<p>Electro-oxidation was used to continuously convert nitrite to nitrate in an undivided flow cell equipped with two parallel graphite electrodes. Electrolyte selection for the continuous-flow tests was guided by batch experiments conducted with KCl, NaHCO₃, and Na₂SO₄. Higher conversion was found in chloride media, for which the process likely proceeded via direct anodic oxidation and a chloride-mediated bulk route associated with electrogenerated active chlorine species, consistent with hypochlorite regeneration. A plug-flow model with a reaction rate governed by mass-transfer accounted for conversion versus flow rate. The fitted mass transfer coefficient independent of flow rate is consistent with gas-evolution-induced convection near the electrodes. The effect of current, nitrite load, and electrolyte composition on conversion and power consumption was investigated using a Box–Behnken response-surface design. Complete nitrite conversion was obtained under specific conditions. Energy demand fell within ranges reported for electrochemical oxidation of pollutants in wastewaters. Interference by nitrate, ammonium, and sulfide was observed, but was suppressed by increasing residence time, whereas humic, hexanoic, and acetic acids showed no detectable effect. The cell used only commercial graphite and operated at conductivities ~ 3 mS cm⁻¹, indicating a low-cost commercial-grade option for nitrite polishing or pre-oxidation prior to denitrification.</p> Graphical abstract <p></p>