Kikale, Pranoti

Pranoti Kikale is a professional at Arcadis, U.S., Inc., supporting water and environmental engineering projects.

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Description: Biosolids Planning for an Uncertain Future - How Regulatory Drivers and Technology...

Biosolids Planning for an Uncertain Future - How Regulatory Drivers and Technology Developments are Influencing Long-Term Infrastructure Decisions

Abstract

Introduction The current era is challenging to plan for long-term biosolids infrastructure upgrades. Over the past decade, many of the traditional solids management outlets have dwindled, with incinerators shutting down due to increasingly strict air regulations, and many landfills starting to limit biosolids loads. Land application is one of the strongest remaining pillars of traditional biosolids management, with its relatively low costs and effective nutrient recycling making it a favorable option. As of 2021, 43% of all biosolids in the USA were land-applied. Given the uncertainty around future regulations restricting land application due to PFAS and other emerging contaminants, this outlet is also facing its existential crisis. While confidence in traditional biosolids outlets waver, at the same time many utilities across the country are grappling with their fast-approaching need for renewal of solids infrastructure. Many of these solid systems built in the 1970s have needed capital upgrades repeatedly deferred to the point that major investment is now needed as these systems reach the end of their service life. Additionally, there has been attrition in O&M staffing across the country due to Covid and other global forces. With limited experienced O&M staff, it becomes difficult to embrace advanced technology, especially purported to destroy PFAS which are very early in their development phase and whose efficacy is as unclear as the future regulations they intend to address. Waiting for these regulatory and technology questions to be answered would be ideal but not feasible for many utilities whose time to act is now. The case study for the City of Toledo, OH forms the basis of this paper. Toledo is planning and procuring funding for one of the largest upgrades in its Bay View WWTPs history. This impending solids system upgrade is viewed as an opportunity to enhance sustainability and reduce GHG emissions by recovering more renewable energy from biosolids. There is also trepidation, however, over pouring major investments into digesters with the looming uncertainty around land application due to future federal PFAS regulations. Existing Conditions This paper presents an overview of the recent solids planning effort for the Bay View WWTP (ADF - 68 MGD). In 2022 the City developed a facility plan that included demolishing plant digesters (built in the 1930s) to clear space for new liquid stream process. The plan included constructing a new solids facility on new plant land created by filling part of the bay on which the WWTP sits. This WWTP currently produces ~ 40,000 wet tons of Class B biosolids annually, which consists of combined thickened primary and WAS that is anaerobically digested and dewatered to Class B cake. These biosolids are land-applied using a 3rd party cake management partner, while occasional loads are sent to landfills during seasonal outlet restrictions. The biogas generated is utilized on-site for digester heating with boilers. Toledo had previously shown advanced thinking and ambition in energy recovery as it constructed a combined cycle turbine CHP plant at the WWTP designed to run of digester gas and landfill gas piped in via a trans-city pipeline. This facility was sitting currently unused due to lack of sufficient fuel, as landfill gas volumes were less than half of the anticipated design values. The City engaged the engineering team to explore various solids processing alternatives and recommend a path forward for their new solids processing facility. The team focused on maximizing energy recovery and enhancing sustainability while recognizing that the City was staff-limited without capacity to take on new advanced technology adding considerable O&M effort. Another driver was to reduce final solids volume and develop alternatives centered around Pyrolysis and Gasification addressing PFAS concerns. Since the City was capital and staff limited, these alternatives were developed with the leading technology manufacturers as 3rd party turnkey projects to be owned and operated by a 3rd party commercial entity. Methods A comprehensive and holistic solids and energy modeling effort was developed to understand complex and interacting impacts of