The treatment of azo dye wastewater was studied in a periodic discontinuous batch reactor (PDBR) at high loading condition (1250 mg/l) under anoxic microenvironments. PDBR performance was evaluated by varying the time period of aerobic microenvironment during the cycle operation [before multiphasing (BMP; Control), 0.014; after multiphasing (AMP): AMPI, 0.84; AMPII, 0.73; AMPIII, 0.65]. Induction of air in anoxic-PDBR facilitated the simultaneous oxidation and reduction conditions and thus resulted higher dye removal efficiency with AMPIII strategy (65%) followed by AMPII (59.4%) and AMPI (54.4%) than the corresponding control operation (BMP: 49.4%). Relatively higher azo reductase enzyme activity was documented with AMP than corresponding BMP operation correlating well with azo dye decolorization. UV-UV-Significant transformational changes of azo dye peaks (618 nm) were documented before and after multiphase operations. Cyclic voltammogram profiles depicted increment in redox catalytic currents during AMPIII operation and also supports the involvement of reducing equivalents towards the dye removal. Derivatives of voltammograms illustrated the involvement of various redox mediators viz., cytochrome-C, quinones, Fumarate/Succinate, Fe(CN)(6)(3-)/Fe(CN)(6)(4-), and flavoproteins. Flexibility in phasing the multiple microenvironments in single bioreactor (PDBR) provides new insights in embodying the required capabilities to treat the recalcitrant azo dye wastewater especially at higher dye load operations (C) 2017 Elsevier B.V. All rights reserved.