Quantitative Evaluation for Inhibitory Effect of Single and Binary Mixture of Heavy Metals on the Growth and Phosphorus Removal of Bacillus Sp.

This study was conducted to quantitatively evaluate the effect of three heavy metals (Cd, Zn, Ni) on growth and P removal efficiencies of the Bacillus sp. 3434 BRRJ., known as phosphorus removing bacteria(PRB). It was cultivated in singles, binary mixtures of batch systems with three heavy metals. IC₅₀ (half of inhibition concentration of bacterial growth) and EC₅₀ (half of effective concentration of phosphorus removal efficiency) were used to quantitatively evaluate the effect of heavy metals on the growth and phosphorus removal efficiency of Bacillus sp. 3434 BRRJ. In addition, the interactive effect between heavy metals was evaluated for using additive index method (AI). As the concentrations of added heavy metals, regardless of the type, were increased, growth and P removal efficiency of the PRB were decreased. P removal efficiency of Bacillus sp. 3434 BRRJ was 92.8%, IC₅₀ of Bacillus sp. 3434 BRRJ were 0.4 mg L^-1 for Cd, 6.45 mg L^-1 for Zn, and 17.89 mg L^-1 for Ni. EC₅₀ of Bacillus sp. 3434 BRRJ was 0.43 mg L^-1 for Cd, 7.15 mg L^-1 for Zn, and 15.65 mg L^-1 for Ni. Cd was the greatest inhibitory factor on growth and P removal efficiency of bacteria, whereas the smallest effect was observed in the Ni. In the binary mixture treatments of heavy metals, the treatments of lowest IC₅₀ and EC₅₀ were the Cd + Zn treatment (IC₅₀=5.22 mg L^-1_, EC₅₀=6.46 mg L^-1), the treatments of highest IC₅₀ and EC₅₀ were the Zn + Ni (IC₅₀=13.53 mg.L^-1_, EC₅₀=15.17 mg.L^-1₎. It appears that this study could provide the basic information about the toxic effects of the single and binary mixtures treatments of heavy metals on the growth and P removal efficiency of PRB.