Mesophilic aerobic degradation of a metal lubricant by a biological consortium

The metal-forming industries require the use of greases to lubricate metal surfaces during manufacturing operations, and the residues of these lubricants must be removed prior to finishing processes to protect and improve the appearance of the final product. An aqueous, biological metal-cleaning process operating under mild conditions (pH 9, 42°C) eliminates the use of environmentally unfriendly cleaning materials such as chlorinated solvents by employing microorganisms to degrade greases and oils naturally. This process was characterized in terms of initial degradation rates of a representative metal lubricant and by phylogenetic identification of the active bacteria. The metal lubricant in a surfactant solution was degraded by a bacterial consortium, and its concentration was determined by a novel gas chromatography assay. The maximum degradation rate V_max and the apparent K_m were obtained as 45 mg/(day mg protein) and 24 g/l on cellular basis, and 4.6 g/(day 1) and 33 g/l on a volumetric basis, respectively. Mineralization of the metal lubricant was shown by analyzing the evolved CO₂ and Cl^-, and the bacterial consortium utilized the metal lubricant as a sole carbon and energy source (μ=0.05±0.01 h^-1 at 0.5 vol% lubricant concentration). The active bacteria in the biological metal-cleaning process were identified as Bacillus licheniformis for the higher lubricant concentrations (3, 5, and 7.5 vol%), Bacillus cereus at 1 vol%, and Pseudomonas aeruginosa, Rhizobiaceae strain M100, and Achromobacter sp. LMG 5431 at 0.3 vol%.