A review on developments in dyeing cotton fabrics with reactive dyes for reducing effluent pollution

Most cotton fabrics are dyed with reactive dyes because they produce a full range of bright fashion colours with a high degree of wash fastness. Application of these dyes, however, causes high and undesirable levels of dissolved solids and oxygen demand in the effluent. This is due to the use of considerable quantities of inorganic salt and alkali to ensure efficient utilisation and fixation of the reactive dyes. Dye that is unfixed on cotton also contributes to effluent pollution. There are two approaches to deal with the effluent problem: 1. alternative dyeing techniques and technology, 2. effluent treatment after dyeing. The effluent treatment requires additional capital investment and high treatment and maintenance costs. Therefore, the first approach is always preferable. There have been a number of options developed to overcome the polluted effluent problem of dyeing cotton fabric with reactive dyes. This paper reviews the options to improve sustainability of the dyeing process through development of reactive dyes, modification of dyeing machinery and processes, chemical modification of cotton fibre prior to dyeing, use of biodegradable organic compounds in dyebath formulation, and effluent treatment processes. The paper highlights the significance and limitations of these ways of improving sustainability in reactive dyeing, and proposes the areas for further improvements.