Interaction in anaerobic biodecolorization of mixed azo dyes of Acid Red 1 and Reactive Black 5 under batch and continuous conditions

Anaerobic biodecolorization of mixed azo dyes of Acid Red 1 (AR1) and Reactive Black 5 (RB5) was investigated by both batch assays and a continuous process consisting of a photo-rotating biological contactor (PRBC) and an aerobic moving bed biofilm reactor (MBBR). Batch assays showed that the decolorization of RB5 in the mixed dye systems is in preference to AR1, and decolorization products of RB5 had acted as redox mediators to stimulate the decolorization of AR1. The addition of a final concentration of 720 mg/L RB5 increased the maximum decolorization rate of 420 mg/L of AR1 by 1.5-fold than RB5-free control. During the continuous treatment of AR1 with abundant cosubstrate, the addition of RB5 increased the biodecolorization efficiency of AR1 from 62.9% to 91.0%. The analysis using cyclic voltammetry (CV) and high performance liquid chromatography/mass spectrometry (HPLC–MS) indicates the mediating properties of the decolorization products from RB5.