Optimization of Cr⁶⁺ Removal by Bacillus subtilis Strain SZMC 6179J from Chromium-Containing Soil

The removal rate of Cr⁶⁺ has been explored by the optimized removal conditions. Five Cr-resistant strains were isolated from chromium-contained soil. The most efficient strain S1 was identified as Bacillus subtilis strain SZMC 6179J through 16S rDNA. Response surface methodology (RSM) was used to investigate the effects of four independent variables, including initial pH, initial Cr⁶⁺ concentration (mg/L), time (h) and inoculation percentage (%). RSM revealed that when pH was 5.02, time was 24.0 h, inoculation percentage was 4.64% (v/v) and initial concentration of Cr⁶⁺ was 55.0 mg/L, the optimal condition was obtained. Under the optimum conditions, the actual response values for Bacillus subtilis strain SZMC 6179J was 93.50%. The pH was the most significant factor towards removal rate of Cr⁶⁺. The result showed that the removal mechanism of Cr⁶⁺ by Bacillus subtilis strain SZMC 6179J was reduction under normal conditions. The removal mechanism of Cr⁶⁺ by Bacillus subtilis strain SZMC 6179J was adsorption under adverse conditions.