Unravelling the effects of temperature shifts on microbial communities and biogas production of digested sewage sludge anaerobic digestion

Anaerobic digestion (AD) is an effective method to generate renewable energy from domestic wastewater via biogas production. AD is heavily dependent on temperature since it impacts the microbial communities, which in turn determines the stability of the AD process. This study investigated how microbial community structure changed during a stepwise temperature upshift from 37 degrees C to 41 degrees C in fed-batch serum vials using digested sewage sludge as inoculum and glucose-based substrate. Results showed that there was a 9% decrease in methane production when the temperature was shifted from 37 degrees C to 39 degrees C. Despite the lower methane yield, the methane content at 39 degrees C is higher than the content at 37 degrees C, followed by a 41% decrease in CO2 production. This condition indicates the activity of hydrogenotrophic Methanobacterium that consumed CO2 to produce methane and syntrophic Acetomicrobium that consumed CO2 to produce acetate to support acetoclastic methanogen, which was dominated by Methanothrix. The abundance of methanogens declined significantly after the temperature was shifted to 41 degrees C followed by a decrease in biogas production. These findings exhibited how in a certain range of temperatures; the growth of methanogens was inhibited which further led to the decline in overall biogas production despite the versatility of syntrophic acetogens as their supports.