Microbial community dynamics associated with biomass granulation in low-temperature (15 °C) anaerobic wastewater treatment bioreactors

Granular biofilms underpin the operation of several categories of anaerobic wastewater treatment bioreactors. Recent studies have demonstrated the feasibility of treating both industrial and domestic wastewaters at their discharge temperatures (usually <18 °C), thereby avoiding the heating expenses of mesophilic (20–45 °C) or thermophilic (45–65 °C) treatments. Previous low-temperature trials used mesophilic inocula and little information is available on the viability of low-temperature anaerobic granulation. Six laboratory-scale, expanded granular sludge bed bioreactors (R1–6) were operated at 15 °C (R1–2 and R4–5) and 37 °C (R3 and R6). R1–3 were fed glucose-based wastewater and R4–6 were fed volatile fatty acid-based wastewater. Quantitative real-time PCR and qualitative denaturing gradient gel electrophoresis of 16S rRNA genes identified the dominance of Methanomicrobiales (mainly Methanocorpusculum-like organisms) during low-temperature granulation. Granulation only occurred in glucose-fed bioreactors. The results suggest that (i) granulation is feasible in low-temperature bioreactors; (ii) carbohydrate decomposition likely favoured granulation, (iii) Methanocorpusculum-like organisms play a critical role in low-temperature granulation.