59    INVESTIGATION INTO THE NATURE AND
EXTENT OF MICROBIAL CONTAMINATION PRESENT
IN A COMMERCIAL METALWORKING FLUID
Keith M . Rinkus, Ph.D. Candidate
Wei Lin, Res. Assistant Professor
Alka Jha, M.S. Candidate
Brian E. Reed, Associate Professor
Department of Civil and Environmental Engineering
West Virginia University
Morgantown, West Virginia 26506-6103
ABSTRACT
A commercial metalworking fluid, 5% stock solution/95% deionized water, was found to contain multiple microbial species including bacteria, most probably Actinobacter, Pseudomonas,
Aerobacter and Bacillus, and fungi Bacterial concentrations in the metalworking fluid increased
with decreasing temperature (5.0 x 107 @ 50%C and 2.5 x 108 @ 37%C). The bacterial population was capable of using all the stock solution components as substrates. However, fatty acids
and fatty acid esters were metabolized at a much greater rate than the other components due to
the ease of the P-oxidation metabolism of these components. Rates of biological growth decreased with increasing temperature.
INTRODUCTION
Metal manufacturing facilities use rolling processes to press large ingots into forms suitable
for various processes and products. For metal rolling operations (MR), lubrication of the machine workpiece area is of major concern for production of high quality products. Lubrication of
the machine workpiece area is achieved through the application of oil-water emulsions referred
to generically as metalworking lubricants or fluids (MWFs). In addition to lubrication effects,
MWFs also serve the purposes of workpiece and tool cooling and rust formation inhibition in the
rolling operation area.
Establishment of an optimum metal rolling operation is dependent upon the establishment of a
stable MWF and therefore, a stable oil-water emulsion. However, an oil-water MWF is inherently thermodynamically unstable. Therefore, if the composition or concentration of the emulsion ingredients, the pH, the ambient temperature or any of a number of different parameters is
changed, the characteristic properties of the MWF may also change, affecting product quality.
One factor which may compromise the integrity of MWF is the presence of microorganisms. The
growth of microorganisms leads to the destruction, through metabolic activity, of lubricant ingredients and a production of acidic materials which leads to a weakening in emulsion stability.
Emulsion breakdown results in oil/water separation, which adversely impacts the primary function of lubrication. Production of acidic materials may also lead to corrosion of equipment and
workpieces, pH imbalances, and objectionable odors.
The purpose of this study was to investigate the nature of the microorganisms inhabiting a
MWF used in an metal rolling operation. This investigation was composed of a microscopic examination, culture of microorganisms in both MWF and various microbiological media and determination of microbial substrate utilization rates using oxygen uptake (OxU) respirometric
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press, Chelsea. Michigan 48118. Printed in
U.S.A.
601