The Preparation, Characterization Of Nickel-based Material And Its Application Of Catalytic Ozonation Of Bio-treated Coking Wastewater

After optimized biological treatment,the complex industrial wastewater,which still remains low concentration of organic pollutants,needs further chemical treatment.It is reported that bio-treated coking wastewater（BTCW）with 30-90 mg/L COD contains non-biodegradable nitrogen heterocyclic compounds,benzene derivatives,alkanes and polycyclic aromatic hydrocarbons and might affect adversely the subsequent desalination process.The catalytic ozonation technologies possess many advantages including small secondary pollution andstrong oxidation capacity,and are able to overcome the basic disadvantage of ozone that selectively oxidizes unsaturated organic compounds.Thus,in this work,NiO catalysts were prepared by modified hydrothermal methods upon different surfactants and applied in the mineralization of BTCW to reduce the environmental danger and achieve the complete mineralization of organic pollutants as well provide information for the application of catalytic ozonation in BTCW.The surface properties of NiO catalysts prepared by hydrothermal methods upon different surfactants were first characterized and compared by XRD,XPS,SEM etc..NiO-1 prepared by the hydrothermal method upon hexadecyltrimethylammonium（CTAB）shows relatively least aggregation and highest specific surface area.The major byproduct during many advanced oxidation processed,oxalic acid was used to test the catalytic performance of NiOs.NiO-1 showed the best catalytic performance and there were 0.8 mg/L Ni²⁺leaching in the bulk solution,which did not show obvious catalytic performance.Moreover,it was found that the acid corrosion of oxalic acid influenced adversely the stability of catalyst.The determination of active oxidation speices presented that the catalytic process is mediated by hydroxyl radicals（·OH）.The high catalytic performance of NiO-1 was attributed to high concentration surface hydroxyl density,strong ability and high electron transfer capability.In addition,the catalytic process is pH-dependent.The increase of initial p H below 7.5 could lead to the improvement of mineralization rate,but excessive pH might influence adversely the catalytic performance by reduce the contact between surface and ozone molecules and oxalic acid.Furthermore,the establishment of a kinetic prediction model based on the ozone inlet concentration,catalyst dosage and initial pH showed ozone inlet concentration and catalyst dosage were more significant factors of the reaction apparent rate than initial pH.Finally,O₃/NiO-1was applied in the treatment of BTCW.The effects of ozone concentration and catalyst dosage were observed and the evolution of COD,TOC and MOC showed that the presence of catalyst leads to a higher mineralization efficiency of BTCW pollutants compared to non-catalytic ozonation.Furthermore,the complete mineralization of BTCW was achieved after 420 min under the following conditions:ozone inlet concentration=30 mg/L,ozone flow rate=1.0 L/min,catalyst dosage=2.0 g/L.In addition,after five consecutive usages,NiO-1 could still show high catalytic performance.The spectroscopic analysis suggested that raw BTCW contained microbial by-product-like substance,tryptophan-like substance and compounds with conjugated structures,which could be significantly removed by both ozonation and catalytic ozonation.O₃/NiO-1 could removal more organic pollutants in response to the wavelength at 225-300 nm than O₃.Moreover,the production of byproducts with aliphatic C–C and O=C–O groups such as organic acids could be observed during both O₃ and O₃/NiO-1.