In this paper, the effect of washing parameters on the quantity of dye discharge from fabric dyed in highly saturated color (FSC) was discussed. Firstly, the FSC was prepared with reactive red 195 to represent the dark clothes. Secondly, the effect of the washing parameters, including washing time, washing temperature, washing water volume, the weight of FSC, and the dosage of detergent, on dye discharge was analyzed through the single factor test. Thirdly, the mathematical relationship between the quantity of dye discharge (DDQ) and the four washing parameters was discussed through the center combination experiment and response surface method. And a quadratic model was built to predict the quantity of dye discharge when the FSC were washed with different washing parameters. The experimental results indicated that the quantity of dye discharge was affected by the four selected washing parameters and the optimal washing parameters to reduce the quantity of dye discharge can be deduced from the quadratic model. The optimized parameters effectively reduced 0.99 mg dye discharge per liter, and the DDQ reduction rate was up to 53.5%.

The faded-on stains of cotton clothes are a common daily phenomenon. The desorption and adsorption of reactive dyes are theoretically responsible for the faded-on stains on cotton clothes in the washing microenvironment, especially when the light color cotton fabrics ( LCFs) are washed together with the cotton fabrics dyed in highly saturated color ( CFSCs). However, the effects of washing parameters on the desorption and adsorption kinetics of reactive dyes and the mitigation of faded-on stains in the washing microenvironment through washing parameter optimization are poorly understood. This study thoroughly discusses the desorption and adsorption behaviors of reactive red 195 in the washing microenvironment from the inhibition of color transfer. Firstly, CFSCs and LCFs were prepared by using reactive red 195 and cotton fabrics. Secondly, the effects of washing parameters, washing temperature, washing liquor ratio, and washing solution pH, on the dye desorption and adsorption rate were studied with the simulated washing device ( SWD), followed by the response surface analysis of washing parameters. Thirdly, the modeling of desorption and adsorption kinetics and velocity were detailed. Finally, the model of dye desorption and adsorption was validated in a drum washing machine ( DWM). The results are helpful for the design of scientific washing procedures to curb the faded-on stains of cotton clothes effectively.

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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.