Molecular-Level Insights into the Degradation of Dissolved Organic Matter from Cyanobacteria-Impacted Water by Electro-Oxidation and Electro-Fenton

Algal organic matter (AOM) generated from cyanobacteria-impacted reservoirs poses a high risk to drinking water. Electrochemical oxidation is an emerging treatment technology expected to be effective in removing AOM. This study presented the removal of AOM extracted from Microcystis aeruginosa (MA) using electro-Fenton (EF) and electro-Oxidation (EO) employing boron-doped diamond (BDD), modified graphene-Fe2O3 (GFe) anode and graphite felt (GF) cathode. Results indicate that H2O2 generation by BDD and GFe in 30 min behave similarly. The BDD-EF and BDD-EO treatment results shows that both EO and EF are applicable with varying efficiencies, to remove extracellular organic matter (EOM), intracellular organic matter (IOM), and mixed AOM suspension. The AOM removal was appears to be influenced by an electrochemical reaction affecting the hydrophobicity change of the AOM. Furthermore, a remarkable degradation of IOM is observed to be higher than that of EOM and a mixture of EOM and IOM, accounting for 85%, 78%, and 48% respectively. Specifically, for AOM suspensions, the soluble microbial product-like (SMPL) substances and low molecular components (<104 Da) fractions are predominantly degraded by EF by both BDD and GFe anodes. The performance of GFe anode is lower than the BDD anode in reducing the AOM. In EOM and mixed AOM suspension, higher molecular components (>104 kDa) and humic substances are reduced in EF and EO processes. However, low molecular components in AOM suspension can be significantly removed by EF alone. In conclusion, the degradation of AOMs by electrochemical oxidation is subject to the molecular fractions of AOM.