Waste Water Engineering Multiple Choice Questions on “Sludge Production and Process Control”.
1. The Activated Sludge Process is a _______ wastewater treatment process.
a) Physical
b) Chemical
c) Biological
d) Biochemical
Answer: c
Clarification: 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
Answer: b
Clarification: 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%
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: d
Clarification: 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
Answer: a
Clarification: 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
Answer: c
Clarification: 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%
Answer: c
Clarification: 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
Answer: c
Clarification: 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