Comparison of Anaerobic Co-Digestion of Buffalo Manure and Excess Sludge with Different Mixing Ratios under Thermophilic and Mesophilic Conditions

Abstract

In this study, the main aim is to evaluate the mixing ratio of co-digestion of buffalo manure (BM) and excess sludge (ES) influenced for methane yield and digestate dewaterability. Five batch experiments with different BM and ES mixing ratios were carried out under thermophilic and mesophilic conditions. The methane yield of co-digestion of BM and ES increased by 10.1–73.5% under thermophilic conditions and 87.9–153.3% under mesophilic conditions, compared with the mono-anaerobic digestion of ES under the same conditions. Shannon and Chao1 indices showed that the bacterial species of the mesophilic digesters were more abundant than that of the thermophilic digesters. With the increase in the BM proportion in the substrate, the normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased. The NCST at thermophilic temperature (8.98–12.54 s∙g−1-TS) was greater than that at the mesophilic temperatures (5.45–12.32 s∙g−1-TS). However, the TS of sediment was not directly related to the digestion temperature. This study has shown that anaerobic co-digestion of BM and ES at the appropriate ratio (BM/ES = 1:1.5) has a significant meaning in a high methane yield.