Anaerobic Co-digestion of Urban Sewage Sludge with Agricultural Biomass

Three different types of urban sewage sludges (the mixed sludge, the dewatered secondary sludge and the sludge filtered by screens) were used for individual anaerobic digestion and co-digestion with agricultural biomass. The initial TS level (4%) and substrate to inoculum ratio (3:1) were maintained into all runs at mesophilic conditions, and the co-substrates was mixed at the recommended VS ratio of 1:1 (sludge: straw under the co-digestion conditions. It was found that the mixed sludge exhibited prominent anaerobic digestion performance, selected as a potential reagent for the co-digestion with biomass. The total volume of the produced methane from co-digestion of the mixed sludge and wheat stalk reached to 187.01 +/- 3.27 mL g(-1) VSadded, which was about 1.52 times higher than that from the individual digestion of the sludge. The experimental value of methane yield from co-digestion of the mixed sludge with wheat stalk is about 9.46% more than that of the estimated value, imply the enhanced interactions between the sludge and biomass during the co-digestion process. The pH of the co-digestion system of the mixed sludge and the wheat stalk was maintained at a relevant stable value around 6.50. It indicated that the buffering capacity of the digestion system could improved by adding the mixed sludge. The modified Gompertz model and the first-order kinetic model were proposed to simulate the co-digestion process between the mixed sludge and agricultural straw. The estimated kinetic parameters indicated that the maximum releasing rate of methane was significantly increased during the co-digestion process. [GRAPHICS] .