A pilot plant, using a four-compartment reactor packed with Biolace media, was operated in the anoxic/aerobic submerged fixed-film (A/ASFF) and the aerobic (ASFF) modes at loadings 0.03 to 0.3 g BOD. g−1 BVS. d−1, 0.01 to 0.11 g NH3. g−1 BVS d−1, HRTs 0.7 to 8 h, C/N of 6, and 28 ± 2 °C. The system proved to be very effective in treating municipal wastewater, achieving removals up to 98% for biological oxygen demand (BOD), 75% for chemical oxygen demand (COD) and 97% for ammonia. Performance was not adversely affected by a 10-fold increase in loading rate. Both modes of operation showed high specific nitrification rates up to 96 mg N. g−1 BVS d−1, but the A/ASFF was more stable and efficient at higher loadings. Its anoxic stage removed more than 90 and 60% for BOD and COD, respectively. The A/ASFF reactor also achieved denitrification, which eliminated 3.35 mg BOD (or 6.6 mg COD) versus 1 mg denitrified NO3-N, that resulted in higher organic removals. Denitrification rate increased linearly with the TON (total oxidised nitrogen) loading applied, and specific substrate removal reached up to 114 mg TON. g−1 BVS. d−1.