Simultaneous removal of nitrogen and phosphorus from urban sewage by synthetic zeolites adsorption: performance, characterization, and mechanism

It is difficult for the urban sewage effluent after secondary treatment to satisfy the standard of urban sewage reuse and recycle, which has a low concentration of nitrogen and phosphorus greatly leading to serious water eutrophication and environmental pollution. This study novelty proposed a kind of synthetic zeolites for effectively removing nitrogen and phosphorus in-depth from urban sewage, the characterization and adsorption mechanism were studied. Results showed an appropriate synthetic zeolites addition (3.0-6.0 g center dot L-1) could result in a high removal efficiency (TN: 60.32%, NH4+-N: 77.5%, PO43--P: 99.9%). Simultaneously, the X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller analysis showed that the synthetic zeolites were mesoporous materials with large specific surface area and uneven pore-size distribution. Further, the adsorption isotherms followed the Freundlich model (R2 = 0.99), thereby confirming a heterogeneous adsorption of nitrogen and phosphorus by the synthetic zeolites. The PO43--P adsorption was complexation effect between PO43- and aluminum complexes in the synthetic zeolites, and NH4+-N adsorption by the synthetic zeolites was ion exchange between NH4+ and Na+. Finally, the equilibrium adsorption capacity of recycled synthetic zeolites proved a good reusability by showing an equivalence to that of initial synthetic zeolites. This study provided a potential strategy for cost-effective use of zeolites on urban sewage treatment.