Meeting the challenges: Membrane processes for water recovery from oily and PVC wastewater

The demand for water recovery in the industry is increasingly important partly due to water shortage and partly due to tightening of regulatory requirements. In this paper water recovery solutions for two challenging types of wastewater - oily and polyvinylchloride (PVC) wastewater - are presented.

The first part of the presentation analyses the operation and performance of a membrane unit operated in an oily waste treatment facility. The facility handles mainly bilge water and industrial oil waste with low concentration of suspended solids. The waste is pre-treated in skimmer tank followed by a band filter before entering an ultrafiltration unit with polymeric membranes. At the entrance of the ultrafiltration unit the oily wastewater contains approx. 1000 ppm emulsified oil, which is then separated into an oil-rich stream which is recycled to the skimmer tank and a permeate stream with less than 2 ppm oil sufficient for direct discharge.

The second part of the presentation focuses on the recovery and reuse of water in the polyvinylchloride (PVC) production. In the PVC production approx. 2.0 - 2.5 m3 of demineralised water is required per ton PVC. In today’s installations 20% of the water used is lost during drying of the PVC or as sealing water. The remaining water is recovered by the PVC decanter. 20 – 25% of the water recovered by the PVC decanter is used for flushing of the facilities, while 75 – 80% is currently discharged to biological treatment. A new concept based on reverse osmosis does not only remove the residual PVC particles but also the inhibitors and conductivity down to levels allowing the direct recycle of decanter water to the polymerisation step and thus reducing water consumption and water treatment costs – both in-take and discharge cost - significantly.

Overall, the case studies presented will demonstrate how membranes can handle even challenging industrial wastewaters at minimal energy costs.