High-rate mesophilic co-digestion with food waste and waste activated sludge through a low-magnitude increasing loading regime: Performance and microorganism characteristics

Abstract

To achieve a high-rate operation of co-digestion with waste activated sludge (WAS) and food waste (FW) for biogas production, a low-magnitude loading regime was investigated in a mesophilic continuous stirred tank reactor (CSTR) over long-term operation for approximately 600 days. The results showed that high-rate mesophilic CSTR co-digestion was realized using the low-magnitude loading regime. A maximum methane production of 12.9 L/L/day was achieved in the mesophilic CSTR co-digestion at an organic loading rate (OLR) of 48.1 g-COD/L/day. Moreover, high-efficiency and stable mesophilic CSTR co-digestion can still be performed at OLR of 50.8–52.1 g-COD/L/day and solid retention time (SRT) of 2.56–2.63 days without volatile fatty acid (VFA) accumulation. A high methane yield, hydrolysis conversion ratio, and methanogenic activity and the key anaerobic digestion enzymes were all maintained during the high-rate operation period. 16S rRNA gene sequencing results indicated that the relative abundance of the class Clostridia and genus Methanosarcina could reach 85.0% and 97.3%, respectively, corresponding to a high hydrolysis rate and VFA conversion rate. The metabolic capability of the genus Methanosarcina was the main reason for the highly efficient and stable operation of the mesophilic CSTR co-digestion. Using metagenomic analysis, Methanosarcina barkeri and Methanosarcina flavescens were established as the main methane-producing species during high-rate mesophilic CSTR co-digestion. The enrichment of the genus Methanosarcina through a low-magnitude loading regime is a promising method for realizing the highly efficient and stable operation of co-digestion with WAS and FW for biogas production at low retention times.