implementing various solids and energy processes in one framework (Figure 1). Each potential combination of processes was quantitatively analyzed for annualized cost, greenhouse gas (GHG) reductions, net power generation, and initial capital cost. Along with determining an operationally sound and cost-effective treatment facility, processes were also examined to meet the goals of generating Class A biosolids, maximizing energy recovery, and utilizing technology that shows promise for reducing PFAS contained in residuals. The technologies investigated under this framework include: Pre-digestion - Gravity Thickening of Primary Sludge - Mechanical Thickening of WAS - Thermal Hydrolysis - Thermal-Alkaline Hydrolysis Digestion - Single Stage Mesophilic Digestion Post Digestion - Dewatering - Thermal Drying Biogas Utilization - Digester heating via boilers - Existing Combined Cycle Turbine CHP - New Combine Heat and Power Engine - Renewable Natural Gas -On-site and 3rd Party - Thermal Drying Biochar Processes - Pyrolysis - Gasification Leading technology manufacturers were consulted to develop 3rd party proposals for Biochar Processes. The proposals included the technology provider and a solids management contractor that would serve as O&M staff and manage all residuals. Two different project delivery methods were considered for biochar technology - turnkey contracting and city finance. Under turnkey contracting, the 3rd party would finance and construct the facility, operate, maintain, and charge Toledo a tipping fee for cake delivered. For the city finance option, the City would pay to build the facility and engage in a long-term O&M and residuals management contract with the 3rd party entity. Results The quantitative results (Table 1) from the energy flow modeling were used as a guide to provide recommendations to the stakeholders, some of which are described below. - Reusing digester biogas for generating renewable natural gas results (RNG) in the increased monetary value of the gas. Current solids loading would generate about $1,700,000 gross RIN revenue annually. Adding the RNG system alone to the existing facility did not meet the project goals since there was no final solids volume reduction. - Addition of a pre-digestion hydrolysis process for WAS changed the overall outlook from a solids volume and energy endeavor. Hydrolysis allowed additional solids to be digested, greater biogas generation and increased the dewaterability of sludge. This alternative reduces GHG emissions more than others while reducing dewatered solids by 33% compared to the baseline. This alternative retain the same solids management program, optimizing the cost and sustainability of the existing solids facility; however, does not create a Class A product or destroy PFAS. - Adding a thermal dryer to the digestion system with enhanced WAS lysis system is recommended to create Class A granules eliminating the export of Class B biosolids. It was still financially advantageous to send biogas to RNG and fuel the dryer with NG. This scenario reduces the amount of solids transported out of the facility by 78% but increases the annualized cost of solids management while increasing GHG emissions. - For mitigation against future PFAS regulations as an end goal, a 3rd Party turnkey solution with either pyrolysis or gasification would need to be considered as the only viable option. Pyrolysis systems appeared to have better financials but did not include as much redundancy as the Gasification system proposed. The syngas produced helped the energy balance of these processes, but both were net energy consumers, driving increased GHG emissions. The turnkey project delivery would reduce the capital spent over the baseline scenario by about $100 million by digesters and eliminating cake storage. The case study findings provided a need to stay flexible while investing capital in upgrading the biosolids facilities. While federal regulatory action is not imminent, using a phased project delivery approach for the solid's upgrade project will be prudent while re-investing in digestion. The initial phase would include the installation of a single WAS-lysis treatment train as a large-scale pilot treating ~50% of the WAS load. Biogas will be utilized to produce RNG, thus increasing the value of the energy resources. Adding a thermal dryer or biochar processes will increase the solids handling systems' cost, complexity, and GHG emissions. These options need to be planned for both budgeting and space allocation, but should be phased for implementation when there is evidence that the market for land-applied cake is reduced or eliminated due to regulatory concerns.

