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[MCQ’s]Industrial Waste Treatment

1. Which of the following is not a physical characteristic?
a) Colour
b) pH
c) Odour
d) Temperature
Answer: b
Explanation: The principal physical characteristics of wastewater include solids content, colour, odour and temperature. The total solids in a wastewater consist of the insoluble or suspended solids and the soluble compounds dissolved in water.
2. Total solids in a wastewater consist of insoluble solids alone.
a) True
b) False
Answer: b
Explanation: The total solids in a wastewater consist of the insoluble or suspended solids and the soluble compounds dissolved in water. The suspended solids content is found by drying and weighing the residue removed by the filtering of the sample.
3. What is the minimum percentage of solids in wastewater?
a) 30 %
b) 40 %
c) 50 %
d) 60 %
Answer: b
Explanation: The organic matter consists mainly of proteins, carbohydrates and fats. Between 40 and 65 % of the solids in an average wastewater are suspended. Usually, about 60 % of the suspended solids in a municipal wastewater are 2 settleable (Ron & George, 1998).
4. What is the percentage of settleable solids in municipal wastewater?
a) 60 %
b) 70 %
c) 80 %
d) 90 %
Answer: a
Explanation: Settleable solids, expressed as millilitres per litre, are those that can be removed by sedimentation. Usually, about 60 % of the suspended solids in a municipal wastewater are 2 settleable (Ron & George, 1998).
5. What is the minimum required the temperature to categorize as volatile solids?
a) 500˚C
b) 600˚C
c) 700˚C
d) 800˚C
Answer: b
Explanation: The minimum temperature to categorize volatile solids is 600˚C. Solids may be classified on various other factors. Volatile solids are usually organic in nature.
6. What is the colour of the wastewater after 6 hours of a generation?
a) Grey
b) Light brown
c) Dark brown
d) Dark grey
Answer: b
Explanation: After six hours of duration the colour of wastewater is light in brown. If the wastewater undergoes some degree of decomposition the colour of the water is light grey.
7. What is the colour of septic wastewater?
a) Grey
b) Black
c) Light brown
d) Dark brown
Answer: b
Explanation: The colour of the septic water is black. If the wastewater undergoes some degree of decomposition the colour of water is light grey.
8. The formation of ferrous sulphide leads to the blackening of water.
a) True
b) False
Answer: a
Explanation: The blackening of wastewater is often due to the formation of various sulphides, particularly, ferrous sulphide. This results when hydrogen sulphide produced under anaerobic conditions combines with divalent metal, such as iron, which may be present.
9. Which of the following is not a volatile organic compound?
a) Hydrochloric acid
b) Acetaldehyde
c) Formaldehyde
d) Dichloromethane
Answer: a
Explanation: Many of organic substances are classified as priority pollutants such as polychlorinated biphenyls (PCBs), polycyclic aromatic, acetaldehyde, formaldehyde, 1, 3-butadiene, 1, 2-dichloroethane, dichloromethane, hexachlorobenzene (HCB), etc.
10. What is the maximum pH that the bacteria can sustain in terms of alkalinity?
a) 7
b) 7.5
c) 8
d) 8.5
Answer: d
Explanation: Operation outside of the pH range of 7.0 to 8.5 can be toxic to bacteria; however, if the change is gradual the micro-organisms can become acclimated to pH levels slightly beyond this range.
11. Which of the following is not correct with respect to the effect of oil on treatment systems?
a) Foam formation
b) Toxic to anaerobic bacteria
c) Interferes with settling
d) Explosive with pure oxygen
Answer: a
Explanation: The oil in treatment systems can be toxic to anaerobic bacteria; it might interfere with settling and be explosive with pure oxygen.
12. Which of the following is not correct with respect to the effects of acids on treatment systems?
a) Destroy microbes
b) Upset anaerobic digester
c) Corrode structures
d) Interferes with settling
Answer: d
Explanation: The acids in treatment systems may destroy all the essential microbes, upset anaerobic digester and corrode the structures in the treatment plant.
13. What is the temperature limit of the plastic pipe?
a) 30˚C
b) 40˚C
c) 50˚C
d) 60˚C
Answer: b
Explanation: Plastic pipe (PVC) has temperature limitations of around (40 °C) and can fail if used for hot water transport (I.W.T, 1999). If the O-rings fail, exfiltration or infiltration of the collection system may occur.
14. What is the neutral pH?
a) 6.0
b) 7.0
c) 7.5
d) 8.0
Answer: b
Explanation: The acceptable pH range for the discharge of industrial wastewater to the POTW collection system, as regulated in much industrial waste or sewer-use ordinances, is 6.0 to 9.0. In some ordinances, the pH range may be widened.
15. What is the minimum excess amount of chlorine required to corrode equipment?
a) 30mg/L
b) 40mg/L
c) 50mg/L
d) 60mg/L
Answer: b
Explanation: Many platers will over-chlorinate their cyanide wastewater to ensure they meet the requirements for cyanide concentrations. However, 40 to 50 mg/L excess chlorine can be corrosive to equipment and dangerous to personnel servicing a pump station.
16. SBR is a type of ________
a) Aerobic process
b) Activated sludge process
c) Anaerobic process
d) Chemical process
Answer: b
Explanation: Sequencing batch reactors (SBR) or sequential batch reactors are a type of activated sludge process for the treatment of wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches.
