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.

Fig. 5. Mass balance for a treatment by direct pre-concentration (Dye: Drimaren HF, PTM = 20 bar, Q = 400 L.h-1, T = 50°C, V0 = 150 L, pH = 5.5, Solvent = distilled water). This innovative process allows to treat and to recycle pure water and mineral salt in the dyeing process. Each parameter of each step was optimised. The re-dyeing with recycled water and electrolyte solution gives no difference (tonality, intensity, kinetic, etc.) with the usual procedure. In this paper, we present the first results [27] of the treatment and valorisation of dye house effluents: a low volume of concentrated hydrolysed reactive dye, pure water and a concentrated brine. The operating conditions of the experiments considered in this paper are those used as industrial conditions and we could estimate the cost of an industrial plant which will be placed on the outlet side of a dyeing machine. Presently, we are studying the treatment of the ultimate effluents very concentrated in dyes and this will be the subject of forthcoming papers.