Attempts to reduce water and chemical usage in the removal of reactive dyes: Part 1 bis(aminochlorotriazine) dyes

Abstract

Dyeings on cotton obtained using three commercial reactive dyes were subjected to three wash-off processes namely, a standard, five-stage method which used a proprietary wash-off agent, a five-stage process in which Na 2CO 3 was used in place of the commercial wash-off agent and a three-stage, chemical-free method. Dyeings that were generally of the same hue and colour strength and which also displayed similar levels of fastness to repeated washing, were obtained using each of the three wash-off processes. The replacement of the commercial wash-off agent in the five-stage, standard wash-off process with Na 2CO 3 reduced, considerably, both the COD and BOD 5 loads of the residual wastewater; the corresponding COD/BOD 5 ratios showed an improvement in the biodegradability of the residual wastewater. Although reducing the number of wash-off stages from five to three and replacing Na 2CO 3 with 98 °C water rinses increased both COD and BOD 5 loads, the ensuing biodegradability of the residual wastewater was improved. Thus, by using a three-bath, water-only wash-off process, not only was the amount of water used for reactive dye wash-off reduced but also the wastewater generated was of higher biodegradability.