Surface specific TAN removal measured as 0order nitrification rates (k0a) were similar (0.14–0.18 g N m−2d−1, p = 0.052) in all sys-tems when measured for 8 h after spiking. In all systems, ammonia concentrations decreased from the added 2.5 mg TAN L−1to at least0.5 mg TAN L−1at the end of the sampling period. Most systems removed TAN fast enough to reach 1 mg N L−1 approximately 4 hinto the 8 h sampling period (p = 0.112). Corresponding volumetric TAN removal rates ranged from 20.7 to 27.5 g N m−3d−1(p = 0.052