Impact of biochar prepared at different pyrolysis temperatures on the methane production and microbial community structure of food waste anaerobic digestion

Abstract

Biochars were prepared through the pyrolysis of sawdust at 300 °C, 500 °C, and 700 °C, respectively, under oxygen-limited conditions. The basic physicochemical properties of biochars were explored by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), surface area and porosity analyzer (BET), and Fourier-transform infrared spectrometer (FTIR). The effects of biochar addition on the methane yield and microbial community structure of anaerobic digestion of food waste were also investigated. SEM images showed that biochar had a honeycomb-like pore structure, EDS analysis showed that the C content in the biochar tended to increase, and the O contents tended to decrease with the increasing temperature. The specific surface area of biochars increased from 1.2014 m²/g (300 °C) to 326.8435 m²/g (700 °C). FTIR analysis showed that the number of different surface functional groups decreased with the increasing temperature. The addition of biochar could increase the cumulative methane volume by 11.63%–25.18%. High-throughput sequencing results showed that biochar addition could increase the relative abundance of Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria, and Spirochaetota, which were associated with the degradation of refractory organic matters. Meanwhile, biochar addition could enrich the relative abundance of methanogens participating in direct electron transfer (Methanosaeta and Methanosarcina), and methanogens producing methane through multiple pathways (Methanobacterium and Methanosarcina). The addition of biochar derived at 700 °C significantly increased the relative abundance of Methanobacterium and Methanosarcina from 1.96% and 0.70% (control group) to 32.68% and 64.69%, respectively and improved methane production by transforming acetoclastic/hydrogenotrophic methanogenic pathways to more metabolically diverse methanogenic pathways.