Unveiling long-term combined effect of salinity and Lead(II) on anammox activity and microbial community dynamics in saline wastewater treatment.

[Display omitted] • The SAAs was inhibited by 15–20 % at Pb(II) concentrations of 0.1 to 0.5 mg L−1. • The SAAs increased at salinity below 10 g/L but declined with higher salinity. • Combined high salinity and Pb(II) reduced nitrogen removal performance and SAAs. • Combined salinity and Pb(II) enhanced EPS secretion with decreased PN/PS ratio. • Decreased Candidatus Kuenenia and enhanced denitrification under combined stresses. The study assessed the effect of salinity and lead (Pb(II)) on the anammox sludge for nitrogen removal from saline wastewater. Results showed decreased nitrogen removal and specific anammox activity (SAA) with elevated salinity and Pb(II). SAA reduced from 541.3 ± 4.3 mg N g−1 VSS d−1 at 0.5 mg/L Pb(II) to 436.0 ± 0.2 mg N g−1 VSS d−1 at 30 g/L NaCl, further to 303.6 ± 7.1 mg N g−1 VSS d−1 under 30 g/L NaCl + 0.5 mg/L Pb(II). Notably, the combined inhibition at salinity (15–20 g/L NaCl) and Pb(II) (0.3–0.4 mg/L) exhibited synergistic effect, while higher salinity and Pb(II) aligned with independent inhibition models. Combined inhibition decreased protein/polysaccharides ratio, indicating more severe negative effect on anammox aggregation capacity. Metagenomics confirmed decreased Candidatus Kuenenia, and enhanced denitrification under elevated salinity and Pb(II) conditions. This study offers insights into anammox operation for treating saline wastewater with heavy metals. [ABSTRACT FROM AUTHOR]