22.  Biological oxidation processes usually referred as biological treatment, are the most common form of
A.primary treatment
B.secondary treatment
C.tertiary treatment
D.all of these

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23. The maximum permissible limit (BIS) of turbidity in drinking water is
A.5 NTU
B.10 NTU
C.15 NTU
D.20 NTU

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24. Sedimentation is a physical process used in wastewater treatment to
A.remove particles that are less dense than water
B.remove particles that are more dense than water
C.remove the pertinacious material from the water
D.none of the above

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25.  The ultimate source of water is
A.rivers and lakes
B.dew and forest
C.rain and snow
D.underground and surface

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26. Permanent hardness of water may be removed by the addition of
A.lime
B.soda ash
C.potassium permagnate
D.sodium bicarbonate

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27. Both temporary and permanent hardness of water can be removed on boiling water with
A.calcium hydroxide
B.sodium carbonate
C.calcium oxide
D.calcium carbonate

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28. Lagoons may be characterized as
A.anaerobic
B.facultative
C.aerated
D.all of these

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