Study On Advanced Treatment Of Biochemical Tail Water From Coking Wastewater By Catalytic Ozone-flocculation

After biological treatment of coking wastewater,the residual COD concentration is in the range of 100 mg/L?300 mg/L,which can not be discharged up to the standard.In face of more and more stringent discharge standards of pollutants in the coking industry,it is necessary to seek an efficient,thorough and economical treatment process of biochemical tail coking wastewater to meet the discharge standard.In this study,a self-designed split fluidized bed reactor combined with catalytic ozone-flocculation process was used to investigate the effects of catalyst dosage,ozone dosage,initial p H of wastewater and flocculant dosage on the treatment effect of the combined process,and to explore the effect of catalytic ozone-flocculation combined process on the treatment of actual wastewater under the optimum process conditions.The results show that under the optimal conditions of catalyst dosage of 30%volume ratio,ozone flow rate of 3 L/min and flocculant dosage of 700 ppm,the final effluent indexes are as follows:COD is 33.1 mg/L and COD removal rate is 83.7%,TOC is 30.9mg/L and TOC removal rate is 72.3%,NH₃-N is 9.5 mg/L and NH₃-N removal rate is70.1%,TN is 45.1 mg/L and TN removal rate is 16.2%.The TP is 0.015mg/L and TP removal rate is 99.6%.Except for total nitrogen,all other indexes are lower than the limit of direct discharge concentration of water pollutants in newly-built enterprises in"GB16171-2012 Coking Chemical Industry Pollutant discharge Standard".The DOM of water samples in each stage of the combined treatment process was characterized by UV-vis absorption spectroscopy,three-dimensional fluorescence spectroscopy and ESI Fourier transform ion cyclotron resonance mass spectrometry.The results showed that there were monocyclic aromatic hydrocarbons,polycyclic aromatic hydrocarbons and heterocyclic compounds in the biochemical tail water of coking wastewater.The fluorescent organic compounds were divided into tryptophan proteins,microbial metabolites,fulvic acid-like substances and humus-like substances.Lignins/carboxylic rich alicyclic molecules and aromatic structures are the main components of DOM in raw water,accounting for 92.8%.After treatment by the combined process,the macromolecular substances in the wastewater are transformed into small molecular substances.The aromaticity and degree of humification of wastewater are significantly reduced.CHOS substances have a high proportion in all stages of wastewater,and CHO and CHOS substances have relatively high retention rates after combined treatment.The element composition,molecular structure,removal and transformation law of wastewater DOM in the combined process were analyzed in detail through ultrafiltration and more intuitive Van Krevelen diagram and KMD diagram.The results showed that,during the catalytic ozonation,lignins/carboxylic rich alicyclic molecules and aromatic structures are removed,which contain less carboxyl groups and lower oxidation degree.Lipids,aliphatic/proteins,lignins/carboxylic rich alicyclic molecules,aromatic structures and tannins are retained or generated,which contain a higher number of carboxyl groups and a higher degree of oxidation.In the flocculation process,lignins/carboxylic rich alicyclic molecules,aromatic structures and tannins are easy to be removed,which contain a higher number of carboxyl groups and a higher degree of oxidation.The retained or generated lipids,aliphatic/proteins,lignins/carboxylic rich alicyclic molecules and aromatic hydrocarbons,which contain fewer carboxyl groups and less oxidation.Catalytic ozonation process and flocculation process complement each other in the removal of material components,and the combination of the two processes realizes the effective removal of DOM in biochemical tail water of coking wastewater.