Study On Removal Effect Of Different Organic Fractions From Bio-treated Effluent Of Dye Wastewater By Chemical Oxidation

At present, dye wastewater treatment commonly use physical-chemical-biological processes, the effluent quality has basically reached the GB4287-1992 in the second-class standard, but it is generally difficult to achieve the first-class discharge standard. Suspended solids, COD and color are in high levels in bio-treated effluent, it will bring potential hazards to environment if discharged into water. With the development of production, urban water shortage becomes one of the main factors to constraint enterprise development. As more and more attention are devoted to environment protection and discharge standard was improved, it is necessary for printing and dyeing wastewater to be deeply treated, in order to further reduce the concentration of pollutants in the water and realize the reuse. This is of great practical significance for alleviating the crisis of water resource and realizing the printing and dyeing industry sustainable development.The dissolved organic matters (DOMs) in the bio-treated effluent of dye wastewater could be classified to four types:hydrophobic acids, non-acid hydrophobics, transphilics and hydrophilics by XAD-4/XAD-8 adsorption resin. As DOC, UV254 and DAMI7.6 indicators, the proportion of the four dissolved organic matters and the removal behaviors of the four dissolved organic matters by Fenton oxidation and UV/H2O2 process were investigated and then the causes of high COD and high color were analysised. It could be helpful for the selection of advanced treatment technologies of bio-treated effluent of dye wastewater.The results showed that, in Fenton oxidation experiments, the pretreatment of bio-treated effluent of dye wastewater by Fenton reagent was studied. With the removal rate of color of the wastewater as the index, different factors that influence the catalytic oxidation of organic matter by Fenton reagent were analyzed through single factor test and orthogonal test. The optimal conditions determined are as follows:the appropriate concentration proportion of [H2O2]/[Fe2+] 6:1, initial pH4.0, H2O2 dosage 3.6 mmol/L, FeSO4 dosage 0.6 mmol/L, and reacting time 30 min. Under the optimal conditions, UV254, DOC and COD removal rate could reach 84%,52%and 84%, the ADMI7.6 removal rate and the dilution characterization of color removal rate could reach 94%and 96%, While, in UV/H2O2 process, the optimal conditions determined are as follows:initial pH7.4-8.1, H2O2 dosage 4.5mmol/L and UV irradiation time of 40 min. Under the optimal conditions, UV254, ADMI7.6, DOC and COD removal rate could reach77%,94%,40% and 69%. The research results on removal characterization of DOM fractions by different treatments showed that, hydrophobic material is the main substance causing color, when characterized by ADMI7.6, the proportion of it could reach 88%, of which 50%is non-acid hydrophobics. It is indicated that removal efficiencies of non-acid hydrophobics and hydrophobic acids are very high through Fenton oxidation, while tasnsphilics and hydrophilics'efficiencies are lower. The research results also showed that removal efficiencies of tasnsphilics, hydrophobic acids and non-acid hydrophobics are high, while hydrophilics'efficiencies are lower through UV/H2O2 process.The molecular weight distribution experimental results showed that, in Fenton oxidation, the contribution of organic matter with molecular weight of 4-1 OK to UV254 increased by 13%, whose contribution to ADMI7.6 reduced by 10%, while the contribution of organic matter with molecular weight less than 4K to DOC increased, reaching 81%. In UV/H2O2 process, the contribution of organic matter with different molecular weight to UV254 change little, the contribution of organic matter with molecular weight over 50K to ADMI7.6 increased significantly,whose contribution to DOC reduced significantly.