Emerging investigator series: mitigation of harmful algal blooms by electrochemical ozonation: from bench-scale studies to field applications†

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 Ni–Sb–SnO₂ anodes to produce locally concentrated ozone (O₃) and hydroxyl radicals (·OH) to achieve ∼100% inactivation of cyanobacteria (indicated by chlorophyll-a degradation) and removal of microcystins within 120 seconds. More importantly, the proof-of-concept evolved into a full-scale boat-mounted completely mixed flow reactor for the treatment of HAB-impacted lake water. The single-pass treatment at a capacity of 544 m³ d⁻¹ achieved 62% chlorophyll-a removal with an energy consumption of <1 Wh L⁻¹. Byproducts (e.g., chlorate, bromate, trihalomethanes, and haloacetic acids) in the treated lake water were below the regulatory limits for drinking water. The whole effluent toxicity tests suggest that ECO treatment at 10 mA cm⁻² posed certain chronic toxicity to the model crustacean invertebrate (Ceriodaphnia dubia). However, the treatment at 7 mA cm⁻² (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.