Abstract
Toxic microcystins (MCs) produced by freshwater cyanobacteria such as Microcystis aeruginosa are of concern because of their negative health and economic impacts globally. An advanced oxidation process using UV/TiO2 offers a promising treatment option for hazardous organic pollutants such as microcystins. The following work details the successful degradation of MC-LA, MC-LR, and MC-RR using a porous titanium–titanium dioxide (PTT) membrane under UV-LED light. Microcystin quantitation was achieved by sample concentration and subsequent LC–MS/MS analysis. The PTT membrane offers a treatment option that eliminates the need for the additional filtration or separation steps required for traditional catalysts. Controlled periodic illumination was successfully used to decrease the total light exposure time and improve the photonic efficiency for a more cost-effective treatment system. Individual degradation rates were influenced by electrostatic forces between the catalyst and differently charged microcystins, which can potentially be adjusted by modifying the solution pH and the catalyst’s isoelectric point.
Highlights
Cyanobacteria are a phylum of phototrophic bacteria capable of producing toxic blooms.Microcystis aeruginosa is a common freshwater cyanobacteria which produces microcystins (MC), a group of cyanotoxins with strong hepatotoxic effects
The results indicated that controlled periodic illumination (CPI) is a viable method for improving the efficiency of photocatalytic
energy per order (EEO) values calculated for terephthalic acid (TPA) conversion determined continuous UV-LED illumination to be less efficient than all the CPI conditions tested, demonstrating the potential of CPI to improve the efficiency of the photocatalytic advanced oxidation processes (AOPs)
Summary
Cyanobacteria are a phylum of phototrophic bacteria capable of producing toxic blooms. A review document produced by Health Canada in 2016 concluded that toxic algal blooms impact drinking water safety in the majority of Canadian provinces [5]. The improved efficiency, when using a catalyst such as the porous titanium–titanium dioxide (PTT) membranes, can be explained by mass-transfer limitations. Because the membrane has a limited surface area for adsorption, the rate of the reaction may be limited by this surface area at high LED duty cycles [25] In this case, periodically illuminated lighting conditions (within the mass-transfer limit) will be effective. In the case of photon-limited reactions (for example, slurry reactors), mass-transfer limitations would not apply because the reaction rate is faster than the adsorption rate Typical light sources such as mercury and xenon lamps require mechanical shutters to produce. 25 Hz were all considered, with the goal of improving the photonic efficiency of the AOP
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