Osmoprotectants boost adaptation and protect methanogenic microbiome during ammonia toxicity events in continuous processes

The excess membrane-permeable free ammonia nitrogen lead to intracellular proton imbalance and increase the energy requirement of membrane transport in methanogenic archaea, which is considered to be the major source of ammonia inhibition. This study is, for the first time, using different osmoprotectants to alleviate ammonia toxicity in continuous anaerobic reactors. The anaerobic microbiome osmoadaptation process and its role to the potential methanogenic recovery are also assessed. Three osmoprotectants (i.e., glycine betaine, MgCl2 and KCl) were respectively introduced in continuous stirred-tank reactors after they were exposed to high ammonia levels, namely RGB, RMg, RK, while a control reactor (RCtrl) operating at the same ammonia levels was also used. The results showed RGB, RMg, RK and RCtrl suffered 39.0%, 36.6%, 39.9% and 36.2% methane production loss, respectively after ammonia was introduced. Osmoprotectants addition improved significantly methane production by up to 68.9%, 54.3% and 32.2% for RGB, RMg and RK, respectively contrary to RCtrl, where methane production increased by 13.6% under the same conditions. The recovered methane production was maintained in RGB and RMg for at least four HRTs, even after the addition of osmoprotectants was stopped, due to the methanogenic microbiota formed by osmoadaptation process, with dominant species of Methanoculleus spp.