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 biodegradability 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 degrees 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(-3) d(-1) and 0.321 m3 CH4 kg(-1) VS(fed)(-1) with an organic loading rate (OLR) of 2.43 kg VS m(-3) d(-1).

Biochemical methane potential (BMP) tests have been carried out to determine the anaerobic digestibility of the waste activated sludge (WAS) and the sludge pretreated by NaOH (PWAS). The optimal NaOH dosage was determined to be 45 meq NaOH/L. The maximum SCOD solubilization was 27.7, 31.4 and 38.3% at the temperatures of 25, 35 and 55 degrees C respectively after 4 hours reaction. The final methane yield of simulated food waste (SFW) was 430 ml CH4/g VS(added), and those of PWAS (25 degrees C), PWAS (35 degrees C) and PWAS (55 degrees C) was 274, 286 and 310 ml CH4/g VS(added) respectively after 20 days. The figures were 66%, 73% and 88% higher than that of WAS. The methane production in anaerobic co-digestion is considerably affected by the fraction of SFW and PWAS in the feed. The anaerobic digestibility of the feed mixture (SFW with PWAS) is higher than that of the feed mixture (SFW with WAS). Anaerobic co-digestion of food waste with the PWAS is found to be an attractive option to reduce the solid waste volume with improved methane recovery.

No abstract

Korean food waste was treated with a single-stage anaerobic codigester (SSAD) using waste activated sludge (WAS) generated from a municipal wastewater treatment plant. The stability and performance of the system was analyzed. The C/N ratio was improved with increasing food waste fraction of feed mixture. The pH, alkalinity, and free ammonia nitrogen concentration were the parameters used to evaluate the digester's stability. The experimentally determined values of the parameters indicated that there were no methane inhibitions in the digester. Digester performance was determined by measuring the total chemical oxygen demand TCOD), volate solids (VS) removal, methane content in biogas, methane production rate (MPR), and specific methane productivity. Methane content in biogas and MPR were significantly dependent on hydraulic retention time (HRT) and ratio of food waste to WAS. The methane content in biogas decreased at shorter HRT or higher organic loading rate (OLR) with increased food waste fraction. Concerning the performance of the codigester, the optimum operating condition of the SSAD was found to be at an HRT of 10 d with a feed mixture ratio of 50% food waste and 50% WAS. A TCOD removal efficiency of 53.6% and a VS removal efficiency of 53.7% were obtained at an OLR of 5.96 kg of TCOD/(m3 d) and 3.14 kg of VS/(m3 d), respectively. A maximum MPR of 1.15 m3 CH4/(m3 d) and an SMP of 0.37 m3 CH4/kg of VSfeed were obtained at an HRT of 10 d with a methane content of 63%.