Recycling, recovery and valorization of effluents in surface treatment workshops

Most surface treatment plants purify their effluent to comply with the French Ministerial Order of June 30, 2006, or with their prefectoral authorization order. Effluent is then discharged into the receiving environment, or into municipal sewage systems connected to a treatment plant.

More and more workshops are working with "zero liquid discharge" on site. However, they do produce concentrated liquid waste, which is usually treated in approved centers.

In this dossier, we look at the techniques most commonly used for :

• Increase bath life and save raw materials by purifying treatment baths and "reassembleable" static baths;

• concentrate rinsing baths: evapo-concentration, reverse osmosis, electrodialysis ;

• recover the most interesting constituents from spent treatment baths and concentrated "non-reassembleable" static baths.

There are six types of technique:

• electric (single-compartment and separate-compartment electrolysis);

• electro-membrane (monopolar and dipolar membrane electrolysis) ;

• membrane (dialysis, ultrafiltration) ;

• surface exchange (ion exchange, activated carbon fixation) ;

• chemical (case-hardening) ;

• thermal (crystallization, evaporation).