Enhancement Methane Generation by Co-Digestion of Cow Dung and Grass (Cynodon dactylon) with Activated Sludge

Anaerobic co-digestion (AD) of Cynodon dactylon grass and cow dung was conducted with four different composition levels. To increase lignocellulose digestibility and methane yield, grass was pretreated with NaOH and thermally-modified bentonite was used to inhibit the ammonia production. The highest cumulative methane yield obtained from treatments C (0.40:0.60), D (0.60:0.40), and B (0.20:0.80) was 427 mL/ g.VS, 333 mL/g.VS, and 303 mL/g.VS, respectively, over a digestion period of 40 days at a mesophilic temperature. Treatment C showed an 89.7% increase in the methane yield with respect to the control, followed by treatment D, which recorded a 48% increase, and treatment B at a 34.6% increase. A modified Gompertz model was used to explain the methane generation scenario. The process stability parameters of the anaerobic co-digestion system, such as pH, chemical oxygen demand (COD), electrical conductivity (EC), total solids, total and free ammonia contents, and volatile solids removal were explained in depth in this study.