Effect of Food Waste Co-Digestion on Dewatering, Cake Quality and Digestion Parameters

Addition of organic wastes to municipal anaerobic digesters to enhance biogas production (co-digestion) has been investigated over the past several years. However, the effect of such addition to dewaterability of digested solids and biosolids odor production has been less understood. This study evaluated the impact of food waste addition on digester operational parameters as well as dewaterability and biosolids odor. Further, changes in microbial community in the digester were also investigated.Bench scale studies were performed by adding various amounts of processed food waste (25 to 58 % of sludge VS) to sludge from Orange County Sanitation District (OCSD), Fountain Valley, CA. Compared to control disgester (no food waste) the gas production as well as specific methane yield increased by up to 110 and 40% in food waste added digesters. Food waste addition altered the Archaea and bacterial population in the digesters. Further, at lower food waste loading the net dewatered cake mass decreased in comparison to the cake from control digester by approximately 5%. At the highest food waste addition, the net cake mass increased by approximately 20%. The biosolids odor decreased significantly at higher food waste addition. Finally, a preliminary economic analyses indicated that a payback period of less than 2 years for OCSD due to implementation of food waste co-digestion program.