Color removal in textile dye wastewaters by means of coagulation

In textile mill wastewater effluent, highly colored and stable dyes are formidable and somewhat insusceptible to removal treatment processes. Recent governmental regulations have made it necessary to remove most color before discharging the treated wastewater to surface waters.

Chemical coagulation is successful in some cases at reducing wastewater color to acceptable levels. Also anaerobic biological treatment is usually successful in destroying the dyes and color in the wastewater. Aerobic biological treatment often does not degrade the dyes or remove significant color, but aerobic treatment, unlike anaerobic treatment, removes a large amount of organics. This thesis explored the color removal in two textile dye wastewaters by means of coagulation in conjunction to the following treatments: no prior treatment, aerobic treatment, anaerobic treatment, and anaerobic-aerobic treatment.

In the first industry, a reactive azo dye washwater (or rinsewater) was evaluated, and the influent into the municipal treatment facility that receives the azo dyes was also evaluated. Polymer coagulation proved to be successful following anaerobic-aerobic treatment in reducing color, solids, and organics. Color removals were most favorable at low pHs of 3 to 5 when using polymer dosages less than 100 mg/L in the washwater and less than 25 mg/L in the municipal wastewater. At higher amounts of coagulant over 100 mg/L in the washwater and 25 mg/L in the municipal wastewater, color removals were similar at pHs 3 to 8.

The second industry uses many dyes that include acid and disperse dyes. Alum addition of 300 to 400 m/L at pH 5 compared favorably to the polymers presently added by the industry. Both the currently used polymers and alum were successful in removing color when utilizing proper settling techniques.