Impact écotoxicologique du traitement chimique des eaux usées de tanneries: Analyse technico-économique
The purpose of our investigation was to evaluate the acute toxicity of chromium tanning and liming-deliming waste waters before and after chemical treatment. The invertebrate Daphnia pulex was used for toxicity test. The toxicity due to these industrial waste waters was revealed by the equations of the regression lines. The results of the toxicity test showed that the waste waters from chromium tanning and from dehairing presented higher toxicity, with respective 24-h IC50 values of 0.15 and 3.36. This toxicity could be explained by higher levels of chromium, sulphides and organic matter in these waste waters. After processing by chemical precipitation, 24-h IC50 values increased from 0.15 to 26.6 and from 3.4 to 11.1 respectively for the chromium tanning and the de-hairing waste waters. Consequently, these processed effluents can be classified as low toxic wastes. This diminution of the toxicity is linked to a reduction of suspended matter (95 %), COD (55 %), Cr (90 %) and sulphides (50 %). Hence, this treatment presents at least two advantages. The first is environmental, as just mentioned; the second is economic, since chromium can be recycled for reuse in leather tanning. The results suggest that the recovered chromium is similar to commercial tanning chromium. In fact, a techno-economical analysis showed that proposed treatment project can be economically beneficial (3112,50 $ per 1000 tons per year).