Comparison of UV-A photolytic and UV/TiO2 photocatalytic effects on Microcystis aeruginosa PCC7813 and four microcystin analogues: a pilot scale study. [Dataset]

Abstract

Cyanobacterial blooms in freshwater reservoirs represent a threat to human and animal health because of the potential release of a wide variety of harmful metabolites, known collectively as cyanotoxins. Microcystins (MCs) are one of the most commonly reported cyanotoxins with over 247 analogues to date. Conventional water treatment (i.e., coagulation, flocculation, sedimentation or flotation and filtration) is used worldwide for treatment of water contaminated with cyanobateria, however, these processes can promote cell rupture and consequently cyanotoxin release into the environment. In order to mitigate the effect of dissolved cyanobacterial toxins entering water treatment plants, advanced oxidation processes (AOPs) such as photocatalysis and photolysis can be used for the control of cyanobacterial cells and toxic metabolites within reservoirs. To date, the high cost of supplying UV irradiation has prevented the widespread application of UV photolysis and titanium dioxide based photocatalysis in removing undesirable organics in the water treatment sector. To overcome this problem, the use of UV-LEDs (365 nm) for photolysis and heterogeneous photocatalysis applying TiO2 coated glass beads under UV-LED illumination (365 nm) in a pilot scale reactor for the elimination of Microcystis aeruginosa PCC7813 and four microcystin analogues (MC-LR, -LY, -LW, -LF) with a view to deployment in drinking water reservoirs was investigated. . UV-A (365 nm) photolysis was shown to be more effective than the UV/TiO2 photocatalytic system for the removal of Microcystis aeruginosa cells and microcystins. The file accompanying this output contains supplementary tables and figures.

Citation

MENEZES, I., CAPELO-NETO, J., PESTANA, C.J., CLEMENTE, A., HUI, J., IRVINE, J.T.S., GUNARATNE, H.Q.N., ROBERTSON, P.K.J., EDWARDS, C., GILLANDERS, R.N., TURNBULL, G.A. and LAWTON, L.A. 2021. Comparison of UV-A photolytic and UV/TiO2 photocatalytic effects on Microcystis aeruginosa PCC7813 and four microcystin analogues: a pilot scale study. [Dataset]. Journal of environmental management [online], 298, article 113519. Available from: https://www.sciencedirect.com/science/article/pii/S0301479721015814#appsec1

• Acceptance Date: Aug 7, 2021
• Online Publication Date: Aug 16, 2021
• Publication Date: Nov 15, 2021
• Deposit Date: Aug 20, 2021
• Publicly Available Date: Aug 17, 2022
• Publisher: Elsevier
• DOI: https://doi.org/10.1016/j.jenvman.2021.113519
• Keywords: Blue-green algae; Cyanotoxins; Water treatment; Titanium dioxide; Cyanobacteria
• Public URL: https://rgu-repository.worktribe.com/output/1411656
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0301479721015814#appsec1
• Related Public URLs: https://rgu-repository.worktribe.com/output/1411601
• Type of Data: PDF file.
• Collection Date: Jul 14, 2021
• Collection Method: Reactors were placed inside acrylic cylinders (1100 x 95 mm) containing 6.5 liters of M. aeruginosa PCC7813 suspension (Figure S1) and sparged with sterile air from the bottom. Triplicate reactors were used for each tested system: UV-only containing UV-A LED strips and empty tetrahedral pods (Figure S1A), TiO2-only containing TiO2 coated beads inside tetrahedral pods (Figure S1B) and UV/TiO2 containing TiO2 coated beads in tetrahedral pods illuminated by UV-A LED strips (Figure S1C). Titanium dioxide porous glass beads were placed inside of tetrahedral pods manufactured from a stainless-steel mesh with aperture of 1.2 x 1.2 mm and wire strength of 0.4 mm. Stainless-steel sheets were cut (15x13 cm) and then folded into the final tetrahedral form of pods (Figure S2). Empty pods were also used during UV photolysis evaluation. Temperature of the solution was measured (Table S2) for each reactor (UV-only, TiO2-only and UV/TiO2) just after sampling had occurred using a digital thermometer (Fisher Scientific, UK). The average temperature for UV-only, TiO2-only and UV/TiO2 was 22.1±0.1, 21.1±0.1 and 22.1±0.2°C respectively, therefore, no marked temperature variation was observed for those reactors containing UV irradiation. Microcystis aeruginosa PCC7813 cellular regrowth was evaluated (Figure S3) over 7 days to evaluate potential cyanobacterial recovery under optimal conditions after different treatments. After the treatments, aliquots containing Microcystis aeruginosa PCC7813 (1.5 mL) were added to BG-11 medium (1.5 mL) inside four 4 mL glass vials that were placed in a 150 mL beaker. The type of statistical model (linear, piecewise, linear-plateau, exponential and logarithmic regression) was selected for each dependent variable for each type of treatment according to the values of R2, adjusted R2, Akaike information criteria (AIC) and Bayesian information criteria (BIC). The models that presented the highest R2 and adjusted R2 and the lowest AIC and BIC were chosen (Table S2). Photoluminescence measurements of both uncoated and TiO2 coated beads were performed to verify if any UV illumination was converted into visible light during treatment. For the photoluminescence quantum yield (PLQY) under 365 nm illumination, the beads were loaded into a UV-transparent cuvette in air and the absolute photoluminescence quantum efficiency was measured using Hamamastu PLQY instrument. Both uncoated and TiO2 coated beads presented deep-blue photoluminescence (Figure S31), with a low quantum efficiency of 4% (uncoated sample) and 7% (TiO2 coated sample). The data showed that the beads do generate additional visible light, albeit with low efficiency. The spectrum had good overlap with the blue absorption peak of chlorophyll a (Figure S32), and so may contributed to growth of the cyanobacteria.