Ž . The Science of the Total Environment 256 2000 6776 Electrochemical degradation of humic acid Artur J. Motheo a,  , Laerte Pinhedo b a Uni  ersidade de Sao Paulo, Instituto de Quımica de Sao Carlos, Cx.P. 780, Sao Carlos, SP 13560-970, Brazil ˜ ´ ˜ ˜ b Faculdade de Tecnologia e Engenharia, Departamento de Engenharia Eletrica, Uni  ersidade Federal do Mato Grosso, ´ Cuiaba, Mato Grosso, Brazil ´ Received 1 November 1999; accepted 5 March 2000 Abstract The treatment of natural water for drinking water production goes through the degradation of humic substances. In this study, humic acid, extracted from a peat area located at the margins of the Mogi Guac ¸ u River at Sao Paulo ˜ State, Brazil, was used to perform electro-oxidation essays in order to evaluate the possibilities of electrochemical Ž . methods in the degradation of humic substances. The working electrodes were dimensionally stable anodes DSA type with the following compositions: TiIr Ti O ; TiRu Ti O ; and TiIr Ru Ti O . The electrolyses 0.3 0.7 2 0.3 0.7 2 0.2 0.2 0.6 2 Ž 1 . 1 were performed by using a solution composed of an electrolyte support 0.1 mol l KCl and 30 mg l of the humic acid. Samples were taken during the electrolyses and analysed by the pH, transmittance, UV-vis spectra and chromatography. The results show that the TiRu Ti O electrode presents the best performance considering the 0.3 0.7 2 elimination of most of the electro-oxidation products after approximately 2 h of electrolysis at 40 mA cm 2 .  2000 Elsevier Science B.V. All rights reserved. Keywords: Humic acid; Electro-oxidation; DSA electrodes; Water treatment 1. Introduction Organic material present in soils is basically a mixture of compounds in different stages of de- composition due to the biological degradation of  Corresponding author. Tel.: 55-16-2739932; fax: 55- 16-2739952. Ž . E-mail address: artur@iqsc.sc.usp.br A.J. Motheo vegetable and animal residues as well as of the Ž synthetic activity of micro-organisms Schinitzer . and Khan, 1972 . These compounds can be conve- niently divided into two groups: non-humic and humic substances. The first group includes those substances with well-defined chemical character- istics such as: carbohydrates; proteins; amino acids; and low molecular weight organic acids, which are easily attacked by micro-organisms. On Ž . the other hand, the humic substances HS are 0048-969700$ - see front matter  2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 8 - 9 6 9 7 00 00469-1