A portable sensor system for bacterial concentration monitoring in metalworking fluids

The detection of bacterial concentrations in metalworking fluids (MWFs), oil-in-water emulsions used in the cutting industries for cooling and lubrication, is important in order to extend the product life-cycle and plan its disposal according to regulations and legislations. The standard method of measuring culturable bacterial concentration is the plate count technique (PCT) that, however, has long response times and is not suitable for automatic implementation outside a laboratory. In this paper a portable sensor system that measures the bacterial concentration in liquid and semi-liquid media exploiting impedance microbiology is presented and tested for the application of MWF microbial monitoring. A set of MWF samples, taken from metalworking plants, have been tested and good agreement has been found between the system response and that of the PCT. The proposed system allows automated bacterial concentration measurements with shorter response times than the PCT (4 to 24 h vs. 24 to 72 h) and is suitable for in-the-field MWF monitoring.