Boron doped diamond electro-oxidation coupled with ultrafiltration for Microcystis aeruginosa and Microcystins removal in offshore environment: The significance of in-situ generation of chloramine and membrane fouling mitigation

Algae blooms and toxins pose a serious threat to the ecological security and human health in coastal areas. Coupling electro-oxidation with ultrafiltration is an effective means of treating algae-laden water. This study was designed to assess the removal of Microcystis aeruginosa and Microcystins in the offshore environment using a hybrid system combining BDD electro-oxidation with ultrafiltration. The results show that under suitable con-ditions, electro-oxidation rapidly inactivated algal cells and completely removed chlorophyll from the algae -laden water. In addition, electro-oxidation was effective in degrading microcystin-LR and dissolved organic carbon, with 83% and 66% removals observed within 30 min, respectively. The system also reduced the con-centrations of proteins and humic acids partly, while converting large molecules to small molecules and increasing the proportion of hydrophilic substances. A large amount of free chlorine was generated and most of the ammonia nitrogen in the water was converted to nitrogen and chloramine during the oxidation process. The electro-oxidation exhibited a better performance in treating algae in the growth phase than in the decline phase. During long-term operation, the hybrid system showed stable removal of chlorophyll, turbidity, and UV254. Applying electro-oxidation treatment prior to ultrafiltration led to slower transmembrane pressure (TMP) in-crease rate in the course of the experiment. The SEM results suggest that after moderate electro-oxidation, the algal cells formed a less compact fouling layers, which alleviated the ultrafiltration membrane fouling.