Effects of mixture ratio and hydraulic retention time on single-stage anaerobic co-digestion of food waste and waste activated sludge

The biochemical methane potential (BMP) test was used to evaluate the anaerobic biodegradabilities of food waste (FW), waste activated sludge (WAS), and the mixtures having the ratios of 10:90, 30:70, 50:50, 70:30, and 90:10 (FW:WAS) on a volatile solid (VS) basis. The carbon/nitrogen (C/N) ratio and the biodegrad-ability of the mixtures improved from 6.16 to 14.14 and increased from 36.6 to 82.6% as the FW proportion of the mixture increased from 10 to 90%, respectively. The stability and performance of the single-stage anaerobic digester (SSAD) for the co-digestion of FW and WAS were investigated, operated at the hydraulic retention times (HRTs) of 10, 13, 16, and 20 days with five mixtures at 35°C, respectively. During all the experiments, there were no indication of failure such as low pH, insufficient alkalinity, ammonia inhibition, and the accumulation of volatile fatty acids (VFAs) in any of the digesters, and the buffer capacity was the highest in the digester fed with a feed mixture of 50:50. The optimum operating conditions of the SSAD were found to be an HRT of 13 days and a mixture of 50:50 in terms of the buffer capacity of the digester and the effluent VS concentration, the methane content of the biogas produced and the specific methane production (SMP). The VS removal efficiency, biogas production rate (GPR), and SMP in this condition achieved 56.8%, 1.24 m3 m-3d-1 and 0.321 m3 CH4 kg-1VSfed-1 with an organic loading rate (OLR) of 2.43 kg VSm-3d-1.