Responses of halophilic microbial communities to changes in salt composition: Comparison between autotrophic nitrification and heterotrophic ammonia assimilation biosystems

[Display omitted] •Both systems achieved high N removal efficiency under varying salt ion composition.•Increasing SO42− proportion improved sludge settleability, CSH and EPS content.•Increasing SO42− proportion enriched AOB, genes hao and amoA in the AN system.•The dominant heterotroph in the HAA system varied with changes in salt composition.•Higher robustness and microbial cooperation in HAA system compared to AN system. The concentration and proportion of chlorine (Cl−) and sulfate ions (SO42−) in actual high salinity wastewater exhibit significant fluctuations due to their diverse sources. This study compared the response of halophilic autotrophic nitrification (AN) and heterotrophic ammonia assimilation (HAA) sludges to changes in salt composition. The results demonstrated that both the AN and HAA systems maintained high ammonia removal efficiency even when exposed to mixed salt ions or pure sulfate conditions. Increasing the concentration of SO42− resulted in an increase in extracellular polymeric substances content, sludge settleability, sludge hydrophobicity, and the relative abundance of Nitrosomonas in the AN system (from 2.3% to 10.4%). The dominant heterotrophic bacteria in the HAA system underwent turnover in response to changes in salt composition conditions. The robustness and the cooperation between microorganisms of the HAA system surpassed those of the AN system. This study provides scientific foundation for treating multi-ion high salinity wastewater.