red, was created which is similar to the Anammox
cultures expounded in previous studies [24-26]. However,
the color of sludge was fixed at the highest concentration
of 400 mg/L, which indicate the application of the
Anammox in high concentrations. So, the color change is
considered as one of the characteristics of Anammox
sludge. In addition, changes in the amount of sludge
granules by measuring VSS (in first and end of the operation
period), were from 12.3 to 23.8 mg/L. Also observing
N2 bubbles produced under anaerobic condition is
another reason to approve Anammox process.
Evaluation of the process performance in UABF reactor
by the kinetic models
The modified Stover-Kincannon model and Grau secondorder
model were used to evaluate the Anammox process
performance in the UABF reactor. During the kinetic
study, the HRT was adjusted at 24 h and gradually
reduced to 6 h, whereas the flow rate increased from
1.8 L/d to 7.2 L/d. Also, the influent ammonium and nitrite
concentrations were increased from 350 and
470 mg N/L to 700 and 924 mg N/L, respectively. Consequently,
The NLR increased gradually from 0.835 gN/L.d
to 6.496 gN/L.d. The results obtained from experiments
during the kinetic study, indicated a meaningful relationship
between the removal efficiency and the hydraulic retention
time. As HRT decreased, total nitrogen
concentration in the effluent increased from 0.07 g/L to
0.2 g/L. Also, the removal efficiency decreased stepwise
from 91.6% to 81.8%. The effect of the nitrogen loading
rate on the substrate removal rate is depicted in Figure 5.
According to Figure 5, with the increase of nitrogen
loading rate, the substrate removal rate increased from
0.765 to 5.316 kg/m3
d and the nitrogen removal efficiency
decreased to 81.8%.
Figure 6 illustrates the experimental data obtained in
this study vs. the predicted values for the effluent total
nitrogen obtained by the modified Stover-Kincannon
and the Grau second-order models in UABF reactor,
which were calculated by Equation (7), respectively. It
can be observed that the predicted data is in agreement
with the experimental data by the modified StoverKincannon
model (R2
=0.978) and the Grau secondorder
model (R2
=0.956) however the Stover-Kincannon
model was more appropriate for nitrogen removal kinetics
in UABF reactor. Table 1 compares the constants