Monitoring for sulfonated azo dyes and their degradation products in industrial and municipal wastewater

Sulfonated azo compounds are one of the most commonly used textile dyes. They pose an environmental problem because they can be difficult to degrade in municipal and industrial treatment systems and can cause effluent wastewaters to violate color standards. Methods were developed to monitor for three reactive azo dyes: Remazol Black B, Remazol Red RB, and Remazol Golden Yellow 3RA, and their degradation products. HPLC/ diode array detector, GC/MS, and LC/MS were utilized to characterize the purified dyes and the wastewaters and identify degradation products of the dyes resulting from several biological and chemical treatment processes. Results indicate that chemical reduction and anaerobic biological treatment of the dyes both result in cleavage of the azo bonds and formation of aromatic amines such as p-(2-hydroxyethylsulfone)-aniline, a reduction product of all three dyes. Some of these amines were unstable and quickly reacted to form other chemical structures. The textile mill effluent contained about thirty organic compounds detectable by GC/MS, including p-(2-hydroxyethylsulfone)-aniline. Anaerobic treatment caused little degradation of these compounds, but aerobic treatment degraded most of them. This research only investigated wastewater from a textile facility which performed pad dyeing of the cotton in a cotton/polyester blend. The sulfonated azo dyes used were reactive dyes typically applied to cotton fabrics.