Anaerobic Co-digestion of Cattle Manure and Wheat Straw Mixture in Liquid State - Optimization of Mix Ratio

This study aimed at optimization of cattle manure (CM) and wheat straw mix (WS) ratio for optimum biogas production. Anaerobic co-digestion study performed on CM and WS at 5% total solids in mesophilic temperature. Anaerobic digestion has been traditionally used as an effective, environmentally sustainable and economical technology for the biological treatment of sewage sludge, which enables energy production as heat, electricity, and/or vehicle fuel, and for the stabilization of volume reduction of sludge. Wheat straw (WS) as agriculture residue and cattle manure (CM) were collected from the local dairy farms near the National Institute of Technology Patna. Biogas was collected using water displacement method. The volume of displaced water was noted down on a daily basis as it is equal to the biogas production from each reactor. CM and WS 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 observed in the reactor fed with 100% CM (100:0). A considerable amount of biogas measured up to 60:40 mix ratio (CM:WS). With the increase in proportion of WS in the mix, biogas production decreased. Reactor stability in terms of pH and volatile fatty acids 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. The modified Gompertz model is able to quantify the maximum biogas production, biogas production rate, and lag phase. While the remaining two models are useful in assessing the hydrolysis rate constant. To forecast total biogas production, three kinetic models—the modified Gompertz model, growth, and monod—were used. Modified Gompertz identified the best model among these.