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Degradation of Metalaxyl by Chemical and Biological Routes
S.M. Correia 1 , N.R.Z. Nogueira 1 , F. Fidalgo 1 , J.L. Faria 2 , A.M.T. Silva 2 , A.J.G. Teixeira 1
1 Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Portugal.
2 Laboratório de Catálise e Materiais (LCM), Laboratório Associado LSRE/LCM, Departamento de
Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Portugal.
The photocatalytic treatment of pollutants has shown a huge potential in environmental
protection, in particular for the treatment of water-soluble pesticides with limited
biodegradability [1]. In this work, the efficiency of the photo-Fenton process was investigated
under different operating conditions. In this process •OH radicals are formed homogeneously
from a mixture of iron (Fe 2+ ) salts and hydrogen peroxide (H2O2) in the presence of light. An
actual persistent pesticide, mainly consisting of metalaxyl, was selected as model pollutant.
The experiments were performed in a batch photoreactor with a UV-vis lamp as light source
and a glass jacket which cuts-off UVB and UVC lights, with the aim to investigate the process
efficiency under visible radiation. In a typical run, the pH of a metalaxyl solution (151 mg/L)
was adjusted to 2.8 and different concentrations of H2O2 were studied. Samples periodically
withdrawn were analyzed by HPLC and TOC. Among the results obtained, Figure 1 shows that
metalaxyl is poorly degraded by direct photolysis. However, when H2O2 is added to the
reaction a pronounced increase in the degradation rate of metalaxyl is observed. The
integration of the solar-driven engineering approach with a biological route is currently being
studied in order to analyze the effect of intermediates formed from the chemical process on
Solanum nigrum plants and to evaluate the efficiency of the designed integrated methodology.
C/C 0 (%)
100
80
60
40
20
0
0 50 100 150 200
Time (min)
Blank
[H 2 O 2 ] = 16 mg/L - dark
[H 2 O 2 ] = 8 mg/L
[H 2 O 2 ] = 16 mg/L
[H 2 O 2 ] = 40 mg/L
[H 2 O 2 ] = 80 mg/L
Figure 1. Degradation vs. time decay curves of metalaxyl during the photo-Fenton experiments using
different H2O2 contents and 2 mg/L of Fe 2+ . Blank: [Fe 2+ ] = 0 mg/L; [H2O2] = 0 mg/L.
Acknowledgements: The authors gratefully acknowledge the Universidade do Porto for financial
support (projecto pluridisciplinar PhotoWeed), with contribution of Santander Totta.
[1] Oller I., Malato S., Sanchez-Perez J.A., Maldonado M.I., Gasso R. (2007), Detoxification of
wastewater containing five common pesticides by solar AOPs-biological coupled system, Catalysis
Today, 129, 69-78.
3 rd meeting of young researchers at UP 251