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Degradation of cyanobacterial toxin microcystin-LR using UV/vacuum-UV advanced oxidation for drinking water treatment

University of British Columbia

Cyanobacterial blooms have been increasing in magnitude and frequency around the world and studies have concluded that climate change, population growth, and industrial development will accelerate this phenomenon. The presence of cyanobacterial blooms in drinking water sources is a concern due to the production of cyanobacterial toxins, which are known to damage internal organs and disrupt nervous system functions. Shallow surface water sources for small water systems are at a greater risk of eutrophication and small, remote communities often lack the resources and infrastructure for adequate treatment. In conventional water systems, instances of cyanobacterial blooms are typically addressed by chemical addition. However, many remote communities are difficult to access and are unable to maintain a consistent supply of chemical oxidants. This study investigated the capability of ultraviolet radiation at 254 nm and 185 nm wavelengths (UV/Vacuum-UV) to degrade microcystin-LR (MC-LR), one of the most commonly occurring and toxic cyanobacterial toxins. Results showed that substantial toxin removal could be achieved solely by direct photolysis with 254 nm. The addition of 185 nm increased MC-LR degradation through advanced oxidation by hydroxyl radicals (•OH). The presence of alkalinity and organic matter (DOC) reduced MC-LR degradation by scavenging •OH. DOC also absorbed 254 nm and 185 nm, requiring additional irradiation time to achieve a target UV dose. Chloride scavenged •OH, but in a reversible reaction, resulting in minimal impact on MC-LR degradation. The order of impact on MC-LR degradation by these common water constituents was DOC>Alkalinity>Chloride. In natural water with a complex matrix, 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. The presence of cyanobacterial cells impeded MC-LR degradation by adding turbidity to samples, absorbing 254 nm photons and scavenging •OH. However, substantial MC-LR degradation could still be achieved in the presence of cyanobacterial cells. UV/Vacuum-UV appears to be a promising chemical-free technology that is capable of MC-LR degradation in a variety of water conditions, and may be a suitable treatment option for small, remote communities.

Text

2017-09-13

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/63028

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/