Efficient and low-cost removal of dissolved organic phosphorus by visible light-enhanced Ti electrocoagulation with self-generated rutile photocatalysts.

Phosphorus is recognized as a major pollutant in municipal and domestic wastewater, but the effective removal of organic phosphorus (OP) using conventional wastewater treatment technologies is difficult. Herein, a novel visible light-enhanced Ti electrocoagulation (EC) technology was proposed for the removal of OP using 2-amino-ethyl phosphonic acid (AEP) as a model compound to elucidate the removal efficiency and mechanisms. The results showed that the irradiation under visible light (670 Lux) effectively enhanced the removal of AEP by Ti EC. The phosphorus removal efficiency in the NaCl electrolyte was much higher than in NaNO3 and Na2SO4 electrolytes due to the low corrosion potential of the Ti anode and generated reactive chlorine species (RCS) in the NaCl electrolyte. Additionally, nanometer-sized dispersed colloids were formed in Ti EC, with small-sized and medium-sized polymers identified as predominant Ti flocculation species. The calculated band-gap energy of Ti flocs containing rutile TiO2 using UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) was 2.65 eV. The positron annihilation lifetime and X-ray photoelectron spectroscopy (XPS) data revealed the vacancy clusters and Ti3+ defects in Ti flocs as the species responsible for the visible light photocatalysis. Quenching and electron paramagnetic resonance (EPR) tests indicated the involvement of both direct oxidation on the Ti anode and indirect oxidation by •OH and RCS in the AEP degradation, providing details of the AEP degradation pathways and mechanisms including electrocoagulation, direct oxidation, indirect oxidation, and visible light photocatalysis. Furthermore, Ti EC displayed excellent treatment performance toward binary mixtures containing phosphate and AEP, other organic phosphorus (> 94 %), and real water samples (> 87 %) during 1-hour tests, with a low cost (0.304 USD/m3, CD 10 A/m2) operation charge. Overall, the proposed Ti EC can efficiently remove soluble non-reactive phosphorus (sNRP) and soluble reactive phosphorus (sRP) from water and wastewater, promising for practical field applications.