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RESEARCH PAPERS

Detoxification of Aqueous Solutions Containing the Commercial Pesticide Metasystox by TiO2-Mediated Solar Photocatalysis

[+] Author and Article Information
A. Arques, A. García-Ripoll, R. Sanchís, L. Santos-Juanes

Departamento de Ingeniería Textil y Papelera, Universidad Politécnica de Valencia, Campus de Alcoy, Plaza Ferrándiz y Carbonell s/n, Alcoy, E-03801, Spain

A. M. Amat

Departamento de Ingeniería Textil y Papelera, Universidad Politécnica de Valencia, Campus de Alcoy, Plaza Ferrándiz y Carbonell s/n, Alcoy, E-03801, Spainaamat@txp.upv.es

M. F. López

Departamento de Ingeniería Química y Nuclear, Universidad Politécnica de Valencia, Campus de Alcoy, Plaza Ferrándiz y Carbonell s/n, Alcoy, E-03801, Spainmalope1@iqn.upv.es

M. A. Miranda

Departamento de Química, Instituto de Tecnología Química, Universidad Politécnica de Valencia, Consejo Superior de Investigaciones Cientificas, Valencia, 46071, Spainmmiranda@qim.upv.es

J. Sol. Energy Eng 129(1), 74-79 (Oct 14, 2005) (6 pages) doi:10.1115/1.2391205 History: Received June 28, 2005; Revised October 14, 2005

A commercial pesticide, namely metasystox, has been chosen to study its detoxification in aqueous solution by means of solar photocatalysis employing titanium dioxide. Initial toxicity/biodegradability has been checked by means of active sludges respirometry and the Zahn–Wellens test. Laboratory scale experiments indicate that significant detoxification (by approximately one order of magnitude) of a 0.05gL solution of the active species can be achieved in only 3h of solar irradiation due to the nearly complete elimination of the active compound, methyloxydemeton. In this case, total organic carbon (TOC) measurements cannot be used to evaluate the process as nonactive organic excipients interfere in the measurement. The experiment has been scaled-up to 25L in a solar pilot plant; also in this case more than 75% elimination of methyloxydemeton is achieved in 5h irradiation (1400kJ). Besides detoxification (80% initial inhibition of the active sludges and 20% at the end of the experiments), and moderate TOC reduction (20%) are observed together with an increase of the surface tension of the solutions, probably due to elimination of excipients having surfactant properties.

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Figures

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Figure 1

Methyl-oxydemeton

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Figure 2

Example of respirometric curve. 2g of sodium acetate were added at the beginning of the experiment (point A) to bring the activated sludge to their maximum OUR. Then the pesticide (250mL of a 0.1g∕L solution of metasystox) was added (point B) and the decrease in the OUR was calculated.

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Figure 3

Determination of the toxicity of metasystox by means of activated sludge respirometry. Left: Example of the relative decrease in the OUR after adding different amounts of the pesticide. Right: Average values obtained in the four series of experiments.

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Figure 4

Zahn–Wellens test performed for metasystox before (▴) and after (◆) solar photocatalysis with TiO2. The biodegradability of diethyleneglycol (∎) is given as a control.

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Figure 5

Solar photodegradation of methyloxydemeton (from a 0.05g∕L solution of metasystox), catalyzed by different amounts of TiO2: 0.2g∕L(◆) and 0.5g∕L(∎). The inset shows that the reaction follows a pseudo first order kinetics.

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Figure 6

Solar photodegradation of metasystox in pilot plant: (◆) relative concentration of methyl-oxydemeton and (∎) TOC, plotted versus accumulated radiation. A logarithmic plot is given as an inset.

Grahic Jump Location
Figure 7

Changes in the toxicity/biodegradability of a 0.1g∕L solution of metasystox along solar irradiation in pilot plant. Left: Plot of the inhibition of the active sludges versus irradiation time. Right: Zahn–Wellens test performed for the untreated solution (∎), after 3h of treatments (▴), and the blank control consisting in an ethyleneglycol solution (◆).

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