Molecular-level insights into the degradation of dissolved organic matter from cyanobacteria-impacted water by electro-oxidation and electro-Fenton with carbon-based electrodes

Abstract

Algal organic matter (AOM) originating from cyanobacteria-impacted reservoirs presents a significant risk to drinking water. Electrochemical oxidation is an emerging technology effective in AOM degradation. This study focuses on the elimination of AOM, including extracellular organic matter (EOM) and intracellular organic matter (IOM), extracted from Microcystis aeruginosa (MA). Electro-Fenton (EF) and electro-oxidation (EO) techniques were used, with a boron-doped diamond (BDD), a modified graphene-Fe₂O₃ (GFe) anode, and a graphite felt (GF) cathode. The results showed that BDD and GFe electrodes can effectively degrade AOM, particularly IOM, via EO and EF. BDD with high overpotential exhibited significant IOM degradation via EF, where dissolved organic carbon reduction reached up to 85%. In EO reactions, H₂O₂ generation by GFe-30 (obtained at the optimal ferric oxide to graphene ratio) is slightly higher than that in BDD, but it cannot fully transform into •OH in the EF process, which inhibits its AOM degradation capability. Furthermore, soluble microbial product-like substances and humics are more effectively degraded by EF and EO using either BDD or GFe. High-molecular weight (>10³ Da) fractions, such as biopolymers and humic substances, are principally degraded by both EF and EO regardless of the BDD and GFe anode. This process leads to significant reductions in the haloacetic acids (HAAs) formation potential. EO and EF with GFe-30 are more effective in reducing specific disinfection by-product formation potential during IOM suspension degradation compared to BDD. In conclusion, GFe serves as a novel electrode material to replace BDD as a potent carbon-based anode when utilizing EO or EF treatments for effective AOM removal from cyanobacteria-infested water for drinking water treatment.