Synergistic transformation of Cr(VI) in lubricant degradation by bacterial consortium.

In recent years, it has become widely acknowledged that heavy metals are often present in oil-contaminated sites. This study utilized three specific types of microorganisms with different functions to construct a composite bacterial consortium for treating lubricant-Cr(VI) composite pollutants. The selected strains were Lysinbacillus fusiformis and Bacillus tropicus. The Back Propagation Neural Network-genetic algorithm was employed to optimize the secondary bacterial addition time to 67 h and the strain ratio to 2:1. The optimized process involved the use of 4.6 g/L glucose and ammonium oxalate as electron donors. After 6 days of treatment with the composite consortium, the removal rates of 1500 mg/L lubricating oil and 50 mg/L chromium reached 90.3% and 84.2%, respectively. Initial analysis using three-dimensional fluorescence to examine the changes in extracellular polymers in the bacteria when exposed to chromium-lubricating oil, showed that 30 mg/L Cr(VI) could induce the secretion of extracellular protein-like substances. These substances may be directly or indirectly involved in the biological detoxification mechanism of chromium. The synergistic removal of complex pollutants has the potential to transform previous "unilateral" removal studies and enhance bioremediation efficiency.