০১। 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 DO. concentration was 5 mg/l. The BOD of raw sewerage is
ক) 100 mg/l
খ) 200 mg/l
গ) 300 mg/l
ঘ) 400 mg/l.
০২। 5 days-biochemical oxygen demand (BOD5) is taken at a temperature of
ক) 0°C
খ) 15°C
গ) 20°C
ঘ) 25°C.
০৩। A circular sewer section is preferred to because
ক) it is cheaper in construction
খ) it provides maximum area for a given perimeter
গ) it provides maximum hydraulic mean depth
ঘ) all the above.
০৪। A cylindrical ejector having its height 2 m fills after every 10 minutes with a peak sewage discharge of 0.0157 cumec. The diameter of the ejector chamber, is
ক) 2.30 m
খ) 2.40 m
গ) 2.45 m
ঘ) 2.50 m.
০৫। A drop manhole is provided if
ক) a sewer drops from a height
খ) a branch sewer joins the main sewer at higher level
গ) a lamp is inserted to check obstruction
ঘ) none of these.
০৬। A manhole is classified as shallow if its depth is between
ক) 0.4 to 0.5 m
খ) 0.5 to 0.7 m
গ) 0.7 to 0.9 m
ঘ) 0.9 to 1.20 m
ঙ) 1.2 to 1.50 m.
০৭। A manhole is generally provided at each
ক) bend
খ) junction
গ) change of gradient
ঘ) change of sewer diameter
ঙ) all the above.
০৮। A nuisance is experienced in diluting water if dilution factor is less than
ক) 100
খ) 60
গ) 40
ঘ) 20
ঙ) 10
০৯। A rain sanitary sewer is constructed to carry
ক) sanitary sewage
খ) storm sewage
গ) surface water
ঘ) ground water
ঙ) all the above.
১০। A rainfall may be classified as acidic if its pH value is less or equal to
ক) 6
খ) 7
গ) 5
ঘ) 6.5
১১। A safety lamp when inserted in the upper portion of a manhole causes flames. It indicates the presence of
ক) Carbondioxide gas
খ) Hydrogen sulphide gas
গ) Methane gas
ঘ) Petrol vapours.
১২। A sewer pipe contains 1 mm sand particles of specific gravity 2.65 and 5 mm organic particles of specific gravity 1.2, the minimum velocity required for removing the sewerage, is
ক) 0.30 m/sec
খ) 0.35 m/sec
গ) 0.40 m/sec
ঘ) 0.45 m/sec
ঙ) 0.50 m/sec.
১৩। A sewer running partially full and hurried with back filled, fails in compression due to
ক) weight of the pipe
খ) weight of the back fill
গ) superimposed traffic loads
ঘ) all the above.
১৪। A well oxidized sewage contains nitrogen mainly as
ক) nitrates
খ) nitrites
গ) free ammonia
ঘ) none of these.
১৫। Acid regression stage of sludge digestion at a temperature 21°C extends over a period of
ক) 15 days
খ) 30 days
গ) 60 days
ঘ) 90 days.
১৬। Aerobic activity is maximum
ক) in freshly produced sewage
খ) at sewer pipes
গ) in sewer treatment plants
ঘ) none of these.
১৭। Aerobic bacterias
ক) flourish in the presence of free oxygen
খ) consume organic matter as their food
গ) oxidise organic matter in sewage
ঘ) All the above.
১৮। Afive day B.O.D. at 15°C of the sewage of a town is 100 kg/day. If the 5 day B.O.D. per head at 15°C for standard sewage is 0.1 kg/day, the population equivalent is