Green synthesis of modified polyethylene packing supported tea polyphenols-NZVI for nitrate removal from wastewater: Characterization and mechanisms

Nano-zero-valent iron (NZVI), as an electron donor, performed excellence in the reduction and remove of nitrate. However, the easy agglomeration and poor antioxidation of NZVI declined the nitrate removal and limited the application in the field of wastewater treatment. Herein, a novel composite packing of tea polyphenol, NZVI and modified polyethylene carrier (TP-NZVI/PE) was prepared and characterized, the removal efficiency of nitrate was verified, and the preliminary removal mechanism was finally investigated. The results showed that the maximum iron loading on TP-NZVI/PE composite achieved under 50 °C, pH of 5.0, 4.0 g/L of Fe²⁺, and 7.2 g/L of TP, respectively, with 3.51 ± 0.12 mg/g. NZVI presented satisfactory antioxidation and anti-agglomeration via TP encapsulation. TP encapsulation of TP-NZVI/PE composite was easily degraded by microorganisms and NZVI was exposed to nitrate during wastewater treatment, which made the reduction of nitrate possible. The nitrate removal efficiency of TP-NZVI/PE composite with microorganism was 79.88 ± 0.17%, higher three times than that of TP-NZVI/PE (25.54 ± 0.21%). The oxidized NZVI was transformed to Fe²⁺/Fe³⁺, which were prone to adsorb nitrate and then co-precipitate. It was favorable for further removal of nitrate. Results suggested a novel approach for fast and eco-friendly preparation and efficient application of NZVI.