Characterization and treatment of effluents loaded with sulphides from two tanneries: Modern and Artisanal

The objective of this work is to characterize and treat wastewater loaded with sulphide ions from two types of modern and artisanal tanneries.  A preliminary diagnosis was made of both types of artisanal and modern tanneries and showed that modern tanneries consume more water and chemicals than traditional tanneries. The most sulphide-laden steps are those of unhairing-liming and lime baths for modern and artisanal tanneries respectively. The physicochemical characterization of the wastewater from the different operating units of the two types of tanneries shows that the unhairing-liming and lime baths steps are the most loaded with sulphides, in addition to their high load of non-biodegradable organic material. However, we note that wastewater from artisan tanneries is less polluting than that from modern tanneries. The treatment of sulphide ions was first carried out on a synthetic solution at different concentrations by precipitating sulphides with ferric chloride at pH adjusted according to the Pourbaix diagram. The results of the treatment of the synthetic solution of concentration 1500 mg.L -1 allowed the reduction of 91% of sulphide to pH = 8.5.The analysis of the precipitate formed by the X-ray diffraction records the presence of gypsum. The treatment of wastewater from the unhairing-liming units of modern and artisanal tanneries by ferric chloride 1.2 and 0.8 mol.L-1 respectively under the optimum conditions raised leads to a reduction of the non-biodegradable organic load of almost 96% and those of sulphide ions of about 90% for both types of tanneries.