Waste water treatment in surface treatment workshops

The oldest and most widely used treatment technique is physico-chemical. It insolubilizes most of the metal ions and certain anions that are harmful to the environment, then separates the solid phase (sludge) from the liquid phase, which is returned to the receiving environment or sewer system after post-treatment.

The various stages of treatment are reviewed: storage, pre-treatment, precipitation-neutralization, liquid-liquid separation, post-treatment and sludge dewatering. Even if this treatment is carried out correctly, the effluent discharged still has a toxicity that can be harmful to the receiving environment and to the proper operation of treatment plants, and certain saline and organic pollutants are not, or only very slightly, eliminated.

Given the increasingly stringent environmental constraints that are becoming more and more difficult to meet by conventional means, without additional treatments requiring costly investment, manufacturers are being encouraged to work towards "zero liquid discharge". The main techniques already used to achieve zero discharge, and the difficulties encountered, are presented here.