Enhanced biological phosphorus and nitrogen removal by high-concentration powder carriers: extracellular polymeric substance, microbial communities, and metabolic pathways.

In this study, diatomite, activated carbon, and iron-carbon (Fe-C) were used as biological carriers for the integrated fixed-film activated sludge process. Biomass, pollutant removal efficiency, and extracellular polymer were tested, and the effect of nitrogen and phosphorus removal, enzyme activity, and microbial diversity were studied after the sludge retention time was changed. The mechanism of carrier enriching microorganism and promoting pollutant degradation was studied. The results showed that the addition of these three carriers contributed to the enrichment of nitrifying bacteria in the system, and the NH-N removal efficiency was above 98%. Diatomite and Fe-C could improve pollutant removal by increasing the activity of the electron transfer system. The abundance of denitrogenation-related reductases and the enzymes synthesizing poly-β-hydroxybutyrate was increased in activated carbon. The addition of Fe-C increased the abundance of denitrifying phosphate-accumulating organisms by approximately 25% and the removal efficiency of total phosphorus by 12.61-14.88% at the end of the long-term operation.