82 / 2021-06-30 18:08:28

Start-up of a 300 L thermophilic dry anaerobic digester for treating distilled grain waste: performance and dynamics of microbial communities

Distilled grain waste; Thermophilic; Dry anaerobic digestion; Loading rate; Microbial communities

Distilled grain waste (DGW) eluted from the Chinese liquor making process poses serious environmental problems. Previous study has converted DGW to biogas by a thermophilic dry anaerobic digestion process in lab-scale. To scale-up the process, this study attempts to start a thermophilic dry anaerobic digester for treating DGW in a short time. A 300-L digester was initial inoculated 240-L mesophilic sludge with TS content of 10.5% and DGW was fed from a loading rate of 2 g-volatile total solid (VTS)/L/day. Although volatile fatty acids (VFAs) accumulated at the start period, they quickly disappeared due to the adaptation of microorganisms to the new substrate. The loading rate was increased from 2 to 10 g VTS/L/d step by step to enhance the sludge TS content to 20% in a short time. Results showed that the digester kept stable when the TS content ≤ 20%, with averaged biogas yield of 463.3 ml/g-VTS_add (CH₄ content of 55.3%). The sludge TS content in the digester reached 20% on the 40^th day. Afterwards, the TS content exceeded 20% when non-dilute DGW was fed, however, the digester became unstable at a higher loading rate of 10 g-VTS/L/d, reflected by deteriorated biogas production and VFAs accumulation. The performance recovered by reducing the TS content to about 20% via adding tap water and operated at a lower loading rate of 2 g-VTS/L/day. The bacterial and archaeal community structures shifted significantly after starting the thermophilic dry anaerobic digestion, and an obvious shift from mesophilic microorganisms to thermophilic microorganisms was observed: genera Methanosaeta and phylum Firmicutes predominated in archaeal and bacterial community in the inoculum slude, respectively. When DGW was fed, genera Methanothermobacter and Methanosarcina became dominant in archaeal community, and the bacterial community was dominated by Thermotogae, Bacteroidetes and Firmicutes.