Performance of anaerobic hybrid reactors for the treatment of complex phenolic wastewaters with biogas recirculation

► Biogas recirculation employed for AHR treating coal wastewater. ► Higher phenolics and COD removal observed at 7.5 L d−1. ► Simultaneous removal of all phenolics. ► Greater attachment of biomass (14.0 g VSS) to support medium. ► Higher methanogenic activity was observed.