1. A well operated digester normally receives sludge at about _ % volatile solids and reduces it to about _ % volatile solids.
a. 70 – 75%, 25 – 30%
b. 90 – 95%, 45 – 50%
c. 90 – 95%, 25 – 30%
d. 70 – 75%, 40 – 45%

2. Chlorine applied minus _ equals chlorine residual.
a. chlorine dose
b. chlorine demand
c. free chlorine
d. total chlorine

3. The following data describes the condition of a secondary sedimentation tank. Which problem needs the most immediate attention?
Collector operating normally
Drive mechanism alarm system functioning properly
Collector speed (RPM) normal
Sedimentation tank level normal
Discharge gates open
Sludge depth in tank too low
Return sludge concentration too low
a. distribution of flow across tank
b. hydraulic load to sedimentation tank
c. raw sewage pump speed below normal RPM
d. return activated sludge pumps operating above normal rate

4. The disadvantage of using a constant percentage return activated sludge flow control system is _.
a. variations in the MLSS are reduced
b. F/M varies more than the constant rate RAS control
c. MLSS remains in the clarifier too long
d. clarifier is subject to maximum solids loading when it contains maximum amount of sludge
e. none of the above

5. One of the greatest advantages of a complete mix activated sludge system is _.
a. it is capable of absorbing sudden shock loads without losing equilibrium
b. the aeration tanks may be designed in any convenient shape or size to fit the available area
c. less air is required than in conventional aeration

Answers:

1. a
2. b
3. d
4. d
5. a