Water Footprint Calculation, Effluent Characteristics and Pollution Impact Assessment of Leather Industry in Bangladesh

Abstract

Leather processing industries consume high volumes of water and chemicals and release effluents into the environment that pollute the surface water and may cause harm to human health. Leather processing involves different wet processing stages such as soaking, liming, chrome tanning, rechroming, neutralization, fatliqouring and dyeing. The pollution generated from the leather processing stages varies in volume, nature and concentrations. Qualitative and quantitative assessments of effluents generated from different stages of leather processing can be useful to understand the stagewise and overall water pollution of leather wet processing and to design and plan pollution abatement initiatives. Water footprints (WF) can help in understanding the total water consumption and water pollution caused by the leather sector. The objectives of this research are to assess the characteristics of effluents generated from different stages of leather processing, calculate the water footprint (WF) and analyze the pollution load of the Bangladesh leather sector. To perform experimental analyses, effluent samples were collected from the following leather processing stages: soaking, liming, deliming and bating, pickling and tanning, wet back, rechroming, neutralization, retanning, dyeing and fatliqouring from four leather processing factories. The key pollution indicating parameters, such as pH, chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved solid (TDS) and total suspended solid (TSS) of the effluent samples were analyzed. The experimental study showed that almost 52% effluents generate from beam house and tan yard operations, and about 48% effluents generate from post tanning operations. Due to the presence of high amounts of salt, insecticides and bactericides, the effluent generated from the soaking stage contains high BOD and TDS. On the other hand, effluent generated from liming contains the highest amounts of BOD, COD, TDS, and TSS. The reduction or segregation of soaking and liming effluents will be effective in improving the environmental performance of the wet processing of leather. To assess the total water footprint of the leather sector, the water footprint of feed crops and raw hides were calculated, along with the water footprint of the leather processing stages. The water footprints of bovine and ovine crust leather were found to be 34,000 m3/ton and 17,300 m3/ton, respectively. The blue water footprint is higher in soaking, liming and finishing. The green water footprint of leather is mainly contributed by feed crops of farming animals. The grey water footprint was found higher in the soaking, liming, fatliqouring and dyeing stages. About 97% of the water footprints of tanneries are contributed by the wet processing stages. The grey water footprint is the most significant part of the total water footprint of the leather sector, which indicates the impact of high water pollution by the leather processing stages. This study can help to understand the overall scenario of water consumption and water pollution caused by the leather sector in Bangladesh. This study can also be useful in designing sustainable leather products by reducing the total water footprint per unit of leather goods. The systematic approach of this study could be useful for other countries in leather processing.