This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Sludge Production and Process Control”.
1. The Activated Sludge Process is a _______ wastewater treatment process.
a) Physical
b) Chemical
c) Biological
d) Biochemical
View Answer
Explanation: The Activated Sludge Process is a biological wastewater treatment process. This means that treatment occurs as pollutants are used as a food source by many different types of micro-organisms.
2. The measure of pH is the ______ ion concentration.
a) Iron
b) Hydrogen
c) Aluminium
d) Sodium
View Answer
Explanation: The measure of pH is the hydrogen ion concentration. pH is used to express the intensity of the acid or alkaline condition of a solution. The scale of pH ranges from 0 to 14, with 7 being neutral. The effluent limit for pH is typically 6 to 9.0.
3. Gravity thickening can achieve up to _____ solid fraction.
a) 5%
b) 10%
c) 15%
d) 20%
View Answer
Explanation: Typical sludge comes at 1% solid fraction. Thickening it to 2% halves the volume, to 10% reduces the volume by a factor 10. [1% solid fraction ≈ 10,000 mg/L]. Gravity thickening can achieve up to 10% solid fraction.
4. ________ is oxidized by heterotypic micro-organisms.
a) Inorganic matter
b) Inert materials
c) Organic matter
d) Water
View Answer
Explanation: Organic matter is oxidised by heterotrophic micro-organisms to produce water and carbon-dioxide in the process known as catabolism. This process requires the availability of an electron acceptor which may be oxygen or nitrate and lead to the production of energy as ATP.
5. What is autotrophic biomass made up of?
a) Inert particulate matter
b) Endogenous residue
c) Biodegradable particle
d) Nitrifying bacteria
View Answer
Explanation: Inert particulate COD derives from the inert particulate COD present in the influent wastewater and entering the plant. Autotrophic biomass is made up of nitrifying bacteria.
6. What is the temperature at which sludge constituting biosolids are composted?
a) 55 degree Celsius
b) 45 degree Celsius
c) 65 degree Celsius
d) 75 degree Celsius
View Answer
Explanation: The sludge constituting biosolids is composted at 55 degree Celsius. Composting is carried out in a vessel. This can also be subjected to static aerated composting.
7. For how many days the sludge constituting biosolids is subjected to composting?
a) 1 day
b) 2 days
c) 3 days
d) 5 days
View Answer
Explanation: Sludge constituting biosolids are treated by composting. This is usually done for 3 days. This is one of the ways to treat sludge constituting biosolids.
8. What is the final water content of sludge after dewatering?
a) 5%
b) 2%
c) 10%
d) 1%
View Answer
Explanation: After dewatering the moisture content of the sludge is reduced to 10 percent. Dewatering can be done by heat dryers. The biosolids are heated up to 80 degree Celsius.
9. To what temperature is a sludge constituting liquid biosolids heated in order to treat it?
a) 450 degree Celsius
b) 200 degree Celsius
c) 180 degree Celsius
d) 300 degree Celsius
View Answer
Explanation: Sludge constituting liquid biosolids is heated to 180 degree Celsius. This sludge is mixed with oxygen in order to maintain aerobic conditions. The sludge is heated for at least 30 mins.
10. At what temperature the sludge constituting biosolids is heated, when it is treated by the pasteurization method?
a) 45 degree Celsius
b) 55 degree Celsius
c) 70 degree Celsius
d) 65 degree Celsius
View Answer
Explanation: Other than heat treated sludge constituting biosolids can be treated by pasteurization also. In this method the sludge is heated at 70 degree Celsius. This treatment is carried out at least for 30 mins.
11. What is the solid retention time assumed when the sludge constituting biosolids is treated anaerobically?
a) 7 days
b) 4 days
c) 15 days
d) 10 days
View Answer
Explanation: The sludge constituting biosolids can be treated anaerobically also. While carrying out anaerobic treatment, the solid retention time assumed is 15 days. The temperature is maintained at 15-20 degree celsius.
12. Which of the following methods is used in both dewatering and thickening?
a) Filter press
b) Centrifuge
c) Gravity belt
d) Rotary drum
View Answer
Explanation: Centrifuge is used for dewatering the sludge. This is also used for thickening the sludge. The other methods for dewatering sludge are done by a filter press, lagoons, sludge drying bed, belt filter press and Reed bed.
13. For a return activated sludge pump what is the type of pump preferred?
a) Plunger
b) Peristaltic pump
c) Submersible
d) Non-clog
View Answer
Explanation: For return activated sludge non-clog type pump is preferred. The return activated sludge is very dilute and also constitutes only fine particles. The non-clog pump should be operated at very low speed for this application.
14. For removing the digested biosolids which type of pump is preferred?
a) Submersible
b) Non-clog pumps
c) Vertical turbine pump
d) Plunger pump
View Answer
Explanation: For the removal of digested biosolids a plunger pump is preferred. Well digested biosolids are homogeneous. These contain 5-8% solids.
15. Which type of pump is preferred to remove trickling filter humus?
a) Submersible cutter pump
b) Non-clog pump
c) Vertical turbine pumps
d) Diaphragm pump
View Answer
Explanation: The pump which is used to remove trickling filter humus is usually a diaphragm type. Humus is usually homogeneous in nature. This can usually be pumped very easily.
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