Microbial fuel cells (MFC) have emerged as a sustainable technology that can directly produce electricity from the oxidation of organic matter by bacteria. A two-chambered up flow MFC with inner loop mode is evaluated for the hydraulic retention time (HRT) effect on MFC electricity generation. The MFC is constructed with a carbon cloth electrode and anion exchange membrane for electricity production. Swine wastewater containing 3300 +/- 300 mg/L of total chemical oxygen demand (TCOD) was used as the substrate for the anode chamber. Potassium ferricyanide was used as the electron acceptor in the cathode chamber. The reactor was operated at 30 degrees C with a external resistance of 100 Omega in feed-batch mode. The TCOD removal rates at HRT 13, 14, and 20 d were 71, 73 and 83%, while the coulombic efficiencies (CE) were 7.1, 2.4 and 0.3%, respectively. The maximum power density at HRT 13 and 14 d were similar, 12 mW/m(2) and 13 mW/m(2), which were 26 fold greater than the HRT at 20 d (0.5 mW/m(2)). The effect of different HRTs on decreasing the organic content by biocatalyzing leads to less organic material for electricity generation, resulting in lower power output. The optimal COD removal efficiency, CE and power density were observed in an up-flow MFC at HRT 14 d. These results demonstrate that up flow MFC using an inner loop with swine wastewater as the substrate could provide both effective organic removal and electricity output. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.