Experimental evaluation of biogas production from anaerobic co-digestion of cactus cladodes, cow dung, and goat manure

Anaerobic co-digestion of organic wastes and plant biomass generates an environmentally friendly energy source. Anaerobic co-digestion of cow dung (CD), goat manure (GM), and cactus cladodes (CC) was investigated under mesophilic laboratory conditions. A 14-day-long daily biogas production potential and methane content were evaluated for the three substrates co-digested at different mix ratios. Physicochemical properties showed significant differences between the raw and digested substrates. Biogas production started after the first day of anaerobic digestion for all substrates, with the peak observed near day fourteen. The anaerobic co-digestion of 66.7% GM and 33.3% CC substrate mixture produced the highest biogas yield. The cumulative biogas production study also revealed that the same substrate combination achieved better biogas yield. The anaerobic digestion of CD, GM, and CC showed a significant increase in biogas yield followed by a reduction in volatile and total solid contents. The 100% CC, 33.3% CC+66.7% CD, 33.3% CC+66.7% GM, and 33.33% CC+33.33% CD+33.33% GM anaerobic digestions achieved biogas with methane content (%) of 56.02, 72.6, 56.65, and 67.95, respectively. The 33.33% CC+33.33% CD+33.33% GM anaerobic co-digestion achieved the highest methane content compared to other substrates. The CC+CD+GM and CC+GM mixtures had a C/N ratio ranging from 20 to 30, contributing to better biogas yield with more methane content than substrates deviating from such a ratio. For all substrates, the methane content of the biogas ranged from 50 to 72.6%. The study also revealed that the co-digestion of CC with GM resulted in a better cummulative biogas yield and cumulative methane content.