It was found that 1-amino-2-naphthol, an intermediate generated during the anaerobic degradation of Acid Orange 7, is a redox mediator which plays a significant role in the transport of electrons to the dye, thus giving to the whole process an autocatalytic nature. Evidences of the autocatalytic behaviour were observed in experimental data previously obtained under batch and fed-batch conditions. In this paper, a kinetic model considering all these factors is proposed and validated. In batch assays, this model agrees satisfactorily with the experimental data. In the case of fed-batch assays, the autocatalytic model only can be applied satisfactorily after the first feeding, since the degradation of Acid Orange 7 after the second and third feedings followed a first-order kinetic. This fact can be explained due to the presence of the redox mediator previously generated during the reactions that took place after the first feeding.

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