Immobilization of cadmium in soils by UV-mutated Bacillus subtilis 38 bioaugmentation and NovoGro amendment

Immobilization of cadmium (10 mg Cd per kilogram soil) in soil by bioaugmentation of a UV-mutated microorganism, Bacillus subtilis 38 accompanied with amendment of a bio-fertilizer, NovoGro was investigated using extractable cadmium (E-Cd) by DTPA. B. subtilis 38, the mutant with the strongest resistance against Cd, could bioaccumulate Cd four times greater than the original wild type. Single bioaugmentation of B. subtilis 38 (SB treatment) to soil however did not reduce E-Cd significantly, while the amendment of NovoGro (SN treatment) reduced E-Cd remarkably. Simultaneous application of B. subtilis 38 and NovoGro (SNB treatment) exhibited a synergetic effect compared to the single SB and SN treatment. The immobilization effect was significantly affected by temperature, soil moisture, and pH. It seems that the immobilization on Cd reached the maximum when environmental conditions favored the activity of microorganisms. Under the optimum conditions, after 90 days incubation, E-Cd was 3.34, 3.39, 2.25 and 0.87 mg kg-1 in the control soil, SB, SN and SNB soils, respectively. NovoGro not only showed a great capacity for Cd adsorption, but also promoted the growth of B. subtilis 38. This study provides a potential cost-effective technique for in situ remediation of Cd contaminated soils with bioaugmentation.