Dry ice – an eco-friendly alternative for ammonium reduction in leather manufacturing

Leather processing involves various unit processes in which deliming is an essential unit process carried out conventionally using ammonium salts. This results in the generation of a huge amount of ammoniacal nitrogen and a considerable amount of total dissolved solids in tannery wastewater. In the current work, an effort has been made to design a deliming process using dry ice (solid carbon dioxide). It was observed that 2% (w/w) dry ice is adequate for the complete deliming of limed pelts of goat skins in 45 min; whereas the conventional process using 2% ammonium chloride requires 60 min. Morphological analysis using scanning electron microscopy shows no surface deposition or grain damage on delimed pelts processed using dry ice. Experimental leathers exhibit organoleptic and mechanical strength properties comparable to that of control leathers. The alternative method developed using dry ice reduces the generation of ammoniacal nitrogen, total dissolved solids, total Kjeldahl nitrogen and chloride from the deliming process by 98, 88, 95 and 94% respectively compared to the control process. This method also helps in reduction of chemical oxygen demand and biochemical oxygen demand in wastewater. Moreover, the methodology of using dry ice for deliming is very simple for practical applications. The option of using dry ice for deliming would be effective for cleaner leather manufacture.