Biodegradability of wastewater from enzymatic soaking and unhairing processes in leather manufacture

Enzyme-treating processes in leather making are usually considered as 'clean technology' in terms of the reduction of pollutants in wastewater. The objective of this study is to investigate the biodegradability of the wastewater collected from enzyme-treating processes. It is of great significance to characterize the pollution properties of this kind of wastewater, and to provide a reference for the biological treatment of such wastewater in effluent treating yard of tannery. The research was typified by enzymatic soaking and unhairing (ESU) processes which are encouraged to be used in leather manufacture for reducing environmental impact. The biodegradability of ESU wastewater before and after settling treatment was investigated, in comparison with that of wastewater collected from conventional soaking and unhairing (CSU) processes. It was found that ESU wastewater had better biodegradability than CSU wastewater. The biodegradation extent of ESU and CSU wastewaters reached 58.5% and 37.7% respectively in 20 days of naturally biodegrading process. Moreover, it was found that, in the presence of activated sludge, 65.5% of the total oxygen-consuming materials in ESU wastewater is biodegradable, while the value of CSU wastewater is 58.2%.