Journal of Hazardous Materials 163 (2009) 152–157 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Performance of nano- and nonnano-catalytic electrodes for decontaminating municipal wastewater Jih-Hsing Chang a,∗ , Tsong-Jen Yang b , Cheng-Hung Tung c a Department of Environmental Engineering and Management, Chaoyang University of Technology, 168 Jifong East Road, Wufong, Taichung County 41349, Taiwan b Department of Materials Science and Engineering, Feng Chia University. No. 100, Wenhwa Road, Seatwen, Taichung 40724, Taiwan c Department of Environmental Engineering, National Chung Hsing University, 250, Kuo Kuang Road, Taichung, 40277, Taiwan article info Article history: Received 24 January 2008 Received in revised form 20 June 2008 Accepted 20 June 2008 Available online 27 June 2008 Keywords: Electrocatalyst Electrochemical treatment Nano Municipal wastewater abstract This research is intended to decompose organic substances in municipal wastewater with nano- and nonnano-scale electrocatalytic electrodes. As an anode, the nano-scale electrodes included lab-made TiO 2 and Cu 2 O electrodes; the nonnano-scale electrodes were a commercial TiO 2 and graphite plate. According to experimental results, the nano- and nonnano-scale catalytic electrodes can effectively remove the organic pollutants in the municipal wastewater. The perforated TiO 2 electrode is the best for eliminating the chemical oxygen demand (COD), and its efficiency is about 90% (COD decreases from 400 to 40 mg L -1 ). The conductivity of municipal wastewater and the electro-catalytic process will increase the pH and eventually remains in the neutral range. The conductivity of municipal wastewater can be lowered to some degrees. The most attractive discovery of electro-catalytic process is that the dissolved oxygen (DO) in the municipal wastewater can be increased by the TiO 2 electrode (nonnano-scale) around 4–6 mg L -1 , but few DO is produced by the nano-scale electrocatalytic electrode. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Electrochemical techniques have been used to treat wastewater for decades. Many metal materials have been used as the anodes to treat different types of wastewater, and results are impressive [1–3]. In such electromechanical techniques, organic pollutants are primarily decomposed by direct oxidation. Yet, regarding cost effectiveness, electrochemical techniques are still unfeasible in comparison with traditional biological techniques. Hence, munic- ipal wastewater is generally treated by biological techniques. So far, electrochemical techniques are usually used to treat pollutants that cannot be degraded by biological techniques. However, elec- trochemical process possesses promising remediation potentials if the promotion of electrode materials can facilitate the degradation efficiency of pollutants. The appearance of catalytic electrodes has been demonstrated that anodes manufactured by new materials present high possibility to treat wastewater [4]. In general, electrochemical techniques apply the electric field on the anode to oxidize the organic pollutants in wastewater. On contacting the anode, the organic pollutants can be oxidized to intermediate products (i.e., organic acids) which will be released ∗ Corresponding author. Tel.: +886 4 23323000x4210; fax: +886 4 23742365. E-mail address: changjh@cyut.edu.tw (J.-H. Chang). into water [5]. In theory, if there is ample time, the organic acids can be consecutively decomposed into CO 2 and H 2 O, and the chemical oxidation demand (COD) can be decreased so that the wastewater is qualified to be discharged. Nevertheless, since there are double layers on the anode surface and organic pollutants penetrate the double layers only by diffusion (molecular and convective); the rate of the direct decomposition is limited, which results in low degradation efficiency of electrochemical techniques. In addition to direct oxidation, the electrochemical reaction for decomposing the water molecules (i.e., water electrolysis) also consumes electricity. As the voltage of the electric field is increased, the decomposition of the water is increased; however, the treatment rate of organic pollutants may not increase proportionally. This extra electric consumption also limits the cost-effective application of electro- chemical techniques. That is, the water decomposition will alter wastewater pH, cause the treatment difficulty, and increase the operation cost. In contrast to tradition electrochemical process, catalytic electrodes can facilitate the decomposition of organic pollutants by producing strong oxidants (i.e., catalytic reactions) such as hydroxyl radicals (OH • ). Even though the tradition electrochemical process can also produce oxidants (e.g., the reaction with chlorides in the wastewater) [6]; the catalytic electrodes can produce oxidants without chemicals addition. These oxidants may be distributed into the bulk solution and are capable of degrading 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.06.072