Co-digestion of tannery waste activated sludge with slaughterhouse sludge to improve organic biodegradability and biomethane generation

Abstract

A novel approach was used to overcome inhibition of anaerobic digestion of tannery waste activated sludge by co-digesting with slaughterhouse sludge. The seasonal characteristics of the tannery sludge varied significantly. Macronutrient ratios were typically not ideal for anaerobic digestion, mainly due to an over-abundance of nitrogen. In addition, potentially inhibitory concentrations of metals were present. Optimal co-digestion with 50% (vol./vol.) slaughterhouse sludge achieved a CH4 yield of 215mLCH4/gVS, and biodegradability of 55.7% VS, 45.5% TS and 48.2% COD. This resulted in a synergistic increase of ≥59.4% in biodegradability and 156% in CH4 yield compared to mono-digestion of tannery waste activated sludge. Furthermore, the regression of the cumulative CH4 yield using the Logistic, Cone and modified Gompertz model (adj R2≥0.998) showed an increase of 20.4–21.9%, 58.6–252%, and 164% in the ultimate CH4 yield, maximum CH4 production rate and the specific rate constant respectively, and 59.3% reduction of the lag phase. An alternative cleaner production technique that vertically integrates the value chain improves solid waste management and provides an income stream was demonstrated through this co-digestion strategy.