Enhancing biogas production from poultry waste: kinetics of co-digestion with cow rumen and grass

Nigeria's poultry industry generates substantial waste, posing environmental and health challenges. Anaerobic digestion (AD) offers a solution, converting this waste into biogas. However, poultry dung (PD) alone has suboptimal carbon-to-nitrogen (C/N) ratio (∼19.77), limiting biogas yield due to potential ammonia inhibition. This study investigates the enhancement of biogas production through co-digesting PD with carbon-rich substrates: cow rumen (RM) and grass (GR). Various ratios in batch digesters under mesophilic conditions were considered over a 28-day retention time. Each experiment was conducted in two batches: the first utilised water in the gas collection system to quantify total biogas production, while the second employed a sodium hydroxide solution in the gas collector to selectively absorb CO 2 and determine methane yield. Results demonstrated that co-digestion significantly improved performance compared to mono-digestion, with PD:RM (3:1) yielding the highest biogas production at 168.7 ml/g VS, and PD:RM (4:1) producing the highest methane yield at 68.6 ml/g VS attributed to an optimised C/N ratio and the introduction of robust microbial consortia from the rumen. In contrast, PD:GR (4:1) recorded the lowest biogas yield while PD:GR (8:1) produced the lowest methane yield. The Modified Gompertz model was fitted to the cumulative biogas and methane production dataset. Strong fitting metrics were obtained indicating excellent Gompertz-type kinetics. This study concludes that co-digesting PD with RM at a 3:1 ratio is a highly effective strategy for maximising biogas production, offering a viable pathway for waste-to-energy conversion and enhancing circular economy practices on poultry farms. • Co-digestion of poultry dung (PD) with cow rumen (RM) significantly enhances biogas yield. • PD:RM ratio of 3:1 identified as optimum for biogas production. • Five kinetic models applied to evaluate and predict digestion trends. • Derived power-law correlation accurately forecasts PD:RM biogas yield under mesophilic conditions. • Temperature shown to dominate, with minimal influence from substrate to water ratio.