The application of membrane technology for reuse of process water and minimisation of waste water in a textile washing range

Recycling of process streams and reduction of waste disposal using membrane technology in a continuous textile washing process after dyeing with reactive dyes have been investigated theoretically. A mathematical process model of a conventional open-width washing range has been extended by membrane processes to determine the benefits and limitations of the modified washing processes. The concentrations of hydrolysed reactive dyes, sodium chloride, urea and caustic soda have been calculated with this process model. Reverse osmosis for desalination and decolourising and nanofiltration for decolourising have been implemented as membrane technology. Reusing filtered wash water in a previous wash step results in more water saving than recycling to the same wash step according to the process calculations. The total fresh water demand can be reduced by 70% and the total waste water volume by 90% compared with the conventional process. Greater reduction of fresh water use is limited by the osmotic pressure difference between the retentate an permeate streams.