Zr-N-codoped TiO2 nano-photocatalyst was prepared through sol-gel method using ammonia water and zirconium nitrate as the source of N and Zr, respectively. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). XRD results showed that codoping with Zr and N elements could greatly inhibit the phase transformation of TiO2 from anatase to rutile. XPS analysis indicated that Zr4+ was incorporated into the lattice of TiO2 through substituting titanium atoms. Meanwhile, N was also incorporated into the lattice of TiO2 through substituting oxygen atoms and existed in the form of N-Ti-O. DRS revealed that the light absorption edge of Zr-N-TiO2 was significantly red-shifted to visible region, leading to a narrower band gap and higher visible photocatalytic activity. The enhanced visible activity was attributed to the well anatase crystallite, intense light absorbance in visible region and narrow band gap.

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This paper used a novel technology, BAF-SCAD, for the advanced nitrogen removal of wastewater after con. BAF stood for biological aerated filter and SCAD meant sulfur-ceramic autotrophic denitrification. The experimental results show that the BAF-SCAD system was successfully started after 2.5 months' starting up. With a NaHCO 3 dosage of 1 g/L, the BAF-SCAD system effectively removed the pollutants. Excellent nitrogen removal was achieved by nitrification in the BAF and denitrification in the SCAD. When the concentrations of NH 3 -N, NO 3 -N, TN in the influent were 10-20mg/L, 8-16mg/L, 25-30mg/L respectively, the concentrations of NH 3 -N and NO 3 -N in the effluent were below 1mg/L and the TN was 1-3 mg/L. The removal efficiency of NH 3 -N was above 95% and the removal efficiency of TN was above 90%. The COD removal efficiency of BAF was between 20%-30%, while COD in the effluent of SCAD increased slightly. The results showed a promising new approach for the biological denitrification of the secondary effluent of municipal wastewater treatment plant under low carbon source.