Greener approach to efficient leather soaking process: role of enzymes and their synergistic effect

Enzymes have been used as one of the most promising substitutes for traditional chemicals in soaking process. In this work, three alkaline proteases, TanG, LimeG and FP50, were used in skin soaking process to select appropriate enzymes. Then the pre-optimized enzymes and additives were mixed to prepare a soaking compound enzyme (KRE). The optimal temperature and pH of the compound enzyme were determined. Finally, the KRE was used in skin soaking process and compared with commercial soaking enzyme (CSE). Environmental impact of KRE was assessed. Protein and hydroxyproline absorbance in soaking bath were chosen as the indexes of the degree of enzymatic hydrolysis to protein and collagen of skin. The results indicated that the combination of TanG and LimeG had a good synergistic effect in soaking process. The optimal temperature of KRE was obtained. KRE had high activity at alkaline pH. Compared with CSE, KRE had stronger hydrolytic action to protein in the skin, but the damage to collagen was of no significant difference from that of CSE. The reduction in turbidity, suspended solids (SS), Biochemical oxygen demand (BOD5) and Chemical oxygen demand (CODCr) content in KRE soaking effluent compared to CSE soaking was evident from environmental impact assessment. Moreover, the BOD5/CODCr of KRE soaking liquor was 0.8976 which indicated that the wastewater was biodegradable. The KRE soaking wastewater would not increase contaminants of the total tanning wastewater significantly. KRE can be regarded as eco-friendly material, reducing the environmental impacts and contributing to the development of cleaner leather processing.