Treatment of waste filature oil/water emulsion by combined demulsification and reverse osmosis

The combined method of demulsification and reverse osmosis (RO) has been employed in the present study to deal with the filature wastewater which is a sort of high-strength and stable oil/water emulsion produced in Shen Ma Industrial Co. Ltd. of China. The influence of varying the conditions for removal of oil, such as the dosage of demulsifier (a kind of cationic surfactant synthesized by authors), the pH of aqueous solution, heating temperature and time on demulsification have been investigated firstly. RO treatment using SE membranes (99.0% of average desalination rate for 2 g/L NaCl) of OSMONICS Co. was then conducted as the next polishing step to further lower both chemical oxygen demand (COD) and oil concentration in order to improve the water quality of permeate. The pilot-scale experiments results show that the removal rate of COD, turbidity and oil from the filature o/w emulsion can be obtained to 99.96%, 100% and 100%, respectively, in 30–50 min at 80–90 °C with demulsifier dosage of 0.1% (w/v) for demulsification, and at 35–40 °C with a driving press of 3.6 MPa and the flow rate of 1.5–1.6 m3/h for RO treatment. It was found that the water quality of permeate from the combined treatment process has been consistently excellent to meet the 1st grade discharge standard set in the Chinese National Standards for Integrated Wastewater (GB 8978-1996) due to both high removal rate of oil by demulsification and high COD rejection by RO.