Guidelines and legislation for dye house effluents.

Increasing attention has been paid over the years to the environmental problems related to industrial activities. Environmental standards have been established and control organisms have been created with a view to applying restrictive legislation. In the dyeing industry, ennoblers discharge in the environment large volumes of strongly coloured effluents that are heavily loaded with pollutants and highly concentrated in salts. This chemical load is generated during the different steps of textile preparation. After reviewing the characteristics of these effluents, this paper gives a comparative review of the current legislations on the dyeing industry emissions. It examines more closely the discharge legislation, first in France and then in other countries around the world. A comparison of the six most representative parameters shows how different the applied constraints are in different countries.

Coagulation-flocculation-decantation of dye house effluents: concentrated effluents.

The treatment and valorization (recycling of water and mineral salts) of dyeing effluents constitutes a major economic and environmental issue. Cotton dyeing using reactive dyes is actually the most polluting in terms of discharge. In order to treat and valorize the effluent from a dyeing process using reactive dyes, the firm Clariant and the LPPE have developed and patented a process allowing the recovery of most of the water and salts present in the effluent and also of a concentrate containing the hydrolyzed reactive dyes and the highly concentrated auxiliaries. This paper describes the coagulation-flocculation-decantation process used to optimize water recovery from the concentrate. Coagulants and flocculants are used in the industry for the treatment of effluents produced by the synthesis of dyes in general (acid, disperse, reactive). Although the settling velocity is relatively low, the results show that it is possible to recycle a great volume of water using a small decanter area, since the concentrate flow rate is low. These effluents are substantially discolored, it possible to envisage recycling them.

Treatment of silica effluents: ultrafiltration or coagulation-decantation.

In the electronics industry, the preparation of silicon plates generates effluents that contain a great amount of colloidal silica. Two processes--decantation and ultrafiltration--are studied with in view the treatment of the effluents released by the firm Rockwood Electronic Materials. The feasibility of each of the two processes is studied separately and their operating parameters optimized. Both processes allow the recovery of a great proportion of the initial effluent (over 89%) as transparent and colorless water that can be reused at the start of a line. In view of the results and of the compared advantages and disadvantages of the two processes, ultrafiltration will be selected for the industrial unit.