Biofilm and granule reactors were employed to remove nitrogen via an anammox reaction applying synthetic nitrogen wastewater, whose concentration was in the range of 20 to 1,400 mg N/L as total nitrogen. A biofilm reactor was packed with non-woven fabric and a granule reactor was filled with anaerobic granular sludge taken from the brewery wastewater treatment plant. Both reactors were seeded with Planctomycetes KSU-1 and operated for 450 days. The biofilm reactor showed high NH4+-N and NO2-N removal efficiencies of over 88% and 94%, respectively, until total nitrogen concentration was reached at 800 mg N/L. However, the biofilm reactor showed severe inhibition at over 1,000 mg N/L of total nitrogen due to nitrogen overloading. The granule reactor revealed better nitrogen removal performance than the biofilm reactor, showing high NH4+-N and NO2-N removal efficiencies of over 90%, even at a total nitrogen concentration of 1,400 mg N/L. However, aggregation of anammox bacteria grown in the sludge bed after long-term operation resulted in the deterioration of nitrogen. The removal ratio of NH4+-N and NO2-N was close to 1:1, suggesting other reactions related to ammonium oxidation could occur simultaneously. Free ammonia inhibition as well as NO2-N could be significant when high-strength nitrogenous wastewater was applied.