Combined thermochemical and fermentative destruction of municipal biosolids: a comparison between thermal hydrolysis and wet oxidative pre-treatment

In this study the comparative destruction of municipal biosolids using thermal hydrolysis (140 or 165 °C) and wet oxidation (220 °C) was followed by biological degradation via mesophilic anaerobic digestion (36 °C). Wet oxidation (WO) destroyed more than 93% of the VSS, while thermal hydrolysis (TH) at 140 and 165 °C destroyed 9% and 22%, respectively. Combined TH and anaerobic digestion resulted in approximately 50% VSS destruction. The ultimate methane potential of the combined fractions from the thermal hydrolysis at 140 and 165 °C improved by 12-13% relative to the untreated control sample. Methane production from the WO material was 53% of the control yield and wholly attributable to soluble organic carbon in the liquid fraction, indicating that the WO destroyed all putrescible carbon from the solids fraction. Point sampling during the BMP assay revealed that methanogenic development, not solids hydrolysis, was the kinetic barrier during anaerobic digestion in this study.