Anaerobic co-digestion of steam-treated Quercus serrata chips and sewage sludge under mesophilic and thermophilic conditions

The biodegradation of Quercus serrata chips was evaluated by anaerobic digestion under various steam explosion conditions. In continuous experiments, untreated chips (W0) and chips steam-treated at less than 1.0 MPa (W1) and 2.0 MPa (W4) were co-digested with sewage sludge (S1 and S2) taken from two different wastewater treatment plants. The apparent methane yield of W1 and W4 co-digested with S1 (thermophilic) was 261 dm3/kg VS (volatile solids) and 248 dm3/kg VS, respectively. The apparent methane yield of W4 co-digested with S2 was 258 dm3/kg VS (mesophilic) and 271 dm3/kg VS (thermophilic). Methane production was inhibited by W0 due to components released during hydrolysis. The methane conversion ratio of pretreated chips obtained in batch experiments varied from 40.5% to 53.8% (mesophilic) and from 49.0% to 63.7% (thermophilic). The methane conversion ratio increased with decreasing acid-soluble lignin content in the chips.