Oxidation-coagulation-filtration processes for the reduction of sulfide from the hair burning liming wastewater in tannery

The liming wastewater in tanneries contain huge amounts of soluble sulfide; upon acidification, this produces toxic hydrogen sulfide, which is a grave environmental concern. In the present study, an approach was made to treat liming wastewater with oxidation-coagulation-filtration techniques; wastewater was treated with hydrogen peroxide to eliminate the emission of hydrogen sulfide and aluminum sulfate was used as coagulant. The physicochemical parameters of untreated liming wastewater were: sulfide 7285.2 ± 11 mg/L; pH 12.5 ± 0.2; total dissolved solids (TDS) 23.8 ± 0.3 g/L; total suspended solids (TSS) 17.8 ± 0.2 g/L; electric conductivity (EC) 40.5 ± 0.2 mS; salinity 23.4 ± 0.1 ppt; and dissolved oxygen (DO) 8.3 ± 0.1 mg/L. The physicochemical parameters of the treated liming wastewater at optimum conditions were: sulfide 81.9 ± 0.5 mg/L; pH 6.9 ± 0.2; TDS 4.5 ± 0.1 g/L; TSS 0.8 ± 0.02 g/L; EC 5.8 ± 0.1 mS; salinity 3.1 ± 0.04 ppt; and DO 7.3 ± 0.03 mg/L. The removal efficiency of sulfide, TDS, TSS, EC and salinity were 99%, 81%, 96%, 86% and 87%, respectively. The most promising outcome of this technique was the efficiency in the removal of sulfide. This simple technique for treating liming wastewater would be very effective in reducing environmental pollutants being emitted by the tanneries.