146
Qin
et al
.,
Comparison on nitrosation and anaerobic ammonium oxidation between activated sludge and biofilm from an autotrophic...
Tecnología y Ciencias del Agua
, vol. VIII, núm. 2, marzo-abril de 2017, pp. 141-149
•
ISSN 2007-2422
TN. The activated sludge in this system showed
good ammonia oxidation activity under aerobic
conditions. Nitrogen transformation by biofilm
during a 48 h cycle is shown in figure 3b. The
ammonia oxidation rate was 72%. Compared
with nitrosation by activated sludge, there was
no obvious inflection point on the ammonia
concentration curve with biofilm. The maximum
rate of ammonia oxidation rate by biofilm was
0.08 mgN mgVSS
−1
d
−1
. The nitrosation activity
of activated sludge was about 2.89 times that of
the biofilm. Ammonia was mainly oxidized to
NO
2
-
-N and the maximum concentration of NO
3
-
-N was only 4 mg/l at the end of the reaction
cycle. The TN removal rate was 6.7%.
Both activated sludge and biofilm showed
high nitrosation activities and there was little
NO
3
-
-N accumulation in either system because
they were acclimated to nitrosating conditions
at the start of the experiment. NOB had been
depleted and so most of the oxidized ammonia
existed as nitrite. There were 158 times as many
AOB as NOB cells in activated sludge samples
while the ratio was 25 times in the biofilm
sample. Accordingly, the aerobic ammonia
oxidation rate of biofilm was less than that of
activated sludge. This also led to a difference in
nitrosation capacity between the two samples.
This experiment used real-time PCR technology
for bacterial quantification. Results showed that
the populations of AOB were 1.88 × 10
11
cells/g
in the activated sludge samples and 1.90 × 10
10
cells/g in biofilm samples. Cell counts in the
sludge sample were about ten times those in the
biofilm. AOB, which were responsible for aero-
bic ammonia oxidization, were mainly found
in activated sludge in this SBBR autotrophic
nitrogen removal reactor.
Studies have shown that there might be
denitrification under aerobic conditions by
aerobic denitrifiers (Robertson & Kuenen,
1990; Chen, Xia, & Ju, 2003; Hung, Mitsuyo, &
Makoto, 2005). However, in this study, aerobic
TN removal rates of activated sludge or bio-
film samples were both low. After 48 h, the TN
removal rates of sludge and biofilm samples
were only 6.7 and 5.3% respectively. The NH
4
+
to NO
2
-
conversion rates of sludge and biofilm
samples were 85 and 83%, respectively. The
concentration of NO
3
-
was low, with the high-
est concentrations seen at the end of the 48
h experiment cycle of just 6.7 and 4.0 mg/l.
Little aerobic denitrification was seen in the
SBBR autotrophic nitrogen removal process.
ANAMMOX activity was limited by continu-
ous aeration to maintain a DO concentration
of 2.0 mg/l, but ANAMMOX which survived
in the activated sludge flocs and the interior of
biofilm might provide the system with some
anaerobic nitrogen removal capability.
Anaerobic ammonium oxidation of activated
sludge and biofilm
Figures 4a and 4b show the anaerobic ammoni-
um oxidation activities of activated sludge and
Figure 3a. Nitrosation by activated sludge. Figure 3b. Nitrosation by biofilm.
