Short Communication Enhanced azo dye removal through anode biofilm acclimation to toxicity in single-chamber biocatalyzed electrolysis system You-Zhao Wang a , Ai-Jie Wang a,b,⇑ , Wen-Zong Liu b , Qian Sun a a State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, No. 73 Huanghe Road, Harbin 150090, PR China b Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China highlights  Azo dye toxicity could shock the bioanode electrochemical activity.  Anode biofilm was acclimated to azo dye toxicity by gradient increase of azo dye concentration.  Enhanced azo dye removal in single-chamber biocatalyzed electrolysis system after bioanode acclimation.  Removing IEM reduced the Rin 3 times than in the presence of IEM by EIS. article info Article history: Received 27 February 2013 Received in revised form 2 May 2013 Accepted 4 May 2013 Available online 23 May 2013 Keywords: Biocatalyzed electrolysis system Anode biofilm acclimation Azo dye removal Single-chamber abstract Azo dye is widely used in printing and dyeing process as one of refractory wastewaters for its high chroma, stable chemical property and toxicity for aquatic organism. Biocatalyzed electrolysis system (BES) is a new developed technology to degrade organic waste in bioanode and recover recalcitrant con- taminants in cathode with effective decoloration. The ion exchange membrane (IEM) separate anode and cathode for biofilm formation protection. Azo removal efficiency was up to 60.8%, but decreased to 20.5% when IEM was removed. However, expensive ion exchange membrane (IEM) not suitable for further prac- tical application, bioelectrochemical activity of bioanode is sensitive to the toxicity of azo dye. A gradient increase of azo dye concentration was used to acclimate anode biofilm to pollutant toxicity. The azo removal efficiency can be enhanced to 73.3% in 10 h reaction period after acclimation. The highest removal efficiency reached 83.7% and removal rates were increased to 8.37 from 3.04 g/h/L of dual- chamber. That indicated the feasibility for azo dye removal by single-chamber BES. The IEM cancellation not only decreased the internal resistance, but increased the current density and azo dye removal. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction A large amount of dyeing wastewater is produced in dyeing enterprises annually (Parikh et al., 2005). High toxicity and chroma make it difficult to remove by traditional methods of wastewater treatment. Among all kinds of dye pollutants, the azo dyes are 80% of total amount of organic dyes. Its chromophore is azo bonds, that could decrease water transmittance and then result in destruction of ecosystem when azo dye enters the rivers, seas, etc. (You et al., 2010). Effective electron reduction methods target at azo bonds and transfer to the amidogen so that high chroma can be removed (Sun et al., 2009). Biocatalyzed electrolysis system (BES) is newly developed de- vice with bio-electrons transport and reductions at bio-electrode. The electrons are produced by exoelectrogens from organic (glu- cose, acetate, etc.) degradation and transported to anode, through external circuit to cathode (Heilmann et al., 2006). At the cathode, oxygen and proton is an electron acceptor generating electrical en- ergy (Logan et al., 2006) and hydrogen energy in initial research (Liu et al.,2008; Wang et al., 2011). In recent years, the scope of electron acceptor has expanded, such as carbon dioxide (Nevin et al., 2011), nitrate (Guoqiang et al., 2012), perchlorate (Butler et al., 2010), nitrobenzene (Mu, 2009) or other pollutants (Tao et al., 2012; Shen et al., 2012; Zhan et al., 2012). Whether in energy generation or pollutants removal, the BES is becoming more recognized on environmental problems and issues. The stability of bioanode electrochemical activity is the basis of BES. In previous studies, the toxicity of pollutants do not influence the anode biofilm in dual-chamber BES, because the ion exchange membrane (IEM) prevents anode biofilm from toxicity of azo dyes in cathode chamber. However, IEM is a costly component of BES, it could cause pH gradient and the increase of internal resistance, that is not suitable for use in engineering application. Although membrane removal is cost-effective for single chamber BES, the toxicity of pollutants could influence the anode biofilm, which 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.05.007 ⇑ Corresponding author. Tel.: +86 4586282195. E-mail address: waj0578@hit.edu.cn (A.-J. Wang). Bioresource Technology 142 (2013) 688–692 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech