Effects of thermal hydrolysis on anaerobic digestion and abundance of antibiotic resistance genes during recuperative thickening digestate treatment of sewage sludge

Abstract

The effects of recuperative thickening (RT) and thermal hydrolysis during anaerobic digestion (AD) on AD performance, microbial communities and reduction of antibiotic resistance genes (ARGs) were investigated. Compared to the results in conventional AD (Phase I), biogas production increased slightly (10%) through RT (Phase II) but increased (63%) via RT with a digestate treatment system (DTS, thermal hydrolysis of thickened digestate) during AD (Phase III). Meanwhile, the three different operating conditions further influenced microbial community structures as well as efficiencies in reducing ARGs: The abundance of hydrolytic bacteria in Phase II and the abundance of acidogenic bacteria in Phase III increased, and 64.3% and 47.4% of the total sum of the relative abundance of ARGs in the substrate were removed in Phases II and III, respectively. Thus, RT-AD with DTS could represent a promising process for improved AD performance, but requires additional refinements to further reduce concentrations of residual ARGs in digestate.