Color Removal of Dyestuff Wastewater by Chemical Coagulation using Various Types of Coagulants

• Main Authors: Yulung Yang, 楊裕隆
• Other Authors: Chihpin Huang
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/39257143253969050217

碩士 === 國立交通大學 === 環境工程所 === 87 === Dyestuff manufacturing is a highly polluting industry which produces wastewater of high color and high salt content. Many plants adopt coagulation to pretreat the wastewater by adding ferrous sulfate and lime at high pH. The drawback of this method is that it consumes large quantities of acids and bases, and produces large amounts of sludge which causes the scale problem in the treatment facilities. In this study, we evaluated the coagulation efficiencies of various types of iron sulfate, including ferrous sulfate, ferric sulfate, and polyferric sulfate, with the aid of lime. The results showed that ferrous sulfate was significantly better than ferric sulfate and polyferric sulfate in that more than 85% color removal and flocs with better settling characteristics. After analyzing the mechanism for coagulation, it is proposed that the soluble pollutants first complex with the ferrous ion. The complex ion is then adsorbed on the surface of the lime particle to form larger flocs. Results also indicate that by combining ferrous sulfate, lime and polyferric sulfate, various dyestuff molecules can be removed and consequently the residual color are significantly lowered. The effect of dosage and the dosing sequence of ferrous sulfate/lime addition on coagulation were also investigated. The results indicated ferrous sulfate was effective in color removal, while lime aided in both color removal and floc blanket settling velocity. Coagulation of lime followed by ferrous sulfate addition was better in color removal but poorer in floc blanket settling velocity. Finally, the response surface methodology and desirability function were used on several batches of effluent of different water quality to determine the optimal dosage. By considering the cost for. ferrous sulfate, it is recommended that the optimal dosage for ferrous sulfate is between 8 g/l ~ 9 g/l and lime is between 3.5 g/l ~ 3.6 g/l.