Bioaugmentation for overloaded anaerobic digestion recovery with acid-tolerant methanogenic enrichment

This study aims to investigate the performance of bioaugmentation with an acid-tolerant methanogenic culture to recover deteriorated anaerobic digestion caused by organic overloading. The function of bioaugmentation was evaluated in terms of substance metabolism, microbial community structure, and gene function. Our findings demonstrate that routine bioaugmentation effectively recovered the failing digester by degrading accumulated volatile fatty acids and increasing pH. In contrast, a non-bioaugmentation reactor (control) did not recover by itself, while abiotic augmentation restored the digestion performance temporarily but the digester failed again at an organic loading rate of 1.5 g L^-1 d^-1. Using whole genome pyrosequencing analysis, we found that after bioaugmentation, the populations of Methanothrix (acetoclastic methanogens) and Methanolinea (hydrogenotrophic methanogens) increased significantly, which may be the main contributors for the positive effect on methane production. On the genic level, bioaugmentation may enhance the function of genes involved in cell motility, signal transduction mechanisms for methanogens, and energy production and conversion for bacteria.