To accomplish the above, varying
quantities of immobilized NBC on wood powder were incubated in 1L seawater
having 15 g/ L salinity. Initially TAN was maintained at 10 mg/ L. Nitrification
was monitored in terms of per day TAN removal and NO2– N
production. On day 1, the TAN removal rates in the systems inoculated with 0.1, 0.2, 0.3, 0.4, 0.5, 0.6,
0.7, 0.8, 0.9, 1 g wood powder immobilized with nitrifying bacterial
consortium were 1.05, 3.98, 4.11, 4.2, 4.2,
4.3, 4.4, 4.62, 4.39, 4.98 mg/ L respectively, whereas in the control it was
0.8 mg/ L. The NO2– N production in the same systems was
0.03, 0.98, 1.83, 2.08, 2.34, 2.01, 2.38, 2.18, 2.09, 2.99 respectively,
whereas in the control it was 0.098 mg/ L (Table.
3). TAN removal per day and quantity of immobilized NBC showed a
positive correlation (0.895).
Evaluation
of nitrifying potency of immobilized nitrifying bacterial consortia in a system
with low stocking density.
TAN removal was obvious from point of addition of NBC to the system nine
days after its initiation (Fig.3). After
two days, the entire TAN (4.99 mg/ L) was removed in the test tanks where average
lowering of 2.75 mg/ L/ day of TAN was observed. In the corresponding control a
lowering of 0.76 mg/ L/ day, three fold lower than the test tanks, was seen. On the second day, the NO2–
N production in the test tank was 2.26 mg/ L and an increased out put of 3.9 mg/
L/ day on the third day. On subsequent days it declined, and by the time NO3-
– N production had commenced (on the 4th day onwards) with a corresponding
decrease of NO2– N (Fig. 4).
A negative correlation was observed between TAN and NO3- N in the
tests (r -0.59) indicating effective nitrification, whereas in the control
tanks elevated levels of NH4+ – N and NO2– N could be recorded.
TAN removal and drop in alkalinity (Fig.5)
in the test tanks were positively correlated (r = 0.838).
Evaluation
of nitrification potency of immobilized NBC in systems with high stocking
density.
In the system with high stocking density, the entire
(9.98 mg/ L) quantity of total ammonia nitrogen in the test tanks could be removed
within five days (Fig.6). Average
lowering of 2.002 mg/ L/ day TAN was observed in the test tanks, whereas in the
corresponding control tanks it was 0.58 mg/ L/ day. In the tests NO2-
–N registered maximum value on the 14th day (3.35 mg/ L), which
declined corresponding to the decline of TAN concentration (Fig. 7). Mean
NO3- – N level increased from 0.1 to 6.39 mg/ L in
the test tanks, and remained at 0.005 to 1.89 mg/ L in the control
systems. NO3- – N levels were significantly higher (P
