The performance of an upflow anaerobic sludge blanket (UASB) reactor and an anaerobic hybrid reactor (AHR) was investigated for the treatment of simulated coal wastewater containing toxic phenolics at different hydraulic retention times (0.75-0.33 d). Fast start-up and granulation of biomass could be achieved in an AHR (45 d) than UASB (58 d) reactor. Reduction of HRT from 1.5 to 0.33 d resulted in a decline in phenolics removal efficiency from 99% to 77% in AHR and 95% to 68% in UASB reactor respectively. AHR could withstand 2.5 times the selected phenolics loading compared to UASB reactor that could not withstand even 1.2 times the selected phenolics loading. Residence time distribution (RTD) study revealed a plug flow regime in the AHR and completely mixed regime in UASB reactor respectively. Energy economics of the reactors revealed that 12,159 MJ d(-1) more energy can be generated using AHR than UASB reactor. (C) 2012 Elsevier Ltd. All rights reserved.