Metagenomic Binning Revealed Microbial Shifts in Anaerobic Degradation of Phenol with Hydrochar and Pyrochar

Abstract

Phenolic compounds, which are difficultly degraded, are one of the main toxic threats faced in the anaerobic digestion (AD) process. It has previously been reported that hydrochar/pyrochar produced by the hydrothermal liquefaction/pyrolysis of biomass can enhance AD by promoting direct interspecific electron transfer (DIET). The present study investigated the effects of different hydrochars and pyrochars on the anaerobic degradation of phenol and provided deep insights into the related micro-organisms at the species level through genome-centric metagenomic analysis. Compared with the control experiment, the addition of hydrochar and pyrochar shortened the lag time. However, hydrochar created a large increase in the maximum methane production rate (Rm) (79.1%) compared to the control experiments, while the addition of pyrochar decreased Rm. Metagenomic analysis showed that the addition of carbon materials affected the relative abundance of genes in the phenol anaerobic degradation pathway, as well as the species and relative abundance of phenol degrading micro-organisms. The relative abundance of key genes for phenol degradation, such as bsdB, bamB, oah, etc., under the action of hydrochar was higher than those under the action of pyrochar. In addition, hydrochar-enriched phenol degradation-related bacteria (Syntrophus aciditrophicus, etc.) and methanogen (Methanothrix soehngenii, etc.). These micro-organisms might improve the phenol degradation efficiency by promoting DIET. Therefore, hydrochar had a more significant effect in promoting anaerobic degradation of phenol.