Hydrolyzed dyes as emerging environmental contaminants: household washing sources and electrochemical degradation

Abstract High-color saturation cotton fabrics dyed with reactive dyes often discharge hydrolyzed dyes during the washing process, resulting in dye transfer and water pollution because of the properties prone to hydrolysis of reactive dyes. To explore the sources of hydrolyzed dyes in the washing microenvironment, the hydrolysis experiment of pure reactive red 195 (RR195) and the washing experiment using some highly saturated colored fabrics (CFSCs) dyed with RR195 in a designed miniature washing device were carried out successively. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used for the analysis of hydrolysis intermediates and final products of reactive red 195. The experimental results indicated that the structure of the dye shed on the fabric is consistent with the final hydrolysate of reactive red 195, which is the main colored contaminant in washing wastewater. To eliminate the hydrolyzed dyes from the source, an electrochemical degradation device was originally designed to degrade hydrolyzed dyes. The degradation parameters, including voltage, electrolyte concentration, and dye shedding concentration are discussed in the electrochemical degradation experiment. The electrochemical degradation device was also successfully implemented and verified in a home washing machine. The results showed that there were three hydrolysis intermediates and one final hydrolysate product in the hydrolysis process of RR195, and the washing and shedding of colored pollutants were the products of simultaneous hydrolysis of double reaction groups. The designed electrochemical degradation device can effectively eliminate the hydrolyzed reactive dyes and reduce the contaminants’ discharge during household washing.