Short-term changes in the anaerobic digestion microbiome and biochemical pathways with changes in organic load

Practical-scale Anaerobic Digestion (AD) systems experience fluctuations in organic loading rate due to waste treatment demand variations. These lead to unstable AD operation which is manifested by low CH4 yield and low pH due to accumulation of volatile fatty acids. Low pH is known inhibit the growth and activity of methanogens which consequently lead to failure of methanogenesis. The microbial community in the samples subjected to varying organic load conditions with starch and hipolypeptone as substrate was analyzed using QIIME2. Both the microbial richness and evenness decreased with increasing organic load. The biochemical pathways predicted by PICRUSt2 were clustered to identify those that increase in abundance with increasing organic load and vice versa. The contributions of microbial groups to predicted pathways were also analyzed. The variations in the microbial community and the predicted biochemical pathways were used to explain the microbial interactions and mechanisms in AD operating at high organic load. Based on these, an overall pathway of utilization of the substrate was proposed providing better understanding of the behavior of anaerobic digesters experiencing high organic load conditions.