Liquid State Anaerobic Co-digestion of Cattle Manure and Wheat Straw at Various Mix Ratios for Optimal Biogas Production

Abstract

Anaerobic codigestion study was performed on cattle manure (CM) and wheat straw (WS) at 5% total solids in mesophilic temperature. CM and WS were mixed on the basis of total solids in six ratios, namely, 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. The highest biogas production of 170.89 mL/g-vsadded was observed in the reactor fed with 100% CM (100:0). A considerable amount of biogas was measured up to 60:40 mix ratio (CM:WS). With the increase in proportion of WS in the mix, biogas production was decreased. Reactor stability in terms of pH and volatile fatty acids were also decreased with increase in the proportion of WS. The last three mix ratios showed low biogas production due to the less methanogenic activity caused by the low pH. Three kinetic models, namely modified gompertz model, growth and monod were employed to predict cumulative biogas production. Among these, modified gompertz was found the most suitable model.