Removal of single and multi-heavy metals from piggery digestate by the electric field-microalgae system: Influences, kinetics and mechanisms

Abstract

Electric field-microalgae system (EFMS) has demonstrated significant potential in removing humic acids and nutrients from the piggery digestate, while its removal of heavy metals (HMs) has not been extensively studied. This study investigated the factors influencing the removal of HMs removal by EFMS, as well as the kinetics and underlying mechanisms. Results showed that the removal of single HM by EFMS was dependent on the initial concentration of HM, with the highest removal efficiency being 85.54 % for Cu²⁺ at 4.00 mg/L, 97.87 % for Zn²⁺ at 10.00 mg/L, and 99.07 % for Cd²⁺ at 2.00 mg/L, respectively. Cu²⁺ was removed preferentially by EFMS when the three HMs coexisted, achieving an efficiency of approximately 86 % within 1 h. Meanwhile, the removal efficiency of Zn²⁺ and Cd²⁺ approached 85 % after 1.5 h. The simultaneous removal of multiple HMs by EFMS was affected by factors including the intensity of the electric field, the concentration of microalgae inoculum, and the pH level. The removal of the three HMs by EFMS followed the pseudo-first-order kinetic model. The primary mechanism of HMs removal by EFMS involved oxidation reactions induced by the electric field, followed by adsorption processes.