Textile dyeing in Mali : possibilities for small scale effluent treatment

Abstract: Water treatment is an important issue in Mali, an arid country where the Niger River is the mainrecipient for a large part of the effluents from industrial and small scale activities. Clothes dyed withsynthetic dyestuffs are an important part of the culture in Mali. Dyeing of textiles is to a large extentan informal activity, mainly performed by women.The objective for this thesis work was to investigate potential capacity of cheap, locally accessiblematerials in treatment of effluents from textile dyeing. Effluents studied were sampled at three siteswith small scale textile dyeing in Bamako, Mali. At two sites the effluents were emitted directly tothe Niger River, at the third site the effluents were collected in a soakaway. The capacity of differentmaterials, both coagulants and adsorbents, to treat the effluents was analysed with jar tests. pH,conductivity, total dissolved solids (TDS), turbidity and dissolved oxygen (DO) were analysed onsamples before and after jar tests, and on river water from spilling site. For some jar tests, UV-Visspectra and content of zinc, nickel and copper were analysed. Properties of dyestuffs were analysedwith spectrophotometry, scanning electron microscopy (SEM) and nuclear magnetic resonancespectroscopy (NMR).Iron(III) chloride coagulated dye effluents, efficiently removing most of the colour from water.Activated carbon, both in granulated form and in the form of powder, showed some capacity toadsorb compounds in dye effluents. Rice chaff, rice bran, laterite, bentonite and aluminium sulfatedid not show capacity to remove dyes from effluents.The composition of the dyestuffs used in small scale dyeing is not known, which is a seriousproblem when developing treatment methods. A significant fraction of the dyestuffs consists ofsubstances which are not part of the colour-yielding dye. Five dyestuffs with different colours wereanalysed with SEM with X-ray fluorescence detector. These dyestuffs contained, except for carbon,oxygen and nitrogen which can not be detected, mainly sulfur, chloride, sodium and, in the case ofgreen, barium. Traces of chromium, vanadium, iron, aluminium and silicon were also detected insome of the dyestuffs. Mixed effluents from two sampling sites contained concentrations of zincand nickel higher than WHO guideline values for drinking water.Further studies are needed to find a cheap treatment method since low cost materials such asrice bran and laterite are ineffective. In addition to be able to remove polluting substances from dyeeffluents, the method should include cheap and readily accessible materials, and be supported by aninfra-structure which allows the effluents to be treated locally. To find a working solution to decreasewater pollution, without threatening the livelihood for dyers, co-operation between universities,dyers and governmental bodies is crucial.