Thermal hydrolysis pre-treatment combined with anaerobic digestion for energy recovery from organic wastes

To investigate the applicability and effectiveness of anaerobic digestion combined with thermal hydrolysis pre-treatment (THP), one pre-treatment condition (170 ℃/10 bar, 30 min) was set to process three different organic wastes (i.e., food waste, swine manure, and sewage sludge) under mesophilic (35 ± 1 ℃) and thermophilic (50 ± 1 ℃) temperatures. The characteristics of raw/pre-treated substrates were analyzed and biochemical methane potential (BMP) tests were performed. Results showed that THP improved organics solubilization as demonstrated by decreased VSS/VS and increased SCOD/TCOD ratios. BMP tests indicated that thermophilic anaerobic digestion (TAD) combined with THP did not significantly promote cumulative methane production (CMP) of food waste and swine manure (p > 0.05). The CMP of pre-treated sewage sludge in mesophilic anaerobic digestion (MAD) condition was higher than those of other digestion conditions. The modified Gompertz model and first-order kinetic model illustrated that THP improved methane production potential, hydrolysis rate as well as methane yield rate of swine manure and sewage sludge except for food waste; TAD had no obvious influence on those parameters. According to net energy estimation, THP enhanced energy production of methane from swine manure and sewage sludge except for food waste; TAD consumed more energy than MAD. The increased energy benefits by THP did not cover its extra energy consumptions in the combination of mesophilic and thermophilic anaerobic digestion in this study.