Application of Membrane Separation Processes to Oily Wastewater Treatment: Cutting Oil Emulsions

Abstract

The problem of treating oily industrial effluents such as used cutting fluid emulsions arises in many types of industry, mainly in metalworking plants and mechanical engineering workshops. In France, these effluents represent a volume to be treated of about 300,000 m³ per year.

This document gives an overview of the state of the art in conventional treatment methods and practices, and presents more recent procedures based on membrane procedures, essentially of the ultra-filtration type. The interest and present limitations of these processes are discussed and examples of their industrial implementation presented.

There follows a summary of the most recent work performed by the authors, demonstrating three original and complementary lines of research which may lead to advances in the treatment of this type of effluent by membrane processes.

The first line of research takes the problem upstream, in the design of clean processes and products; i.e. it consists of studying and suggesting new formulations for cutting fluids which would be less polluting and easier to treat than the cutting fluids on the market at present.

The second is aimed at pushing back the economic limits of the ultrafiltration process when applied to the treatment of macro-emulsions. At the moment these economic limits are mainly imposed by the low permeate flows obtained because of concentration polarisation phenomena, which means that installations require too great a total membrane area when the processed flow exceeds 5 m³/h. A new method based on a combination of partial chemical destabilization and ultrafiltration has been studied, proposed and patented. The first results of this study show that high productivity gains can be achieved with this process under certain conditions.

Finally, the treatment of used micro-emulsion effluents with high soluble TOD loading was studied. The third line of research consisted of gathering knowledge in this domain on treatment processes using different membrane techniques, ultrafiltration, reverse osmosis and nanofiitration, so as to be able to propose a process and operating conditions resulting in an oil-free treated effluent having a reduced soluble TOD content.