Over a period of 24 months of operation, we optimised a physicochemical plant for the decontamination of surface treatment industrial wastewater. This article presents the abatements obtained in the levels of chemical pollution after the various optimisations validated in the laboratory and then transposed to the industrial site. The optimisation of the plant reduced the effluent organic load, nitrite and zinc levels by about 70%, 85% and 80%, respectively. To evaluate the utility of each optimisation proposal, standard bioassays based on lettuce seed germination were carried out on the final effluent. Decreasing concentrations of pollutants in the effluent led to a reduction of its impact on seed germination. The bioassays confirmed the environmental benefits obtained from the optimisation of the treatment plant. The biological tests proposed seem to be good indicators of the contaminant concentrations present in wastewater.