Waste Water Engineering Multiple Choice Questions on “Facultative Ponds”.
1. The facultative pond functions like a ________
a) Primary clarifier
b) Secondary clarifier
c) Aerator
d) Sedimentation unit
Answer: a
Clarification: The facultative lagoon in the pond sequence functions like the primary clarifier of a conventional sewage treatment system. Heavy solids will settle to the bottom of the lagoon and lighter solids will float.
2. The surface area of facultative ponds should be small.
a) True
b) False
Answer: b
Clarification: The surface area provided for facultative ponds must be large and an atmospheric oxygen transfer rate adequate to prevent anaerobic conditions on the lagoon surface.
3. In facultative ponds, micro-organisms are able to oxidize only dissolved organics.
a) True
b) False
Answer: b
Clarification: The dissolved and suspended organics from the original wastewater and the products of anaerobic catabolism on the bottom of the lagoon are oxidized by the intermediate depths of the lagoon.
4. ______ occur when the rate of oxygen transfer from the lagoon surface is less than the rate of oxygen consumption in the lower levels of the lagoon.
a) Temperature rise
b) Objectionable odour
c) Raised pH
d) Temperature fall
Answer: b
Clarification: Objectionable odours are formed when the rate of oxygen consumption is more in the lower levels of the lagoon than the rate of oxygen transfer from the lagoon surface.
5. How much amount of oxygen should one acre of facultative lagoon must provide per day?
a) 10 pounds
b) 50 pounds
c) 75 pounds
d) 90 pounds
Answer: b
Clarification: A 4000 sqm area which is equal to 1 acre facultative lagoon might provide 50 pounds of oxygen per day (5 grams of oxygen per square meter per day) for biochemical catabolism.
6. ______ weather requires large oxygen transfer.
a) Cold
b) Warm
c) Rainy
d) Normal
Answer: b
Clarification: During cold weather, waste can get accumulated and cause short-term warm weather oxygen requirements to exceed long-term waste loading rates. Warm weather will require large oxygen transfer rates.
7. Ice mats _____ the oxygen transfer surface.
a) Alter
b) Increase
c) Reduce
d) Maintain
Answer: c
Clarification: Algal respiration can require additional oxygen during darkness but algae can provide surface oxygen during daylight hours. Ice or scum mats can reduce the oxygen transfer surface.
8. What is the depth range of facultative ponds?
a) 0.5-0.8 m
b) 0.8-1.0 m
c) 1-1.2 m
d) 1.2-1.5 m
Answer: d
Clarification: Secondary facultative ponds are 1.20 – 1.50 meters deep and are designed for BOD removal on the basis of a relatively low surface loading of 100 – 400 kg BOD/ha-d at the temperature between 20°C and 25°C.
9. What is the maximum allowable temperature in facultative ponds?
a) 15˚C
b) 20˚C
c) 25˚C
d) 30˚C
Answer: c
Clarification: Facultative ponds are designed for BOD removal on the basis of a relatively low surface loading of 100 – 400 kg BOD/ha-d at the temperature between 20°C and 25°C.
10. Which colour are the facultative ponds?
a) Blue
b) Green
c) Brown
d) Black
Answer: b
Clarification: Due to the presence of algae, facultative ponds are coloured dark green. These can optimize their vertical position in the pond water column in relation to incident light intensity and temperature more easily than non-motile forms (such as Chlorella, although this is also fairly common in facultative ponds).