A new reactor concept designed as a bubble column staged with fibrous catalytic layers is tested on pilot-scale for the reduction of nitrite to nitrogen by hydrogen. Carbon dioxide is used to neutralize the hydroxide ions produced during hydrogenation of nitrite. The effective reaction rate was found to depend on the superficial gas velocity u(g0). The fibrous catalysts demonstrated a high selectivity towards nitrogen. The influence of the mass transport on the effective kinetics is discussed and the volumetric liquid-solid mass transfer coefficient k(S)a(S) is estimated as a function of the superficial gas velocity u(g0). The selectivity was found to be independent of the hydrodynamics.