microcystin and titanium-dioxide

Photocatalysis has been shown to successfully remove microcystins (MC) in laboratory experiments. Most research to date has been performed under ideal conditions in pure or ultrapure water. In this investigation the efficiency of photocatalysis using titanium dioxide was examined in a complex matrix (waste stabilisation lagoon water). A flow-through photocatalytic reactor was used for the photocatalytic removal of four commonly occurring microcystin analogues (MC-YR, MC-RR, MC-LR, and MC-LA). Up to 51% removal for single MC analogues in waste lagoon water was observed. Similar removal rates were observed when a mixture of all four MC analogues was treated. Although treatment of MC-containing cyanobacterial cells of Microcystis aeruginosa resulted in no decline in cell numbers or viability with the current reactor design and treatment regime, the photocatalytic treatment did improve the overall quality of waste lagoon water. This study demonstrates that despite the presence of natural organic matter the microcystins could be successfully degraded in a complex environmental matrix.

Topics: Cyanobacteria; Marine Toxins; Microcystins; Microcystis; Titanium; Waste Disposal, Fluid; Wastewater; Water Pollutants, Chemical

Topics: Humans; Light; Microcystins; Nanoparticles; Plasma Gases; Titanium; Ultraviolet Rays; Water Purification

Microcystins and nodularin are toxic cyanobacterial secondary metabolites produced by cyanobacteria that pose a threat to human health in drinking water. Conventional water treatment methods often fail to remove these toxins. Advanced oxidation processes such as TiO2 photocatalysis have been shown to effectively degrade these compounds. A particular issue that has limited the widespread application of TiO2 photocatalysis for water treatment has been the separation of the nanoparticulate powder from the treated water. A novel catalyst format, TiO2 coated hollow glass spheres (Photospheres™), is far more easily separated from treated water due to its buoyancy. This paper reports the photocatalytic degradation of eleven microcystin variants and nodularin in water using Photospheres™. It was found that the Photospheres™ successfully decomposed all compounds in 5 min or less. This was found to be comparable to the rate of degradation observed using a Degussa P25 material, which has been previously reported to be the most efficient TiO2 for photocatalytic degradation of microcystins in water. Furthermore, it was observed that the degree of initial catalyst adsorption of the cyanotoxins depended on the amino acid in the variable positions of the microcystin molecule. The fastest degradation (2 min) was observed for the hydrophobic variants (microcystin-LY, -LW, -LF). Suitability of UV-LEDs as an alternative low energy light source was also evaluated.

Topics: Catalysis; Cyanobacteria; Glass; Microcystins; Microspheres; Particle Size; Peptides, Cyclic; Photochemical Processes; Spectrophotometry, Ultraviolet; Titanium; Water Pollutants, Chemical; Water Purification

The increasing incidence of algal blooms in fresh water supplies and the consequent possibility of cyanobacterial microcystin contamination of potable water is a cause of recent concern. Heterogeneous photocatalytic oxidation forms part of a family of advanced water treatment technologies comprising the generation of reactive oxidizing species in water media and results in the complete oxidative degradation (mineralization) of organic pollutants to yield carbon dioxide, water and inorganic ions. A new experimental laboratory-scale 'falling film' reactor has been developed to study the photocatalytic degradation of microcystins in aqueous solution. The reactor consisted of a fiberglass sheet impregnated with immobilized titanium dioxide (TiO2) catalyst over which the microcystin solution was pumped (as a falling film) while being irradiated from UV-C germicidal lamps. The design of the system obviated the necessity to separate suspended catalyst from treated water as required in slurry reactors. The photocatalytic degradation was characterized by pseudo-first order reaction kinetics. Rapid degradation of microcystins LR, YR and RR was observed in natural lake water with half lives less than 10 min, while even faster rates were achieved in laboratory distilled water. Although low pH (pH 3) marginally improved reaction rates. the presence of radical scavengers such as sulfate ions was detrimental to the photocatalytic oxidation process.

Topics: Catalysis; Coloring Agents; Eutrophication; Hydrogen-Ion Concentration; Microcystins; Oxidation-Reduction; Peptides, Cyclic; Photochemistry; Titanium; Ultraviolet Rays