| Metalworking fluids (MWFs) are used in manufacturing as coolants, lubricants, and corrosion inhibitors. Growing MWF acquisition and disposal costs, together with concerns about microbiological health hazards and environmental impact have led to increased interest in MWF recycling, contaminant control, and alternative application strategies. Membrane filtration can remove microbes, particulate, and tramp oils that contaminate metalworking fluids and has the potential to reduce health risks and extend MWF life in the machine tool industry. However, poorly understood relationships between the compatibility of metalworking fluid ingredients, contaminants, membrane materials, and membrane pore-size distributions have precluded the widespread industrial application of the technology.; This research assesses the mechanisms of productivity decline during the microfiltration of an uncontaminated synthetic MWF using aluminum oxide membranes and develops a model to assist the design of membrane filtration systems for microbial control. It is revealed that while the majority of synthetic MWF ingredients have a negligible impact on microfiltration productivity, specialty additives such as lubricants, defoamers, and biocides can significantly reduce productivity. This is due to adsorption of these ingredients to the membrane surface that serves to increase resistance to MWF flow through the membrane pores. MWF ingredient characteristics such as solubility, hydrophobicity, and electrostatic charge can influence adsorption and productivity-loss during microfiltration. These findings demonstrate that the chemistry and concentration of specialty additives are important considerations to be accounted for during the design of membrane filtration systems for MWF recycling.; The design of membrane filtration systems is also influenced by the rate of contaminant build-up in the MWF. Microbiological population growth can grow to potentially hazardous levels in extremely short time-scales. Membrane filtration systems designed to control microbial populations must remove microbes from the MWF at a rate faster than population growth. A model is developed to relate microbiological parameters such as growth rate, yield, and substrate consumption to membrane filtration system design parameters. The model is used to determine if microbial growth control is possible for a given metalworking fluid, membrane filtration system, and membrane cleaning schedule. |
