Hair burning liming in tanneries: a potential sulfide source to the environment

In tannery, liming is the first and indispensable chemical operation where raw hides/skins are treated with sodium sulfide and calcium hydroxide. Liming process releases wastewater containing soluble sulfide in the effluent. In this study, soluble sulfide in the wastewater was estimated during hair burning liming process in the tannery. The soluble sulfide content in liming wastewater was determined by titrimetric method following the official methods of analysis of Society of Leather Technologist and Chemists. It was estimated that, in Bangladesh, yearly 208-623 metric ton soluble sulfide is discharged only from the cowhide processing during hair burning liming process. The sulfide has an adverse impact on the environment including water bodies, atmosphere, land, and plant. Liming wastewater mixing with lower pH wastewater releases hydrogen sulfide gas which has negative effects on the human health and atmosphere. Tanner should use the alternative unhairing methods, e.g., enzymatic, sweating for the cleaner production.