Study On O₃-coagulation Enhanced Pretreatment And O₃-SBBR Advanced Treatment Of Wastewater From A Printing And Dyeing Industrial Park In Foshan

Textile printing and dyeing industry is a traditional pillar industry in China.A large amount of printing and dyeing wastewater is produced in the production process.If it is improperly treated and discharged into the water body,it will cause great pollution to the water environment.Printing and dyeing wastewater has the characteristics of high toxicity,high chroma,high pH,high temperature,high salinity and poor biochemistry.It is difficult to treat.Printing and dyeing wastewater has complex composition and contains polar groups dominated by heterocyclic compounds or aromatic hydrocarbons（such as:-SO₃Na,-N=O）and chromogenic groups（such as:-N=N-,-N=O）also contains printing and dyeing auxiliaries,such as expansion agent,surfactant and other pollutants.The wastewater quality of printing and dyeing industrial park is more complex,and the efficiency of traditional coagulation treatment is low.In addition,the concentrated water produced by reclaimed water treatment will make it difficult for the residual toxic substances and total nitrogen in biochemical tail water to reach the standard stably.Therefore,it is necessary to add advanced treatment,and it is urgent to develop economical and applicable advanced treatment technology.Taking the sewage treatment plant of a printing and dyeing industrial park in Foshan as an example,based on the diagnosis and evaluation of its existing wastewater coagulation pretreatment,biochemical treatment and advanced treatment subsystems,this study carried out the analysis of characteristic pollutant sources and the study of composite pollution characteristics.The technical strategies of enhanced coagulation pretreatment by O₃-coagulation combined process and advanced treatment of biochemical effluent by O₃-Sequencing Biofilm Batch Reactor（O₃-SBBR）denitrification combined process were put forward.The process research was systematically carried out,including influencing factors,operating conditions,degradation efficiency and apparent kinetics.The optimal regulation strategy of combined process based on process parameters was put forward.The process mechanism research was carried out in depth,including the main object of O₃-coagulation and material transformation and removal,as well as the material transformation in the denitrification process of O₃-SBBR.The morphological characteristics of biofilm and the evolution information of microbial community were obtained,and the promotion mechanism of O₃-coagulation and the denitrification process mechanism of O₃-SBBR were clarified.The pilot reactors of O₃-coagulation combined process and O₃-SBBR denitrification combined process were built,the feasibility of the combined process was verified,the operability of the regulation strategy was verified,and the economy of the combined process was evaluated.The main results were as follows:1.The physical and chemical indexes of different types of typical printing and dyeing wastewater had a compound pollution effect after mixing.The coagulation pretreatment system had a good removal effect on the conventional indexes,but the aniline treatment did not decrease but increased.The reagent cost was 0.35～0.45 yuan/m³,which was economical.The effluent concentrations of COD,chroma,ammonia nitrogen and total nitrogen of the biochemical treatment system were 78.2 mg/L,136.0 times,1.4 mg/L and 6.6 mg/L respectively,and the operating electricity charge was 0.30～0.36 yuan/m³,which was economical.There were some problems in the biochemical treatment system,such as filamentous sludge bulking,large fluctuation of effluent TN and unstable effluent color.The removal rates of COD,chroma and ammonia nitrogen in the advanced treatment system were60.5%,88.2%and 50.0%respectively,but there were some problems such as poor denitrification effect and high PVA content after treatment.The cost of chemicals and electricity was 0.65～1.00 yuan/m³,with moderate economy.2.Under the suitable conditions of O₃-coagulation combined process,the removal rates of color,SS,chemical oxygen demand（COD）,total phosphorus,total hardness,aniline,sulfide,magnesium,calcium,antimony and silicon were 83.2%,93.4%,30.1%,74.6%,27.9%,77.2%,66.4%,20.2%,29.4%,25.0%and 44.8%,respectively.The inhibition rate of enzyme activity decreased from 83.4%of the raw water in the regulating tank to 6.6%after O₃-coagulation.The