Biodegradation of azo and anthraquinone dyes in continuous systems Jörgen Forss * , Ulrika Welander School of Engineering, Linnæus University, Vejdes Plast 6, SE-351 95 Växjö, Sweden article info Article history: Received 7 October 2010 Received in revised form 8 November 2010 Accepted 8 November 2010 Available online 15 December 2010 Keywords: Textile dye Industrial wastewater Lignocellulosic material Native microflora from forest residues abstract The purpose is to develop a complete microbiological model system for the treatment of wastewater from textile mills in developing countries. Artificial wastewater was treated by microorganisms growing on wood shavings from Norway spruce during unsterile conditions. The microorganisms were inoculated from forest residues. Mixtures of the azo dyes Reactive Black 5 and Reactive Red 2 were degraded in batch as well as continuous experiments. Reactive Red 2 mixed with the anthraquinone dye Reactive Blue 4 was also treated in the continuous system. The system consisted of three reservoirs e the first two with an anaerobic environment and the third with an aerobic. The dye concentrations were 200 mg l 1 of each dye in the continuous system and the retention time was approximately 4 days and 20 h per reservoir. Samples from the process were analysed with spectrophotometer and LC/MS to monitor the degradation process. 86-90% of the colour was removed after a treatment of 4 days and 23 h in the continuous process. Two metabolites were found in the outlets of reactors one and two, but they were degraded to below the detection limit in the aerobic reactor. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Dyes and textiles were two of the foundations of early indus- trialism and chemical engineering, and in some way still are. Our needs and demands for textiles and different clothing are greater than ever. Today, much of the textile and dyeing industry is located in developing countries, often with poor wastewater treatment. It is well documented that the effluents from the colouring process give rise to problems in the environment; the dye molecules can cause direct problems, such as toxins, and block sunlight for photosyn- thetic processes. The dyes can also be degraded to other toxic products. Some azo dyes, which are known to lead to carcinogenic aromatic amines (Pinheiro et al. 2004), are restricted for use and distribution in the EU (Directive 1976/769/EEC; EU 2002). It is estimated that almost 10 9 kg of dyes are produced annually worldwide (Kri zanec and Marechal 2006). Azo and anthraquinone are two of the most common groups of dyes used in colouring different textiles (Delée et al. 1998; Bisschops 2003). Different chemical (Jozwiak et al. 2007) and physical treatments methods are used for wastewater treatment (Vandevivere et al. 1998), though these methods are expensive in both the reconstruction of textile mills and maintenance. Therefore, our aim is to develop new, effi- cient and relatively cost effective biotechnical treatment methods for textile industry wastewater, based on natural ligno-cellulosic material. However, to do this, the addition of nutrients and a carbon source needs to be kept at a minimum, with preserved treatment efficiency. The microorganisms need to compete and survive successfully in the environment of the wastewater treatment facility. The wastewater from a textile mill might have a very complex chemical composition that includes dyes, salts, fats, detergents and other compounds (Bisschops 2003; Alex 2009). The composition of the wastewater influences the growth of microor- ganisms and some of the components might act as nutrients and a carbon source. The environment in a wastewater treatment plant is rough and often demands a mixed culture to get an efficient process. A pure culture will often be outcompeted when trans- ferred to a complex environment (Andersson 2001; Bento et al. 2005). The use of a mixed culture makes it difficult to evaluate the exact degradation pathways, since products formed by one microorganism might be degraded by the next. However, the degradation process needs to be monitored to avoid any toxic molecule products being released from the dyes. Extensive research has been performed regarding different treat- ments of coloured wastewater during the last 15 years. White rot fungi have a proven efficiency with their extracellular enzymes to attack unspecific molecules and break larger molecules into smaller pieces (Lucas 2006; Mohor ci c 2006; Nilsson et al. 2006; Zhao et al. 2006). However, in our previous experiments with Bjerkandera sp. (Nordström et al. 2008), the fungus was shown to be sensitive to bacterial contaminations. Different bacteria have shown the ability * Corresponding author. Tel.: þ46 470 70 82 33; fax: þ46 470 70 87 56. E-mail address: jorgen.forss@lnu.se (J. Forss). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2010.11.006 International Biodeterioration & Biodegradation 65 (2011) 227e237