Immobilization of NBC on wood powder

            The substrate consumption
and product formation during mass immobilization of NBC meant for 15 g/ L
salinity culture system is illustrated in Fig. 2. The system which started with  10
mg/ L residual NH4 + – N consumed 583.6  mg/ L  NH4+- N over a period of
75 days  with a total corresponding
output of 415.6 mg/ L NO3– N. Growth curve
showed that there was  progressive build
up of NO2– N until seven days and subsequently it
rapidly declined and NO3– N began to accumulate. After that,
no residual nitrite could be detected and oxidation of NH4+
– N and NO2- -N was found to take place simultaneously to
form NO3- -N.

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Determination of immobilized nitrifying bacterial biomass
based on ATP bioluminescent method

            The immobilized nitrifying bacterial biomass  estimated at stationary phase of the
culture  was  4.24 x 107 CFU g/L. This result
was based on the relationship 1.61 log CFU g/ L = 3.18 log fg/ L ATP (Ukuku et
al. 2005).

Determination
of nitrifying potential of immobilized NBC on wood powder

            The immobilized NBC was dried under different conditions, such as
desiccation under vacuum and with out vacuum, and by spreading on polythene
sheet all at room temperature (RT).

 The results showed that TAN removal took place
within a day in the experimental system inoculated with immobilized NBC. In the
system inoculated with NBC dried in vacuum desiccator the TAN removal and NO2-
– N production were 1.07 and 0.25 mg/ L/ day respectively. In the system
inoculated with NBC dried in dessiccator with out vacuum the removal and
production were 7.09 and 3.7 mg/ L/day respectively. However, in the
system inoculated with NBC dried by spreading at room temperature, TAN removal
was 8.9 and NO2- – N production was 4.18 mg/ L/day. On
day 2nd in the systems inoculated with NBC dried in desiccator  with out vacuum and dried at room temperature
no residual TAN was detected, however, the one inoculated with vacuum
desiccated NBC the TAN removal was negligible. Following a similar trend,
highest NO2- – N production was recorded in the systems
inoculated with NBC dried by spreading at room temperature (Table. 1).

Determination of shelf life of immobilized NBC

                             In this experiment,
total NH3+ – N removal (10 mg/ L) took place within 48 h
with respect to the immobilized NBC stored for three weeks. The immobilized
NBC, which were stored for 8 weeks, could consume NH4+ –
N (10 mg/ L) within 72 h, and others having a storage period up to 12 weeks
took 96 h for the same (Table. 2). 

On considering the rate of ammonia
consumption by the immobilized consortia stored over a period, the one, which
was stored for a week, could consume NH4+ – N up to 110 mg/ L with in 288 h. Meanwhile, the samples
stored for prolonged period were showing reduced rate of consumption during the
same period. 

Determination
of the quantity of immobilized nitrifiers required for treating unit volume of
water

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
< 0.05) in the treated systems compared to the control systems through out the experimental period. TAN removal and drop in alkalinity were positively correlated (r 0.769) Fig.8.

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