on removal of residual dyestuff in effluent from yarn dyeing process by physical and chemical methods

Abstract

In this experimental study two methods of pretreatment of effluents from dyeing processes were investigated. The main objective was to reduce the colour strength of the effluents. The first method was chemical pretreatment using oxidation and reduction to destroy the conjugate double bonding system of the chromophore structure. The other method was the physical pretreatment using activated carbon to adsorb the colourant. The parameters studies were chemical auxiliaries, colour strength, conditions and types of dyestuff. Results of chemical pretreatment showed that the factors effecting the reaction were dye structure and characteristics of the dyes. The removal of colour strength was achieved by using reduction reaction to change the chromophore structure of each dyestuff by destroying the conjugate double bonding system forming non chromophore structure. Sodium dithionite was used for reduction. It was found that colour strength removal efficiency isdirect >acid > reactive > basic > disperse. The reduction time was 30 minutes. Factors effecting the physical treatment were conditions of the dyeing solution, time of treatment and height of activated carbon. It was found that the most suitable solution condition was acidic in nature, time of contact between 1-2 hours and amount of activated carbon is 100 - 200 gram/liter of dye effluent. The dye removal efficiency is basic > acid > disperse > direct > reactive. However, the choice of treatment method varies, depending on the size of the plant, amount of effluent released and unit cost of treatment.