Characterization Of Dissolved Organic Pollutants In Bio-Treated Effluents Of Dyeing And Textile Wastewater And Removal Behavior During Coagulation Process

In this paper, experiments were performed to characterize the bio-treated effluents from a dyeing and textile wastewater treatment plant by tandem resin fractionation, molecular weight distribution, biological toxicity test,3-dimensional fluorescence excitation-emission matrix and UV-Visible spectrophotometry etc. The optimal dosage condition and removal behavior of its major organic constituents in coagulation treatment and permanganate pre-oxidation process were studied. Results showed that the high molecular weight hydrophobic organic fractions were the largest group of the total dissolved organic carbon and the dominating cause for the color of this bio-treated effluent, it also had higher aromatic carbon contents than other organic fractions. Meanwhile it had some degree of biological toxicity. Ferric chloride (FeCl3), aluminum sulfate (Al2(SO4)3·18H2O) and magnesium sulfate (MgSO4·7H2O) were applied as the coagulants to treat the bio-effluents. The optimal dosage conditions were:400mg/L, pH=5.0; 800mg/L, pH=5.0; 300mg/L, pH=12.0, respectively. The coagulation process had a direct removal effect on the color-caused dissolved organic matters, removal efficiency are 65%～86%(in term of ADMI7.6),66%～82%(in term of dilution ratio), 26%～68%(in term of TOC) and 49%-65%(in term of UV254). And the treatment effect on coagulation process was stable even with different grab samples. Nearly all of the large molecular and a major portion of hydrophobic matters were removed during the coagulation process, effluents after coagulation contained large part of small molecular weight hydrophilic matters and small part of hydrophobic matters. At the same time, coagulation process can reduce the bio-toxicity significantly. Among them, ferric chloride had the best removal performance. Permanganate pre-oxidation and coagulation process can improve the removal efficiency better than the coagulation process solely, the increase in term of ADMI7.6, DOC and UV254are 9%～16%; 5%～15%; 4%～5%, respectively. It also had a significant increase on the removal efficiency on the large molecular hydrophobic matters. The characteristic of effluents after treatment was the notable increase and large portion of small molecular weight hydrophilic matters. Both two treatment process should combined with other treatment that have a better removal effect on small molecular weight hydrophilic matters, to enhance the total removal performance.