Removal of Calcium from Pelt During Bating Process: An Effective Approach for Non-ammonia Bating

Abstract

Ammonium salts can improve the performance of bating by trypsin. But it is one of the main origins of ammonia nitrogen (NH3-N) in tannery wastewater. In this study, the action mechanism of ammonium sulfate (AS) on trypsin bating was investigated. It was found that the activity of trypsin was actually not influenced by AS (1~30 g/L) or pH variation caused by the addition of AS. In fact, the activity of trypsin was partially inhibited by calcium remained in pelts, particularly those concentrated in the grain layer. The main function of AS in bating is to remove calcium so as to maintain the proteolysis activity of trypsin. Based on these findings, several calcium chelating agents, including sodium hexametaphosphate and the composite of sodium citrate and citric acid, were employed in the trypsin bating process. The extents of calcium removal from pelts by using these chelating agents were higher than AS, and the bating performances were better in terms of protein and hydroxyproline contents in bating liquor.