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

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 Na2CO3 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 Na2CO3 reduced, considerably, both the COD and BOD5 loads of the residual wastewater; the corresponding COD/BOD5 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 Na2CO3 with 98 °C water rinses increased both COD and BOD5 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.