ABSTRACTThe utilization byAlcaligenes faecalisof electrodes as the electron donor for denitrification was investigated in this study. The denitrification rate ofA. faecaliswith a poised potential was greatly enhanced compared with that of the controls without poised potentials. For nitrate reduction, althoughA. faecaliscould not reduce nitrate, at three poised potentials of +0.06, −0.06, and −0.15 V (versus normal hydrogen electrode [NHE]), the nitrate was partially reduced with −0.15- and −0.06-V potentials at rates of 17.3 and 28.5 mg/liter/day, respectively. The percentages of reduction for −0.15 and −0.06 V were 52.4 and 30.4%, respectively. Meanwhile, for nitrite reduction, the poised potentials greatly enhanced the nitrite reduction. The nitrite reduction rates for three poised potentials (−0.06, −0.15, and −0.30 V) were 1.98, 4.37, and 3.91 mg/liter/h, respectively. When the potentials were cut off, the nitrite reduction rate was maintained for 1.5 h (from 2.3 to 2.25 mg/liter/h) and then greatly decreased, and the reduction rate (0.38 mg/liter/h) was about 1/6 compared with the rate (2.3 mg/liter/h) when potential was on. Then the potentials resumed, but the reduction rate did not resume and was only 2 times higher than the rate when the potential was off.