Microbial fuel cells (MFCs) were investigated for use in removing total ammonia nitrogen (TAN) and residual COD from effluent digested in an anaerobic digester (AD) fed with actual swine wastewater for 32 days in batch mode. Cumulative COD removal in the AD was as high as 59,647 +/- 2096 mg/L (80.5% removed), whereas TAN removal in the AD was negligible at 296 +/- 116 mg-N/L (5.8% removed), causing a decrease in the COD/TAN ratio from 14.5 to 3.0. In a subsequent MFC system, 77.5% of TAN was removed at 36 days, leading to an increase in COD/TAN ratio from 4.6 to 8.1. As a result, the COD in the anode was further reduced from 19,319 +/- 417 mg/L to 7519 +/- 554 mg/L (61.1% removed). From these results, removing the TAN in MFCs was found to increase the COD/TAN ratio, with the COD being further degraded. (C) 2015 Elsevier Ltd. All rights reserved.