Photoelectrocatalysis Applied in Water Disinfection Contamined By C. Parapsilosis using Nanoporous Electrodes of W/WO3 Prepared By Electrochemical Anodization

The photoelectrocatalysis is a successful alternative for the inactivation of microorganisms, because it promotes inactivation in a short time and no formation of undesirable by-products and harmful to the people [1]. Tungsten trioxide has been an excellent alternative material in photoelectrocatalytic process, since presents small band gap energy (2.4 - 2.8 eV) and can to be photoexcited in the visible region [2]. This work reports the application of photoelectrocatalysis for disinfection water contaminated by fungus C. parapsilosis by using W/WO₃ thin films grown onto tungsten substrate by electrochemical anodization with the aim to treat hemodialysis water. The nanoporous electrode was characterized by scanning electron microscopy and showed high porosity and organization, respectively. The presence of W and O was confirmed by EDS and the monoclinic form by X-ray diffraction. The PEC reactor is based on W/WO₃ film acting as photoanode, Pt grid as counter electrode and Ag/AgCl as reference electrode. A solution of NaCl 0.1 mol.L^-1 was tested as supporting electrolyte (pH 7) in function the high percentage of this salt in the hemodialysis water. High pressure Hg lamp (125W) was used as a source of electromagnetic radiation and the applied potential was 1.5V. In order to evaluate the method efficiency it was investigated the microbial death, system mineralization, chlorate and perchlorate ions and active chlorine generation during degradation. Therefore, aliquots were removed during 120 min of treatment and analyzed for microbial count, total organic carbon removal, ion chromatography and spectrophotometric measurements, respectively.  The best condition for treatment was investigated and after only 1 min of the photoelectrochemical treatment Candida sp was inactivated under UV and visible light irradiation and 59.5 % of the organic matter mineralization, with kinetic constant equal to -0.0056 min^-1. According to the chromatograms obtained was not verified the formation of potentially harmful ions. Spectrophotometric measurement confirms the low active chlorine formation at pH 7, but is higher at acidic medium. Ion chromatographic test indicates the no occurrence of chlorate and perchlorate. These result shows that the chloride ion present in the reaction system is only acting in conducting electrical current, not attending  possible secondary reactions and death the fungus occurs due breaking the cell wall by the generation of hydroxyl radicals in rational way. The obtained results indicated that photoelectrocatalysis is a promising method for fungi degradation and disinfection of water and hemodialysis water under UV and visible light irradiation. Further studies are in progress to test organochlorides formation.

References:

[1] Brugnera, M. F., Myata, M., Zoccolo, G.J., Leite, C. Q. F., Zanoni, M. V. B. Electrochimica Acta, v.85. p. 33– 4, 2012.

[2] Fraga, L.E.; Zanoni, M. V. B. Journal Brazilian Chemical Society, v. 22, p. 718-725, 2011.