Opportunities and challenges of using ultrafiltration for the concentration of diluted coating materials

The use of cross-flow ultrafiltration for the recovery of coating material from aqueous streams started about 30 years ago with electro-deposition paint in the automotive industry. This early success can be related to both environmental and economical advantages of using ultrafiltration. Ultrafiltration recovers and concentrates electro-deposition paint on the retentate side and produces purified water on the permeate side. Based on this success, the focus more recently moved to other coating materials, such as paper coatings, latex and flexographic ink. Similar to electro-deposition paint, the concept is to recover the diluted coating materials with ultrafiltration to obtain a solid-free permeate stream, which can be either recycled or easily treated, and a retentate stream, which contains the coating materials preferably at concentrations suitable for recycling or disposal. The advantages can be directly translated into very short payback times for ultrafiltration systems of typically less than two years. Application studies focusing on the coating recovery in a paper mill, the concentration of latex from the tank wash at a latex producer and the recovery of flexographic ink at a producer of printed cartons will highlight these benefits.