Elucidating the elevated salinity effect on removal of carbon and nitrogen in coupling aromatic degradation to anaerobic denitrification

Denitrification-dependent aromatics anaerobic degradation in saline environments have been unsuspected recently. In this study, the elevated salinity inhibition on denitrification-dependent degradation of aromatic compounds was investigated in an up-flow anaerobic fixed bed (UAFB) reactor, microbiota associated with aromatics and nitrogen conversion, and osmoregulation triggered by different salinities were also deciphered. Results showed that increasing salinity from 0% to 3% significantly limited the removal of organics and nitrate, decreasing from 72.47% to 72.20%, 25.14%, and 19.80%, respectively. The gene abundance of nirB decreased from 0.011 to 0.015% to 0.003–0.005%, inhibiting the nitrate reduction process under salt stress. Methane yield also significantly declined from 27.33 to 58.18% to 1.19–2.85%, which was attributed to acetate accumulation and increased ammonia concentration under salt stress. And the enriched genera Pelotomaculum, candidate_division_Zixibacteria, Syntrophus, Mesotoga, and candidate_division_Hyd24-12 under salt stress were involved in the salinity inhibition on methanogenesis. Increasing salinity facilitated the osmoregulation capacity of compatible solutes, and glutamate, and trehalose were dominant at 3% salinity, accompanied by Na+/K+ expulsion. It provided a deeper understanding of the simultaneous removal of carbon and nitrogen under saline stress.