7. Conclusions
This paper has explored the range of options available to textile manufacturers to reduce the toxic environmental impact of dyeing with reactive dyes. Some of them have commercially been adopted. One can also choose and make various combinations of these options to design a pollution free dyeing. Development of bifunctional dyes provided prominent improvements in the dye fixation efficiency. The introduction of commercial low-salt reactive dyes and the dyes fixable at neutral pH led to reductions into the use of inorganic chemicals. Ultra low liquor ratio dyeing machines, padders with low trough volume capacity and Econtrol dyeing machine are commercially successful developments for considerably reducing the amount of polluting chemicals in the effluent. Therefore, the wider use should be encouraged. Cationisation of cotton is an effective way of reactive dyeing of cotton without inorganic salt and alkali. However, catio nisation using natural biodegradable polymers may be a more preferred environmentally sustainable approach. Replacement of inorganic chemicals with biodegradable organic compounds is another way of reducing effluent pollution effectively The emerging technologies such as ultrasonic energy and supercritical carbon dioxide have been the focus of many researchers. Commercial developments into these technologies for dyeing cot ton fabrics have environmentally sustainable future. Most of the environmentally sustainable options are more costly. Thus, industrial dyers were not encouraged to implement it in past. However, f currently throughout the world, governments and water authorities are introducing tougher load based discharge permits, charges d and penalties. The relative higher costs of environmentally sustainable options may be offset, in whole or part, by the costs of effluent purification or by penalties on more polluted effluent. As many industries are motivated to do effluent purification and recycling, a brief account of effluent purification treatments has s also been provided in this review. Membrane separation techniques y are widely practiced due to their simplicity and recycling advantages. Adsorption on activated carbon, biological and electrochemical treatments. AoPs and AEops are other technologies. However, the effluent treatments are expensive. Therefore, the first obvious choice should always be more sustainable dyeing techniques and technologies.