Utilization of pumice for improving biogas production from poultry manure by anaerobic digestion: A modeling and process optimization study using response surface methodology

The aim of the present work was to optimize and to model the biogas production yield from anaerobic digestion (AD) of poultry manure (PM) using response surface methodology (RSM). The influence of total solid percentage (TS%), inoculum ratio (%), the amount of pumice (g L-1), and particle size of pumice (mm) was investigated for cumulative biogas production, methane content in produced biogas (CH4%), and the removal percentage of chemical oxygen demand (COD% removal). The results showed that RSM with central composite design (CCD) was successfully applied to predict and model the biogas production from AD of PM. From the analysis of variance (ANOVA) results, the obtained models were highly significant with coefficient values (R-2) of 0.98, 0.98, and 0.99 for cumulative biogas production, CH4%, and COD% removal, respectively. The results indicate that the obtained quadratic models are significant for the selected responses, as well as acceptable for the relationship between the investigated parameters and the responses. The optimum conditions of the investigated parameters were found by the numerical analysis method based on RSM. At the obtained optimal AD process conditions, the maximum cumulative biogas production, CH4%, and COD% removal were 8965.87 mL, 71.298%, and 68.4711%, respectively.