Microbiology in Water-Miscible Metalworking Fluids

Abstract

Water-miscible metalworking fluids (MWFs) are used in metal removal and forming operations. For end use, formulation concentrates are diluted in water, providing conditions conducive to microbial growth and metabolism and potentially causing fluid biodeterioration and microbiologically influenced corrosion. Microorganisms in the environment are highly diverse, and bacteria and fungi have been recovered from these fluids at population densities of >106 CFU mL−1. Thus, to control microbial bioburdens in MWFs, microbicides are often incorporated into MWF formulations, used as tankside additives, or both. Some microbicides are suspected as being responsible for adverse health effects. Consequently, their usage has been restricted in recently adopted regulations. Given the limited number of microbicides currently approved for use in MWFs, alternative microbial contamination control strategies are needed. Some of these strategies have already been employed in the market. Studies on microorganisms in MWFs are often hindered by the complexity of the media, especially when trying to examine in-use samples. Historically, microbiological analyses were primarily based on cultivation assays using nutrient-rich media. These analyses have severe disadvantages, and the adoption of more reliable test methods is of utmost importance. Here, we review MWF microbiology, discussing possible consequences and options for both control and condition monitoring testing.