In treatments 2 and 3, the outlet concentration of TKN, ammonia
and organic nitrogen was significant lower than the inlet concentration
under both operating conditions (Fig. 2). Removal of all three
of these was better in the flood/drain biofilters compared with the
submerged biofilters. The outlet concentration was significantly
lower in the flood/drain biofilters than in the submerged biofilters
in treatment 2 for TKN and ammonia (both Mann–Whitney
U, p < 0.05), and also in treatment 3 for TKN and ammonia and
organic nitrogen (all Mann–Whitney U, p < 0.05).