Savings and re-use of salts and water present in dye house effluents

Cotton dyeing using reactive dyes generates warm wastewater strongly colored, containing suspended solids,concentrated NaCl and widely varying acid amounts. Dyeing one kilogram of cotton with reactive dyes requires from70 to 150 L water, 0.6 kg NaCl and 40 g reactive dye. We have worked out a process for the treatment of used reactivedye baths which consists of 4 steps: pre-filtration, neutralization, nanofiltration and reverse osmosis. At the end of this treatment a recyclable brine is obtained which contains the total salt added in the initial dye bath, pure waterwhich is reusable for further operations and a small volume of concentrated liquor containing hydrolyzed reactivedyes and dyeing auxiliaries. In this study, we used industrial effluents resulting directly from an industry of dyeing.All the types of dyestuffs used by the dyer were studied. The tests were first carried out on small volumes (15 L) then larger (300 L) to validate the process. No difference was found between re-dye obtained either by usual process orusing the brine recycled. Every step of the process was studied separately then together so as to optimize the whole process.