Phenolic wastewaters treatment by electrocoagulation process using Zn anode Ana S. Fajardo a , Raquel F. Rodrigues a , Rui C. Martins a , Luis M. Castro a,b , Rosa M. Quinta-Ferreira a,⇑ a CIEPQPF – Centro de Investigação em Engenharia dos Processos Químicos e Produtos da Floresta, GERST – Group on Environment, Reaction, Separation and Thermodynamics, Department of Chemical Engineering, Faculty of Sciences and Technology, University of Coimbra, Pólo II, Rua Sílvio Lima, 3030-790 Coimbra, Portugal b Polytechnic Institute of Coimbra, Department of Chemical and Biological Engineering, Rua Pedro Nunes, Quinta da Nora, 3030-199 Coimbra, Portugal highlights  Zn anode material applied to an electrocoagulation system to treat OMW.  Medium pH and electrolyte type greatly affected the efficiency of the system.  Sequence of feed-batch trials showed almost constant activity during the operation time.  Low biodegradability and still ecological impact were detected.  Electrocoagulation process is essentially a primary treatment method. article info Article history: Received 3 December 2014 Received in revised form 17 March 2015 Accepted 24 March 2015 Available online 2 April 2015 Keywords: Electrocoagulation Zn anode Phenolic acids Olive mill wastewater abstract Electrocoagulation using a Zn anode was applied for the first time to remove the organic load of a liquid effluent. Different operating conditions (pH, current density, distance between electrodes, nature of elec- trolyte and kind of cathode) were tested with synthetic phenolic wastewater, in order to optimise the process. Both the medium pH and the type of electrolyte that were used greatly affected the efficiency of the system, followed by the influence of the current density and the cathode material, in a lesser extent. The effect of the distance between electrodes was quite negligible. Furthermore, a sequence of fed-batch trials involving the electrodes reuse showed almost constant activity during the operation time. The optimum operating conditions achieved were initial pH of the effluent equal to 3.2, current density of 250 A/m 2 , distance between electrodes of 1.0 cm and 1.5 g/L of NaCl. Moreover, the Zn anode/stainless steel cathode pair revealed the most interesting results. These parameters led to 84.2% and 40.3% of total phenolic (TPh) content and chemical oxygen demand (COD) removal, respectively. In addition, the depuration of a filtered real olive mill effluent without NaCl addition achieved the abate- ment of up to 72.3% of TPh and 20.9% of COD. An energy consumption of 40 kW h/m 3 and 34 kW h/m 3 was observed for the treatment of the simulated and the real wastewater, respectively. Furthermore, the ecological impact of the treated effluent was detected by bio-luminescence techniques. This study shows the potentiality of the electrocoagulation process as a pre-treatment of other meth- ods, namely the electrochemical oxidation, to ensure the legal limits values of the wastewater to be dis- charged into the aquatic environment regarding their organic load. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Olive production is a common agro-industry in Mediterranean countries such as Spain (2.4 million ha), followed by Italy (1.4 mil- lion ha), Greece (1.0 million ha), Portugal (0.5 million ha) and France (40 thousand ha), with significant economic, social and environmental impact [1]. Olive mill wastewater represents an important ecological problem, due to its seasonal production, high pollution load and toxicity [2–4]. These properties hinder the use of biological treatments since the presence of phenolic compounds, which are recalcitrant substances, inhibit microorganisms’ action. Therefore, the development of more effective processes emerges as an alternative to this actual environmental threat. Even though novel approaches on advanced oxidation processes appear to be promising and attractive options. However, handicaps, for example http://dx.doi.org/10.1016/j.cej.2015.03.116 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +351 239798723; fax: +351 239798703. E-mail addresses: sofiafajardo@eq.uc.pt (A.S. Fajardo), martins@eq.uc.pt (R.C. Martins), rosaqf@eq.uc.pt (R.M. Quinta-Ferreira). Chemical Engineering Journal 275 (2015) 331–341 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej