Biodecolorization of the Azo Dye Reactive Red 2 by a Halotolerant Enrichment Culture

Abstract

The decolorization of the azo dye Reactive Red 2 (RR2) under anoxic conditions was investigated using a mesophilic (358C) halotolerant enrichment culture capable of growth at 100 g/L sodium chloride (NaCl). Batch decolorization assays were conducted with the unacclimated halotolerant culture, and dye decolorization kinetics were determined as a function of the initial dye, biomass, carbon source, and an externally added oxidation-reduction mediator (anthraquinone-2,6-disulphonic acid) concentrations. The maximum biomass-normalized RR2 decolorization rate by the halotolerant enrichment culture under batch, anoxic incubation conditions was 26.8 mg dye/mg VSSÁd. Although RR2 decolorization was inhibited at RR2 concentrations equal to and higher than 300 mg/L, the halotolerant culture achieved a 156-fold higher RR2 decolorization rate compared with a previously reported, biomass-normalized RR2 decolorization rate by a mixed mesophilic (358C) methanogenic culture in the absence of NaCl. Decolorization kinetics at inhibitory RR2 levels were described based on the Haldane model (Haldane, 1965). Five repetitive dyeing/decolorization cycles performed using the halotolerant culture and the same RR2 dyebath solution demonstrated the feasibility of biological renovation and reuse of commercialstrength spent reactive azo dyebaths. Water Environ. Res., 79, 2446Res., 79, (2007.

Anthraquinone compounds as redox mediators for enhanced continuous-flow anaerobic biotransformation of reactive dyes under hypersaline conditions

“…The specific biomass concentration in the AFBR after over three years of operation under anaerobic hypersaline conditions was 58.7 ± 2.9 mg volatile solids/g support media. Details on the development and operation of the AFBR system have been reported before [4,9,14,17]. …”

“…Given the relatively high molecular weight of the dyes, their reductive biodecolorization has been attributed to a microbially mediated process that channels reducing equivalents from a biodegradable carbon and energy source to the dyes, which serve as electron acceptors in a non-energy yielding, and thus non-growth-related, process [10][11][12]. The reductive decolorization of azo and anthraquinone dyes takes place by the two-step reductive cleavage of the azo bond and formation of the corresponding amines [13,14] Downloaded by [University of Saskatchewan Library] at 23:29 03 January 2015 and the two-step reduction of the anthraquinone moiety to dihydroxyanthracene, respectively [15,16]. Although a substantial number of reports have documented the microbial reductive decolorization of reactive azo and anthraquinone dyes, very limited research dealing with microbial decolorization under hypersaline conditions has been conducted.…”

“…Successful, batch microbial reductive decolorization of reactive azo and anthraquinone dyebaths by a suspendedgrowth, halotolerant enrichment culture under hypersaline conditions has been reported [4,9,14,17]. However, application of the suspended-growth culture for the treatment of spent reactive dyebaths at a commercial scale is limited because it requires biomass separation before reusing the decolorized solution.…”