Abstract
Processing poultry slaughterhouse wastewater as a biogas substrate is a sustainable solution. The current study aimed to optimize methane production from poultry slaughterhouse wastewater at various hydraulic retention times, biochar addition levels, and biochar addition types. Optimization of the anaerobic digestion process was determined through response surface methodology with central composite design. The input variables were hydraulic retention times (10, 20, and 30 days), biochar levels (5, 10, and 15 g/L), and biochar types (chicken litter and rice straw). Meanwhile, the response variable was methane production. The results revealed that the resulting central composite design model was significant (p < 0.05) with an R-squared of 0.94, indicating a high model suitability. The analysis of variance showed that hydraulic retention times, biochar levels, and biochar types significantly affected methane production (p < 0.05). Based on optimization, the highest methane production was achieved at a 30-day hydraulic retention times, a biochar level of 15 g/L, and a biochar type of rice straw, which was 473.00 mL/g volatile solid. These results emphasize the importance of determining the correct hydraulic retention times and biochar addition (level and type) to optimize methane production.