivalent (MT CO2e) - half of its legislated reduction goal of 4 million MT CO2e in 2030. The scale of these benefits drove the passage of California's Senate Bill (SB) 1383, which legislated organics diversion from landfills and went into effect in 2022. However, large scale co-digestion has not yet been realized in California, in large part because of remaining barriers to successful implementation and sustained operations. So what are these barriers and how can they be overcome? The projects listed above included identification of the physical and logistical elements required to implement co-digestion, determination of operational impacts and unintended consequences, environmental justice considerations such as truck traffic and odors, documentation of conflicting regulatory drivers, and estimates of capital and operational costs. Having identified these barriers and determined their scale, we suggest strategies to overcome the obstacles which have hampered large-scale implementation thus far. A few such strategies developed from these and other projects include: - Matching pre-processing technology to current municipal solid waste collection system (i.e. source separated vs combined waste) to avoid added costs for different collection schemes. - Regional facilities (combined or separate pre-processing and digestion facilities) that can distribute the burden of capital and operating costs broadly and offer opportunity to offset some costs through tipping fees charged by the entity operating the associated systems. - Public/private partnerships that reduce capital burden and risk for public utilities. - Collaboration with disparate regulatory agencies to develop cohesive strategies towards common goals, especially related to production and use of biomethane and biosolids. - Bench scale studies with expected feedstock to better assess and mitigate operational impacts, including biomethane production, nutrient loads in recycle streams, foaming potential, and dewaterability of digested sludge. (See Figure 3 for foaming potential and volume expansion in digesters with varying amounts of food waste.) We will present eight ways to implement these strategies to address practical barriers for consideration by utilities and regulators as they seek to facilitate co-digestion to meet their climate change mitigation objectives . By incorporating such guidance, utilities can incorporate sustainable co-digestion into their WRRFs as the Los Angeles County Sanitation Districts (LACSD) has done through it's regional food waste processing system. RELEVANCE TO AUDIENCE This presentation will identify practical barriers to large-scale implementation of co-digestion and offer strategies to overcoming these obstacles such that co-digestion becomes more feasible in the short-term and remains viable in the long-term.

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

SpeakerGupta, Rashi

Presentation time

14:10:00

14:30:00

Session time

13:30:00

15:00:00

SessionConsiderations for Long-Term Biosolids Planning

Session number5

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Biosolids treatment, Circular Economy, Co-Digestion With Other Organic Sources, Market Analysis, Master Planning, PFAS/Emerging Contaminants, Resiliency, Resource Recovery, Sustainability, Triple Bottom Line Plus

Author(s)

Gupta, Rashi, Polo, Christine, Charbonnet, Elizabeth

Author(s)R. Gupta1, C. Polo1, E. Charbonnet1

Author affiliation(s)Carollo Engineers, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159814

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count10

Description: Improving Biosolids Management Resiliency Through Regional Collaboration Among 15...

Improving Biosolids Management Resiliency Through Regional Collaboration Among 15 Agencies

