The coupling of micro-electrolysis cell (MEC) with an up-flow anaerobic sludge blanket (UASB) system in pilot scale was established for enhanced treatment of Fischer-Tropsch (F-T) wastewater. The lowest influent pH (4.99 +/- 0.10) and reduced alkali addition were accomplished under the assistance of anaerobic effluent recycling of 200% (stage 5). Simultaneously, the optimum COD removal efficiency (93.5 +/- 1.6%) and methane production (2.01 +/- 0.13 m(3)/m(3).d) at the lower hydraulic retention time (HRT) were achieved in this stage. In addition, the dissolved iron from MEC could significantly increase the protein content of tightly bound extracellular polymeric substances (TB-EPS), which was beneficial to formation of stable granules. Furthermore, the high-throughput 16S rRNA gene pyrosequencing in this study further confirmed that Geobacter species could utilize iron oxides particles as electron conduit to perform the direct interspecies electron transfer (DIET) with Methanothrix, finally facilitating the syntrophic degradation of propionic acid and butyric acid and contributing completely methane production. (C) 2017 Elsevier Ltd. All rights reserved.