A Road Map for Navigating Biosolids Disposal Challenges at SESD Through Application of Existing and Emerging Technologies

South Essex Sewerage District (SESD) is a regional agency that owns and operates a Wastewater Treatment Plant (WWTP) in Massachusetts that serves 185,000 people and businesses in Salem, Peabody, Beverly, Danvers, Marblehead, and small portions of other communities. The District's WWTP operates a pure oxygen BOD removal process. Waste activated sludge from this process is currently thickened with gravity belt thickeners and blended with primary sludge. The blended primary and thickened waste activated sludge is subsequently dewatered with belt filter presses. Unstabilized dewatered cake is trucked offsite by a contract hauler for final beneficial use or disposal via composting, landfilling, or incineration. The District is undergoing a comprehensive wastewater facilities master planning process to address aging infrastructure at its WWTP, which underwent its last comprehensive upgrade in the late 1990s. A critical element of the facilities planning effort was to evaluate long-term options for managing the WWTP's biosolids. Biosolids are a key concern at the District's WWTP, as biosolids beneficial use and disposal currently comprise a significant percentage of the annual operations and maintenance budget at a disposal cost of approximately $132/wet ton. A market survey of was performed as a part of the facilities planning effort to assess the long-term reliability and cost of biosolids disposal including for unstabilized cake, stabilized cake, and dried biosolids. The cost of biosolids beneficial use and disposal has increased considerably in New England due to high uncertainty in future disposal options due to limited landfill capacity, limited land disposal outlets in the wake of Maine banning biosolids disposal, and challenges with aging incinerators in the region, among other factors. Thus the market survey found the future cost or biosolids disposal is highly uncertain with new biosolids beneficial use and disposal contracts expected to be significantly higher than the District's current contract. Alternatives were evaluated for the long-term management of biosolids at the District's WWTP with both established and emerging technologies, including conventional mesophilic anaerobic digestion (MAD), MAD with thermal hydrolysis pretreatment (THP), thermal drying, gasification/pyrolysis, and super critical water oxidization (SCWO). The 20-year life cycle cost was estimated for these alternatives and include a sensitivity to the final biosolids beneficial use and disposal costs for all the alternatives. The evaluation indicated that at current biosolids disposal costs, both MAD and MAD with THP have higher life cycle costs than the current sludge dewatering operations. However, as biosolids beneficial use and disposal costs increase, MAD and MAD with THP become more favorable. The evaluation of thermal drying, gasification, and SCWO indicated a similar favorability at high biosolids beneficial use and disposal costs, though the disposal costs at which these technologies become favorable are considerably lower than the MAD alternatives. The evaluation shows that as sludge hauling, beneficial use, and disposal costs increase in New England and across the nation, technologies that reduce the mass of solids for beneficial use and disposal, particularly thermal drying and emerging technologies (gasification and SCWO), become favorable from a life cycle cost perspective. The master planning process incorporated the conclusions from the long-term biosolids management analysis through the use of a biosolids management 'road map' that addresses the District's short-term and long-term needs while providing flexibility based on market and regulatory drivers. This paper and presentation will review the results of the biosolids end user market survey completed as part of the master planning process, describe the methods and results of the long-term biosolids management analysis and the District's biosolids management 'road map', and provide updates on the District's next steps for biosolids management. The results will be beneficial to other utilities undertaking similar master planning processes.