Quinone-reducing enrichment culture enhanced the direct and mediated biotransformation of azo dye with soluble and immobilized redox mediator

Anthraquinone-2,6-disulfonate (AQDS) was used as an electron acceptor to promote the establishment of a community of quinone-reducing microorganisms from an anaerobic sludge using acetate and glucose as energy sources. The enriched and control (not enriched with AQDS) sludge were used for the direct and mediated biotransformation of congo red. For the mediated reduction, AQDS was used soluble and immobilized on granular activated carbon (GAC). The adsorption capacity of AQDS on GAC was 87.6 mg/g, which improved the electron-accepting capacity of the material 2.26-times compared to the unmodified GAC. The rate of decolorization of congo red with the enriched sludge was 2.94-times higher than the value achieved with the control sludge for the direct biotransformation. For the mediated biotransformation using AQDS immobilized, the rates with the enriched sludge were improved 3.79-and 1.13-times respect to the incubations with the control sludge lacking AQDS and with AQDS immobilized, respectively. The microbial analysis revealed a change in the bacterial composition of the enriched sludge compared to the control sludge. In contrast, the profiles of the archaeal composition remained the same in the two types of sludge. The results presented in this study confirm the potential use of quinone-reducing microorganisms enriched to improve the redox biotransformation of electron accepting pollutants (e.g. azo dyes) by direct reduction and mediated with soluble and immobilized redox mediators.