Phosphorus Depletion as a Green Alternative to Biocides for Controlling Biodegradation of Metalworking Fluids

Metalworking fluids (MWFs) are used as lubricants and coolants in the manufacturing operations. Their biodeterioration, while in operation, is a widespread problem leading to poor performance and worker health issues. Adding biocides, though effective in reducing microbial growth, leads to the production of more recalcitrant wastewaters that are difficult to dispose or recycle on-site. Increasing environmental concerns have led to robust legislation for reducing/eliminating the use of toxic biocides in MWFs, stimulating a growing interest in the development/application of alternative biological preservation strategies. In this study, inducing nutrient imbalance was investigated for controlling microbial growth in MWFs. Phosphorus was immobilized employing insoluble La 2 O 3 o form LaPO 4 . Concentrations of La 2 O 3 greater than 0.08%w (%w = weight percent) completely inhibited microbial growth (from 1.4 × 10 7 o 0 CFU/mL) and hindered biodegradation. Raman spectroscopy suggested that La 2 O 3 converted intracellular phosphorus into LaPO 4 . The growth inhibition potentials of both 0.06%w La(NO 3 ) 3 and La 2 O 3 were found to be superior to formaldehyde. The antimicrobial property of La 2 O 3 (i.e., inhibition) was tenable by adding sufficient phosphate, acting as an on/off switch for controlling microbial growth in MWFs. This technology offers the potential to reduce/eliminate the use of biocides in MWFs, improves the feasibility of end-of-life biological treatment, and closes the water loop.