N2O production in a single stage nitritation/anammox MBBR process

of N2O during aeration was slightly higher and that the maximum concentration reached
was lower than during intermittent aeration.
Initial and maximum % N2O production was calculated to be in the range of 2-3.2% and
5.6.-6.2% of removed inorganic nitrogen respectively, the result is presented in Table
11.
Table 11. Average N 2O concentration in the water phase during aeration. Calculated initial and
maximum N 2O production rates, mean O 2 concentrations during aeration, mean nitrogen
concentration, reduction and removal rates for studies at continuous operation mode DO ~1.5
mg/l.
Produced N 2O in % of
Average
N 2O
removed inorganic N-
concentration O 2
mean N-concentration
mg/l
N-red. Removal
Date µmol/l initial max mg/l NH 4-N NO 3-N NO 2-N % gN/m 2 d
091006 4.3 2.8 5.6 1.3 249 25.2 0.3 66 1.3
091007 2.9 2.1 5.6 1.8 246 28.9 0.0 64 1.3
091010 3.3 3.2 6.2 1.8 220 36.3 0.0 72 1.3
4.3.4 Continuous operation at DO ~1.0 mg/l
Two measurements were performed at a constant aeration with a DO concentration of 1
mg/l. Registered N2O accumulation was the lowest so far and the initial N2O production
was below 2% of reduced inorganic nitrogen. Maximum production varied between 2-
4.3%. Table 12 presents the results from continuous operation at DO concentration of~1
mg/l.
12
10
4.5
3.75
N₂O (µmol/l)
8
6
4
2
3
2.25
1.5
0.75
DO (mg/l)
N₂O
(µmol/l)
DO
(mg/l)
0
0
0 20 40 60 80
Time (min)
Figure 18. Concentration profiles of N 2O and O 2 obtained from measurement during the period of
continuous reactor operation at a DO concentration of ~1.0 mg/l.
As seen in Figure 18 N2O was only accumulating for the first 5-6 minutes of the
unaerated period then there was a short time span when produced N2O and N2O flows
that left the reactor were in equilibrium. The N2O concentration measured in the water
phase decreased before aeration started again.
37