A Perspective on Removal of Cyanotoxins from Water Through Advanced Oxidation Processes

Abstract

This perspective discusses the challenges associated with the removal of cyanotoxins from raw water sources for drinking water treatment and the emergence of sulfate radical-based advanced oxidation processes (SR-AOPs) as an effective treatment technique. The advantage of SR-AOPs is that they can be activated using a variety of methods, including heat, UV radiation, and transition metal catalysts, allowing for greater flexibility in treatment design and optimization. In addition, the byproducts of SR-AOPs are less harmful than those generated by ^•OH-AOPs, which reduces the risk of secondary contamination. SR-AOPs generate sulfate radicals (SO₄ ^•-) that are highly selective to certain organic contaminants and have lower reactivity to background water constituents, resulting in higher efficiency and selectivity of the process. The presence of natural organic matter and transition metals in the natural water body increases the degradation efficiency of SR-AOPs for the cyanotoxins. The bromate formation is also suppressed when the water contaminated with cyanotoxins is treated with SR-AOPs.

Keywords: advanced oxidation processes; cyanotoxins; sulfate radicals.

Figure 1

Types and effects of harmful cyanotoxins involved in lethal algal bloom events.

Figure 2

a) Harmful algal incidents occurred in the last two decades. b) Effect versus incidents aerosolized toxins effects (ATE); amnesic shellfish poisoning (ASP); azaspiracid shellfish poisoning (AZP); ciguatera fish poisoning (CFP); cyanobacterial toxins effects (CTE); diarrhetic (diarrheic) shellfish poisoning (DSP); neurotoxic shellfish poisoning (NSP); paralytic shellfish poisoning (PSP); Other. c) Nature of harmful algal events.

Figure 3

Cyanotoxins removal techniques.

Figure 4

Potential pathways of oxidative reactions produced by the activation of PMS and PDS. Reproduced with permission.^{[ 49 ]} Copyright 2020, American Chemical Society.

Figure 5

Main degradation pathways of cylindrospermopsin by SR‐AOPs. Reproduced with permission.^{[ 77 ]} Copyright 2014, Elsevier.

Figure 6

Four different pathways of Microcystin‐LR with SR‐AOP a). Multiple Hydroxylation of MC‐LR with Sulfate Radicals, b). Decarboxylation of Glu Amino Acid with Sulfate Radicals, c). Simultaneous Hydroxylation of the Aromatic Ring and the Diene Bond of MC‐LR with Sulfate Radicals, d). Simultaneous Oxidation of the Cyclic Structure and the Chain of MC‐LR with Sulfate Radicals. Adapted with permission.^{[ 61 ]} Copyright 2010, American Chemical Society.