Performance and microbial community analysis of anaerobic sludge digestion enhanced by in-situ microaeration

The effectiveness of in-situ microaeration was investigated with varied air dosages [0–25 mL/(L·d)] to enhance mesophilic anaerobic digestion (AD) of sludge in semi-continuous systems in terms of specific biogas production and volatile solids (VS) removal rate, focusing on performance evaluation, microbial community analysis, and underlying mechanisms. The optimal dosage of 12.5 mL/(L·d) increased specific biogas production by 15.8 ± 7.3% and enhanced VS removal by 18.3 ± 1.6%. In-situ microaeration stimulated activity of hydrolytic enzymes, enlarged sludge particle size, and improved sludge dewaterability. MiSeq sequencing analysis showed that dominant bacterial and archaeal communities were remarkably different between in-situ microaeration and obligate AD process. The presence of oxygen enriched relative abundances of Deltaproteobacteria, Anaerolineae, Clostridia, Synergistia and Caldilineae, enabling the acid-producing process to metabolize more types of substrates. Due to the selective enrichment, in-situ microaeration significantly enriched aceticlastic methanogens rather than hydrogenotrophic methanogens in the AD reactor. Analysis of coupling microaeration pretreatment and in-situ microaeration for anaerobic digestion indicated that excessive microaeration decreased VS removal rate and methane yield owing to substrates consumption by facultative bacteria. In-situ microaeration-based AD could be a promising process for sludge treatment and bioenergy recovery.