Add time:08/21/2019         Source:sciencedirect.com

This study investigated the capability of ultraviolet radiation at 254 nm and 185 nm (UV/VUV) to degrade cyanotoxin microcystin-LR (MC-LR). Results showed 70% toxin reduction solely by 254 nm direct photolysis (ε 254 = 13225 ± 814 M-1cm-1; Φ254 = 0.29 ± 0.03 mol/Einstein). The addition of 185 nm increased MC-LR degradation through advanced oxidation by •OH (k•OH,MC-LR = 2.25 ± 0.39 × 1010 M-1s-1). Alkalinity and organics (DOC) reduced MC-LR degradation by scavenging •OH (kobs,MilliQ = 0.117 cm2/mJ; kobs,50ppmAlk. = 0.0497 cm2/mJ; kobs,6ppmDOC = 0.019 cm2/mJ). Chloride absorbed 185 nm, impacting •OH formation and generating Cl•, while also scavenging •OH. However, Cl• is reactive and •OH scavenging is reversible, resulting in relatively low impact on MC-LR degradation (kobs,50ppmCl = 0.0939 cm2/mJ). In natural water, MC-LR could be degraded from a typical concentration (˜15 µg/L) to below detection (<0.5 µg/L) with a UV254 fluence of 200 mJ/cm2 using UV/VUV. The presence of cyanobacterial cells impeded MC-LR degradation; however, 90% MC-LR degradation could still be achieved. UV/VUV is a promising chemical-free technology capable of MC-LR degradation in a variety of water conditions, and a potentially suitable treatment option for small, remote communities.

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