Probing the performance and mechanisms of Congo red wastewater decolorization with nanoscale zero-valent iron in the continuing flow reactor

Abstract

Rapid and efficient decolorization is great challenging for wastewater treatment, and nanoscale zero-valent iron (nZVI) was recognized as an environmental-friendly and economical-cost agent for effective decolorization of textile wastewater. Herein, the performance and mechanisms of Congo Red (CR) wastewater treatment with nZVI were probed in a continuous flow nano-iron reactor (NIR), which included the “reaction, separation and reuse” process. CR wastewater (initial concentration up to 500 mg·L−1) was successfully decolorized by nZVI in the NIR during the 125 d continuous running period. The color removal efficiency achieved 98.59%, accompanied with a large removal capacity of 6.64 mg-CR/g-nZVI at an average low nZVI dose (0.075 g-nZVI/L-CR). The decolorization mechanism of CR wastewater was ascribed to the chromophore groups (–N=N–) breaking, the final productive products were 4-Amino-1-naphthalene sulfonic acid and 4,4′-diaminodiphenyl, which were proved by liquid chromatography coupled to mass spectrometry, X-ray photoelectron spectroscopy, UV–Vis spectrophotometer, infrared spectroscopy. Decolorization efficiencies were up to 77.82% and 87.95% on average for two actual textile wastewater in the NIR, during the 83.5 h and 445 h continuous running period. This work provides proof that the nZVI technology can offer tremendous potential for the decolorization of recalcitrant organic dye wastewater.