During the cutting process, the metalworking fluid is changed due to chemical reactions between its substances; tool surfaces and workpieces; the presence of particles and high temperatures on contact surfaces. Except changes in chemical composition is the biggest problem with the bacterial contamination. Changes in the composition and contaminants such as bacteria pose risks to workers and influence the quality and economy of the whole machining process. To eliminate bacteria mostly biocides are added to the tank side however biocides also pose some health risks for the workers. Tightening legislation creates pressure on the minimizing of the hazardous substances and therefore the utilization of ozone instead of biocides for the sterilization of MWFs was studied. The main aim was to investigate ozone appropriateness for bacteria elimination for in-use metalworking fluid samples while three different kinds (semi-synthetic, synthetic and emulsion type) were tested. It was find out that ozone is able to eliminate bacteria in all tested samples and types of MWFs. When taken into account ozone concentration, with increased amount of ozone, shorter treating time was needed for total bacteria elimination. With decreased initial bacterial load (from 107 to 104 CFU/ml) treating time drastically decreased from 20 to only 2 minutes when 15 g/hour of ozone was applied (in the case of semi-synthetic sample). However ozone application caused on the other hand also small decrease in pH value. The pH decrease might be the critical point in the ozone utilization as a sterilizing agent however the protection function of the fluid against corrosivity was not harmfully affected during the experiment in semi-synthetic or synthetic type of fluid.
