Optimization of operating parameters for biogas production using two-phase bench-scale anaerobic digestion of slaughterhouse wastewater: Focus on methanogenic step.

Abstract

The objective of the present study was an optimization of operating parameters and the performance of the methanogenesis reactor in phased anaerobic digestion (AD) of slaughterhouse wastewater at 37.5°C. Accordingly, the feedstock of the methanogenic reactor was effluent from the hydrolytic-acidogenic reactor operating at HRT of 3-days and OLR of 1789 mg/L. The methanogenesis phase was also investigated at different hydraulic retention time (HRT) values ranging from 12 to 3days at 3-day intervals, and organic loading rates (OLR) of 149, 199, 298, and 596mg of COD/L. The methanogenesis reactor effluent concentrations of TN, TP, PO4-3, SO4-2, and S2-2 were ranging between 424-464, 83-117, 63-86, 130-197, and 0.98-1.02mg/L, respectively. The removal efficiencies of TN and TP were vary from 10-17% to 17-21%, respectively. The average biogas production was 125 ± 16, 150 ± 10, 185 ± 4, and 154 ± 17mL at HRT of 12, 9, 6, and 3days, respectively. Methane quality (%) and yield (mg/L of COD) were 55-67% and 0.02-0.03, respectively. Furthermore, the average stability indicator parameter values of (total volatile fatty acid (TVFA) = 520 ± 19mg/L, total alkalinity (TotA) = 1424 ± 10mg/L, TVFA:TotA. Ratio = 0.36, salinity = 1172mg/L, pH = 6.92) and performance indicator parameters removal efficiency (RE) for (chemical oxygen demand (COD) = 81%, volatile solid (VS) RE = 95%, biogas production = 185 ± 4mL, methane yield = 0.03 per mg COD consumed) were achieved at HRT of 6days and OLR of 298mg of COD/L. Low removal efficiencies of TP and TN at all HRT/OLR were observed for the methanogenic reactor signifying further treatment system.