Waste Water Engineering Multiple Choice Questions on “Sludge Treatment Process – 1”.
1. Sludge treatment aims at reducing sludge weight and volume.
a) True
b) False
Answer: a
Clarification: Sludge treatment aims at reducing sludge volume and weight to reduce disposal costs and potential health risks of disposal options.
2. Solids removal can reduce sludge volume.
a) True
b) False
Answer: b
Clarification: Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting or incineration.
3. How are the pathogens destroyed?
a) Mechanical means
b) Thermophilic conditions
c) Chemical treatment
d) Aeration
Answer: b
Clarification: Pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting or incineration. Water removal is the primary means of weight and volume reduction.
4. Which of the following methods are not used for pathogen destruction?
a) Composting
b) Incineration
c) Mechanical stirring
d) Thermophilic digestion
Answer: c
Clarification: Composting is not used often. The methods generally used for pathogen destruction are incineration, composting and heating by thermophilic digestion.
5. Energy may be recovered from sludge as ________
a) Hydrogen gad
b) Methane gas
c) Air
d) Liquid petroleum gas
Answer: b
Clarification: Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting or incineration. The choice of a sludge treatment method depends on the volume of sludge generated and comparison of treatment costs required for available disposal options.
6. Toxic chemicals are removed from liquid sewage by _______
a) Adsorption
b) Absorption
c) Desorption
d) Sorption
Answer: d
Clarification: Coarse primary solids and secondary sewage sludge may include toxic chemicals removed from liquid sewage by sorption onto solid particles in clarifier sludge.
7. Reducing the sludge volume increases _______
a) pH
b) temperature
c) concentration
d) water
Answer: c
Clarification: Toxic chemical concentration in the sludge may increase while reducing sludge volume. Toxic chemicals are present in coarse primary solids and secondary sewage sludge removed from liquid sewage by sorption onto solid particles in clarifier sludge.
8. Which is the first step in the sludge treatment process?
a) Thickening
b) Dewatering
c) Digestion
d) Phosphorus recovery
Answer: a
Clarification: Thickening is often the first step in a sludge treatment process. Primary or secondary clarifier sludge may be stirred (often after addition of clarifying agents) to form larger, more rapidly settling aggregates.
9. What is the percentage of thickness that can be achieved for primary sludge?
a) 2-3 %
b) 4-5 %
c) 6-8 %
d) 8-10 %
Answer: d
Clarification: Secondary sludge may be thickened to about 4 percent solids while the primary sludge may be thickened to about 8 or 10 percent solids.
10. What is the percentage of thickness that can be achieved for secondary sludge?
a) 1 %
b) 2 %
c) 3 %
d) 4 %
Answer: d
Clarification: Secondary sludge may be thickened to about 4 percent solids while the primary sludge may be thickened to about 8 or 10 percent solids.
11. What is the percentage of thickness that the sludge should have to undergo additional treatment?
a) Greater than 10
b) Less than 10
c) Equal to 10
d) 0.1
Answer: b
Clarification: Thickened sludge with less than ten percent solids may receive additional sludge treatment while liquid thickener overflow is returned to the sewage treatment process.