Effects of organic loading rates on the anaerobic co-digestion of fresh vinegar residue and pig manure: Focus on the performance and microbial communities

Abstract

The 70 L mesophilic semi-continuous stirred tank reactor (semi-CSTR) for co-digestion of fresh vinegar residue (FVR) and pig manure (PM) was operated for 180 days to evaluate the behavior of process stability, inhibition and recovery, as well as the succession of microbial community structures with the increasing organic loading rates (OLRs). The maximum tolerable OLR for co-digestion was determined to be 5.0 g-VS/(L·d), achieving an average methane yield (MY) of 233.77 mL/g-VS. The feeding was paused for 7 days due to the accumulation of volatile fatty acids (VFAs), and then recovered at 5.5 g-VS/(L·d) with the maximum MY of 230.09 mL/g-VS. Meanwhile, the effect of OLRs on the microbial community was analyzed. It showed that there is a significant correlation between most of the major bacteria and VFA. PCA showed that stopping feeding and reducing OLR could change the bacterial community, but not archaeal community. The aceticlastic Methanosaeta was dominant at stable stage, and gradually replaced by the hydrogenotrophic methanogen, leading to the accumulation of acetate with increasing OLR. In the recovery stage, Methanosarcina became dominant to utilize the residual acetate. Due to the vigorous aceticlastic pathway of methanogenesis, the hydrogenotrophic pathway was depressed and the H2 pressure increased, causing the accumulation of propionate in a short time. With the relative abundance of Methanosarcina increasing constantly, the VFA except propionate decreased, suggesting that Methanosarcina transformed acetate and hydrogen into methane during the recovery stage.Supplementary Material_V4.doc