Anaerobic Digestion of Agricultural Waste Using Microbial Inocula: Performance and Characterization of Bacterial Communities Using 16S rRNA Sequencing Approach

Anaerobic digestion is considered a beneficial treatment for biogas production (BP). To improve the performance of this bioprocess, the addition of well-selected inocula could be an interesting approach that affects the overall efficiency of the BP. In this study, the reactor performance and energy analysis of liquid-state anaerobic digestion of cattle manure (CM) at high solids concentration (TS%) (94.87%) with six different inocula-two cellulosic (C.I1, C.I2), one lipidic (Li.I), two lactic (La.I1, La.I2), and one saccharidic (Sacc.I)-were investigated. The results showed that inocula improved the biogas production and yield during anaerobic digestion of CM by 109%, 86%, and 52.4%, respectively, when the cellulosic (C.I1), lipidic (Li.I), and lactic (La.I1) inocula were added, compared with the substrate production alone at a substrate/inoculum (S/I) ratio of 5:3 (v/v). The addition of inocula in an appropriate range is useful for the performance of the anaerobic digestion process. In our study, the 16S rRNA sequencing approach was followed to investigate microbial community structure and diversity in the substrate CM and the three inocula that showed a significant improvement in biogas production (C.I1, Li.I, and La.I). The most abundant bacterial populations were found to be Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria, with different abundance percentages. Interestingly, C.I1, which resulted in the highest biogas production, showed the dominance of Cyanobacteria (53.44%) belonging mainly to the class Nostocophycidae. This study highlighted the role of inocula in improving biogas production from cattle manure (CM) thanks to their microbial diversity.