Advanced Treatment Of Printing And Dyeing Wastewater By O₃/H₂O₂ Process

Printing and dyeing industries discharge a great amount of wastewater every year, posing a serious threat to the environment. After the conventional process of physico-chemical and biological treatment, although most contaminants in the dyeing wastewater may be removed, the residuals usually present a considerable concentration of contaminants in the wastewater, which needs further processes to meet the increasingly strict discharge standards. A dyeing wastewater after the conventional physico-chemical and biological treatment was further treated by O3/H2O2 process in this study. The influences of operating conditions on its performance were investigated. The typical properties of effluent organic matter (EfOM) and its removal behaviors were characterized as well. Besides, the performance of biological aerated filter process for the further treatment of ozonized wastewater was evaluated.O3/H2O2 process greatly improved the treatment of dyeing wastewater compared with only using ozone alone. It was believed that reactions with hydroxyl radicals would be the major pathways for the degradation of organic contaminants by O3/H2O2 process. The efficiency of O3/H2O2 process for the wastewater treatment was investigated in terms of reaction time, pH vaule, H2O2 dosage, ozone concentration. The results showed that the removal rates of COD and chroma were up to 82.2% and 96.9% respectively, and BOD5/COD increased from 0.10 initially to 0.32, under the optimal conditions including pH of 9, gas flow of 0.2 L·min-1, reaction time of 100 min, ozone concentration of 116 mg·L-1 and H2O2 dosage of 9.79 mmol·L/-1. To further clarify the results of improving the biodegradability by O3/H2O2, the dyeing wastewater after O3/H2O2 process was further treated by biological aerated filter process. The result showed that the effluent COD was lower than 30 mg-L"1, indicating a good removal effect of organic pollutants.XAD resin absorbents, gel permeation chromatography and three-dimension fluorescence excitation-emission matrix (3DEEM) were applied to investigate the typical characteristics of EfOM and its removal behaviors. It was found that dissolved organic matter (DOM) was the main component in EfOM. Soluble microbial products and humic-like compounds showed high fluorescence intensity. The results of relative molecular weight distribution suggested that macro molecule substances were predominant in EfOM. Analysis of the hydrophilicity/hydrophobicity showed that hydrophobic substances were the most abundant fractions in EfOM, hydrophobic acids and non-acid hydrophobics collectively accounted for 89% of the DOM measured as dissolved organic carbon (DOC). After the treatment, the fluorescence peak location and intensity changed largely.3 DEEM fluoresence spectra of EfOM was almost similar to that of demineralized water. Low molecule weight substances increased significantly. Besides, the hydrophilic fractions of the wastewater obviously increased, different from that before the treatment.