Recently, the advanced oxidation processes (AOPs) based on sulfate radicals (SRs) for organics degradation have become the focus of water treatment research as the oxidation ability of SRs are higher than that of hydroxyl radicals (HRs). Since the AOP-SRs can effectively mineralize organics into carbon dioxide and water under the optimized operating conditions, they are used in the degradation of refractory organics such as dyes, pesticides, pharmaceuticals, and industrial additives. SRs can be produced by activating persulfate (PS) with ultraviolet, heat, ultrasound, microwave, transition metals, and carbon. The activation of PS in iron-based transition metals is widely studied because iron is an environmentally friendly and inexpensive material. This article reviews the mechanism and application of several iron-based materials, including ferrous iron (Fe2+), ferric iron (Fe3+), zero-valent iron (Fe0), nano-sized zero-valent iron (nFe0), materials-supported nFe0, and iron-containing compounds for PS activation to degrade refractory organics. In addition, the current challenges and perspectives of the practical application of PS activated by iron-based systems in wastewater treatment are analyzed and prospected.

This research was conducted to investigate the treatment of hexavalent chromium (Cr(VI)) by iron powder (Fe(0)) columns of simulated permeable reactive barriers with and without calcium carbonate (CaCO 3). Two columns filled with Fe(0) were used as Cr(VI) removal equipment running at a flow velocity of 10 ml/min at room temperature. After 200 days running of the two columns, the results showed that Fe(0) was an effective material for Cr(VI) reduction with an average removal rate of above 84.6%. The performance of Column 2 with CaCO 3 was better than Column 1 without CaCO 3 in terms of average Cr(VI) removal rate. The presence of CaCO 3 buffered the increasing pH caused by Fe(0) corrosion in Column 2 and enhanced the removal rate of Column 2. Scanning Electron Microscopy (SEM) images of Fe(0) in the three stages of running of the two columns illustrated that the coat layer of Column 1 was a little thicker than that of Column 2. Energy-dispersive spectrometry (EDS) results showed that the surface of Fe(0) of Column 2 contained more chromium elements. Raman spectroscopy found that all iron oxide was generated on the Fe(0) surface of Column 1 and Column 2 and chromium class objects were only detected on Fe(0) surface in Column 2.

A B S T R A C TDynamic and static test methods were used to investigate the removal efficiency of trichloroethylene (TCE) from ground water by different media of zero-valent iron (ZVI), two kinds of granular activated carbon (GAC), and a mixture of ZVI and GAC. The test results showed that ZVI, GAC, and the mixture of ZVI and GAC could effectively remove TCE. Under static conditions, the TCE removal rate by ZVI was 68.32%, the TCE removal rate by coconut shell GAC was 55.2%, and the TCE removal rate by ZVI + GAC was 90%. Under dynamic station, the mass ratio of one mixture of ZVI and GAC had the best TCE removal rate of over 85% at a flow rate of 25 ml/min.

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