Study On Electro-enzymatic Catalysis And Heterogeneous ElectroFenton For Degradation Of Refractory Organic Pollutants

Refractory organic pollutants show a dire threat to environmental security andhuman health, so their efficient removal is a hotspot and difficulty in environmentalfield. In this work, coupled with enzymatic catalysis and electro-generation ofhydrogen peroxide, a novel electro-enzymatic process was developed and applied foraqueous pentachlorophenol （PCP） removal; and based on electro-generation ofhydrogen peroxide and heterogeneous catalysis, a novel heterogeneous electro-Fentonprocess was developed and used for advanced treatment of coking wastewater. Themain contents and results are listed as follows:A novel horseradish peroxidase （HRP）-coenzyme NADH catalyzed H₂O₂/O₂oxidation system was developed. The presence of superoxide anion radical （·O₂^-） andhydroxyl radicals （·OH） were confirmed using EPR spectra in this system. Theremoval of PCP and chlorobenzene from water were studied by this system. Theparameters were optimized; the products of PCP degradation were analyzed and anew mechanism of enzyme-coenzymatic catalysis was proposed.2-ethyl, anthraquinone modified carbon nanotubes/glass carbon （EAQ/CNTs/GC）and polypyrrole/EAQ modified graphite felt （PAQ/GF） electrodes were prepared andused for electro-generation of H₂O₂. Cyclic voltametry （CV） measurements indicatedthat CNTs promotes the electron transfer process between EAQ and GC electrode;EAQ enhances the two-electron reduction reaction of oxygen on electrode. PAQ/GFas a cathode was carried out in a proton exchange membrane cell at neutral aqueoussolution, producing 15 mM H₂O₂ with 52% of current efficiency after 10 h reaction atcathodic potential of -0.5 V （vs. SCE）.A novel enzymatic electrode was prepared by immobilizing HRP and NADH onPAQ/GF. This emzymatic electrode show high activity for both H₂O₂ decompositionand electro-generation of H₂O₂ from O₂ reduction reaction. It was used for PCPdegradation in an electro-enzymatic reactor in the presence of O₂. After one hourelectrolysis, 65.6% of PCP was removed.Fe/Cu-Y350 and CuxO-AlM41-H250-O350 were prepared by ionexchange/calcination and H2 reduction/calcination methods, respectively. Theprepared catalysts were characterized by transmission electron microscope （TEM）,X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, diffuse reflectance（DR） UV-vis spectra, respectively. The activity of catalysts was evaluated by chemical probe （p-chlorobenzoic acid）-HPLC technique. Results indicated that Fe and Cu wereintroduced into the framwork of zeolite Y with original crystal form andmicrostructure, resulting in high stability and H₂O₂ efficiency;CuxO-AlM41-H250-O350 produced a nano scale （4-22 nm） Cu oxide composite, anda high steady-state concentration of hydroxyl radicals was obtained. According toradical trapping and scavenging experiments, the major reactive oxygen species was?OH, which was generated from multi-valent CuOx surface-catalyzed H₂O₂decomposition.A heterogeneous electro-catalytic reactor coupling with Fe/Cu-Y350 catalysts andPAQ/GF cathodes was assembled and used for advanced treatment of cokingwastewater after biological process. The technological parameters were optimized; theCOD, BOD, TOC, color and acute toxicity of wastewater before and afterelectro-catalytic oxidation were analyzed; and organic pollutants in wastewater wereanalyzed by GC-MS technique. The mechanism of electro-catalytic reaction was alsoproposed.A pilot scale experiment of 1m3/d was tested, and the COD value, chromaticity andpH value of wastewater effluent, in a period of 30 days, met the national first level forwastewater discharge of China.