Environmental Impacts and Cost Analysis of Municipal Wastewater Treatment Anaerobic Digestion Expansion Options

Authors: 
Ma, X., U.S. Environmental Protection Agency
Communities throughout the U.S. are shifting from the paradigm of waste disposal to viewing “waste” as a resource. Several industries are vying for the opportunity to utilize abundant organic waste streams. The presented research uses life cycle assessment and life cycle cost analysis to evaluate a Massachusetts wastewater treatment facility (WWTF), treating 23.5 million gallons per day, as it upgrades for resource recovery. The facility recently installed additional anaerobic digestion (AD) and combined heat and power (CHP) capacity, allowing acceptance of source separated organic (SSO) waste, boosting biogas production, and avoiding traditional food waste disposal. The planned capacity of the AD project will allow the facility to accept 40% of the current organic material available in the greater Boston region. We also analyze composting through windrow and aerated static pile (ASP) systems as an alternative disposal pathway for food waste. Co-digestion and composting are then compared to legacy food waste treatment options such as landfill and waste-to-energy combustion. The WWTF inventory data were developed using plant records and GPS-X™ modeling software. Scenario and sensitivity analyses assess the effect of SSO acceptance rate, AD performance, avoided disposal processes, and cost parameters on results. Sensitivity results demonstrate the benefit of food waste co-digestion as compared to disposal via landfilling or waste-to-energy combustion. Food waste composting requires much lower capital costs compared to co-digestion, but is not able to capture the energy potential and associated environmental benefit of food waste energy recovery through co-digestion.