The Nitrogen removal efficiency was investigated in the MFCsystem under different conditions. The enhanced total nitrogen (TN) and NH4+-N removal rates at the anode in a single-chamberMFC could be achieved up to 91% and 97%, respectively when theblue–green algae were supplied as the substrate under the closed-circuit condition in 12 days, which were much higher than thoseunder the open-circuit condition [8]. Zhang et al. reported thatthe TN removal efficiencies in a single-chamber MFC under boththe closed and the open circuit conditions were 82.1 ± 0.5% and59.4 ± 3.3%, respectively [9]. Similar nitrate removal efficiencieswere obtained in a double-chamber MFC under both the closed-circuit and the open-circuit conditions when more than 30 mg L−1COD was present in the cathodic compartment. However, a higherdenitrification rate was achieved under the closed-circuit conditionthan under the open-circuit condition when the COD concentrationwas less than 30 mg L−1, which was probably due to the con-sumption of the electrons from the anode for denitrification [10].However, the exact reason which led to the different TN removalefficiencies obtained from the closed and the open-circuit condi-tions is not clear yet. Although SND process was ever reported atthe biocathode of the MFC, the nitrogen removal rate was onlyabout 0.0043–0.1 kgN m−3day−1[11]. Therefore, more studies arestill necessary to improve the nitrogen removal efficiency duringthe MFC treatment of wastewater.