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

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. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

High-rate mesophilic CSTR co-digestion of waste activated sludge and food waste achieved efficient methane production with a maximum yield of 12.9 L/L/day at an OLR of 48.1 g-COD/L/day. The stable operation was maintained at OLR of 50.8-52.1 g-COD/L/day and SRT of 2.56-2.63 days without VFA accumulation, highlighting the key role of the genus Methanosarcina in high-performance anaerobic digestion.