Dynamic response of partial nitritation-anammox systems to salinity stress with additional carbon input for stable...

This study investigated the response and adaptation mechanisms of the partial nitritation-anammox (PNA) process under salinity stress, with additional carbon input introduced to evaluate its influence on nitrogen removal pathways and microbial community dynamics. Building on a baseline experiment with an influent salinity of 8 g/L, different levels of carbon were added to examine effects on community structure, extracellular polymeric substance (EPS) composition, and overall nitrogen conversion. The PN/A system maintained relatively stable nitrogen removal despite variations in C/N ratio. Specific anammox activity (SAA) assays and functional gene analyses indicated that the anammox pathway persisted throughout the 136-day operation, although its contribution declined with increasing carbon input. At higher COD levels, competition for nitrite intensified, favoring heterotrophic denitrifiers and leading to a shift in the dominant nitrogen removal pathway from autotrophic anammox to heterotrophic denitrification. Nevertheless, this metabolic shift enabled the system to sustain a total nitrogen removal efficiency of around 80 %, reflecting the resilience of PN/A under salinity stress even at lower C/N ratios. Systematic monitoring of microbial activity and EPS indicators revealed key physiological and metabolic adaptations that enhanced sludge stability and functional robustness. These findings provide valuable insights into microbial adaptation under salinity stress and highlight practical strategies for optimizing PN/A technology in saline wastewater treatment systems with variable carbon inputs.