The nitrogen profiles of the influent and effluent are shown in
Fig. 3a. The influent NO3
-N that was present in all the phases came
from the tap water itself, while NH4 + -N was artificially added to the
influent in phases I, II and III. The influent nitrite in phases II and III
was attributable to the natural NH4 + -N oxidation in the influent
tank, while the nitrite in phase IV was the result of the artificial
addition. After the adaptive phase I, the biofilter performed well
in the removal of NH4 + -N and NO2
-N, the effluent concentrations
of NH4 + -N and NO2
-N were at trace amount levels.