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In a BOD test, 1.0 ml of raw sewage was diluted to 100 ml and the dissolved oxygen concentration of diluted sample at the beginning was 6 ppm and it was 4 ppm at the end of 5 day incubation at 20°C. The BOD of raw sewage will be
A
100 ppm
B
200 ppm
C
300 ppm
D
400 ppm
Correct Answer:
200 ppm
3.0 ml of raw sewage is diluted to 300 ml. The D.O. concentration of the diluted sample at the beginning of the test was 8 mg/l. After 5 day-incubation at 20°C, the D.O. concentration was 5 mg/l. The BOD of raw sewerage is
A
100 mg/l
B
200 mg/l
C
300 mg/l
D
400 mg/l
In a well aerated and agitated microbial culture, the 'supply' of oxygen is equal to 'demand' (uptake) of the growing culture. The K
L
a for such a system will be (K
L
a = volumetric mass transfer coefficient, C* = dissolved oxygen concentration in liquid in equilibrium with gaseous oxygen, C = instantaneous value of dissolved oxygen concentration, 'r' = specific oxygen uptake rate per unit weight of cells, X = dry weight of the cells per unit volume)
A
$$\frac{{\left( {rX} \right)}}{{\left( {C* - C} \right)}}$$
B
$$\frac{{\left( r \right)}}{{X\left( {C* - C} \right)}}$$
C
$$\frac{{\left( {C* - C} \right)}}{{\left( {rX} \right)}}$$
D
$$\frac{{\left( X \right)}}{{r\left( {C* - C} \right)}}$$
The treatment system includes a WAC, SAC, followed by a WBA and SBA. There is a degasser in this system. Calculate the amount of SBA resin required for the following data. M Alkalinity: 100 ppm as CaCO3 P Alkalinity: 100 ppm as CaCO3 Silica: 30 ppm as CaCO3 CO2: 45 ppm as CaCO3 EMA: 100 ppm as CaCO3 Capacity: 37 Kg/m3 Correction factor: 0.9 Flow rate: 35 m3/hr Operation hours: 10 hrs
A
0.5 m3
B
0.9 m3
C
1.9 m3
D
1.5 m3
Mine water flowing at 1.5 m
3
/s with 2 mg/l dissolved oxygen, joins riverwater flowing at 7 m
3
/s containing 6 mg/l dissolved oxygen. The saturated value of the dissolved oxygen in the mixture is given to be 9.3 mg/l. On the basis, the initial oxygen deficit of the mixture in mg/l is
A
2.4
B
4.0
C
6.8
D
14.6
A bacterial culture having a specific oxygen uptake rate of 5 mmol O
2
(g DCW)
-1
hr
-1
is being grown aerobically in a fed-batch bioreactor. The maximum value of the volumetric oxygen transfer coefficient is 0.18 s
-1
for the stirred tank bioreactor and the critical dissolved oxygen concentration is 20% of the saturation concentration (8 mg mL
-1
). The maximum density to which the cells can be grown in the fed-batch process without the growth being limited by oxygen transfer, is approximately
A
14 g L<sup>-1</sup>
B
26 g L<sup>-1</sup>
C
32 g L<sup>-1</sup>
D
65 g L<sup>-1</sup>
If a 2% solution of sewage sample is incubated for 5 days at 20°C and the dissolved oxygen depletion was found to be 8 mg/l. The BOD of the sewage is
A
100 mg/l
B
200 mg/l
C
300 mg/l
D
400 mg/l
The relative stability of a sewage sample, whose dissolved oxygen is same as the total oxygen required to satisfy BOD, is
A
1
B
100
C
Infinite
D
Zero
The treatment system includes a WAC, SAC, followed by a WBA and SBA. There is no degasser in this system. Calculate the amount of resin required for the following information. M Alkalinity: 100 ppm as CaCO3 P Alkalinity: 100 ppm as CaCO3 Silica: 45 ppm as CaCO3 CO2: 45 ppm as CaCO3 Capacity: 37 Kg/m3 Correction factor: 0.9 Flow rate: 35 m3/hr Operation hours: 10 hrs
A
1.5 m3
B
1.1 m3
C
7.9 m3
D
7.5 m3
The concentration of oxygen at the inner surface of the vessel is maintained at a level C depending on the pressure in the vessel, while the concentration at the outer surface is reduced to zero by the escape of oxygen to the surroundings. A steady state will eventually be reached when the concentration everywhere reaches a constant value. Provided D is independent of concentration there will be a single concentration gradient in the wall and the thickness of the wall is L, the flux is given by________________
A
DC/L
B
DL/C
C
CL/D
D
DC/L + K (some constant)
“In BOD test, the quantity of O2 used is determined by the difference in the dissolved O2 in the water in the beginning of the test and at the end of five days” above given statement is
A
True
B
False
C
Not sufficient data
D
None of the mentioned