Working Towards a Sustainable Outlet for Maine Biosolids through a Regional Solution

Background Throughout New England, decreased biosolids management capacity has been a rising concern. Much of the region relies upon landfills and incinerators, but beneficial use has served as a reliable option for a number of utilities, including in Maine. Concerns over PFAS prompted legislative action to prohibit land application in Maine. This law leaves wastewater utilities with landfill as the only option for solids management in the state. Landfilling has gotten more challenging with limited capacity and adoption of additional laws impacting the availability of bulking agents. A company has been working with the regulators in Maine and individual utilities, including the Portland Water District (PWD), to explore approaches to alleviating some of these challenges. The Maine Department of Environmental Protection (DEP) contracted to evaluate the current situation for biosolids management in the state and make concrete recommendations for change. PWD and the company worked together to determine the feasibility of onsite and offsite processing technologies. The technology evaluation for Maine DEP and PWD focused on digestion, drying, and thermal treatment technologies. These technologies were selected for consideration for their following attributes, among others: (1) Anaerobic Digestion. Biologically degrades solids, reducing their mass and generating energy-rich biogas. (2) Thermal Drying. Removes nearly all the entrained water in dewatered solids. This reduces the amount of solids to manage and can remedy capacity and structural limitations at landfills. (3) High Temperature Thermal Processing. Submits solids to high temperatures for further mass reduction and treatment of emerging contaminants such as PFAS. Pyrolysis and gasification are emerging, non-incineration thermal processes that employ high temperatures to generate a carbon-dense beneficial reuse product or an ash and a gas stream with an appreciable energy value. Hydrothermal treatment technologies were also considered-including super critical water oxidation and hydrothermal carbonization/liquefaction. Objectives This paper will detail the specific challenges facing biosolids management in the state (which echo the situation in many other parts of the country) and proposed 'levers' for the state government to address concerns. The situation will be further elucidated by looking in detail at the realities facing PWD and options available to the utility. Status The study for Maine DEP recently has been completed so final results will be presented. The company continues to work on refinements with PWD, but the main analysis has been completed. Methodology The company evaluated public data sources and DEP records to determine the amount of biosolids generated and the amount going to different end use locations. A questionnaire was sent to landfill operators to estimate future capacity for biosolids and barriers to landfills accepting biosolids. Questionnaires were also sent to organizations with interest in developing regional solutions and to providers of technology purported to reduce PFAS. To provide a guide for utilities throughout Maine, lifecycle cost analysis was performed on promising technology approaches at different scales using representative costs for the state. For PWD's specific situation, the team completed the following outreach and assessment tasks to identify and compare current market offerings.

*Request for Information (RFI): BC developed and issued an RFI for technology suppliers. The goal was to identify interested providers and to compare commercial offerings based on lifecycle cost and 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 could present information about their technology.

*RFI Submission Review: Each submission was evaluated based upon set criteria.

*Alternative Evaluation: Based on the top three ranked onsite and offsite system supplier offerings, concept level designs were developed for a business case evaluation (BCE). Findings The company projected capacity within the state to manage biosolids; under certain scenarios capacity would be greatly exceeded by the amount of biosolids generated in as little as five years (see Figure 1). The company developed a range of recommendations for Maine government, including addressing limits on bulking agent availability at landfills, pushing for landfill expansions, funding pilots of PFAS treatment technologies, providing grants for volume reduction and dryer projects, and making changes to state regulations. The results of the BCE for PWD are shown in Figure 2, with the twenty-year net-present cost broken out by capital and operations and maintenance costs. The RFI submissions and BCEs enabled the team to identify a potential phased path forward for PWD that will address near term solids needs at the plant while continuing to explore regional processing options. Significance The challenges facing Maine are not unique to the state. The recommendations for Maine are transferable to other parts of the country. And many utilities around the country are looking at the same technologies-digestion, drying, thermal treatment-as approaches that reduce exposure to these challenges, so the results of the BCE for PWD will be of interest to many around the country