Monitoring and optimization of a wastewater decontamination station operating in the surface treatment industry: Chemical abatement and ecotoxicological impact
The surface treatment (ST) industry is currently undergoing major upheavals, particularly concerning environmental aspects, due to increasingly stringent standards. ST uses large volumes of water and chemicals in its manufacturing processes and its wastewater is acknowledged as being among the most polluting. Although considerable efforts have been made by the industry over the last 20 years, the problem of water pollution remains a significant concern. The main environmental problem facing ST plants is the high pollution load of the effluent they generate. The wastewater is complex and difficult to process as it contains a range of pollutants, some of which can react with each other. However, the tighter legislation in many countries means that the ST industry has reduced its environmental impact. The way decontamination is generally approached by ST plants involves physicochemical treatment to make the contaminants insoluble by adding chemicals then separating the two phases, water and sludge, by physical means. It is in this context that, over a period of 24 months of operation, we analyzed and optimized a physicochemical unit for the treatment of ST industrial wastewater. This article presents the abatements obtained in the levels of pollution after the various chemical optimizations validated in the laboratory and then transposed to the industrial site. The optimization of the station reduced the organic load, nitrite and zinc by about 70%, 85%, and 80%, respectively. To evaluate the utility of each optimization proposal, standard bioassays based on the germination of lettuce seeds were carried out on the influent and effluent of the treatment plant. Decreasing concentrations of pollutants in the effluent led to a reduction of its impact on seed germination. Bioassays based on plant growth also confirmed the environmental benefits obtained after optimization of the station. The biological tests proposed are thus good indicators of the contaminant concentrations present in wastewater pre- or post-treatment. These simple and inexpensive tests are reliable and can be used routinely to assess the impact of effluent.