The use of ultrafiltration and nanofiltration membranes in the treatment of metal-working fluids

Membrane filtration is used for separating oil from water and treating waste metal-working fluids. This work presents two different filtration systems and investigates the possibility of reusing their permeates. The first system consists of an ultrafiltration membrane (UF) followed by a nanofiltration membrane (NF). In this case, two types of PVDF ultrafiltration membranes, of 200 kD and 100 kD molecular weight cut-off, are used. The second system consists of direct filtration of the metal-working fluids by a nanofiltration membrane. Filtration experiments are carried out in a large-scale, semi-batch process of volume 200 1. The performance of each filtration system is discussed and compared. The permeate resulting from each system is used to prepare fresh metal-working fluid, to simulate the reuse of water in the manufacturing process. Characterisation tests, such as foaming and emulsion stability, are compared for the same metal-working emulsion when made with tap water in order to assess the feasibility of such water reuse.