Advanced Treatment Of Bio-treated Coking Wastewater By Granular Activated Carbon Activated Peroxymonosulfate Oxidation Process

After the biological treatment,the COD and color of the coking wastewater effluent cannot satisfy the new“Emission standard of pollutants for coking chemical industry”?GB16171-2012?,meanwhile,it restricts effluent for the use of recycling within the coking plant.The bio-treated effluent of coking wastewater still contains some organic pollutants that are not easily degraded by microorganisms.Most of these substances with highly toxic and carcinogenic properties could threaten ecological safety and human health.Therefore,it is necessary to carry out advanced treatment of coking wastewater.In this paper,aimed at the advanced treatment for the bio-treated coking wastewater from the coking plant in Changzhi City,Shanxi Province,the static experimental study was carried out using granular activated carbon?GAC?activated peroxymonosulfate?PMS?oxidation technology.Some factors of effecting GAC catalyzed PMS oxidation of bio-treated coking wastewater were studied which included GAC dosage,KHSO₅ dosage and initial p H.The adsorption and oxidation of GAC on PMS under optimal conditions were investigated.The decomposition rate of PMS in GAC/PMS system was studied,as well as the recycling situation of GAC.The comparison of the activation properties about the three common oxidants by GAC was investigated.The degradation mechanisms was explained by analyzed some representations of specific surface area,Fourier transform infrared spectroscopy,GC/MS and three-dimensional fluorescence spectroscopy.Based on the static experimental study,dynamic experiments were carried out using homemade activated carbon columns.The effects of flow rate and KHSO₅ dosage on the dynamic treatment of bio-treated coking wastewater were investigated.GAC adsorption and GAC activated PMS oxidation system were used to compare the treatment performance for bio-treated coking wastewater.The conclusions were as follows:?1?In the static experimental study,the optimal conditions for the advanced treatment of bio-treated coking wastewater with PMS oxidation catalyzed by GAC were:normal temperature?25°C?,initial pH value of 5,GAC dosage of10 g/L,KHSO5 dosage of 2 g/L,and reaction time of 5 h.Under the optimal conditions,up to 75.7%,80.3%,and 96.0%of TOC,UV254,and color were removed over a 5-h period,respectively.Owe to the obvious synergistic effect,the removal effect of GAC/PMS system for bio-treated coking wastewater was better than only PMS and GAC systems.PMS oxidation system and GAC/PMS system could effectively decolorize bio-treated coking wastewater,which was better than GAC adsorption system.The decomposition of PMS in the GAC/PMS system followed a first-order kinetics behavior and had a good fitting result with linearly dependent coefficient R²>0.98.Almost half of the removal rate of TOC and UV₂₅₄54 was retained after four uses of GAC.After four times of repeated use of GAC,however,the color removal rate remained at a relatively high level.In the GAC/PMS system,the GAC adsorption capacity for removing organic pollutants gradually decreased with the increase of the number of reuse,but the contribution of PMS oxidation activated by GAC to the degradation of organic pollutants remained basically unchanged.In the GAC/PMS system,the catalytic activity of GAC had the ability to regenerate in situ.The three oxidants of H₂O₂,PS and PMS commonly used in advanced oxidation technology could be activated by GAC.The degradation of bio-treated coking wastewater is the worst in GAC/H₂O₂ system,and the degradation effect of GAC/PS system is slightly lower than that of GAC/PMS system.?2?The characterization analysis of GAC indicated that the specific surface area and the zero charge point p H_ZPCPC of GAC after GAC/PMS system reaction reduced,the total acidity increased and the total alkalinity decreased.The oxidation of PMS for GAC in GAC/PMS system resulted in the increase of the number of acidic functional groups such as carboxyl group,lactone group and phenolic hydroxyl group on the surface of GAC.Three-dimensional fluorescence and GC/MS analysis demonstrated that humic-acid-like substances of the main pollutants contained in the bio-treated coking wastewater were greatly reduced after the GAC/PMS system treatment.Most of the organic matter was oxidatively degraded and completely mineralized or converted into small molecules.After PMS oxidation activated byGAC,theexistedsubstancessuchashexanamide,2,4-dimethyl-1,8-naphthyridine,and 9-Phenanthrol in the water were completely removed,andsomeweremostlyremoved,suchas2,6-Ditret-butyl-4-methylphenol,adipic acid bis?2-methylpropyl?ester,etc.,with the rest still remain in the effluent.In addition,there were some new organic substances generated.?3?The study of dynamic treatment for bio-treated coking wastewater using PMS oxidation activated by GAC through activated carbon column showed that,the lower flow rate could result in the lower concentration of organic pollutants in the effluent and the longer time of superior effluent water quality;The higher amount of KHSO₅ dosage resulted in an increase in the removal rate of organic matter in effluent,whichwas able to obtain better effluent quality and higher treated water yield,but the increase was limited.If the effluent quality was under TOC concentration of 15 mg/L,when the flow rate was 1.5 mL/L and the KHSO₅ dosage was 0.5 g/L,the activated carbon column could acquire about 14L of treated water yield.In the only GAC adsorption system,the GAC in the column was close to the adsorption saturation after about 50 h of treatment for bio-treated coking wastewater with the activated carbon column,and the wastewater cannot be further treated.If the same TOC concentration of 15 mg/L is used as the boundary,when the flow rate is 1.5 mL/min,the activated carbon column could only continuously treat the wastewater for 30 h with the treated water yield of 2.7 L.However,when the KHSO₅ dosage is 2.0g/L,the treatment effect of the activated carbon column on the bio-treated coking wastewater became significantly better,and could be continuously treated for 200 h with the treated water yield of 18 L.?4?In this paper,the study on the advanced treatment of bio-treated coking wastewater with PMS oxidation activated by GAC has accumulated some experimental data and theoretical experience,which could provide some technical parameters and theory guide for the application of GAC activated PMS oxidation technology in the advanced treatment of coking wastewater.