A rapid technique for determining microbial loads in metalworking fluids

Abstract An indirect method for estimating the degree of microbial contamination in metal working fluids is described. The technique circumvents the time delay associated with plate counts or dipslide procedures by correlating the microbial count with specific microbial enzyme levels. The 15 min procedure was evaluated in synthetic, semi-synthetic and petroleum base metalworking systems under laboratory conditions. The microbial load of a 18 925 litre (5000 US gal) industrial system was also monitored over a three month period using both standard plate counts and the indirect technique. The results indicated that the method could rapidly assess the microbial load in industrial metalworking coolants. In addition, laboratory tests showed that the technique can detect preservative effectiveness in a coolant within a one hour period. The ability to determine the microbial load and biocide effectiveness without an excessive time delay should greatly enhance rancidity control in the metal working industry