Thermophilic anaerobic digestion: Effect of start-up strategies on performance and microbial community

Effects of two different start-up methods were compared during conversion from mesophilic to thermophilic anaerobic digestion of sewage sludge. During the batch operation, a transient increase in both total bacterial concentration and relative abundance of thermophilic bacteria in R1 (a one-step increase method) resulted in 34% higher volatile solids (VS) removal efficiency by R1 compared to R2 (a step-wise increase method). Meanwhile, higher total archaeal concentration and increased relative abundance of thermophilic archaea in R2 were attributed to 65% higher methane production by R2 compared to R1. The same trends for VS removal and methane production were observed during the subsequent continuous mode, although the microbial composition of the two reactors became similar. These findings may prove helpful for determining the preferred start-up method for thermophilic anaerobic digestion: a one-step method can be proposed for higher VS removal efficiency, or a step-wise method can be selected for enhanced methane production.