Purification and recycling of tannery degreasing wastewater by ultrafiltration with polyimide membrane

Tannery degreasing wastewater contains a large quantity of fatty substances which constitute a source of pollution that is difficult and expensive to treat. In order to reduce the pollution, the wastewater was purified by ultrafiltration with polyimide membrane and recycled in the degreasing process. The effects of the ultrafiltration parameters on wastewater flux and COD rejection were investigated during the purification. The characteristics of wastewater, as well as membrane regeneration were measured during the recycling. The results show that a steady flux of over 13.1L/m²h with a rejection of above 90% of COD can be obtained at 25°C under a trans-membrane pressure of 0.085MPa during the ultrafiltration at pH 9. The fatty substances in wastewater can be reduced from 31824 mg/L to less than 178 mg/L by the ultrafiltration. Neither in wastewater nor in degreased pigskin the accumulation of fatty substances was found during the recycling. The purification and recycling process has the good potential for industrial application.