250+ TOP MCQs on Methods of Sludge Processing and Disposal – 1 and Answers

Waste Water Engineering Multiple Choice Questions on “Methods of Sludge Processing and Disposal – 1”.

1. Primary sludge includes __________
a) Total suspended solids
b) Suspended solids
c) Removable solids
d) Settleable solids
Answer: d
Clarification: Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers.

2. Secondary sludge includes treated sewage sludge.
a) True
b) False
Answer: a
Clarification: Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors.

3. Sludge treatment helps is reducing treatment costs.
a) True
b) False
Answer: a
Clarification: Reducing sludge weight and volume to reduce disposal costs is the aim of sludge treatment. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options.

4. Which of the following methods are used in rural communities?
a) Aerobic digestion
b) Mechanical dewatering
c) Dewatering
d) Composting
Answer: d
Clarification: Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.

5. From which of the following methods can toxic chemicals be removed?
a) Sorption
b) Adsorption
c) Absorption
d) Dewatering
Answer: a
Clarification: Coarse primary solids and secondary sewage sludge may include toxic chemicals removed from liquid sewage by sorption onto solid particles in clarifier sludge. Reducing sludge volume may increase the concentration of some of these toxic chemicals in the sludge.

6. What is the term used for reuse of sewage sludge?
a) Compost
b) Solids
c) Biosolids
d) Sludge
Answer: c
Clarification: “Biosolids” is a term often used in engineering publications and public relations efforts by local water authorities when they want to put the focus on reuse of sewage sludge after the sludge has undergone suitable treatment processes.

7. In which year was the term Biosolids introduced?
a) 1990
b) 1995
c) 1998
d) 2000
Answer: c
Clarification: The term “biosolids” was introduced by the Water Environment Federation in the U.S. in 1998. However, some people argue that the term is a form of “propaganda” with the aim to hide the fact that sewage sludge may also contain substances that could be harmful to the environment when the treated sludge is applied to land.

8. What is the first step in the sewage treatment process?
a) Dewatering
b) Thickening
c) Phosphorus recovery
d) Digestion?
Answer: b
Clarification: Thickening is often the first step in a sludge treatment process. Sludge from primary or secondary clarifiers may be stirred (often after addition of clarifying agents) to form larger, more rapidly settling aggregates.

9. What is the amount of solids released into wastewater by human beings?
a) 30 gpcd
b) 40 gpcd
c) 60 gpcd
d) 70 gpcd
Answer: d
Clarification: Humans deposit about 70 g per capita per day of solids into wastewater. With ‘garbage grinders’, this can reach 100g per day. The impurities present in the wastewater must either be transformed into innocuous end-products or be effectively separated from the effluent stream.

10. What is the percentage of aerobically digested sludge?
a) 0.2-0.5
b) 0.3-0.6
c) 1.0-2.0
d) 1.5-3.0