A combined bioelectrochemical and sulfur autotrophic denitrification system (CBSAD) was evaluated to treat a groundwater with nitrate contamination (20.9-22.0 mg NO(3)(-)-N/L). The reactor was operated continuously for several months with groundwater to maximize treatment efficiency under different hydraulic retention times (HRT) and electric currents, The denitrification rate of sulfur autotrophic part followed a half-order kinetics model. Moreover, the removal efficiency of bioelectrochemical part depended on the electric current. The reactor could be operated efficiently at the HRT ranged from 4.2 to 2.1 h (corresponding nitrogen volume-loading rates varied from 0.12 to 0.24 kg N/m(3) d; and optimum current ranged from 30 to 1000 mA), and the NO(3)(-)-N removal rate ranged from 95% to 100% without NO(3)(-)-N accumulation. The pH of effluent was satisfactorily adjusted by bioelectrochemical part, and the sulfate concentration of effluent was lower than 250 mg /L, meeting the drinking water standard of China EPA. (c) 2008 Elsevier Ltd. All rights reserved.