Continuous treatment of coloured industry wastewater using immobilized Phanerochaete chrysosporium in a rotating biological contactor reactor

Abstract

Coloured industry wastewaters often contain dyes and other toxic ingredients, and, therefore, pose serious threat to the receiving environment. Among the available methods the eco-friendly biological method has gained maximum attention due to its many advantages over the traditional methods. In the present study, continuous biological treatment of coloured wastewater from a textile dyeing industry was investigated using the white rot fungus Phanerochaete chrysosporium in a rotating biological contactor (RBC) reactor. The raw wastewater was diluted with an equal volume of either distilled water or media containing glucose at varying concentrations to study its effect on the decolourization process. Results revealed that the wastewater could be decolourized to an extent of more than 64% when diluted with media containing glucose; and, a maximum decolourization efficiency of 83% was obtained with 10 g/l glucose concentration. COD removal efficiencies were also found to be consistent with the decolourization efficiencies of the wastewaters. Further, the results were correlated with the enzyme activities of manganese peroxidase (MnP) and lignin peroxidase (LiP) by the fungus, which were found to play some significant role in decolourization of the wastewater. Results of replacing the costly carbon source glucose in the decolourization media with the more cheap molasses, however, revealed very high COD removal efficiency, but low decolourization efficiency of the industry wastewater.

Introduction

Wastewater originating from textile industries is a complex mixture of potentially polluting substances which imposes serious threat to the receiving environment. Normally, 1–15% of dyes used in the process remains and is often found in the effluent wastewater stream (Barka et al., 2009). Generally, colours are noticeable at a dye concentration of 1 mg/l and an average concentration of 300 mg/l has been reported in effluents from textile manufacturing processes (O’Neill et al., 1999). The absorption of light due to such coloured wastewater from industries creates problems to photosynthetic aquatic plants and algae. Compared to wastewaters from other industries, effluent from textile and dye manufacturing industries is most difficult to treat mainly due to the presence of synthetic dyes of complex aromatic chemical structure that render these compounds highly stable and hence recalcitrant to degradation (Kaushik and Malik, 2009). Wastewater decolourization can be, however, achieved by chemical and physical methods including adsorption, coagulation-flocculation, oxidation and electrochemical methods (Lin and Peng, 1996). On the contrary, these existing techniques suffer from one or more drawbacks, such as high cost, formation of hazardous by-products, intensive energy requirement etc. (Saratale et al., 2009). Further, while decolourization under anaerobic conditions can lead to toxic degradation products (Brown and DeVito, 1993), exposure to oxygen may cause reverse colourization of the degradation products (Knapp and Newby, 1995). On the other hand, microbial decolourization process offers to overcome all these drawbacks by reducing the complex colour components in the wastewater into simple compounds like carbon dioxide, ammonia and water in a cleaner and safer way than the conventional methods (Paszczynski et al., 1992).

Among the various microorganisms, the white rot fungus Phanerochaete chrysosporium secretes non-specific, extracellular ligninolytic enzymes and can degrade a wide variety of recalcitrant compounds like xenobiotics, dyestuffs, etc. Due to the extracellular enzyme system, substrate diffusion limitation is not observed which is generally encountered in bacteria. Another advantage of using P. chrysosporium is that they do not require preconditioning with the pollutant as enzyme production and secretion depends on nutrient limitation, which can be carbon or nitrogen, rather than the pollutant itself. In fact, the fungus has been extensively tested in decolourization studies due to its ability to degrade, partially or completely, a broad range of dyes such as heterocyclic, azo, anthraquinone, and vat (Rodriguez et al., 2000; Mielgo et al., 2003). Further, the extracellular enzyme system enables the white rot fungus to tolerate even high concentrations of such pollutants (Kapdan et al., 2000a, b).

Compared with other reactors, the rotating biological contactor (RBC) reactor is proving effective in treating complex wastewaters (Alemzadeh et al., 2002; Kapdan and Kargi, 2002; Axelsson et al., 2006), mainly because it offers high interfacial area generated in the rotating disc to establish good contact between the microbial species and pollutants in the system. Although a few studies have been performed on decolourization of wastewater using the immobilized fungus in laboratory-scale RBC reactors, all these studies are restricted only to synthetic wastewater prepared in the laboratory and/or under batch operated conditions. In addition, coloured wastewater from industries contains complex mixture of dyes and other ingredients, and, hence, there is a need to evaluate potential of the bioreactor system in decolourizing such real wastewaters. The present study was, therefore, aimed to decolourize wastewater from a textile dye industry using immobilized P. chrysosporium in a continuously operated RBC reactor.