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The chemical most commonly used to speed sedimentation of sewage is

A.	sulphuric acid	B.	copper sulphate
C.	lime	D.	sodium ermanganate

The gas from sludge digestion tanks is mainly composed of

A.	nitrogen	B.	hydrogen sulphide
C.	methane	D.	carbon monoxide

The quantity of chlorine in ppm required to satisfactorily chlorinate sewage is usually

A.	125-150	B.	95-120
C.	60-90	D.	0-25

Most of the bacteria in sewage are

A.	pathogenic	B.	anaerobic
C.	saprophytic	D.	parasitic

The ratio of oxygen available to the oxygen required for stabilization of sewage is called

A.	biochemical oxygen demand	B.	relative stability
C.	bacterial-stability factor	D.	oxygen-ion concentration

In the design of grit chambers

A.	temperature is an important factor	B.	the maximum velocity of flow is 1 ft/s
C.	the detention period should be at least 30 min	D.	there should be a 5 to 1 ration of length to depth

The process of lagooning is primarily a means of

A.	increasing the capacity of storage reservoirs	B.	increasing flow of sewage through Imhoff tanks
C.	reducting the excessive flow in sewers	D.	disposing sludge

The biochemical treatment of sewage effluents is essentially a process of

A.	reduction	B.	oxidation
C.	dehydration	D.	alkalinization

In treating turbine water a popular coagulant is

A.	calcium sulphate	B.	chlorine
C.	ferric sulphate	D.	iodine

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Septic tanks are primarily used for

A.	the aerobic decomposition of deposited sweage solids	B.	separation of deposited solids
C.	anaerobic decomposition of deposited solids	D.	separation of oil and grease scums.