Managing Biosolids in Maine: Challenges and Potential Solutions

Background Portland Water District (PWD) has four wastewater treatment facilities (WWTFs) with a capacity of more than 25 million gallons per day. Two of the four facilities - East End and Westbrook - process most of the solids in the system and were the focus of PWD's comprehensive approach to assess the current solids system and develop a strategic plan that outlines the necessary upgrades, process modifications, and state-of-good-repair projects that PWD should undertake during the next 20-year planning period. PWD began contemplating this planning effort not only due to aging infrastructure, but rather due to increasing concern over lack of biosolids management options and rising public concern around per- and polyfluoroalkyl substances (PFAS) in biosolids. Throughout New England, decreased biosolids management capacity has been a rising concern. Much of the region relies upon landfills and regional incinerators, but beneficial use (land application) has served as a reliable, sustainable option for a number of utilities. In Maine, land application had been an accepted practice, with good market understanding of the benefits of biosolids, including biosolids based compost and thermally dried products. Concerns over PFAS in wastewater residuals, or solids, prompted legislative action to prohibit land application of treated wastewater solids (biosolids) and products containing biosolids in Maine (LD 1911 [An Act to Prohibit the Contamination of Clean Soils with So-Called Forever Chemicals]). The Governor signed this bill in April 2022, and it is currently in effect as Public Law 2021 Chapter 641. This law leaves Maine wastewater utilities with landfill as the only option for solids management within the state-and few, costly options outside the state. Instate wastewater solids landfilling became more challenging with the passing of solid waste bill, LD 1639 (An Act To Protect the Health and Welfare of Maine Communities and Reduce Harmful Solid Waste) in April 2022, and enacted February 1, 2023. This bill restricts the importation of out-of-state solid waste for processing in the state of Maine. Dewatered wastewater solids cake is considered a 'wet waste' by landfill operators and is typically mixed with bulking agents at landfills to avoid stability issues. Out-of-state solid waste (e.g., oversized bulky waste and construction and demolition debris) was one of the main sources of bulking agents for stabilizing wastewater solids. When the availability of these bulking agents decreased, the landfill operators handling most of the biosolids disposal in the state reported they needed to consequently reduce the amount of wastewater solids they accept. This left many utilities scrambling for alternatives, including costly long-distance hauling to Canada. Despite a two-year reprieve to LD 1639 (via LD 718, An Act to Facilitate the Management of Wastewater Treatment Plant Sludge at the State-owned Juniper Ridge Landfill), wastewater utilities in Maine, including Portland Water District (PWD), are still restricted to landfilling instate in the short-term, and following the two-year reprieve will face severe challenges in the long-term. Methodology This project was completed to define the technical, economic, and programmatic considerations for implementing a regional anaerobic digestion, drying, and thermal treatment biosolids processing facility. These technologies were selected for consideration for their following attributes: - Anaerobic Digestion. Anaerobic digestion biologically degrades solids, reducing their mass by 40-50 percent and generating energy-rich biogas. Anaerobic digestion can process a wide variety of liquid organic wastes, including food and beverage processing wastes and fats, oils, and grease waste. Anaerobic digestion and biogas utilization offer substantial opportunities for greenhouse gas reduction at a WWTF and for the region when processing imported organic waste. Anaerobic digestion can also treat solids to United States Environmental Protection Agency (USEPA) requirements for Class B or A stabilization and improves downstream processing by improving and homogenizing solids quantities and quality. - Thermal Drying. Thermal drying removes nearly all the entrained water in dewatered solids, reducing solids mass by 4 to 5 times. This reduces the amount of solids needing to be hauled and can remedy capacity and structural limitations associated with landfilling of dewatered solids. Thermal drying can also meet USEPA Class A stabilization requirements, which provides nearly unrestricted beneficial reuse opportunities in other states. - High Temperature Thermal Processing. Thermal processing submits solids to high temperatures for further mass reduction and treatment of emerging contaminants such as PFAS. This has traditionally been performed by sewage sludge incineration (SSI), which oxidizes all solids to an ash. However, SSI air permitting regulations have become especially onerous and make SSI adoption in New England unlikely today. Pyrolysis and gasification are emerging, non-incineration thermal processes that employ high temperatures at oxygen free or starved conditions to generate a carbon-dense beneficial reuse product called biochar and a gas stream with an appreciable energy value. The technology is still in a developmental stage with one commercial biosolids pyrolysis facility in operation in the US at Silicon Valley, CA. In 2020, the USEPA found the Silicon Valley pyrolysis system removed PFAS from biochar to below reportable levels (Thoma et al., 2021). BC, with Silicon Valley Clean Water and the Water Environment Federation are scheduled to perform a PFAS air emissions test early 2024 to evaluate PFAS destruction in the gas phase. The Silicon Valley pyrolysis system uses a thermal oxidizer for emissions control and heat recovery and previous work by the USEPA demonstrated thermal oxidation as suitable for designation as a Best Available Control Technology for PFAS and capable of meeting permitted PFAS destruction criteria (Barr, 2022; Beahm, 2019; Focus Environmental Inc., 2020). While pyrolysis and gasification require solids be dewatered and dried for processing, a new class of thermal processes is also emerging called hydrothermal treatment, that treat solids in a liquid, slurry form at high temperatures. Super critical water oxidation is one example where all organics (including organoflourines such as PFAS) are intended for oxidation within a flow-through reactor. Hydrothermal carbonization and hydrothermal liquefaction use heat without an oxidant to refine the solids into solid and liquid biofuels, respectively. Conclusions The BC and PWD team completed the following outreach and assessment tasks to identify and compare current market offerings for the solids processing technologies mentioned above. The investigation included assessment of commercially available equipment and overall project delivery and operation under the following tasks. - Request for Information (RFI): BC developed and issued an RFI digestion, drying, and thermal processing system suppliers. The goal of issuing this RFI was to identify interested technology and/or solution providers and to compare current commercial offerings based on lifecycle cost and key non-economic criteria. - Technology Summit: Responders to the RFI could participate in a two-day in-person and virtual technology summit, in which each participant had 20 minutes to present information about their technology. These presentations were recorded and are available on the PWD website. - RFI Submission Review: Each submission was evaluated based upon set criteria, established in the RFI document. Table 1 summarizes the scores for the highest ranked submissions. - Alternative Evaluation: Based on the top three ranked system supplier offerings/technologies, facility concept level designs were developed for a business case evaluation (BCE). The Alternatives BCE evaluated three onsite and three regional technology alternatives. These alternatives are summarized along with their BCEs in Table 2. - Recommendations: The RFI submissions and BCEs enabled the PWD and BC team to identify a potential phased path forward for PWD. The purpose of this report is to summarize and describe the methodology BC employed, as well as the economic and noneconomic findings, from the evaluation of a regional, offsite biosolids processing facility. Ultimately, the goal is to characterize the economic viability and noneconomic attributes to assist PWD in determining a path forward to manage