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  1. The gas from sludge digestion tank is mainly composed of

  2. A.

     Nitrogen

    B.

     Carbon dioxide

    C.

     Hydrogen sulphide

    D.

     Methane


  3. The maximum efficiency of BOD removal is achieved in

  4. A.

     Oxidation pond

    B.

     Oxidation ditch

    C.

     Aerated lagoons

    D.

     Trickling filters


  5. The minimum and maximum diameters of sewers shall preferably be

  6. A.

     15 cm and 100 cm

    B.

     15 cm and 300 cm

    C.

     30 cm and 450 cm

    D.

     60 cm and 300 cm


  7. The biochemical treatment of sewage effluents is essentially a process of

  8. A.

     Oxidation

    B.

     Dehydration

    C.

     Reduction

    D.

     Alkalinization


  9. Sewerage system is usually designed for

  10. A.

     10 years

    B.

     25 years

    C.

     50 years

    D.

     75 years


  11. Sewage treatment units are normally designed for

  12. A.

     5 - 10 years

    B.

     15 - 20 years

    C.

     30 - 40 years

    D.

     40 - 50 years


  13. Generally the detention period for grit chambers is kept as

  14. A.

     1 minute

    B.

     5 minutes

    C.

     24 hours

    D.

     12 hours


  15. Activated carbon is used for

  16. A.

     Disinfection

    B.

     Removing hardness

    C.

     Removing odours

    D.

     Removing corrosiveness


  17. The polluted water is one which

  18. A.

     Contains pathogenic bacteria

    B.

     Consists of undesirable substances rendering it unfit for drinking and domestic use

    C.

     Is safe and suitable for drinking and domestic use

    D.

     Is contaminated


  19. 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

  20. A.

     100 ppm

    B.

     200 ppm

    C.

     300 ppm

    D.

     400 ppm