Coupling of anaerobic digester and microbial fuel cell for COD removal and ammonia recovery

• COD and TAN removal using MFC.
• AD leading to the decrease in COD/TAN ratio.
• Decreased COD removal and CH4 production in AD due to the decreased COD/TAN ratio.
• TAN removal in MFC resulting in an increased COD/TAN ratio.
• Increased COD/TAN ratio leading to further degradation of COD.

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.