Abstract
In this study, microbial community dynamics were explored during biological degradation of azo dyes with different chemical structures. The effect of the different molecular structures of the azo dyes was also assessed against the simultaneous removal of color and the bacterial community. Winogradsky columns were inoculated with dewatered sludge and separately fed with six different azo dyes to conduct the sludge acclimatization process, and nine bacterial decolorizing strains were isolated and identified. The decolorization and biodegradation performances of the acclimated system and isolated strains were also determined. Results showed that the bacterial isolates involved in decolorization and the degradation of the azo dyes were mainly associated with the azo dye structure. After 24 h acclimatization at room temperature without specific illumination, immediate decolorization of methyl red (89%) and methyl orange (78%) was observed, due to their simple structure compared to tartrazine (73%). However, after 8 days of acclimatization, methyl red was easily decolorized up to 99%, and about 87% decolorization was observed for orange G (87%), due to its complex chemical structure. Higher degrees of degradation and decolorization were achieved with Pseudomonas geniculate strain Ka38 (Proteobacteria), Bacillus cereus strain 1FFF (Firmicutes) and Klebsiella variicola strain RVEV3 (Proteobacteria) with continuous shaking at 30 °C. The azo dyes with benzene rings were found to be easier to decolorize and degrade with similar microbial communities. Moreover, it seems that the chemical structures of the azo dyes, in a sense, drove the divergent succession of the bacterial community while reducing the diversity. This study gives a deep insight into the feasible structure-based artificial manipulation of bacterial communities and offers theoretical guidance for decolorizing azo dyes with mixed bacteria cultures.
Highlights
Azo dyes containing one or more azo bonds(–N=N–), represent the largest class of dyes used in the textile industry, because of their low cost, easy synthesis, high stability and wide variety of available colors compared to natural dyes [1]
We explored the effect of the molecular structures on the biodegradation rate of six different azo dyes, using nine bacterial strains isolated from the dewatered activated sludge
The effect of the time interval on azo dye decolorization was tested for a range of 1 to 8 days, and the data were categorized into three groups according to the time interval
Summary
Azo dyes containing one or more azo bonds(–N=N–), represent the largest class of dyes used in the textile industry, because of their low cost, easy synthesis, high stability and wide variety of available colors compared to natural dyes [1]. It is believed that the microbial community structure and diversity may significantly affect the performance and stability of biological processes (e.g., dye degradation) as reported elsewhere [11]. Azo dyes with various chemical structures and molecular weights were observed to exhibit different removal and decolorization rates [14]. The evaluation of the microbial community structure against different by-products of the dyes can help to identify the critical microorganisms and mechanisms associated with the transformation process. To best of our knowledge, in-depth evaluations of functional microorganisms and microbial communities against the degradation mechanisms of different azo dyes have still not been performed. We explored the effect of the molecular structures on the biodegradation rate of six different azo dyes, using nine bacterial strains isolated from the dewatered activated sludge. A canonical correspondence analysis (CCA) was utilized to analyze the relationship between the microbial habitat and various factors in the different domestication treatments
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