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 similar to 90.0% for Pb2+ and 74.3 similar to 80.6% for Cu2+, respectively. However, the removal efficiency for Ni2+ was only 0 similar to 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.

Automated summary

Activated sludge process is a low-cost alternative method for treating heavy metal-containing wastewater, and it can effectively remove Pb2+ and Cu2+, but has poor removal efficiency for Ni2+. The adsorption capacity of activated sludge is Pb2+ > Cu2+ > Ni2+, and the adsorption mechanisms include ligand exchange, electrostatic adsorption, and surface organic complexation.