Experimental Study And Application For The Printing And Dyeing Wastewater Treatment

The printing and dyeing wastewater is a kind of high strength and poor biodegradable organic wastewater, containing complex compositions. The multi treatment processes of "coagulation- flotation + hydrolytic acidification + biological contact oxidation" were used in this study to treat printing and dyeing wastewater. The effect of different coagulants on wastewater purification was investigated and the optimal conditions of coagulation were determined. The performance of different units included in the treatment processes was clarified and the influence of main running parameters on contaminant removal was also analyzed.The A12(SO4)3, FeCl3; PAC and PFS wereu sed as coagulants in coagulation and sedimentation treatment of printing and dyeing wastewater and PAC was proven to be the best. The optimal coagulation conditions were determined as coagulant dosage of 0.8 mg·L-1 and pH of 8. The maximum removal rates of COD and SS were 40.8%and 90.5% under these conditions.The fibers were filled in both hydrolytic acidification bioreactor and biological contact oxidation bioreactor. During start-up period, the organic loading rate was increased gradually and the aeration condition was controlled. When the influent flow rate was 160 L·d-1, the COD removal rate was higher than 80.0% and stable, indicating the completion of start-up period. In the stage of increasing organic loading rate, the DO concentration was controlled at 3-4 mg·L-1 in the biological contact oxidation bioreactor and the reflux ratio was controlled at 2. After a continuous running of 30 d, the average concentrations of COD, BOD5 and chromaticity in the effluent were 120 mg·L-1,35 mg·L-1 and 70 times, respectively. The corresponding average removal rates were 83.3%, 84.9% and 65.8%, respectively. These results indicated the satisfied performance of pollutant removal in hydrolytic acidification bioreactor and biological contact oxidation bioreactor under the controlled conditions.In addition, when HRT was 6h in the hydrolytic acidification bioreactor, the organic loading rate was about 2.85 kgCOD·(m3·d)-1. When HRT was 12h in the biological contact oxidation bioreactor, the organic loading rate was about 0.9 kgCOD·(m3·d)-1 and the best performance was obtained at DO concentration of 3～4 mg-L"1.When the multi treatment processes of "coagulation- flotation + hydrolytic acidification+biological contact oxidation" were used in a practical treatment project of printing and dyeing wastewater, the total investment was 4.26 million Yuan and the cost of wastewater treatment was 1.18 Yuan per ton. In the practical treatment project, the average concentrations of COD, BOD5, and chromaticity in the effluent were 115 mg-L' 33 mg-L-1 and 68 times, respectively. The corresponding average removal rates were 83.7 %,85.0% and 65.9%, respectively. So such a combined treatment process was suitable for printing and dyeing wastewater treatment due to efficient pollutant removal and stable operation.