Biogas Production and Microbial Communities in the Anaerobic Digestion of Sewage Sludge Under Hydrothermal Pretreatment with Air and a Catalyst

Hydrothermal pretreatment (HTP) of sewage sludge (SS) has been shown to improve the subsequent biogas production by anaerobic digestion (AD), but the effect of catalysts on HTP performance was less explored. This study intended to investigate the SS pretreatment by wet air oxidation (WAO) with the addition of K2CO3 as a catalyst on the performance of methane production by AD. WAO was found to improve the solubilization of SS, the soluble chemical oxygen demand, dissolved organic carbon, and total dissolved nitrogen. The methane yield from WAO increased from 202 mL/gVSin with no catalyst added to 277 mL/gVSin with 10 wt% of K2CO3 added at 180 °C with 30 min of residence time. Under this pretreatment condition, the highest methane production rate could achieve 15.8 mL/gVSin day, and the percentage of methane reached 73%. The structure of the microbial community involved in the AD was affected by the residence time, working gas, and catalyst of the HTP process. The results showed that Bacteroidetes, Bacteroidia, and SC103 were the dominant phylum, class, and genus of bacteria, respectively, of almost all of the samples. In addition, the most abundant archaeal order was Methanosarcinales, while Methanosaeta was the dominant archaeal genus of most of the samples. However, Methanosarcina largely increased the relative abundance, corresponding to the amount of K2CO3 catalyst used. The findings in this study demonstrated the potential use of K2CO3 during WAO of SS and implied the link between shift of methanogen community and the enhanced methane yield in AD.