Enhanced removal of Microcystis aeruginosa in BDD-CF electrochemical system by simple addition of Fe2+

•Simple addition of Fe2+ greatly enhanced M. aeruginosa removal in BDD-CF system.•Enhancement with Fe2+ was dominated by heterogeneous electro-Fenton mechanism.•Electrochemical reduction on CF cathode sustained the cycle of Fe(III)/Fe(II).•Fe2+ addition intensified the lipid peroxidation and degradation of microcystin.•The added Fe could be easily recycled due to its complete deposition on CF cathode.

This study presented a significant enhanced removal of Microcystis aeruginosa by simple addition of Fe2+ at circumneutral pH in the electrochemical system with boron-doped diamond (BDD) anode and carbon felt (CF) cathode. Results showed that over 99.9% of the M. aeruginosa cells were removed in 60 min when 0.2 mM Fe2+ was added to the system. The pseudo-first order rate constant for BDD-CF-Fe2+ system was almost 15 times higher than that (0.005 min−1) for BDD-CF system. The excellent performance of the BDD-CF-Fe2+ system over the BDD-CF system was observed over a wide range of pH from 3 to 9. Based on the evolution of Fe2+/Fe3+, pH, H2O2 and OH, mechanism of enhanced removal of M. aeruginosa was revealed in the BDD-CF-Fe2+ system. H2O2 was electrochemically generated through reduction of dissolved oxygen on the surface of the CF cathode, and the added Fe2+ was rapidly adsorbed and precipitated also on the CF cathode. Comparisons of BDD-CF-Fe2+, BDD-CF-Fe3+ and BDD-CF-Fe2+/Fe3+ systems proved that the electrochemical reduction of Fe(III) to Fe(II) could guarantee the sustainable cycle between Fe(II) and Fe(III). Through heterogeneous electro-Fenton reactions, much higher amount of OH would be continuously generated compared with the BDD-CF system. Thereby, the lipid peroxidation on the cell membrane of M. aeruginosa was intensified through the addition of Fe2+. Moreover, the degradation of intracellular microcystin was remarkably accelerated, and the extracellular microcystin was controlled more safely due to Fe2+ addition. This study provided an alternative method to enhance the electrochemical mitigation of cyanobacteria-polluted waters.