Investigating the Process Constraints of the Addition of Codigestion Substrates to Temperature Phased Anaerobic Digestion

The City of Tacoma is evaluating the feasibility of a co-digestion program at its Central Treatment Plant. As part of this evaluation an understanding of the impact the addition of codigestion substrate will have on the digestion process is required. This study presents data associated with testing of co-digestion substrates in the temperature phased anaerobic digesters that serve as the primary mechanism for solids reduction at CTP. Bench-scale, continuous systems and batch (Biochemical Methane Potential), tests were used to evaluate process impacts and methane generation potential from a variety of substrates. BMP testing indicated that there is the potential for toxicity with some substrates, but data was insufficient to determine the mechanism. BMP testing also indicated that most of the substrates tested had greater methane potential than the raw sludge solids. Bench-scale testing showed that, for the loading rates tested, there were no adverse effects and there is potential for synergistic enhancement of solids destruction for some materials.