Zinc ferrite catalysts for ozonation of aqueous organic contaminants: phenol and bio-treated coking wastewater

Abstract

Abstract The studies in ozonation catalysis present a trend in development of advanced oxidation processes (AOPs) applied to the wastewater treatment. The zinc ferrite (ZnFe 2 O 4 , ZFO) catalysts were synthesized hydrothermally (ZFO-H) and using the citrate sol–gel (ZFO-C) method with their characterization by XRD, Raman spectrum, SEM, XPS and FT-IR techniques. The objectives of this study include examining the performance of the catalysts in oxidation of phenol and pollutants in biologically treated coking wastewater (BTCW), compared to non-catalytic ozonation, and evaluating the ozonation reaction kinetics. The changes in the composition of BTCW on course of treatment were determined by ultraviolet–visible (UV) absorption and three-dimensional excitation–emission matrix spectroscopy (3DEEMs) analyses. The experimental results showed the ZFO-H catalyst accelerating the degradation of phenol for about 1.5 times as compared to non-catalytic ozonation. The catalytic activity of ZFO-H surpassed that of ZFO-C in phenol removal, attributed to the larger contact surface area and higher surface hydroxyl group density. The higher catalytic activity of ZFO-H was also confirmed by the ability of decomposing ozone and generating hydroxyl radicals ( OH). The empirical model developed in the research indicates the catalyst concentration and the ozone concentration to be the most significant factors of the reaction apparent rate; the role of pH appeared to be minor. The presence of catalysts leads also to a higher mineralization efficiency of BTCW pollutants compared to non-catalytic ozonation. The UV and 3DEEMs analysis demonstrated effective removal of the aromatic and conjugated structural compounds in BTCW by catalytic ozonation. The performance of the catalysts is determined primarily by their synthesis method defining the surface properties.