The object of this study was to investigate the capability of nitrate removal by nanoscale zerovalent iron (nZVI) particles in a re-circulated flow reactor of 4.3 L liquid volume. Nitrate removal of 70% was observed with the initial pH of 6.4 with the solution being pre-purged by N gas (anoxic 2 condition) at a rate of 50 mL min-1. However, when the solution was bubbled with CO (anoxic con- 2 dition), the nitrate removal efficiency was less than 5% with the initial pH of 4.0. As the pH was adjusted by H SO and NaOH to the range of 6-8, nitrate removal efficiency of 80-84% could be 2 4 obtaine d. Suc h resul ts demonstra te th at carbon ic ac id generate d from CO bubbling may play strongly 2 an inhibiting role in nitrate removed by the nZVI. In addition, based on nitrate mass balance, the end product was mostly dominated by ammonium at the initial pH 10. For the initial pH such as 6 and 8, some other nitrogen-containing species have been formed in the reaction, in addition to nitrite and ammonium.