Ferrate(VI) oxidation of bisphenol E-Kinetics, removal performance, and dihydroxylation mechanism

Bisphenol E (bis (4-hydroxyphenyl) ethane, BPE), as a typical endocrine disrupting chemical, is commonly detected in source water and drinking water, which poses potential risks to human health and ecological environment. This paper investigated the removal of BPE by ferrate(VI) (Fe^VIO₄^2-, Fe(VI)) in water. Under the optimal condition of [Fe(VI)]₀:[BPE]₀ = 10:1 and pH = 8.0, a removal efficiency of 99% was achived in 180 s. Sixteen intermediates of BPE were detected, and four possible reaction pathways were proposed, which mainly involved the reaction modes of double-oxygen and single-oxygen transfer, bond breaking, carboxylation and polymerization. The double-oxygen transfer mechanism, different from traditional mechanisms, was newly proposed to illustrate the direct generation of di-hydroxylated products from parent BPE, which was demonstrated by theoretical calculations for its rationality. Significantly, NO₂^-, HCO₃^-, Cu²⁺, and humic acid, constituents of water promoted the removal of BPE. Additionally, samples from river, tap water, synthetic wastewater, and secondary effluent were tested to explore the feasibility of Fe(VI) oxidation for treating BPE in water. It was found that 99% of BPE was degraded within 300 s in these waters except for synthetic wastewater. The toxicity of BPE and its intermediates was evaluated by ECOSAR program, and the results showed that Fe(VI) oxidation decreased the toxicity of reaction solutions. These findings demonstrated that the Fe(VI) oxidation process was an efficient and green method for the treatment of BPE, and the new insights into the double-oxygen transfer mechanism aid to understand the reaction mechanisms of organic pollutants oxidized by Fe(VI).