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Research Papers

Comparative Study of Phenolics Degradation Between Biological and Photocatalytic Systems

[+] Author and Article Information
J. A. Herrera Melián

Fotocatálisis y Electroquímica Aplicada al Medio-Ambiente (FEAM), Unidad Asociada al Instituto de Ciencia de Materiales de Sevilla, (CSIC), CIDIA (Dipartimento de Química), Edificio del Parque Científico Tecnológico, Universidad de Las Palmas de gran Canaria, Campus Universitario de Tafira, 35017 Gran Canaria, Españajherrera@dqui.ulpgc.es

J. Araña, J. A. Ortega, F. Martín Muñoz, E. Tello Rendón, J. Pérez Peña

Fotocatálisis y Electroquímica Aplicada al Medio-Ambiente (FEAM), Unidad Asociada al Instituto de Ciencia de Materiales de Sevilla, (CSIC), CIDIA (Dipartimento de Química), Edificio del Parque Científico Tecnológico, Universidad de Las Palmas de gran Canaria, Campus Universitario de Tafira, 35017 Gran Canaria, España

J. Sol. Energy Eng 130(4), 041003 (Sep 04, 2008) (7 pages) doi:10.1115/1.2969800 History: Received November 13, 2007; Revised December 03, 2007; Published September 04, 2008

Phenol and phenol compounds are toxic organics that can be found in many industrial wastewaters. Biological wastewater treatments are considered to be the most convenient methods owing to their efficiency and low economic cost. Nonetheless, many organic pollutants are refractory to bacterial degradation. Photocatalytic methods can be an interesting alternative as pretreatment to improve biodegradability and reduce toxicity of industrial effluents. The goal of this study was to compare and combine TiO2-photocatalysis with constructed wetlands to obtain a low-cost method for the treatment of phenolic wastewater. The degradation of phenol was studied by means of TiO2-photocatalysis (solar and UV-lamp) in batch reactors. The degradations of phenol and two of its photocatalytic degradation intermediates, catechol and hydroquinone, were studied in wetland reactors with and without two wetland plants: common reed (Phragmites australis) and papyrus (Cyperus alternifolius). The application of pseudo first-order kinetics to the elimination of phenol in the wetland reactors provided high correlation coefficients (R2=0.850.99), allowing the comparison of the biological and photocatalytic methods. Although higher concentrations of phenol (250400mgl) could be treated, the elimination of 50ppm was usually accomplished in batch experiments in less than 15h, the time in which low or nil solar radiation is available for TiO2-photocatalysis. As a consequence, this concentration can be considered to be the upper limit for the wetland influent. The degradations of catechol and hydroquinone showed higher rate constants (0.20.4h1) than that of phenol (about 0.15h1), particularly in the reactor with common reed (12h1). The degradation of phenol by the photocatalytic methods was three to four times faster than those obtained with the wetland reactors. By using solar TiO2-photocatalysis, concentrations of phenol up to 100ppm were reduced down to 16ppm and 27ppm of phenol and hydroquinone, respectively, in about 7h. However, it was toxic. When this sample was continuously (38mlmin) added to wetland reactors with common reed, phenol and hydroquinone concentrations were below their detection limits (1ppm and 2ppm, respectively). Solar TiO2-photocatalysis is a promising technique for the treatment of phenol but its application is limited to daytime periods with appropriate weather conditions. Constructed wetlands can also eliminate phenol and phenolic compounds without these limitations, but the toxicity of the influent must be as low as possible. The combination of both methods can provide a low-cost method for the treatment of phenolic wastewater.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Phenol, DO, and NPOC evolution during phenol degradation in the wetland reactor containing only gravel

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Figure 2

Degradation of different concentrations of phenol in the wetland batch reactor containing only gravel

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Figure 3

Degradation of phenol and its TiO2-photocatalytic intermediates, catechol, and hydroquinone, in the wetland reactor containing only gravel

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Figure 4

Evolution of phenol alone, in the presence of catechol (23.4ppm) and hydroquinone (22.8ppm) in the wetland reactor containing only gravel.

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Figure 5

Lemna minor growth inhibition test for phenol (◆), catechol (◻), and hydroquinone (▲).

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Figure 6

Solar degradation efficiency of phenol, as ppm degraded divided by the total accumulated energy versus initial phenol concentration

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Figure 7

Degradation of phenol (57.3ppm) versus accumulated energy in the solar pilot-plant. The evolution of catechol and hQ, TOC, and solar radiation are also shown. The experiment lasted 7h, from 10hto13h and 30min on the 16th and 17th of November 2005.

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Figure 8

Degradation of phenol (110ppm) versus accumulated energy in the solar pilot-plant. The evolution of catechol and hQ, TOC, and solar radiation are also shown. The experiment lasted 8h, from 9hto17h, on the 14th of November 2005.

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Figure 9

Initial degradation rate of phenol at different concentrations for the photocatalytic and wetland reactors

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