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 the abundance of Clostridiaceae and Syntrophobacter might be the main reason for the poor performance under ammonia stress.  Correspondence to: Y Sun, No. 2 Nengyuanlu, Tianhe District, Guangzhou 510640, PR China. E-mail address: [email protected]