Enhancement of nitroaromatic compounds anaerobic biotransformation using a novel immobilized redox mediator prepared by electropolymerization Lihua Li, Jing Wang, Jiti Zhou * , Fenglin Yang, Chengyou Jin, Yuanyuan Qu, Ang Li, Long Zhang School of Environmental and Biological Science and Technology, Dalian University of Technology, Linggong Road, Dalian 116024, China Received 6 August 2007; received in revised form 16 January 2008; accepted 20 January 2008 Available online 6 March 2008 Abstract Functionalized polypyrrole (PPy) composites were prepared by incorporation of a model redox mediator, anthraquinonedisulphonate (AQDS), as doping anion during the electropolymerization of pyrrole (Py) monomer on active carbon felt (ACF) electrode. Then, the resulting composite, ACF/PPy/AQDS as a novel immobilized redox mediator for catalyzing anaerobic biotransformation of the model nitroaromatic compounds (NACs), such as nitrobenzene (NB), 2,4- and 2,6-dinitrotoluene (DNT), were investigated in detail. The results showed that ACF/PPy/AQDS exhibited good catalytic activity and stability, and its addition effectively accelerated the NACs anaerobic reduction to the corresponding amino compounds. In order to estimate the relationship between community dynamics and the function of immobilized redox mediator, a combined method based on fingerprints (ribosomal intergenic spacer analysis, RISA) and 16S rRNA gene sequencing was used. The results indicated that the existence of ACF/PPy/AQDS made the potent AQDS-reducing bacteria keeping predominant in the catalytic systems. Based on the results above, it can be concluded that this novel immobilized redox mediator is fea- sible and potentially useful to enhance NACs anaerobic reduction. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Electropolymerization; Anthraquinonedisulphonate; Nitroaromatic compounds; Community dynamics; Ribosomal intergenic spacer 1. Introduction Because of their ecotoxicity at relatively low concentra- tion and widespread use in the manufacture of explosives, pesticides, dyes and medicines, nitroaromatic compounds (NACs) have been listed as US EPA priority pollutants (Cheng et al., 1998; Ye et al., 2004). Early studies on the biodegradation of NACs suggested that they are generally resistant to aerobic biotransformation due to the strong electron attracting of nitro group (Cheng et al., 1998; Boopathy et al., 1998). However, under anaerobic condi- tions they are readily converted to the corresponding aryl- amines, which are easily degraded aerobically. Therefore, sequential or integrated anaerobic–aerobic treatment is thought to be the most logical strategy for the complete removal of NACs. The transfer of reducing equivalents from a primary electron donor (co-substrate) to a terminal electron accep- tor (NAC) generally acts as the rate-limiting step in anaer- obic NACs reduction. It has been shown that the addition of redox mediators, including quinone-type compounds and a variety of transition metal complexes can accelerate this electron transfer, and higher reductive efficiency can be achieved in bioreactors operated with a low hydraulic retention time (Hofstetter et al., 1999). Among them, anthraquinonedisulphonate (AQDS) as a model quinonoid compound has received the greatest attention for its eury- topicity. It can not only accelerate the reduction of NACs, 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.01.037 * Corresponding author. Tel.: +86 411 84706250; fax: +86 411 84706252. E-mail address: dlut502@yahoo.com.cn (J. Zhou). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 6908–6916