Salinity-driven heterogeneity toward anammox distribution and growth kinetics

Anaerobic ammonium oxidation (anammox) has been widely applied for biological nitrogen removal in freshwater systems, and there is a potential for its extension in saline water systems. In this study, the abundance and biodiversity of anammox bacteria were investigated in both saline and freshwater full-scale sewage treatment plants (STPs). The anammox bacteria were widely found in four tested STPs with abundance of 10 5 –10 7 copies per mL of 16S rRNA gene. Phylogenetic results showed that Ca. Scalindua and Ca. Brocadia dominated in saline and freshwater STPs, respectively. Ca. Kuenenia dominated in one of freshwater STPs. However, redundancy discriminate analysis (RDA) indicates the distribution of Ca . Kuenenia in both saline and freshwater conditions. To further elucidate these observations, the Monod model was integrated with Gauss equation for the evaluation of salinity-induced kinetics. Model results reveal that when nitrite concentration ( S NO2 − ) is higher than nitrite affinity constant ( K NO2 − ), salinity (over ~ 3.0%) is responsible for Candidatus Scalindua dominance over Candidatus Kuenenia . Conversely, in nitrite-depleted conditions ( K NO2 − ≥ S NO2 − ), high nitrite affinity leads to the predominance of Ca . Scalindua in all salinities. This study provides fundamental insights into saline anammox applications.