Efficiencies And Mechanisms For Printing And Dyeing Wastewater Treatment Based On SO₃^2-/S₂O₈^2-System

Printing and dyeing wastewater is one of the refractory wastewater because of its large emission,high chroma and complex organic matter content and other characteristics.In this paper,a novel advanced oxidation technology was studied for the production of sulfate radicals(SO4-·)based on persulfate activated by sulfite(SO32-),and its degradation efficiefficiencies and mechanisms for printing and dyeing wastewater were analyzed.This study not only promotes the development of persulfate activation systems,but also provides a feasible technical solution for advanced treatment of dye wastewater.The main research results are as follows:(1)The activation mechanism and oxidation theory of SO32-activated persulfate(S2O82-)to produce SO4-were studied.Using methyl orange(MO)as the target pollutant,through its degradation in SO32-/S2O82-,S2O82-,SO32-three systems,ESR and UV-vis,FT-IR characterization comparison showed that sulfite can activate persulfate significantly to produce SO4-·,induced the transition of electrons to single electrons on the azo group,and formed the active transition which could combine with protons quickly,destroying the conjugated system of azo bond.SO32-/S2O82-system has a better decolorization and degradation effect.(2)The influencing factors of SO32-/S2O82-system were investigated.The results showed that the appropriate amounts of SO32-could promote the activation of S2O82-and enhance the degradation of MO.The degradation of MO could be inhibited when S2O82-was excessive,it is also found that the system has a wide range of adaptation to the initial pH(3.0-11.0).The percent removal ratio of MO reached 96.1%under the conditions:the initial pH of 3.0,the molar ratio of sulfite to persulfate of 1:1,the dosage of persulfate of 20 mM and the reaction time of 300 min.Aqueous chloride anions(Cl-)could enhance the degradation efficiency of the system in the range of 0-25 mM.The oxidation process analyzed by kinetics under the different initial concentrations was found that it fits well perso second-order reaction kinetics.The reaction kinetic constants vary from 1.8212×10-4 min-1 to 2.4649×10-4 min-1.The increasing of temperature can promote the removal of MO,according to the perso second-order reaction rate constants(2.6×10-4 min-1-7.2×10-4 min-1)at different temperatures were calculated Arrhenius activation energy Ea=44.9 kJ/mol.(3)Removal of soluble organic containments from dyeing biochemical effluent by SO32-activated peroxymonosulfate system optimized by response surface methodology were investigated,as well as its fluorescence and molecular properties.The results showed that the system can degrade COD and remove aniline remarkably.The contribution order of influencing factors to COD and aniline treatment were as follows:temperature>n(SO32-)/n(HSO5-)>n(SO32-)>initial pH value and n(HSO5-)>n(SO32-)/n(HSO5-)/initial pH value>temperature.The percent removal rates of COD and aniline were 33.05%and 90.02%respectively under the experimental conditions by the experiment optimization:pH of 6.8,temperature of 53?,concentration molar ratio SO32-to HSO5-of 1.6 and HSO5-dosage of 37.1 mM.EEM found that aromatic proteins and soluble microbial metabolites were the main components of DOM in the biochemical treatment effluent of dyeing wastewater(BREDW).The fluorescent DOM content in the oxidized effluent decreased significantly under different conditions,and the fluorescent area volume was reduced by 42.03%-77.67%.At the same time,the peak in the oxidized effluent was observed to blue shift of 5-10 nm.Polycyclic aromatic hydrocarbons in BREDW are decomposed into small molecules,the number of conjugated groups and aromatic rings decreases;GPC revealed that the proportion of macromolecules(0.45 ?m-100 kDa)is 41%,that of medium molecules(12-100 kDa)is 48.9%,that of peak molecular weight(Mp)is 56.324 kDa,and that of Mw/Mn=2.168.After treatment,the effluent Mp mainly distributes in the range of 12.28-17.56 kDa,with more small molecular substances,more structures and species.GC-MS synchronously reveals that the alkanes in the oxidized effluent are greatly reduced,and the main by-products are esters,alcohols and fatty acids,which create conditions for further biochemical treatment.