Anaerobic co-digestion of molasses vinasse and three kinds of manure: A comparative study of performance at different mixture ratio and organic loading rate

Studies have shown that animal manures have a promoting effect in improving anaerobic digestion (AD). In this study, swine manure, chicken manure, and cattle manure (named in order SM, CM, and BM groups) were selected as co-digestion substrates of molasses vinasse (MV). The AD performance of three combinations was compared at the same organic loading rate (OLR) of different ratios (manure SCOD: MV SCOD of 1:1, 1:3, 1:5, 1:7, 1:9, stage I), and at the same ratio with increased OLR (ratio of 1:7, stage II) conditions. In stage I, all groups worked well for the 1:7 ratio, with CM performing better than the other groups. As the ratio increased to 1:9, the AD performances of all groups obviously decreased, while the BM group was more stable, with a soluble chemical oxygen demand (SCOD) removal rate 11.7% higher than for the SM group and 12.2% for CM group. In stage II, the SCOD removal efficiency of the CM group was the best and reached 70.9 ± 0.4%. The microbial community analyses indicated that the hydrogenotrophic methanogen Methanobacteriaceae were dominant in the CM group. Synergistaceae with the function of acetogenesis, and Anaerolineaceae with the function of hydrolyzing polysaccharides, were enriched in stages I and II, respectively. In stage I with the ratio of 1:9, the Anaerolineaceae and acetotrophic methanogens Methanosarcinaceae played an important role in the BM group. This study utilized waste as a mixed raw material without increasing the cost of raw materials, the optimal mixed co-digestion ratio and the tolerance to high OLR impact of the stable and efficient MV anaerobic system reactor were determined. The results provide a reference for the treatment of animal manure as a substrate for anaerobic co-digestion of MV and also provide promising potential for the engineering application of anaerobic co-digestion of MV in biogas plants.