A Unique Approach to Biosolids Management with Energy Recovery

NEW Water (Green Bay Metropolitan Sewerage District) located in Green Bay, WI is a wholesale provider of wastewater treatment services to 15 municipal and two direct industrial customers in Northeast Wisconsin. NEW Water treats on average of 41 million gallons per day (mgd) at its two wastewater treatment facilities in Green Bay and De Pere. NEW Water has processed biosolids using incineration (multiple hearths) since the 1974. NEW Water needed to replace the biosolids handling facility at its Green Bay Facility to meet more stringent environmental regulations, increased capacity needs, and to replace an aging infrastructure. The solids upgrade project to address these concerns is called the Resource Recovery and Electrical Energy project (R2E2). The R2E2 project is the most capital expensive project in the history of the utility. Facility improvements included in the project are: - Mesophilic anaerobic digestion - Centrifuge dewatering - Scalping drying - Fluid bed incineration - Advanced air pollution control equipment - Biogas cleaning - Biogas storage - Biogas internal combustion engine generators - Heat recovery - Thermal oil system - Nutrient recovery - Odor control - New primary substation. The most unique aspect of the R2E2 project was the pairing of anaerobic digestion with incineration as these technologies are traditionally used separately from each other. The project signified a change in organizational philosophy at NEW Water: treating waste as a resource to recover, rather than something to dispose in the most cost-effective manner. While NEW Water needed to address regulatory, capacity, and infrastructure concerns, the organization took advantage of an opportunity to become a Utility of the Future through this unique approach. The R2E2 project has addressed operational concerns while saving ratepayers money by generating electricity from digestion and recovering heat from processes. The R2E2 project is a resource recovery project that was initiated because of stricter environmental regulations, the need to increase capacity, and need to replace aging solids processing infrastructure. There were also aspects of the project that included energy efficiency improvements and renewable energy components. The project has provided the organization with an opportunity to recover biogas from high strength waste through anaerobic digestion. The recovered biogas is treated and supplies two biogas electrical generators capable of producing a total of 4 MW of electricity. The flue gas from the fluid bed incinerator, along with the jacket water and exhaust gas from the biogas engines, is used throughout the processes for building heat, sludge drying, and digester heating. The new fluid bed incinerator has the capability to operate autogenously without the use of auxiliary fuels (diesel or natural gas). This technology replaced two multiple hearth furnaces that required significant amounts of supplemental fuel (natural gas) in order to operate. There has been a 32% reduction in the purchase of utility electricity since the R2E2 project has been in full operation since May 2018. In 2021, the R2E2 facilities are generating close to 45% of the Green Bay Facility's electrical needs. In 2020, the R2E2 facility recovered 120,163 MMBtu's of heat from the fluid bed incinerator and biogas engines. The recovered heat is used for building heat, sludge drying, and digester heating. The project includes the ability to receive high strength waste. In 2020, the facility received over 24 million gallons of high strength waste that was used to produce biogas. The R2E2 project saves customers approximately $2,000,000 per year in avoided energy costs. Year to date annual recovered costs are provided below. 2021 Recovered Costs (through September) - HSW Revenue - $248,610 - Heat Recovery - $308,472 - Electrical Offset - $1,270,290 - Total - $1,827,372 Project process alternatives (seven alternatives evaluated) were reviewed and scored by staff utilizing a multi-attribute utility analysis that included the following criteria: Operations, Social/Community Impacts, Environmental, and Financial. The cost of each alternative was estimated, including the costs of construction, operation and maintenance, engineering, and NEW Water administrative and legal costs. The costs were used to estimate the 20-year and 40-year present worth of each alternative. Sensitivity analyses focusing on areas of uncertainty (cost of energy, capital costs) were performed to further refine the cost-effectiveness for each alternative. The R2E2 alternative was selected because it had the lowest life cycle cost and had helped mitigate exposure to escalating energy prices. All of the R2E2 project improvements are currently operational, with the exception of the nutrient harvesting system. This presentation will discuss project need, systems start-up and optimization. It will also present the most current operational data, including energy recovery. Operational challenges will be presented.