Figure 3 shows NH4+ and NO3− profiles in different
operational stages. NH4+ in anaerobic zone was
brought by the influent and the pre-anoxic effluent,
with the addition of organic nitrogen ammonification
in itself. As shown in Fig. 3 (a), NH4+ was higher in
anaerobic zones of run 3 and run 4, 26.5 and 22.8
mg·L−1, respectively, while that of run 1 and run 2 was
18.1 and 18.6 mg·L−1, respectively