Many industries are charged fees based on the organic loads in effluents. Therefore, it can be advantageous to reduce the wastewater strength prior to discharge. We investigated the use of microbial fuel cells (MFCs) to reduce the chemical oxygen demand (COD) of a paper-plant wastewater while at the same time producing electricity in a continuous flow system. At a hydraulic retention time (HRT) of six hours, COD removal using an unamended wastewater (506 mg/L COD) (organic loading rate, OLR = 2.0 kg COD/(m3 d)) was 26 +/- 2%, with a power density of 5.9 +/- 0.2 W/m3 (210 +/- 7 mW/m2). This amount of power was similar to the maximum power density (5.2 +/- 0.4 W/m3) produced in fed-batch tests using a slightly lower strength wastewater in the same device (405 mg/L COD). Increasing the HRT to 25 h (OLR = 0.5 kg COD/(m3 d)) increased COD removal (41 +/- 2%) but substantially decreased power (2.8 +/- 0.3 W/m3). While wastewater strength affected removal rates, the solution conductivity (0.8 mS/cm) was primarily a factor in low power production. These results demonstrate that MFCs can be used to reduce organic loads in effluents at relatively short HRTs, while at the same time generating power.