Biohydrogen production by anaerobic co-digestion of municipal food waste and sewage sludges

Food waste (FW), primary sludge (PS) and waste activated sludge (WAS) were characterized and found to be complementary in the concentrations of carbohydrates, total Kjeldahl nitrogen (TKN), PO₄–P and some metal for biological hydrogen production. Moreover, FW was found to have low pH buffering capacity while the values for PS and WAS were relatively higher. An anaerobic toxicity analysis (ATA) derived from a methanogenic ATA protocol showed that these waste materials had no toxicity to hydrogen production. Adding phosphate buffer to the FW significantly improved hydrogen production while initial pH was 7.0. Co-digestion of FW and sewage sludge was studied using a batch respirometric cultivation system. All combinations of the feedstocks (FW+PS, FW+WAS and FW+PS+WAS) showed enhanced hydrogen production potential as compared with the individual wastes. A mixing ratio of 1:1 was found to be the best among the ratios tested for all three co-digestion groups. A hydrogen yield of 112 mL/g volatile solid (VS) added was obtained from a combination of FW, PS and WAS. This yield was equivalent to 250 mL/g VS added if only FW contributed to hydrogen production. The reason for the enhancement of hydrogen production was postulated to be multifold in which the increase in buffer capacity in the co-digestion mixture was verified.