Mitigation of Cyanobacterial Harmful Algal Blooms by Electrochemical Ozonation: From Bench-scale Studies to Field Applications

Cyanobacterial harmful algal blooms (HABs) are an emerging threat to ecosystems, drinking water safety, and the recreational industry. As an environmental challenge intertwined with climate change and excessive nutrient discharge, HAB events occur more frequently and irregularly. This dilemma calls for fast-response treatment strategies. This study developed an electrochemical ozonation (ECO) process, which uses a Ni-Sb-SnO2 anode to produce locally concentrated ozone (O3) on electrodes to inactivate cyanobacteria and destroy microcystins within minutes. More importantly, the proof-of-concept was evolved into a full-scale boat-mounted completely mixed flow reactor for the treatment of HAB-impacted lake water at a treatment capacity of 544 m3/d and energy consumption of < 1 Wh/L. Both lab-scale and full-scale investigations show that the byproducts (e.g., chlorate, bromate, trihalomethanes, and haloacetic acids) in the ECO-treated lake water were below the regulatory limits for drinking water. The whole effluent toxicity tests suggest that ECO treatment at 10 mA/cm2 posed certain chronic toxicity to the model invertebrate (Ceriodaphnia dubia). However, the treatment at 7 mA/cm2 (identified as the optimum condition) did not increase toxicity to model invertebrate and fish (Pimephales promelas) species. This study is a successful example of leveraging fundamental innovations in electrocatalysis to solve real-world problems.