Development of simplified anaerobic digestion models (SADM's) for studying anaerobic biodegradability and kinetics of complex biomass

• Co-digesting cow manure and waste paper (75:25) optimized biogas.
• Hill's based biogas yield rate model described experimental data.
• Half saturation constant was estimated as 0.228 g/L.
• Biodegradable and recalcitrant fractions were 0.628 and 0.371 respectively.

The anaerobic co-digestion of cow manure and waste paper at ambient temperature condition was observed to be optimized at a mix proportion of 75:25 respectively. The development and testing of a set of simplified anaerobic digestion models (SADM's) for this mixture revealed that the Hill's based biogas yield rate model was most appropriate in describing the kinetics of biogas production. Parameter estimation using non-linear regression revealed that the half saturation constants expressed as acidified substrate and volatile solids equivalents were 0.228 g/L and 5.340 g VS/L respectively, and the maximum specific biogas yield rate and biodegradability were 2.2 mL/g VS/day and 0.313 respectively. The coefficients “n” and “m” indicative of acidogenic bacterial adaptation for degradation and acetogenic/methanogenic bacterial cooperativity were estimated to be 1.360 and 2.738 respectively, while hydrolysis/acidogenesis was considered the rate limiting step. The need of bacterial adaptation may be an important factor to consider during anaerobic modeling of complex biomass.