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

SpeakerKikale, Pranoti

Presentation time

11:15:00

11:45:00

Session time

08:30:00

11:45:00

SessionGreenhouse Gas Emissions at Wastewater Treatment Plants

Session number11

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicBiosolids Management Planning, Decision Making, Holistic Design

Author(s)

Kikale, Pranoti

Author(s)P. Kikale1, E. Auerbach1, A. McClure2

Author affiliation(s)Arcadis U.S., Inc. 1; Arcadis U.S., Inc.1; City of Toledo 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159438

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count19

Lessons Learned from Biogas Sales Contracting: Success Stories and Pitfalls from Selling Biogas into the RNG Market

Abstract

Introduction It is a complicated proposition when Water Resource Recovery Facilities (WRRF) elect to sell biogas to a commercial 3rd party to make Renewable Natural Gas (RNG) or to make and sell RNG for themselves. These endeavors involve markets, contracts, commitments, uncertain outcomes, and partnerships that lie far outside the typical world of those working at or designing WRRFs. Engaging in this type of gas sales process can be daunting and risky if projects are not pursued in a manner that retains proper benefits and sets manageable responsibilities for the WRRF. The authors of this paper include biosolids and biogas engineers working at or on behalf of municipal WRRFs that have undertaken biogas and RNG sales contracting successfully. The case studies presented will highlight specific keys to successful outcomes in each. However, the authors feel there is one major aspect that generally drives success that the WRRF and engineers working on their behalf must take the lead on devising the gas sales agreements and partnerships with commercial 3rd parties. WRRFs can benefit significantly from gas sales agreements but only when commercial entities are forced to compete around the items that matter and when a true partner can be identified that is willing to share benefits and risks with the WRRF. Roles and Responsibilities in Biogas to RNG Understanding the main entities, roles, and their responsibilities is crucial for navigating biogas-to-RNG sales contracting. Figure 1 provides a schematic representation of the participating entities and their roles in a typical biogas-to-RNG contract. -Biogas Producer: The entity that owns and operates the digester infrastructure, which converts organic feedstock into raw biogas (typical for WRRFs). -Biogas Upgrader: The entity that owns and operates the biogas upgrading infrastructure, which converts raw biogas to RNG product gas (optional role for WRRFs). -Gas Broker: The entity that purchases the RNG Product Gas itself as a commodity, as well as the rights to the Environmental Attributes (EAs) that are generated. The Gas Broker is also typically responsible for registering the RNG project with appropriate authorities to generate EAs and conducting EA sales in response to tracking of market pricing. -Natural Gas Utility Pipeline: If RNG is not dispensed directly to end users, a NG Utility Pipeline will physically accept the RNG-produced gas into their pipeline infrastructure. -Final End User: The entity that ultimately purchases RNG from the Gas Broker and utilizes it in a variety of ways, including fueling compressed natural gas (CNG) vehicles, for campus heating, or for the generation of other energy products. Case 1 - City of Dayton Dayton identified selling of biogas to generate RNG as a priority project in their 2019 Masterplan. This was in the wake of the significant RIN price boom in 2017. Interestingly, Dayton had already constructed and installed a PSA upgrading system back in 2012 to clean gas ahead of their boilers and cogeneration engines. Dayton elected to solicit commercial 3rd parties to purchase their biogas for beneficial use. Under this type of arrangement, the solicitation and selection process is the essential tool that the WRRF has at its disposal to ensure it is identifying a true partner and entering into an agreement that adequately shares risks and rewards. Dayton's selection process is summarized below. RFQ Phase - An open solicitation was issued for interested parties. Ahead of the RFQ, Dayton conducted a pipeline interconnection feasibility study with the local NG utility and included detailed results in the RFQ (see Fig 2). Along with a technical approach, the solicitation called for respondents to provide evidence/experience that they could execute all necessary aspects of an RNG project (see Fig 3). This was key because there are many varied elements required for successful RNG projects and finding a partner that can do all and not some of them is the main goal of an RFQ. The Dayton solicitation received 12 responses of which 3 were shortlisted for invite only RFPs. RFP Phase - The RFP phase required significant detail from invitees that matched the approach promised in the RFQ. Dayton