Adsorption of heavy metal tolerance strains to Pb 2+ and Cd 2+ in wastewater

Abstract

The functional strains with high tolerance to heavy metal Pb²⁺ and Cd²⁺ were screened from soil obtained in a heavy metal waste accumulation area. The immobilized biological adsorbent was made by embedding method and used for treatment of wastewater containing heavy metals. The effects of initial concentration of heavy metals, adsorption time, pH value of wastewater, and dosage of adsorbent on adsorption performance were investigated. The study showed (1) the strains tested were Brevibacterium and their maximum tolerable concentrations for Pb²⁺ and Cd²⁺ were 2200 and 700 mg/L, respectively; (2) the maximum adsorption rate for Pb²⁺ and Cd²⁺ was 87.77% and 57.50% respectively when the dosage of adsorbent was 10 g/L and the pH value of wastewater was 6; (3) Pb²⁺ and Cd²⁺ could be adsorbed in the equilibrium solution for 40 min and the maximum adsorption capacity reached 114.36 mg/g and 82.12 mg/g, respectively; and (4) when the initial pH value of the wastewater was 5–7, the adsorption rate decreased with the increase of the concentration, and the initial concentration of Pb²⁺ had a greater effect on the adsorption rate than Cd²⁺. Langmuir and Freundlich equation showed that the adsorption of Pb²⁺ and Cd²⁺ was mainly on the surface of monolayer. And the pseudo-second-order kinetic equation indicates that Cd²⁺ has a relatively greater adsorption rate than Pb²⁺ does.