Dyeing Wastewater Reuse And Its Influencing Factors

The recycling of dyeing wastewater is a developing technology concerning environmental issues and textile industry. This technology is playing a very important role in saving water and environmental protection in recent years. As increasing limitation of discharge and enhanced on the cost of tap water charge, dyeing corporation attach more and more importance to cleaning production, so people regard the reuse of dyeing wastewater more highly. The mid-temperature reactive dyes, including Reactive Red MS, Reactive Yellow MS and Reactive Blue B, and acid dyes, including Acid Red G, Acid Light Yellow 2G and Acid Black 10B, were selected, and used for dyeing cotton fabric and wool fabric, respectively. The exhaustion process of two fabrics mentioned above was carried out in tap water, then the dyeing effluence were classified and collected after dyeing. The dyeing effluence were degraded by oxidation technique of ferrous oxalate complex/H₂O₂ photo-catalytic, then the treated effluence (called reuse water, including reuse waterI , reuse water II and reuse water III) were obtained and used in dyeing process above again. Reuse water were characterized and effecting degree of dyeing parameters were determined. The coloration of the fabrics was investigated with respect to K/S curve and color characteristics (total color difference DE^*) of dyed fabric and take-up rate curve of dyes. Moreover, a few factors effecting dyeing using reuse water as the dyeing medium including inorganic salt and organic component in reuse water were examined. The dyeing parameters were adjusted according to content of inorganic salt in reuse water, and dyeing were carried out using reuse water as the dyeing medium. Then comparison between.dyed fabrics and fabrics dyed in tap water (called fabric I )were made. Finally, the possibility of recycling dyeing effluence for coloration of the fabric was investigated.The results indicated that there are 11 g/L and 3 g/L inorganic salt in reuse waterI and reuse water II, respectively. And reuse water III has little inorganic salt. Reuse water I and reuse water III have very lower organic substance than reuse water II. Coloration of cotton fabric with reactive dyes, the effecting of inorganic salt (sodium chloride) to dyeing was improved significantly. Increasing concentration of inorganic salt led to increasing K/S value of dyed fabric. When concentration of inorganic salt was changed between 20-50 g/L, there was a proportional relationshipbetween K/S value in the maximal wavelength(called K/S_λmax) of dyed fabric and concentration of inorganic salt. When reuse water was used as the dyeing medium, it is found that there was a similar proportional relationship between K/S_{λ max} and concentration of inorganic salt concentration. When the concentration of inorganic salt in reuse water was adjusted to 40g/L(routine dyeing content), K/S curves of reuse water fabric was similar to that of fabric I, and DE^* were less than 1.5. The exhaustion curves and fixation curves of three reactive dyes between reuse water and tap water were similar. Finally, recycle dyeing was carried out using reuse water I for three times. Inorganic salt of reuse water I was served as dyeing promoter. Coloration of wool fabric with acid dyes, the effecting of inorganic salt (sodium sulfate) to dyeing was improved significantly. The concentration of inorganic salt in reuse water III was adjusted to 2 g/L(routine dyeing concentration) by the way of mixing reuse water III and tap water. To compare with tap water dyed fabrics, K/S curves of reuse water dyed fabrics were similar to that of fabric I , and DE^* were less than 1.5. The exhaustion curves and fixation curves of three acid dyes between reuse water and tap water were accordant, and final uptakes in the two dyeing mediums were near. Finally, recycle dyeing was carried out using reuse water III for three times.