Biosolids Solutions Tailored to Fit Small Facilities

Introduction Rising disposal costs, flexibility in biosolids beneficial reuse end use, the desire to optimize bioenergy use, and the uncertainty around future regulations require utilities to balance proactivity with their inevitably constrained capital budgets. This presentation will review two customized planning solutions developed for smaller utilities (2 million gallons per day (mgd) and 12.6 mgd), helping them prepare for future changes without committing to large-scale capital expenditures prematurely. Case Study 1: Opequon Biosolids and Bioenergy Planning The Opequon Water Reclamation Facility (OWRF), located in Winchester, VA, is permitted to treat 12.6 mgd. The OWRF uses mesophilic anaerobic digestion (MAD) and dewatering to produce Class B cake for beneficial use. The OWRF accepts fats, oils, and grease (FOG) and high strength waste (HSW) from industrial customers for co-digestion. The OWRF generates electricity using digester gas in a combined heat and power (CHP) system. While co-digestion increases digester gas production available for beneficial use, it is believed to also reduce dryness of final cake product, increasing hauling and management costs. A biosolids and bioenergy evaluation was conducted for Frederick-Winchester Service Authority (FWSA), the owner/operator, and included the following considerations: 1.Digester gas production in excess of what can be beneficially used in the current CHP, 2.Existing CHP reaching the end of its expected useful life, 3.Significant increases in biosolids hauling and management costs from the third party contractor, exacerbated by the low percent total solids in the final cake product due to industrial flows 4.Potential for future regulations on emerging constituents of concern in biosolids, including PFAS and microplastics Approach Alternatives Development A world-of-options list of biosolids management and digester gas beneficial use technologies was developed. The list was narrowed down through a multi-criteria, non-cost evaluation that scored the technologies against the OWRF's weighted objectives: market sensitivity, future flexibility, ease of operations and maintenance, environmental impact, and community impacts. A short list of alternatives was identified for evaluation in the next phase, which included development of an energy balance and financial analysis evaluation. The alternatives to be considered were combinations of the following: - Baseline solids management: continue MAD and production of Class B cake - Baseline gas management: replacement in kind of the CHP system - Advanced thermal processing (drying with pyrolysis or gasification) - Supercritical water oxidation - Upsizing the CHP system Vendor outreach was conducted to understand the sizing options commercially available as well as estimated capital and O&M costs and site-specific implementation considerations. Operating, maintenance and plant design data was used to conduct preliminary sizing of potential alternatives and in completing a 20-year net present value lifecycle cost evaluation. Energy Balance and Financial Analysis Using the Power BI-based Energy Balance Analysis Tool (EBAT), a framework was developed to provide a sensitivity analysis of the short-listed alternatives against the input parameters. Mass and energy balances were completed to determine the likely energy use/generation potential. Comprehensive 20-year lifecycle costs of each combination of biosolids and bioenergy alternatives were calculated including O&M costs, financing costs for demolition and construction, biosolids disposal costs, and any bioenergy-recovery benefits, such as energy savings and/or revenues. FWSA benefits from analysis using EBAT because they can adjust inputs and variables to simulate how future conditions may evolve. For example, by reducing the capital costs (anticipated as technology matures) or increasing Class B hauling costs (as regulations evolve), the most cost-effective alternative changes. Results Figure 1 shows part of the EBAT dashboard, illustrating the user functionality and visualizations. The tool makes it very easy to prepare projections and conduct justifiable decision-making for stakeholders. Figure 2 shows the 20-year net present value of each combination of alternatives. Two different sizing options for advanced thermal processing were considered to explore if a piloting approach would make financial sense for the OWRF. Nominal decrease in 20-year net present cost was predicted with a pilot demonstration of an advanced thermal process over a full-scale; this approach could be considered to further explore viability of the technology. The results of the evaluation suggest that at current market and regulatory conditions, the most cost-effective option is to continue digestion and replace the CHP in kind, due to the marginal estimated benefit of upsizing the CHP. The OWRF plans to continue PFAS sampling and monitoring regulations. The development of this dashboard provided a path for FWSA to understand the cost of implementing improvements to reduce hauling costs and justification to continue with the status quo. As conditions evolve, FWSA can continue to use the EBAT to evaluate changing conditions. Case Study 2: Dorsey Run Drying Technology Evaluation The Dorsey Run Advanced Wastewater Treatment Plant (AWWTP), located in Jessup, MD, is permitted to treat 2 mgd. The AWWTP uses lime stabilization and dewatering to produce a Class B biosolids product for land application. Maryland Environmental Service (MES), who owns and operates the AWWTP was interested in conducting an evaluation to explore implementation of thermal drying, to explore the following: 1.Long-term feasibility and cost of implementing a thermal drying system, 2.Consideration for producing a Class A product in lieu of current Class B product to expand options for beneficial use, and 3.Preparation for future implementation of gasification or pyrolysis if required due to possible future PFAS regulations, which requires dried material as the feedstock. Approach Historical data and plant capacity, and operational strategies were used to develop design loads and flows for a thermal drying system. Inquiries were put out to thermal drying manufacturers of three different technologies: belt, screw/paddle, and tray dryers. Manufacturer information from the vendor and from references was used to present advantages, challenges, and site-specific implementation considerations of each to MES. The evaluation suggested that paddle and screw dryers are most feasible for a facility of 2 mgd. A short list of three drying systems was established for further evaluation: Paddle #1, Screw, and Paddle #2. The next phase of evaluation included development of full capital and lifecycle costs. Comprehensive 20-year lifecycle costs for each drying system included: demolition and construction costs and O&M costs; including but not limited to manpower, utilities, and maintenance. Conceptual layouts were developed for each of the three drying systems, and the most conservative (largest) is shown in Figure 3. For all three alternatives the existing lime stabilization system would be demolished and an elevated platform for the drying system installed. Finally, a multi-criteria evaluation was completed using cost and non-cost criteria to determine the most favorable alternative. Results The 20-year lifecycle costs were one factor in the multi-criteria evaluation shown in Figure 4. The criteria and weightings were developed with input from MES to ensure the appropriate priority was given to each consideration. This desktop evaluation allowed MES to prepare for the next level in biosolids processing and understand the current vendor and technology landscape to make an informed decision in design. MES plans to wait to design the drying system due to budgeting constraints. It is anticipated that funding will be secured if and when regulations require it. At that time, they plan to install a thermal drying and PFAS destruction process.