Abstract

[b]APPLICABILITY[/b] Over the past several years, wastewater treatment plants across the country have experienced restrictions and disruptions to biosolids end uses driven by legislative and regulatory actions. Among these challenges are limitations on land application and landfill availability, legislative threats, increasing costs, and consolidation of providers. Collectively, these factors have reduced agency resiliency. Other agencies possess greater levels of resiliency but seek to reduce costs and risk or further diversify their portfolios for long-term reliability. Within this landscape, 15 Southern California (SoCal) agencies, Participating Agencies (PAs), joined to form the Southern California Regional Biosolids Coalition (SoCal RBC) and complete a study to determine the feasibility of establishing a regional, publicly owned and operated biosolids management facility. This facility would be one of the largest of its kind and would treat the biosolids generated by a significant portion of SoCal's population. The study was split into phases, with Phase 1 completed. This phase sets the basis for facility sizing, siting, viable technologies, and considerations related to governance and public engagement. [b]RESULTS [/b] [b]Methodology[/b] The methodology of the feasibility study focused on five elements: •[i]Current practices:[/i] A survey was developed which covered each PA's project drivers, biosolids management strategies, biosolids characteristics, and biosolids contributions to the proposed facility. •[i]Regulations and market conditions:[/i] The regulatory and market considerations in SoCal for building a biosolids facility and distributing biosolids for beneficial use were analyzed. Other regional efforts across the US were also reviewed and lessons learned were incorporated into our guidance. •[i]Alternatives development:[/i] The universe of potential sites and technologies were evaluated to develop a shortlist of three sites and treatment options. •[i]Governance:[/i] Governance models were reviewed, and three governance options identified. •[i]Strategic public engagement:[/i] Key messaging themes for public engagement were developed and a plan for public outreach was established. [b]Results[/b] [i]Current Practices[/i] Figure 1 shows the current biosolids end uses and backup management options for each of the PAs. This study determined that a regional facility would be initially sized to accommodate a low-capacity 2030 estimate with room to expand up to a high-capacity 2060 estimate. [i]Regulations and Market Conditions[/i] Many large agricultural counties in SoCal have severe restrictions on land application, which increases hauling distances for beneficial use. Additionally, while per- and polyfluoroalkyl substances (PFAS) regulations are not yet implemented in California, concern about these contaminants is mounting and considering the potential for future PFAS regulations is prudent. Additionally, three air districts were considered relative to siting a regional facility. The most restrictive air district would likely require a Title V permit and offsets. A market assessment was also conducted and concluded that the SoCal RBC should focus on producing a Class A product because it is the most resilient, understanding that it is unlikely to generate reliable or significant revenue. [i]Alternatives Development[/i] Figure 2 shows the universe of site and technology alternatives considered. Due to the evaluation criteria chosen by the PAs, advanced thermal technologies were eliminated during screening. However, to address PFAS concerns, the future addition of such technology was considered when assessing footprint. Three sites and biosolids treatment options were ultimately chosen for more detailed analysis, shown in Figure 3. Class 5 capital cost estimates and site layouts were developed, and 20-Year Net Present Worth costs were calculated. Figure 4 shows the non-economic evaluation conducted and Figure 5 shows the cost comparison. As shown in Figure 5, composting has the lowest capital cost but highest operations and maintenance costs. Of the two dryer alternatives, total costs are lower for rotary drum drying. While operated at a lower temperature than drum drying, belt drying has a greater natural gas (NG) cost to handle higher exhaust volume due to the increased NG requirements for RTO operation which is required for the SoCal air districts. [i]Governance[/i] This study also evaluated possible governance structures for the SoCal RBC. The three viable governance structures identified are shown in Figure 6. [i]Strategic Public Engagement[/i] This study also identified key messaging themes for future public engagement, shown in Figure 7. From there, a public engagement plan for implementation in future project phases was developed and stakeholders identified. [b]Conclusions[/b] This collaboration among 15 PAs focuses on advancing a resilient biosolids management solution and represents one of the largest collaborations of its kind. Subsequent phases of this project will advance one of the short-listed options through preliminary design and possibly through to final implementation. The approach taken and key findings from this work, including siting, technologies, governance, and public engagement may be useful for other regions and groups considering options to increase their biosolids management resilience

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

SpeakerCharbonnet, Elizabeth

Presentation time

13:50:00

14:00:00

Session time

13:30:00

15:00:00

SessionAdvancing Biosolids Planning Through Optimization and Collaboration

Session locationErnest N. Morial Convention Center

TopicBiosolids and Residuals, Circular Water Economy, Public Communication and Outreach, Utility Management and Leadership

Author(s)

Charbonnet, Elizabeth, Stewart, Kevin, AghaGholizadeh, Erica, Berninghaus, Ashley, Chapman, Thomas, Chavan, Seema, Gonzalez, Dana, Guevarra, Karla, Gupta, Rashi, Judy, Caroline, Ma, Persephone, Rossetto, Sarah, Sierra, Natalie, Young, Michelle

Author(s)E. Charbonnet1, K. Stewart2, E. AghaGholizadeh2, A. Berninghaus1, T. Chapman2, S. Chavan2, D. Gonzalez1, K. Guevarra3, R. Gupta1, C. Judy4, P. Ma2, S. Rossetto6, N. Sierra2, M. Young1

Author affiliation(s)Carollo Engineers, 1Brown and Caldwell, 2Carollo Engineers, 1Brown and Caldwell, 2Brown and Caldwell, 2Carollo Engineers, 1Pierce County, WA, 3Carollo Engineers, 1Project Finance Advisory Limited, 4Brown and Caldwell, 2Brown and Caldwell, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2026

