Activated sludge process enabling highly efficient removal of heavy metal in wastewater

Activated sludge process was a low-cost alternative method compared to the conventional physicochemical process for the treatment of heavy metal-containing wastewater. In the present study, the removal efficiency of Pb²⁺, Cu²⁺, and Ni²⁺ from wastewater by a sequencing batch reactor (SBR) activated sludge system was investigated, and the mechanism was revealed by static adsorption experiment of activated sludge. The results showed that the activated sludge in the SBR system was effective in removing Pb²⁺ and Cu²⁺ from wastewater at 10 mg·L^-1 initial concentration, with a removal efficiency of 83.1 ~ 90.0% for Pb²⁺ and 74.3 ~ 80.6% for Cu²⁺, respectively. However, the removal efficiency for Ni²⁺ was only 0 ~ 6.2%. Static adsorption experiments showed that the adsorption capacity of activated sludge for three heavy metals was shown as Pb²⁺  > Cu²⁺  > Ni²⁺. When the initial concentration was 20 mg·L^-1, the equilibrium adsorption capacity of activated sludge for Pb²⁺, Cu²⁺, and Ni²⁺ was 18.35 mg·g^-1, 17.06 mg·g^-1, and 8.37 mg·g^-1, respectively. The main adsorption mechanisms for Pb²⁺ and Cu²⁺ were ligand exchange, electrostatic adsorption, and surface organic complexation processes, but Ni²⁺ removal mechanism mainly included electrostatic adsorption and surface organic complexation processes, showing that Ni²⁺ removal was inhibited in the presence of Pb²⁺ and Cu²⁺. The physicochemical properties and microbial diversity of activated sludge were greatly affected by the heavy metals in the SBR system, and genus Rhodobacter was found to be dominant bacteria enabling resistance to heavy metal ions.