Effect of High Strength Food Wastes on Anaerobic Codigestion of Sewage Sludge

Anaerobic codigestion has been practiced at water resource recovery facilities to increase methane production, but the impact of many variables is still not well understood. In this study, the feasibility of codigesting fats, oils, and grease (FOG), and other high strength wastes (HSWs) with municipal sewage sludge was investigated. Four laboratory-scale digesters were operated at a working volume of 9.75 L, 15 days solids retention time (SRT), and at a temperature of 37 °C. Wastes including whey (cheese), juice, grease trap waste (GTW), and dissolved air flotation waste (DAF), along with municipal sewage sludge, were fed to the digesters in varying amounts. The addition of HSWs led to higher methane production at lower organic loadings. However, at higher organic loadings, the GTW appeared to be toxic to methanogens, leading to a decrease in digester pH and biogas production, and an accumulation of volatile fatty acids within the digester.