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International Journal of Aquaculture, 2014, Vol.4, No.25 1
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3
in the first pond may be related to excessive growth of
plants which prevent the light penetration into the
water column. Whereas, the other pond surfaces were
free from macrophytes so that light rays can reach the
bottom and increase the water temperature. Aquatic
organisms are sensitive to changes in pH hence it is
necessary to control or monitor its level in the
biological treatment of sewage (Jeffrey et al
.,
1998).
The pH values in all the three ponds varied between 6
and 8. The observed values are within the permissible
limits for the culture of freshwater fish (Boyd, 1998;
Dutta et al., 2010). This variation may be due to the
oxidative processes with the aid of photosynthetic
plankton in the water. The dissolved oxygen was found
to be very low or below detectable level in pond 1
where the water surface is covered with
Eichhornia
plants.The plant cover prevents the dissolution of
atmospheric oxygen and hence aerobic decomposition
of organic matter results in depletion of oxygen in the
water. In pond 2 and 3, the average values were 5.66
mg/l and 5.61 mg/l respectively. The slightly higher
dissolved oxygen (DO) 5.7 mg/l was recorded in the
oxidation pond 2 which could be due to photosynthetic
activity of the large population of phytoplankton as
stated by Nandini (1999). The photosynthetic activity
in such ponds may be intensified by the availability
of light and increased temperature (Meijun Chen et
al
.,
2011). The amount of carbon dioxide varied from
0.9 mg/l to 4.4 mg/l in sewage ponds. The highest CO
2
level was noticed in the oxidation pond 1. There was a
gradual decline in CO
2
from pond 1 to 3. In the
absence of DO in pond 1, the decomposition of
organic matter through anaerobic process results in
the accumulation of CO
2
. Whereas, in the other ponds
which are exposed to sunlight the carbon dioxide
evolved during decomposition are used up by
phytoplankton for photosynthesis during the day time
as mentioned by Sreenivasan (1980).
Table 1 Physico-chemical parameters of the water
Parameters
Pond 1
Pond 2
Pond 3
1 week
2 week
3 week
1 week
2 week
3 week
1 week
2 week
3 week
Temperature ( ºC)
18
18
19
20
20.5
21
22
21.5
22
pH
6
6
7
7
8
8
8
8
8
Conductivity (µs/cm)
1317
1257
1134
1423
1312
1311
1336
1311
1147
Chloride (mg/l)
134.7
134.7
124.08
152.4
152.4
138.25
163.07
163.07
163.07
Alkalinity (mg/l)
300
300
200
200
200
300
200
200
200
DO (mg/l)
nil
nil
nil
5.6
5.7
5.7
5.6
5.63
5.6
CO
2
(mg/l)
4.4
4.0
3.9
2.2
2.0
2.4
1.4
1.2
0.9
The condutivity in all the three ponds varied from 1134
to 1423 µS/cm. The maximum conductivity was
observed in the oxidation pond 2 and minimum in pond
1. In general the values declined in the third week
associated with the variation in the ionic composition
of the water. Ions that determine the conductivity are
hydrogen, hydroxyl ions and nutrients such as
phosphate and nitrate (Dusan et al
.
, 1994).The main
process that reduces conductivity in wastewater
treatment is nutrient removal (Aguado et al., 2006;
Maurer and Gujer, 1995) through biofiltration by the
plants. The plants in the pond 1 utilize the nutrients,
phosphates and nitrate, along with many elements
required for their growth in large amount than the
phytoplankton and the bacteria.
The amount of chloride in pond 3 was greater (163.07
mg/l) than the other oxidation ponds. In the first
oxidation pond the chloride was comparatively less
and it was reduced at the end of the observation.
Earlier studies have indicated that the chloride values
tend to fluctuate between 49 -315 ppm (Solamalai et
al., 2003) in the treatment ponds. Hence the observed
level of chloride was within the permissible limit for
the culture of fish. The alkalinity of the water in the
ponds varied from 200 mg/l – 300 mg/l however, in
pond 3 the variation was negligible. According to
Solamalai et al. (2003) in the domestic sewage the
alkalinity values vary from 180 - 300 ppm and it
depends on various climate, composition, and
treatment conditions. The high alkalinity values
indicates the rate of biogeochemical process,
anaerobic mineralization of organic matter and
photosynthesis that is happening in the water in the
epilimnion, as well as the NH
4
and NO
3
assimilation
(Carmouze, 1986; Ahamad et al
.
, 2011). According to