Minimization of algogenic organic matter from cyanobacteria-laden water by electrochemical oxidation: molecular degradation signature of disinfection by-products precursors by electro-oxidation and electro-Fenton

Abstract

Algogenic organic matter (AOM) generated from cyanobacteria-impacted reservoirs poses a significant risk to drinking water. This study aimed to investigate the molecular degradation signature of Microcystis aeruginosa (MA)-derived AOM by electrochemical oxidation and the corresponding disinfection by-product formation potential (DBPFP). Boron-doped diamond (BDD)-based electro-oxidation (EO) and electro-Fenton (EF) were implemented at pH 3 and 10 mA cm−2 within 1 h. The fluorophore of extracellular organic matter (EOM), the mixture of EOM and intracellular organic matter (IOM), were characterized, and their corresponding molecular weight (MW) were fractionated. The results showed that dissolved organic carbon (DOC) degradation efficiency for BDD-EF treatment is superior and maintains DOC attenuation up to 84% for the EOM suspensions alone, while a low degradation efficiency occurs for IOM-EOM mixture. In contrast, BDD-EO exhibits a maximum DOC degradation around 66% for EOM suspensions alone, but DOC reduction is as low as 20% for IOM-EOM mixture. The H2O2 generated by BDD-EO preferentially degrades humic acid-like substances in EOM suspensions, whereas BDD-EF effectively degrades multiple fluorescent AOM by •OH. For IOM-EOM mixture, BDD-EO efficiently decomposes humics, but BDD-EF preferentially minimizes soluble microbial product-like and aromatic protein-like substances. Meanwhile, BDD-EF favors degrading biopolymers, humics, and low-MW substances, while BDD-EO merely degrades partial biopolymers and humic substances. After either EF or EO, specific DBPFP decreases as EOM presents alone where the toxicity of corresponding DBPs is mitigated effectively, instead the increased specific DBPFP appears for IOM-EOM mixture where the toxic potency ([DBP]/LC50) of corresponding DBPs increases. In summary, EO and EF are powerful in attenuating MA-derived DBP precursors of EOM in the absence of IOM, depending on the molecular signature.