Enhancing methane production from chicken manure mono-digestion: Optimisation of temperature and dilution parameters via response surface methodology

Chicken manure (CM) is a nitrogen-rich waste stream with significant potential for renewable energy recovery; however, its mono-digestion is often constrained by ammonia inhibition, limiting process efficiency and scalability. This study investigates the optimisation of CM mono-digestion using response surface methodology (RSM) based on a central composite design, focusing on the effects of dilution ratio and temperature on biogas production performance. Biochemical methane potential assays were conducted to evaluate cumulative biogas production, methane composition and chemical oxygen demand (COD) removal efficiency. The developed models were statistically significant ( p  < 0.05), confirming the suitability of RSM for process optimisation. Temperature was identified as the dominant factor influencing biogas production, while the dilution ratio significantly affected COD removal efficiency. Optimal conditions were obtained at a CM : water ratio of 1 : 10 and 27 °C, resulting in a cumulative biogas production of 178 mL, a methane composition of 97%, a COD removal efficiency of 78% and an estimated methane yield of 30 mL CH ₄ /g VS. The enhanced performance under psychrophilic conditions is attributed to reduced ammonia toxicity and improved process stability. These findings highlight the importance of operational optimisation in improving energy recovery and treatment efficiency from CM. From a practical perspective, the ability to operate at lower temperatures may reduce heating energy requirements, thereby improving the economic feasibility of CM-based biogas systems. Further studies are required to evaluate long-term performance and scalability under continuous operating conditions.