One South Carolina Utility's Biosolids Plan: Forging a Path Amidst Rising Tip Fees and Regulatory Uncertainty

Spartanburg Water, through the Spartanburg Sanitary Sewer District (SSSD), owns and operates eight wastewater treatment facilities (WWTFs) throughout Spartanburg County. Sludge generated by the seven smaller facilities are typically hauled to the A. Manning Lynch WWTF (AM Lynch), where it is blended with grease trap waste (GTW) that is also hauled in from around the County, then centrifugally dewatered. The dewatered cake is then hauled to two local landfills. SSSD wanted to take a fresh look at their biosolids management strategy due to: -Rising landfill tip fees and the risk landfills can stop accepting sludge with little notice -Regulatory uncertainty, especially around per- and polyfluoroalkyl substances (PFAS) -Changing biosolids treatment technology landscape A Biosolids Master Plan and Roadmap was developed that compares the current biosolids management approach to a range of potential new technologies and beneficial end uses. The master plan approach first evaluated the local market for biosolids derived products, which informed potential management strategies and technology selections. A detailed evaluation was conducted of SSSD's current and preferred sludge management practices and critical existing processes to customize the alternatives to SSSD's on the ground realities. A large list of alternatives was screened incrementally down to the five most attractive strategies, which then received a cost and non-cost analysis. BC developed an implementation plan that immediately reduces costs and risks to SSSD's sludge management program, while providing flexibility to respond to regulations and market conditions that may further alter the sludge management landscape in the coming years. The result is a Biosolids Master Plan that identifies near-, mid-, and long-term options for biosolids management that are informed by the existing and projected regulations and market demand for biosolids, and customized to SSSD's size, operating budget, and preferences. The plan includes a dynamic roadmap for implementing the selected biosolids management strategies, with timing of selected near-, mid- and long-term strategies informed by various triggers. Biosolids Market Study The biosolids market study shed light on actual demand for different biosolids derived products (compost, dried Class A biosolids, Class B Cake, and biochar) in SSSD's local market. This helped inform the attractiveness of different biosolids management strategies and technologies. Evaluating actual local market conditions first reduced risk and uncertainty around making capital investments to access different biosolids end use markets. In addition to identifying markets for beneficial reuse, the team also evaluated alternative disposal options for SSSD's sludge and separate processing of GTW to improve dewatering operations. Regionalization Considerations Detailed evaluation was conducted to determine sludge production and projections at all plants, and trucking logistics to bring thickened sludge to the centralized solids processing facility at AM Lynch WWTF. The sludge projections and AM Lynch mass balance indicate that the sludge storage tank is running out of capacity to effectively equalize, blend, and decant SSSD's sludge and GTW prior to centrifugal dewatering. By 2025, there will not be enough capacity to equalize average week sludge loads and maintain decant operations. If decant abilities were completely lost, SSSD would have to increase centrifuge weekly run time by 55%, and would experience reduced centrifuge performance (e.g., lower cake solids concentrations), both of which will increase operational costs. Table 1 outlines options to increase sludge storage to allow for reliable decanting in the future and to provide peak week equalization to limit required processing capacity of downstream equipment. Technology Screening Fifteen (15) technologies were identified as being attractive for SSSD. Eight (8) technologies remained after a pre-screening effort, which eliminated any technologies that: -Could not achieve Class A Biosolids -Increased the volume of biosolids to manage -Were embryonic (did not have a successful full-scale municipal sludge installation in the US) Conceptual designs (equipment sizing and site plans), along with pros and cons were presented for the eight (8) prescreened options in the Initial Screening Workshop. At the workshop, the team came to consensus on the five (5) alternatives to advance for detailed evaluation; the alternatives and their reason for selection are summarized in Table 2. Long-Term Alternatives Analysis Lifecycle cost and non-cost analyses were conducted for the five (5) alternatives. Sensitivity analyses were performed on landfill tipping fees, chemical prices, land application cost. Off-site composting by a third party had the best non-cost rating, lowest capital costs, and lowest operating costs of all the options being considered. The biosolids market study determined that compost also had the greatest local market demand. There is also strong interest from two experienced and successful large-scale composters to build a new facility and have SSSD as their main client. For all these reasons, BC recommended moving forward with off-site composting immediately, as it will reduce risk and should reduce biosolids management costs on day one. BC is currently assisted SSSD in releasing an RFP for off-site 3rd party processing services. A summary of considerations for each alternative will be discussed in the manuscript. Biosolids Road Map BC developed an implementation plan that immediately reduces costs and risks to SSSD's sludge management program, while providing flexibility to respond to regulations and market conditions that may further alter the sludge management landscape in the coming years. Near-Term Recommendations (2022-2025): SSSD should focus on diversifying their solids management, improving sludge storage and dewatering at AM Lynch, and monitoring regulations on PFAS. This includes: -Letting an RFP for off-site third-party processing of the majority of SSSD's dewatered cake. -Evaluate third party processing of the GTW accepted and stored at AM Lynch, as well as evaluating centrifuge optimization options. -Build a redundant sludge storage tank to provide required volume for equalizing peak week loads and to continue decanting operations. SSSD is currently moving forward with all of these recommendations. Mid-Term Recommendations (2026-2035): SSSD should re-evaluate this biosolids master plan and make capital improvements necessary for aging equipment. This includes: -A master plan update that evaluates how satisfied SSSD is with the off-site third-party composting contract, provides an updated regulatory landscape regarding PFAS's impact on biosolids beneficial reuse, quantifies the increased costs and risks of trucking sludge (which will inform both sludge hauling to AM Lynch, and trucking of dewatered cake from AM Lynch), as well as an updated evaluation of landfill access/fees and the local biosolids market. -A condition assessment of critical equipment should be included prior to or as part of this master plan update. -Replace the two older centrifuges and their ancillary systems, as well as any other capital improvements identified as part of the condition assessment and master plan update. Long-Term Recommendations (2036-2045): Given the current regulatory uncertainty, and the luxury of pursuing off-site third-party composting to reduce risks and control sludge management costs over the next decade, no significant investments that would alter the sludge handling process at AM Lynch are recommended. The recommendations reduce risks and control costs in the near- to mid-term and buys SSSD time to see how PFAS regulations will unfold, how expensive and restrictive landfill disposal of sludge becomes, and how the many new advanced sludge destruction technologies perform at full scale municipal WWTFs in the US. The long-term recommendations will be decided in the biosolids master plan update schedule for 2029-2030, which will be based on the outcome of the above variables, as well as results of the condition assessment. Capital Improvements Planning: To facilitate CIP planning, three alternative budgets of solids management capital investments were developed associated with these recommendations: 1.Recommended budget assumes off-site composting by a third-party remains the long-term biosolids management strategy for SSSD 2.This alternative budget represents investments needed if market triggers result in SSSD adding a thermal belt dryer at AM Lynch to reduce costs and risks. 3.This alternative budget represents investments needed if regulatory triggers result in SSSD adding a sludge destruction technology at AM Lynch to reduce costs and risks.