Electrochimica Acta 46 (2000) 389 – 394 Three-dimensional electrodes for the electrochemical combustion of organic pollutants A.M. Polcaro *, S. Palmas, F. Renoldi, M. Mascia Dipartimento di Ingegneria Chimica e Materiali, Uniersita ` degli Studi di Cagliari, Piazza d’Armi, 09123 Cagliari, Italy Received 18 November 1999; received in revised form 10 March 2000 Abstract The ability of a fixed bed of carbon pellets to work as anode in destroying chlorophenols (ClPhs) was verified. The applied current is able to continuously regenerate the external active sites of the carbon surface on which oxygen and organic are adsorbed. The low organic coverage degree of carbon, which can be maintained during runs, hinders phenol diffusion to the interior of the pellets: only the external pores are involved in the process. Preliminary runs are also presented at dimensional stable anodes (DSA ® ) based on Ru–Ti oxides. The results indicate that if a divided electrochemical cell is used, the behaviour of DSA ® approaches that of Ti/SnO 2 electrode: the reactant can be oxidised without accumulation of cyclic intermediates, thus limiting the toxicity of the resulting solution. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Organic oxidation; Chlorophenols; Activated carbon; DSA; Three-dimensional electrodes www.elsevier.nl/locate/electacta 1. Introduction Widespread contamination of soil and groundwater by persistent organic compounds (POCs) has been recognised as an issue of growing importance which, in recent years, has focused the attention of the industrial and academic world. Among the various technologies to degrade these persistent compounds, Advanced Oxidation Processes (AOPs) are particularly useful: very reactive agents, such as OH  radicals, are produced which are responsi- ble for powerful oxidation. In some instances, the ac- tion of intermediate agents, such as chlorine/hypochlorite or OH  , represents the only way to disrupt the organic pollutant and to mineralise it. Depending on the chemical composition (concentra- tion levels, kind of compounds and ionic strength) of the waste water, AOPs such as Fenton oxidation [1–4], photo-chemical oxidation [5 – 8] or indirect electrochem- ical oxidation (by OH  electrogenerated from water demolition) [9–11] can be used to good effect to re- move persistent organic pollutants. In particular, when the effluent presents sufficiently high conductivity, and its organic load is not elevated (the effluent from a biologic plant could be an exam- ple), an electrochemical oxidation process may become competitive with respect to the other AOPs, if attention is paid to the correct selection of suitable electrode materials. This represents the crucial point in determin- ing high efficiencies of the global process. In fact, based on the following two equations: 1. 2H 2 O 2OH  +2H + +2e - 2. 2OH  2H + +O 2 +2e - OH  can be effectively generated if the electrode mate- rial presents overpotential, which is low for step (a) but high for step (b) of O 2 evolution. Most experimentation has been performed on the oxidation of phenols (Phs) and chlorophenols (ClPhs), * Corresponding author. Tel.: +39-70-6755059; fax: +39- 70-6755067. E-mail address: polcaro@dicm.unica.it (A.M. Polcaro). 0013-4686/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(00)00596-X