Shift in bacterial community structure in response to salinity in a continuous anaerobic ammonium oxidation (anammox) reactor

The effect of gradual salt adaptation on nitrogen removal performance was examined in a continuous flow anaerobic ammonium oxidation (anammox) process. Specific anammox activity (SAA) batch test was conducted to observe the effect of salinity shock loads. SAA rapidly reduced from 100% to 2.3% when salinity increased from 0 g.L-1 to 5.0 g.L-1 NaCl. On the contrary, high total nitrogen removal efficiency (TNRE) of 85% was obtained when salt concentrations gradually increased up to 25.0 g.L-1 NaCl, after 264 d of the continuous anammox operation. Then, the additional increase of salinity by 2.5 g.L-1 resulted in critical negative effect of 63.8% reduction in TNRE. Candidatus Jettenia sp. was dominant as a salt-tolerant anammox species in the salt ranges of 0-27.5 g.L-1 NaCl. In contrast, Candidatus Kuenenia stuttgartiensis was observed at 10-27.5 g.L-1 NaCl with smaller relative abundance than that of Ca. Jettenia sp. This indicates that Ca. Kuenenia sp. would build limited niche in the competition with Ca. Jettenia sp. under sudden increase of salinity stress. Interestingly, heterotrophic bacteria became dominant in autotrophic nitrogen removal process in response to the increase in salt concentration, which could be a cause of anammox system failure.