Elimination of chemical sludge for treatment of tannery wastewater and its effect on biogas generation

Disposal of sludge generated during treatment of tannery wastewater poses a major challenge owing to scarcity of land available for implementation of secured landfill facilities. Considering the magnitude of the problem, the present study focused on reduction of the volume of chemical sludge generated during physico-chemical treatment of wet-blue to finish tannery wastewater, by adopting plain sedimentation followed by anaerobic treatment for biogas generation. Apart from monitoring the effect of suspended solids on biogas generation, the effect of chromium concentration and COD/SO4 ratio on biogas generation was also investigated in detail. During anaerobic treatment of composite tannery wastewater without plain sedimentation, biogas generation of 204 mL/g of COD removed was observed. Whereas, with 2 h settlement, the biogas generation observed was 255 mL/g of CODremoved. The amount of sludge generated during treatment of 1 m3 of tannery wastewater with plain sedimentation for a period 2 h was only 0.5 kg/m3, whereas with addition of chemical coagulant and coagulant aids, it was about 3.03 kg/m3. Hence, for the tannery wastewater generated from wet-blue to finish tanning operations, plain sedimentation followed by anaerobic treatment is an environmental friendly option for elimination of chemical sludge.