A novel photo-assisted activated persulfate strategy for selective oxidation of ammonia nitrogen to dinitrogen using sodium silicate and sodium sulfite as regulators

Persulfate (PS)-based advanced oxidation processes (SR-AOPs) is a promising approach for the removal of ammonia nitrogen (NH3-N) from wastewater, but it suffered from the low removal efficiency and the excessive oxidation of NH3-N to nitrate (NO3−) or nitrite (NO2−) in the absence of in-situ generated chlorine radicals. Therefore, it is still a challenge to improve the efficiency of NH3-N removal and the selectivity of NH3-N oxidation products towards dinitrogen (N2) by SR-AOPs without chlorine radicals. Herein, a novel photo-assisted activation of SR-AOPs involving sodium silicate (Na2SiO3) and sodium sulfite (Na2SO3) was developed for NH3-N removal from wastewater. In this system, Na2SiO3 was acted as a green buffer to maintain NH3-N in the form of un-ionized ammonia (NH3) with strong reducibility, promoting the efficiency of NH3-N removal as well as ensuring the neutral effluent by receiving the H+ from PS activation. Na2SO3 could inhibit the excessive oxidation of NH3-N by regulating the redox potential of the solution and generating hydrated electrons (eaq−) under light (hv) irradiation, enhancing the selectivity of NH3-N oxidation products towards N2. 100 % of NH3-N removal efficiency and more than 98 % of N2 selectivity were obtained after 30 min at the initial pH of 3–9 and the initial NH3-N concentration of 30 mg N/L. Based on the quenching experiment, EPR test and probe experiment, the HO and SO4− were the main reactive oxygen species (ROS) to be responsible for NH3-N oxidation. This study proposed a new approach for treatment of wastewater containing NH3-N by SR-AOPs.