Technoeconomic Analysis of Energy-Producing Small-Scale Wastewater Resource Recovery Facility Using Anaerobic Codigestion and Renewable Energy Technologies

Many conventional wastewater treatment plants are exploring strategies to transform into energy-producing water resource recovery facilities (WRRFs). Retrofitting small-scale facilities with renewable energy technologies can offer favorable economics due to lower capital relative to large scale capital construction. Anaerobic digestion of sludge alone often falls short of producing sufficient methane for net-energy-positive operation. This study evaluates the technoeconomic feasibility of integrating four renewable energy strategies to enable net energy production: (1) anaerobic codigestion of sludge with food scraps and fats, oils, and grease; (2) replacing existing boiler technology with combined heat and power (CHP); (3) integrating photovoltaic (PV) solar electricity; and (4) integrating pyrolysis of dewatered biosolids. Accordingly, a baseline and three technology scenarios were assessed using data from an 8710 m3/d WRRF with existing anaerobic digestion. Energy balances and cost modeling were used to estimate renewable energy contributions and 25 year net present value (NPV). Results suggest that a combination of CHP and PV is optimal, achieving net-energy-positive conditions with the least negative NPV (−$10.7M). Pyrolysis reduced solids handling costs by ∼85% but introduced greater capital cost and operational complexity. These findings indicate that small-scale WRRFs can feasibly become net-energy producers, though robust waste characterization and strategic technology integration are essential for economic viability. This comparative framework provides a transferable analytical approach for evaluating energy and cost trade-offs in emerging WRRF configurations, supporting evidence-based design and policy decisions.