Using Long-Term Biosolids and Biogas Planning to Improve Short-Term Decisions

INTRODUCTION It is often said that beginning with the end in mind is important when making decisions. This presentation will show how long-term biosolids and biogas planning can be an important part of informing short-term operational and upgrade decision making. Developing a long-term plan helps make informed technology decisions now to improve future adaptability to a shifting regulatory environment and volatile markets for biogas and biosolids products. This presentation will show how long-term planning informed a dewatering alternatives analysis and biogas utilization study for Oneida County, New York. The Oneida County Water Pollution Control Plant (WPCP) treats and disposes of primary solids, waste activated sludge (WAS), and high-strength organic waste (food waste) from an adjacent solids waste authority. Digested solids are dewatered with belt filter presses (BFPs) and trucked by the solids waste authority for disposal in a landfill. Biogas is treated before being used in microturbines for combined heat and power used at the facility. THE PROBLEM The County has observed poor performance of the existing BFPs leading to high costs in disposal, as well as high downtime of microturbines leading to increased flaring and natural gas use for boilers. These concerns led the County to seek an alternatives analysis to evaluate dewatering technologies and biogas utilization strategies. METHODOLOGY To develop informed alternative analysis that would allow for flexibility and limit stranding existing assets in the future, a long-term biogas and biosolids plan was developed in conjunction with the dewatering and biogas utilization studies. Several evaluations were conducted to inform long-term planning including a regulatory environment evaluation, market analysis to determine local markets for biosolids of varying qualities, and a utility survey to determine local interest in regionalization. Long-term strategies evaluated included solids drying, advanced digestion, and advanced thermal treatment for PFAS removal. Representative technologies were selected from these strategies to develop a trigger-based roadmap to guide future decision making. In concurrence to long-term planning, a short-term evaluation of dewatering and biogas utilization was completed. An alternatives analysis for dewatering technologies was conducted. Sludge samples were analyzed to determine key characteristics impacting dewaterability and historical process data was analyzed to develop design criteria. Three dewatering technologies, BFPs, centrifuges, and screw presses, were evaluated using economic and non-economic decision criteria. A biogas utilization alternatives analysis focused on three strategies, continuation of combined heat and power (CHP), upgrading to produce renewable natural gas (RNG) or compressed natural gas (CNG). These were evaluated using economic and non-economic criteria considering market variability. RESULTS Short-term dewatering and biogas evaluation findings included: -Dewaterability testing shown in Table 1 provided a basis for performance assumptions of dewatering technologies. Cost estimates for the dewatering technologies were developed based on siting options and dewatering and conveyance equipment (see Figure 2). -BFPs and Centrifuges were evaluated with non-economic criteria and scored criteria weighted by WPCP staff while screw presses were eliminated due to footprint constraints (see Table 2 and Table 3). RNG, CNG, and CHP were evaluated where equipment was sized and layouts, capital costs, and O&M costs were developed including a Monte-Carlo analysis to evaluate the impact of market variability on the economics of each alternative (see Figure 4). A long-term biosolids and biogas plan was developed in which technologies were selected to represent potential long-term strategies (solids drying, advanced digestion, and advanced thermal technologies for PFAS removal) (see Figure 5) and developed: -A baseline evaluation completed based on existing conditions/assumptions (see Figure 6 and Figure 7), -A sensitivity analysis to determine trigger points for different strategies (see Figure 8) which revealed that advanced digestion could be implemented to improve RNG production and dewaterability, and drying and advanced thermal technologies were demonstrated to be advantageous for increased hauling cost scenarios and to address potential future regulations, respectively. Based on the alternatives evaluation and informed by the long-term plan, alternatives were selected that best allowed for future adaptability. For dewatering centrifuges were the preferred option to allow for better dewatering and an easier transition to solids drying in the future. For biogas a combination of continued CHP combined with a transition to RNG or CNG was selected. CONCLUSION Oneida County developed a long-term biosolids and biogas plan to inform a short-term dewatering and biogas utilization study. This case study is significant to attendees of this presentation because it: -Demonstrates how long-term planning can inform short-term decision making. -This strategy helps avoid stranding assets in the future and maximizes the value of near-term upgrades.