In order to ascertain the effects of different carbon sources (methanol, glucose, starch and NaHCO3) on denitrification in BESs, the experiment was conducted in a constant current, 3.5 of chemical oxygen demand to nitrate ratio in a greenhouse. Among the four carbon sources investigated in BESs, NaHCO3 showed the highest nitrite accumulation and the ratio of soluble microbial products to soluble chemical oxygen demand (SMP/SCOD) with a value of 3.68 +/- 0.68 mg/L and 94%, respectively. And the addition of organic substrates could reduce SMP production and enhance the denitrification process. In the constant voltage experiment, it was observed that the organics could be used by microbes to generate electrons at the anode. And a maximal current value of 11.0 mA in the BESs fed with starch indicated that the complex carbon source was easier to be used by microorganisms to generate electricity than the simple carbon source. (C) 2012 Elsevier Ltd. All rights reserved.