Anaerobic Co-Digestion on Dairies in Washington State

This factsheet briefly reviews the role of co-digestion within anaerobic digestion (AD), explains the potential regulatory concerns, and details the solid waste handling permit exemption conditions. An overview of other major regulatory requirements for AD facilities operating on dairies is also provided. Anaerobic digestion facilities that digest dairy manure have begun to co-digest pre-consumer organic wastes (such as food-processing wastes) to increase biogas productivity, improve digester performance, and increase revenue. Legislation passed in Washington state in 2009 provides that AD operations located on or near dairies that co-digest organic wastes with manure may qualify for an exemption from obtaining a solid waste handling permit provided they follow specified guidelines designed to address nutrient management and other potential concerns. Co-digestion that is not in compliance with the requirements could jeopardize the digester’s conditional exemption from a solid waste handling permit or obligate the Washington State Department of Ecology (“Ecology”) to regulate the dairy farm as a solid waste disposal site.

Download PDF