created 20-year pro-forma spreadsheets that matched the RFQ approaches and required respondents to fill in key values that elucidated both their projected risks and returns, and their offered royalty rate back to Dayton. Dayton also authored and provided a draft contract for respondents to review and provide exceptions. Exceptions were allowed but negatively affected the RFP response score. Thus, respondents were forced to compete not just on financial benefit, but on the contracting responsibilities they would accept. For example, Dayton provided historical biogas production information (see Fig 4). Risk was shared by Dayton's agreement to a minimum gas production floor and the biogas upgrader's agreement to accept gas up to a ceiling value exceeding current production. Outcome - Dayton selected to partner with DTE Vantage (DTE) for biogas sales. DTE offered extremely lucrative benefits due to the fact they already owned and operated an RNG system at a nearby landfill(see Fig 5), already had a functioning natural gas pipeline interconnection, and already had a vehicle offtaker and D3 RIN sales in place. None of this was known to Dayton prior to the solicitation so the thorough and comprehensive selection process resulted in major dividends. The Dayton biogas started flowing to DTE's pipeline in November 2024 and Dayton's net financial returns are currently estimated at approximately $750k annually. Case 2 - Capital Region Water Through biosolids and energy planning, Capital Region Water (CRW) in Harrisburg, PA identified upgrading biogas and selling it as RNG as a priority project. Electing to own and operate the RNG upgrading system themselves in order to maximize revenue and fund other fundamental infrastructure upgrades to their WRRF. Another aspect of their decision was the existence of a NG pipeline injection company (UGIES) who already owned and operated a NG pipeline interconnection into the low-pressure distribution system less than 500 feet from CRW's digesters. UGIES was also able to serve as the gas broker in addition to its role as the pipeline interconnection which further incentivized cooperation. With a known partner in hand, the key to CRW's success was crafting a series of agreements with UGIES that allowed successful execution of the gas sales. CRW and engineers working on their behalf crafted the principal versions of the following agreements to ensure benefits and reasonable responsibilities were maintained. Interconnection Agreement - This set the interconnection construction responsibilities of both parties, established methods of payment to UGIES for construction, and reserved unfettered access to the NG pipeline interconnection for CRW if gas quality met the required standards. Some benefits to highlight include delegating the construction and upkeep of jurisdictional pipeline to UGIES who already had certified labor and expertise for this work seeing as they are a NG pipeline company. It also involved eliminating the typical redundant Gas Chromatograph monitoring stations on both sides of the fence. Due to the extreme proximity and cooperative nature of the parties, a single monitoring station was owned and operated by UGIES and readings could be shared back to SCADA at CRW. Biomethane Transaction Agreement - This set the ground rules and the pricing structure under which UGIES would purchase both the commodity NG and the RNG related environmental attributes (EAs) from CRW. One notable benefit was the absence of an RNG supply floor minimum guarantee from CRW. The price paid to CRW for EAs was based on a percentage of a public price index (RIN pricing data as published by the EPA) to allow full price transparency. There was also an Alternatives Markets clause (which was exercised) if both parties agreed that pursuing RINs was not the most beneficial route for monetization. All direct costs which refer to the gas broker's logistical costs for monetizing EAs were kept solely as the responsibility of UGIES and could not be passed back to CRW. Outcome - The RNG upgrading and interconnection was completed and RNG was flowing to the pipeline in late 2025. CRW established an RNG sales pathway while retaining the vast majority of sales revenue to fund other critical infrastructure upgrades. Partnering with a single entity serving as both the gas broker and NG interconnection point significantly simplified the contracting structure CRW needed to pursue. It also provided mutual incentive to get the interconnection constructed in a timely manner and kept open allowing both parties to benefit from the production and sales of RNG.

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

Presentation time

15:50:00

16:10:00

Session time

15:30:00

17:00:00

SessionKeys to Successful Renewable Natural Gas Project Delivery

Session locationKansas City Convention Center

TopicResource & Energy Recovery

Author(s)

Kikale, Pranoti, Auerbach, Eric, Kube, Peter, Ludwig, Patrick, Rosentel, Jess