Anaerobic co-digestion of raw glycerol and swine manure: microbial communities

In the present study, we evaluated the biogas production from the anaerobic co-digestion of raw glycerol (RG) in combination with swine manure (SM) and the interaction of the microbial community during anaerobic co-digestion. In the same way, different RG and SM concentrations were examined in the range of 6 to 15 g L−1 and 7.5 to 22.5 g L−1, respectively. According to the results, the highest values for biogas yield and methane yield were observed in test 1(6 g RG/7.5 g SM) with 340 mL g−1 COD, test 2 (6 g RG/22.5 g SM) with 330 mL g−1 COD, test 4 (15 g RG/22.5 g SM) with 344 mL g−1 COD, and test 5 (3.75 g RG/15 g SM) with 328 mL g−1 COD. Although the concentration of substrates increases, glycerol remains between 20 and 21% of RG for both tests (2 and 5). An increase in the concentration of RG (> 21% w/w) generated inhibitory effects for the co-digestion process since there was an overload of organic acids, which increase the impurity concentration and lower the biogas yield. Thus, the microbial consortium is a function of the organic load of the RG/SM ratio. The greater the concentration of RG, the higher the population of clostridium and low biogas yield in anaerobic co-digestion.