Influence of NH and NH on anaerobic digestion and microbial population structure at increasing total ammonia nitrogen concentrations.

Despite the extensive research dedicated to ammonia inhibition, the effect of NH and NH on each anaerobic digestion stage and the associated microorganisms is still not completely understood. In the past, the focus was mainly on methanogenesis and either on NH or total ammonia nitrogen (TAN). Here, anaerobic digestion of two defined substrates, namely starch/NHCl and casein, was investigated particularly regarding the effects of different NH/NH ratios on the involved microorganisms. TAN affected bacteria, primarily gram-positive ones, whereas archaea responded largely to the NH concentration. These sensitivity differences are attributed to differences in the corresponding cell-membrane structures. A TAN decrease via stripping performed in two full-scale agricultural biogas plants resulted in increased bacterial diversity, with a pronounced increase in the propionate acetogens' abundance. Based on these data, it is suggested that inhibition can be avoided and processes stabilized in biogas plants by adjusting the NH/NH ratio, when feeding nitrogen-rich substrates.