Biological conversions of nitrogenous compounds closely resembling the chemistry of the anammox reaction were developed and maintained for approximately two years in fixed-bed, continuous-flow unit processes. Using a novel nonwoven matrix for biomass attachment, the anaerobic, autotrophic biofilm cultures were robust enough to survive occasional operational anomalies and to rebound quickly from temporary setbacks. Using a 2.7-l reactor with a hydraulic retention time of 7.5 hours, influent ammonium (NH₄⁺) and nitrite (NO₂^–) concentrations of approximately 250 mg N/l, each, were successfully treated with a total nitrogen (T-N) removal efficiency of 60%. T-N and NH₄⁺ volumetric removal rates of 40 and 20 mg N/l·h, respectively, were maintained for a one-year period of operation, which are in a suitable range for industrial applications. Using the nonwoven material of the 2.7-l reactor as a seed for a larger 14-l reactor, a fast transition to a stable, relatively high T-N mass removal rate of approximately 300 mg/h (NH₄-N removal, 150 mg/h) was possible. These results suggest that attached-growth processes such as employed here, with a nonwoven matrix, could serve well not only as a means of nitrogen abatement but also for mass cultivation of the slowly growing anaerobic ammonium-oxidizing cultures for use in development of new reactors.