Benefits and Costs of Co-Digestion for a large Utility

CDM Smith Inc. (CDM Smith) recently completed an evaluation for the Massachusetts Water Resources Authority (MWRA) to explore the benefits and costs of co-digestion of wastewater biosolids and other organic wastes at the Deer Island Treatment Plant (“DITP”). This study was very timely since the Massachusetts Department of Environmental Protection intends to ban the landfilling or incineration of some source-separate organics such as food wastes from supermarkets and food-producing industries. The study examined the types and characteristics of organic wastes that might be available, the logistics of transporting the wastes to the plant, the required modification of plant facilities, the expected additional biogas production, and the side stream impact of co-digestion on the wastewater treatment process (sidestream impacts), impacts on biosolids subsequent dewatering, thermal drying and biosolids product marketability.The MWRA’s objectives were to make better use of existing assets, reduce reliance on purchased power and increase revenues to help stabilize user rates. Co-digestion would also assist the State of Massac husetts in their goal of increasing recycling rates. The State intends to ban the incineration or landfilling of source-separated organics (SSO) potentially diverting up to 350,000 tons per year (317,500 tonnes per year) by 2020. SSO would typically include food wastes from commercial and industrial sources such as supermarkets, restaurants, and food producers.