Abstract
Despite the extensive research dedicated to ammonia inhibition, the effect of NH3 and NH4+ 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 NH3 or total ammonia nitrogen (TAN). Here, anaerobic digestion of two defined substrates, namely starch/NH4Cl and casein, was investigated particularly regarding the effects of different NH3/NH4+ ratios on the involved microorganisms. TAN affected bacteria, primarily gram-positive ones, whereas archaea responded largely to the NH3 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 NH3/NH4+ ratio, when feeding nitrogen-rich substrates.
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