DOI10.2175/193864718825160466

Volume / Issue

Content sourceWEFTEC

Word count11

Resilient Biosolids Management Planning in Southern California

Abstract

Introduction Eastern Municipal Water District (District) operates four Regional Water Reclamation Facilities (RWRFs) in Southern California that collectively treat an average flow of 48.7 million gallons per day and generate about 173 wet tons per day (wt/d) of digested, dewatered Class B biosolids, which are hauled to Arizona for land application. Rising hauling costs, potential regulatory changes, aging infrastructure, and new statewide requirements have increased the risk of depending on a single biosolids management outlet. To address these challenges, the District prepared a Biosolids Master Plan that provides a coordinated strategy for the next twenty years. The plan evaluates regional market opportunities, identifies near term and long-term needs, and examines the feasibility of future Class A biosolids product. The following sections summarize the key findings and present a roadmap to future biosolids management decisions. Background The District currently hauls all Class B biosolids to Arizona, but rising costs, per- and polyfluoroalkyl substances (PFAS)-related regulations, and legislation such as Arizona's House Bill 2669 have revealed the risks of relying on a single outlet. This prompted the need to reassess solids processing, address aging infrastructure, and plan for a more resilient long term approach. The Biosolids Master Plan evaluates each RWRF and compares solids handling technologies to support a diversified strategy that strengthens the District's goals across the near, mid, and long term. Biosolids Market Opportunities Biosolids management represents one of the most significant risks faced by a utility, which is why the Biosolids Master Plan began by evaluating feasible markets for both current Class B material and potential future products. The assessment focused on technologies that could produce products accepted by regional end users and examined California's beneficial use opportunities along with the regulatory and market conditions that shape what the District can successfully produce and distribute, as shown in Table 1. Although many biosolids products are viable in California, practical implementation depends on capital cost, program needs, and operational considerations. Immediate Needs An evaluation of solids handling systems at each facility identified capacity and performance limitations, including an immediate need for additional digestion capacity that will be added to the District's capital improvement program (CIP). Several thickening and digestion alternatives were compared, and the selected option provided the lowest overall cost, allowed a single near term construction effort, and avoided the limited value of rebuilding aging infrastructure. Class A Post-Dewatering Facility Challenges The Biosolids Master Plan evaluated regional post dewatering technologies, including belt drying, drum drying, and composting, and compared their layouts, capital and operating costs, net present costs, and overall performance. The assessment found that developing a regional post-dewatering Class A facility would require substantial capital investment (as shown in Figure 1) that significantly increases cost per wet ton and does not offer an economic benefit over continuing to haul dewatered cake to Arizona. These results indicate that decisions on future biosolids management should also weigh non-cost factors to better understand risk, long term sustainability, and opportunities to diversify end uses. Roadmap Increasing regulatory uncertainty, especially around PFAS, is making biosolids management more complex. In response, an adaptable implementation roadmap was developed in the Biosolids Master Plan and is a key to low-risk and economical long-term biosolids management with built-in diversification. The roadmap in Figure 1 outlines treatment technologies, end use markets, and the decision points that determine when actions should move forward, and it is fully integrated with the 20-year CIP to align investments with anticipated costs, risks, and regulatory conditions. It also expands opportunities for the District's Class B biosolids by incorporating new contracts and technologies that strengthen program resilience and open access to emerging markets. Audience Takeaways Effective biosolids planning starts with understanding the intended end-use, which drives technology selection and long term program success. The market assessment showed that California can accommodate many biosolids products, but implementation depends on capital cost, operational needs, and program requirements. The planning process was critical for identifying near term capacity needs. Although a post dewatering Class A regional facility is not economically competitive with hauling Class B material to Arizona, long term decisions should consider non cost factors such as risk, sustainability, and opportunities to diversify outlets. The implementation roadmap brings these elements together by outlining viable technologies and markets and defining the decision points that guide future actions.

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

Presentation time

10:30:00

10:45:00

Session time

10:30:00

12:00:00

SessionThe Biosolids Life Cycle: Case Studies and Round Tables

Session locationKansas City Convention Center

TopicThermal Processes

Author(s)

AghaGholizadeh, Erica, Picazo, Abdiel, Chapman, Thomas, Gupta, Rashi, Charbonnet, Elizabeth, Berninghaus, Ashley, Sierra, Natalie, Ma, Persephone, Noone, Serena, Valenti, Alexis

Author(s)E. AghaGholizadeh1, A. Picazo2, T. Chapman1, R. Gupta3, E. Charbonnet3, A. Berninghaus, N. Sierra1, P. Ma1, S. Noone1, A. Valenti1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2026

DOI10.2175/193864718825160243

Volume / Issue

Content sourceResiduals, Biosolids and Treatment Technology Conference

Word count8

Seasonal Impacts of Nonpotable Reuse on DPR Feasibility

Abstract

APPLICABILITY
California's new direct potable reuse (DPR) regulations allow agencies to accurately consider DPR implementation costs and challenges. The City of Napa (City) and the Napa Sanitation District (NapaSan) conducted an evaluation that illustrates key considerations for utilities interested in DPR, and sheds light on strategies that can be used to incorporate DPR into a system that has an existing nonpotable reuse (NPR) program with seasonal demands. Innovative approaches for augmenting wastewater flows with stormwater were evaluated for augmenting DPR and NPR supplies when NPR demands are high, taking advantage of 'one water' principles.

