Effects of ammonia on propionate degradation and microbial community in digesters using propionate as a sole carbon source

BACKGROUND Propionate accumulation may lead to digester failure. This study aimed to investigate the effect of ammonia, a metabolic product of protein, on propionate degradation. The shift of microbial community was also investigated. RESULTS Propionate accumulated over the experimental period in the reactor with a total ammonia nitrogen ( TAN ) concentration of 2.5 g N L −1 , as a result the digester failed after 4 hydraulic retention times ( HRT ) at an organic load rate ( OLR ) of 0.8 g propionic acid ( HPr ) L −1 d −1 . The average HPr degradation rate was below 54% during the fourth HRT , while >97% of the degraded HPr was converted to methane. The reactor without ammonia stress did not experience HPr accumulation and OLR was increased stepwise to 1.2 g L −1 d −1 at the 8th HRT . The average HPr degradation rate and methane recovery rate of this reactor in the last HRT was 99% and 74%, respectively. According to the shifts of microbial community, acetoclastic methanogen was more vulnerable to ammonia than hydrogenotrophic methanogen CONCLUSION TAN concentration of 2.5 g N L −1 inhibited propionate degradation more severely than methanogenesis. The loss of abundance of Clostridiaceae and Syntrophobacter might be the main reason for the poor performance under ammonia stress. © 2017 Society of Chemical Industry