Composite carrier enhanced bacterial adhesion and nitrogen removal in partial nitrification/anammox process

The rapid start-up and stable operation of one-stage (Partial nitrification/anammox) PN/A process for low-ammonium wastewater are difficult to be achieved, and many carriers are designed to solve this problem. Here, a composite carrier was developed, in which sepiolite and non-woven fabrics were assembled in polypropylene spherical shells. At the start-up phase, PA reactor using the composite carriers reached a higher nitrogen removal rate of 134.50 +/- 19.60 mg center dot N center dot L-1d-1, in contrast to that of 48.85 +/- 19.64 mg center dot N center dot L-1d-1 in the PB reactor without sepiolite carriers. When the final influent ammonium concentration of PN/A process is 100 mg/L, the total nitrogen removal efficiency can reach 72 +/- 0.03%. High biomass immobilization ability of composite carrier was evidenced by the greater adsorp-tion trend between sludge and sepiolite than that between sludge and non-woven fabrics, where hydrophobic interac-tion and Van der Waals interaction played a major role. Extracellular protein (PN) content and the ratio of PN and extracellular polysaccharide of samples in PA were significantly higher than those in PB, verifying higher biofilm for-mation ability on the composite carrier. The composite carrier also increased the abundance of dominant bacteria in PN/A process, especially AOB, the relative abundance of which reached 46.11 %. And it increased the abundance of essential functional genes for nitrogen conversion as their perfect acid neutralizing effects. This study is of great signif-icance in improving the start-up speed and stable operation of this process.