The Napa evaluation compared treatment alternatives for DPR including both raw water augmentation (RWA) and treated water augmentation (TWA). Regulatory requirements for operations and monitoring, impacts on staffing, and project costs were also assessed. More specifically this study evaluated challenges related to discharge permit compliance, seasonal DPR impacts and limitations, supplemental dry weather urban runoff to increase available water for reuse, interagency collaboration and visioning for DPR, and RO concentrate disposal.

NapaSan has a long history of water recycling. In winter when non-potable demand is lower, excess water is discharged to the Napa River. As a result, both agencies were interested in exploring how excess water could be used for DPR supply. However, costs of intermittent DPR treatment operation were expected to be high. Therefore, an assessment of collecting and conveying dry weather urban runoff stormwater to NapaSan to supplement the seasonal supply fluctuations expected at the DPR facility was performed.

While portions of the Napa feasibility study are site-specific, the outcome highlights the broader implications of what elements are necessary and important to consider in the early stages of a DPR project. Attendees will gain an understanding of the overall challenges that arise with DPR project implementation and potential solutions.

DEMONSTRATED RESULTS AND OUTCOMES
Methodology and Results
Sizing the DPR Facility
To size the treatment facility, the study assessed seasonally-available flow at NapaSan after meeting NPR demands. Figure 1 illustrates historical existing river discharge and recycled water flows at NapaSan, and seasonal precipitation as an indicator of the potential for capturing and reusing stormwater runoff.

Dry weather urban runoff and wet weather stormwater flows can be used to augment supplies and increase the percent utilization of the DPR facility. The evaluation considered three different DPR facility sizes. It was determined that the capture and use of large wet weather flows would require cost prohibitive equalization basins in the collection system. However, targeted connections to divert known sources of dry weather urban runoff and small wet weather flows (subject to wastewater collection system availability) could prove useful in increasing the overall supply to the NPR and DPR facility while dampening the temporal variability. Table 1 shows the percent utilization with and without the addition of dry weather urban runoff.

Infrastructure Considerations
For Napa, both TWA and RWA were considered. With TWA, purified water is discharged directly into the potable distribution system (Figure 2). With RWA, purified water is sent to the water treatment plant prior to potable distribution (Figure 3). RWA will require more pipelines than TWA including the pipe used to send water from the DPR facility to the water treatment plant along with the disposal pipelines needed at the DPR facility.

Staffing and Agency Discussions
Potable reuse requires collaboration between water and wastewater agencies. To understand how a future DPR project could be governed, interviews and a workshop were conducted with both agencies. Three governance structures (Contract, Joint Powers Agreement, and Merger) were reviewed and evaluated. Both agencies identified project components of concern (cultural differences, underperformance, and water delivery) and compared these against the proposed governance structures. These discussions allowed both agencies to initiate and work through potential issues that could arise in coordinating a DPR project.

Conclusions/Outcomes
The Napa study illustrates the key elements that should be considered in a DPR feasibility study, with strategies to identify and address potential implementation challenges. The Napa DPR feasibility study takes a holistic approach to considering the project viability and corresponding regulatory, operational, and structural components that make up these projects. By integrating dry weather urban runoff, utilities may be able to effectively augment recycled water supplies and optimize NPR and DPR systems.

RELEVANCE TO AUDIENCE
Utilities and agencies interested in DPR will gain an understanding of the project elements that should be considered at the initial stage of a DPR project, and strategies for augmenting recycled water supplies with stormwater. The presentation will highlight potential challenges and solutions that are applicable beyond the Napa project. DPR projects are in the initial stages of analysis, design, and implementation across California, Texas, Colorado, and Utah. Consequently, as the need for recycled water grows, it will be beneficial to learn from others.

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

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionShaping the Future of Water Reuse: Drivers, Feasibility & Challenges

Session locationMcCormick Place, Chicago, Illinois, USA

TopicAdvanced Water Treatment and Reuse

Author(s)

Lemar, Cora, Charbonnet, Elizabeth, Salveson, Andrew, Damron, Andrew

Author(s)C. Lemar1, E. Charbonnet1, A. Salveson1, A. Damron2

Author affiliation(s)Carollo Engineers1, Napa Sanitation District2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160059

Volume / Issue

Content sourceWEFTEC

Word count9

Base text size -

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