Strengthening operational stability of decentralized rural sewage bio-trickling filters under fluctuating influent loads by activating microbial oxidative stress in oligotrophic regions

Bio-trickling filters are commonly applied for the on-site treatment of decentralized rural sewage under fluctuating influent loads. However, the existence of oligotrophic layers with organic content below 50 mg/L constrains further improvements in treatment efficiency. To overcome the limitations of oligotrophic layers, biomass density and metabolic activity were enhanced by leveraging microbial adaptive responses to oxidative stress. This regulation strategy was implemented by incorporating a ventilation interlayer, achieving an 11.3% increase in total nitrogen removal efficiency. Under fluctuating influent conditions, denitrification was significantly enhanced, accompanied by a 3.4% increase in the abundance of denitrifying bacteria (DNB). Simultaneously, the concentrations of extracellular polymeric substances (EPS) increased under oxidative stress, thereby reinforcing biofilm integrity and enhancing interspecies mass transfer within the microbial community. Heterotrophic bacteria and algae utilized EPS as a medium for metabolite exchange, providing supplemental substrates for DNB in oligotrophic layers, thereby enhancing their growth and denitrification efficiency. Biological interactions were regulated by microbial oxidative stress, primarily manifested as enhanced metabolic activity, including carbon metabolism, mass transfer, and quorum sensing. The microbial response to oxidative stress collectively mitigated the adverse effects of loading fluctuations on treatment performance. This study provides a theoretical foundation for enhancing the treatment efficiency and stability of decentralized rural sewage treatment systems.