oxidation of aniline in printing and dyeing wastewater by O₃conformed to the fitting kinetics of the pseudo first-order model,and the maximum rate constant obtained was 0.0110min^-1（at pH 7.0,O₃concentration of 24.0 mg/L and O₃dosage of 250 mg/L）.3.Ozonation of aniline in printing and dyeing wastewater was a process of direct O₃oxidation supplemented by hydroxyl radical reaction.The possible degradation pathway of aniline was to oxidize aniline with O₃to produce intermediates such as p-benzoquinone,and then deamination by hydroxyl radical and decomposition of benzene ring to produce glutaric acid or L-pyroglutamic acid until mineralization.Ozonation can reduce the absolute value of zeta potential,viscosity,COD and UV₂₅₄of printing and dyeing wastewater,so as to reduce the colloidal stability in the wastewater,destroy the organic coating,reduce the electrostatic repulsion and steric resistance to promote coagulation.4.Under suitable conditions of O₃-SBBR combined process,the removal rates of total nitrogen,ammonia nitrogen,nitrate nitrogen,nitrite nitrogen,PVA and aniline were 67.3%,58.3%,71.0%,83.3%,40.3%and 90.41%respectively.In addition to all the additional carbon sources being utilized,part of the organic matter in the biochemical tail water of printing and dyeing can also be used as a carbon source for biological denitrification after being oxidized by O₃.Ozonation can improve the biodegradability of wastewater and reduce the toxicity of biochemical tail water of printing and dyeing.The ozonation degradation of organic nitrogen in biochemical tail water of printing and dyeing conformed to the fitting kinetics of pseudo first-order model,and the maximum rate constant was 0.01035 min^-1（at pH 8.5,O₃concentration of 35.0 mg/L and O₃dosage of 100 mg/L）.SBBR denitrification of biochemical tail water of printing and dyeing conformed to the fitting kinetics of pseudo first-order model.Under appropriate conditions,the degradation rate constants of ammonia nitrogen and total nitrogen in SBBR denitrification group were 5.5 times and 2.5 times higher than those in the control group,respectively.Microorganisms had a significant effect on the degradation rate of ammonia nitrogen and total nitrogen.5.Among the SBBR reactors under various experimental conditions,Thauera was one of the strains with the highest relative abundance.The five phyla levels with the highest relative abundance percentage were Proteobacteria,Bacteroides,Planctomycetes,Firmicutes and Patescibacteria.6.Under suitable conditions,direct ozonation was mainly combined with hydroxyl radical reaction to act on the biochemical tail water of printing and dyeing to convert the organic nitrogen in the wastewater into nitrate nitrogen.At the same time,ozonation products were used as the carbon source for subsequent denitrification.The abundance of ammonia monooxygenase coding genes amo A and denitrification functional enzyme coding genes（narG,napA,nirS,nirK,norB and nosZ）in SBBR reactor was significantly improved.The simultaneous nitrification and denitrification process based on dissolved oxygen gradient in biofilm was accelerated.7.The removal efficiencies of chromaticity,SS,COD,calcium,total phosphorus,total nitrogen,sulfide,silicon and antimony in the pilot scale pretreatment of O₃-coagulation combined process were 80.7%,92.8%,47.8%,32.9%,75.4%,17.9%,84.3%,53.8%and38.3%respectively.On the contrary,aniline increased by 29.6%,which may be due to the strong dependence of oxidation removal of aniline on O₃concentration.The inhibition rate of E.coli in raw water decreased from 79.0%to 30.5%in effluent.It had good technical economy.8.The removal efficiencies of total nitrogen,ammonia nitrogen,nitrate nitrogen,nitrite nitrogen,PVA and aniline were 59.2%,53.6%,69.1%,66.7%,38.2%and 97.1%respectively,and the effluent could meet the requirements of target value TN≤2.5mg/l.The COD before and after treatment were 20.7 mg/L and 22.5 mg/L respectively,and the additional carbon source was basically used for biological denitrification.It had good technical economy.The research results can provide technical and theoretical basis for the process selection and operation strategy of wastewater in printing and dyeing industrial park,and can provide reference for the large-scale treatment of wastewater in printing and dyeing industrial park by O₃-coagulation combined process pretreatment and O₃-SBBR combined process denitrification advanced treatment combined process.