Enhancing the production of biogas through anaerobic co-digestion of agricultural waste and chemical pre-treatments

Abstract

Large amounts of agricultural solid wastes (ASWs) and animal dung are produced annually causing serious environmental problem that requires proper treatment. The present study proposes a strategy for optimizing the anaerobic co-digestion of ASWs and cow dung (CD), identifies the key factors governing the co-digestion performance and evaluates the effect of NaHCO3 alkalinity treatment on improving the economy and performance of anaerobic digestion (AD). The results revealed that the highest cumulative methane production (CMP) of 297.99 NL/kgVS can be generated by co-digestion of ASWs and CD at a ratio of 60:40. Further improvement was achieved via alkalinity treatment with 1.0 g of NaHCO3/gVS leading to decrease in lignin, cellulose, and hemicellulose contents of feedstock by 3.5%, 10.5% and 15.9%, respectively, converting them to soluble fractions and improving the CMP by 11.2–29.7% based on substrate quality. The improved CMP in the chemically treated substrates reflects a 19% increase in the generated revenue. The kinetics of the AD process was successfully fitted to modified Gompertz model with very low standard deviation residuals (SDR) ≤ 5.21 and R2 ≥ 0.979. Results confirm that the proposed strategy is an effective method for producing biogas from co-digestion of ASWs and CD.