Microbial adaptation to high ammonia environment in submerged anaerobic membrane bioreactor under volatile fatty acids and ammonia stresses

Anaerobic membrane bioreactor (AnMBR) is a high-rate bioreactor which is preferred over other configurations due to its potential to completely decouple solid retention time from hydraulic retention time. However, limited information is available on the bioreactor behavior under stressed environment, particularly during the startup period. The objective of this study was to investigate the effects of ammonium (NH4+) and organic loading rate (OLR) on the digestion performance and microbial population of submerged AnMBR. The findings revealed that high NH4+ was positively correlated with high methane concentration while high OLR increased methane production. The microbial analysis showed that both bacteria and archaea were influenced by the change of NH4+ and OLR. Particularly, at high OLR, Bacteroidetes were shown to be more sensitive to high NH4+ than Firmicutes, and Chloroflexi tolerated NH4+ even up to 2.5 g/L. Moreover, NH4+ was possibly the first driving factor in the change of methane production pathways from acetoclastic methanogenesis to hydrogenotrophic and methylotrophic methanogenesis. Membrane biofouling was also caused mainly by bacterial community (Firmicutes and Chloroflexi), while the contribution of archaeal community was minimal (Methanosaetaceae).