Stabilizing Solids Management | Southwest Ohio's First-Phase Evaluation of Regional Solids Handling

Like many entities across the nation, the neighboring Southwest Ohio Counties of Greene, Butler, Montgomery, and Warren (Counties) have faced increasing challenges with respect to solids management. These include: Stability. The Counties have generally relied on short-term contracts for solids management. Short-term contracts leave utilities vulnerable to unexpected price increases and, at a minimum, hinder projections for long-term financial planning. Most solids-processors and disposal outlets also prefer long-term contracts, and so short-term contracts can have higher costs. Resiliency. The biosolids sector is experiencing nearly unprecedented upheaval due to regulatory actions in some states and the issuance of the controversial EPA Office of Inspector General (OIG) report. A changing regulatory landscape, coupled with increasing public concerns regarding emerging contaminants and biosolids outlet availability, are driving the need for a biosolids program that can withstand these pressures. Cost-effectiveness. Costs remain a critical consideration for solids management. In addition to cost uncertainties associated with short-term contracts, the Counties are seeking approaches that maximize the value of each dollar spent via solids reduction and resource recovery. Moving to a regional approach for solids management can address these challenges and is the basis for the Southwest Ohio Regional Biosolids Collaborative Strategies Development project. The first phase of the project was conducted over most of 2020 whereby monthly virtual workshops were conducted with representatives from each of the Counties, along with representatives from the Ohio EPA to provide feedback and input into the development of project critical success factors, screening and identification of preferred solids stabilization technologies, identification and weighting of evaluation criteria, and development and evaluation of conceptual regional solids handling strategies. Feedstocks considered for processing at a regional facility included solids from each of the Counties wastewater treatment facilities, food scraps and yard waste from the Counties' municipal solid waste (MSW) programs that could potentially be recovered, and potential fats, oils, and grease (FOG) production from within the Counties. The facilities could potentially process other desirable feedstocks from commercial and industrial sources within the study area, but the focus for this first phase of the project was on organics generated by the Counties. A brief review of regulatory requirements and potential solids markets in the region was conducted to provide a framework for selecting those solids stabilization technologies considered to be the most suitable for the Counties to implement a regional solids handling approach. Four solids stabilization technologies were shortlisted in this first phase: composting, drying, thermal hydrolysis process (THP) with co-digestion, and high solids digestion. Three of these technologies were expanded into two strategies to facilitate potential phasing of implementation and a gradual introduction of feedstocks resulting in the following seven initial conceptual regional solids handling strategies. Refer to Table 1 for a summary of the anticipated solids and energy inputs and product outputs for each of these strategies.Strategy 1: Composting. Haul biosolids cake from regional treatment facilities and regional yard waste and food waste to a composting facility and produce a Class A compost. Strategy 2A: Drying. Haul biosolids cake from regional treatment facilities to a thermal drying facility and produce a Class A dried product. Strategy 2B: Drying and Composting. Haul biosolids cake from regional treatment facilities and regional yard waste and food waste to a dual drying and composting facility and produce a Class A dried product and compost. Strategy 3A: THP w/ Co-digestion. Haul biosolids cake from regional treatment facilities and regional FOG and food waste to an anaerobic digestion facility with THP pretreatment and produce a Class A cake. Strategy 3B: THP w/ Co-digestion and Composting. Haul biosolids cake from regional treatment facilities and regional FOG, food waste, and yard waste to a composting facility with THP and anaerobic digestion pretreatment and produce a Class A compost. Strategy 4A: High Solids Digestion. Haul biosolids cake from regional treatment facilities and regional FOG and food waste to an anaerobic digestion facility and produce a Class B cake. Strategy 4B: High Solids Digestion and Drying. Haul biosolids cake from regional treatment facilities and regional FOG and food waste to a drying facility with anaerobic digestion pretreatment and produce a Class A dried product. These conceptual strategies were evaluated using a quadruple bottom line framework consisting of four evaluation criteria categories: financial, social, environmental, and functional. Strategies which initially appear to offer the greatest benefits with manageable risks are planned to be further developed and evaluated as part of the next phase of the project. In addition to these strategies, other strategies may be evaluated in the next phase which consider the following key drivers: Long term regulatory compliance. With new data continuously being produced on emerging contaminants, namely polyfluorinated alkyl substances (PFAS), the Counties may be interested in evaluating thermal type solids stabilization technologies such as incineration, gasification, or pyrolysis, which may reduce these contaminants. Public private partnership. With the potential for biosolids from multiple wastewater treatment facilities and organics from multiple other sources directed to a regional facility, the Counties may be interested in partnering with a third party who could operate and maintain the facility and manage/market the reuse of the resulting solids product. Expanded regional participation. Given the notable capital cost anticipated to implement a regional solids handling facility, the Counties may be interested in seeking other participants who may benefit from directing their biosolids/organics to a regional facility and who could share in the upfront costs and risks. This manuscript provides an overview of the findings of this first phase conceptual level evaluation that has provided the Counties with foundational planning for the potential implementation of a regional solids handling approach which could serve the Counties and potentially other utilities in the Southwest Ohio region. It will also review some of the next steps that are anticipated to be included in the next phase of the project.