17. The one tank is aerating and filling while the other one is decant.
a) True
b) False
Answer: a
Explanation: The tanks have a “flow through” system, with raw wastewater (influent) coming in at one end and treated water (effluent) flowing out of the other. One tank is in settle/decant mode the other is aerating and filling in multiple tank systems.
18. Bio-selectors direct the flow.
a) True
b) False
Answer: a
Explanation: In some systems, tanks contain a section known as the bio-selector, which consists of a series of walls or baffles which direct the flow either from side to side of the tank or under and over consecutive baffles.
19. ___________ helps to mix the incoming influent and the returned activated sludge.
a) Walls
b) Orifice
c) Manifold
d) Bio-selector
Answer: d
Explanation: This helps to mix the incoming Influent and the returned activated sludge (RAS), beginning the biological digestion process before the liquor enters the main part of the tank.
20. How is mixing done in SBR?
a) Manual
b) Mechanical
c) Air stripping
d) Agitation by air
Answer: b
Explanation: The inlet valve opens and the tank is being filled in, while mixing is provided by mechanical means (no air). This stage is also called the anoxic stage.
21. In which stage of the SBR is aeration performed?
a) First
b) Second
c) Third
d) fourth
Answer: b
Explanation: The fixed or floating mechanical pumps are used or air is transferred into fine bubble diffusers fixed to the floor of the tank during the second stage aeration of the mixed liquor.
22. In which stage are the aeration and mixing avoided?
a) First
b) Second
c) Third
d) Fourth
Answer: c
Explanation: No aeration or mixing is provided in the third stage and the settling of suspended solids starts. During the fourth stage, the outlet valve opens and the “clean” supernatant liquor exits the tank.
23. The multiplication of _________ is encouraged by the addition of oxygen.
a) Bacteria
b) Aerobic bacteria
c) Anaerobic bacteria
d) Fungi
Answer: b
Explanation: Aeration times vary according to the plant size and the composition/quantity of the incoming liquor, but are typically 60 to 90 minutes. The multiplication of aerobic bacteria is encouraged by the addition of oxygen.
24. ______ is used to remove phosphorus compounds from the liquor.
a) Aluminium nitrate
b) Aluminium phosphate
c) Aluminium sulphate
d) Sodium nitrate
Answer: c
Explanation: To remove phosphorus compounds from the liquor, aluminium sulphate (alum) is often added during this period. It reacts to form non-soluble compounds, which settle into the sludge in the next stage.
25. The _________ is usually the same length in time as the aeration.
a) Screening stage
b) Mixing stage
c) Clarification stage
d) Settling stage
Answer: d
Explanation: The settling stage is usually the same length in time as the aeration and during this stage, the sludge formed by the bacteria is allowed to settle to the bottom of the tank.
26. Which part of the tank is suitable for anaerobic bacteria to flourish?
a) Top
b) Bottom
c) Sides
d) Middle zone
Answer: b
Explanation: The aerobic bacterium multiplies until the dissolved oxygen is all used up. The bottom conditions are more suited for the anaerobic bacteria to flourish.
27. ______ is removed by Anammox.
a) Nitric oxides
b) Nitrate
c) Nitrite
d) Ammonia
Answer: d
Explanation: An anaerobic process uses anoxic methods to remove ammonia, such as the removal of ammonia via Anammox or the study of slow-growing micro-organisms.
28. How many types of BOD are present?
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: BOD can be used as a gauge of the effectiveness of wastewater treatment plants. It is listed as a conventional pollutant in the U.S. Clean Water Act. The two major types of BOD are soluble BOD and insoluble BOD.
29. BOD is a physical procedure for determining DO needed for aerobic biological organisms.
a) True
b) False
Answer: b
Explanation: BOD is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material.
30. Primary sludge includes __________
a) Total suspended solids
b) Suspended solids
c) Removable solids
d) Settleable solids
Answer: d
Explanation: 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.
31. Secondary sludge includes treated sewage sludge.
a) True
b) False
Answer: a
Explanation: 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.
32. Sludge treatment helps is reducing treatment costs.
a) True
b) False
Answer: a
Explanation: 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.
33. Which of the following methods are used in rural communities?
a) Aerobic digestion
b) Mechanical dewatering
c) Dewatering
d) Composting
Answer: d
Explanation: 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.
34. From which of the following methods can toxic chemicals be removed?
a) Sorption
b) Adsorption
c) Absorption
d) Dewatering
Answer: a
Explanation: 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.
35. What is the term used for reuse of sewage sludge?
a) Compost
b) Solids
c) Biosolids
d) Sludge
Answer: c
Explanation: “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.
36. In which year was the term Biosolids introduced?
a) 1990
b) 1995
c) 1998
d) 2000
Answer: c
Explanation: 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.
37. What is the first step in the sewage treatment process?
a) Dewatering
b) Thickening
c) Phosphorus recovery
d) Digestion?
Answer: b
Explanation: 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.
38. 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
Explanation: 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.
39. 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
Answer: c
Explanation: The solids concentration in thickened, aerobically digested sludge is generally in the range 1.0% – 2.0% as determined by digester design and operation.
40. Ws = Wsp + Wss
What does Wsp stand for in the above equation?
a) Total dry solids
b) Raw primary solids
c) Suspended solids
d) Polluted solids
Answer: b
Explanation: Waste solids production in primary and secondary processing can be estimated using the calculation above. Ws stand for total dry solids. Wsp stands for raw primary solids. Wss stands for secondary biological solids.
41. Sludge from the primary clarifier is ______
a) Brown and flocculant like appearance
b) Dark in colour
c) Gray and slimy
d) Dark brown in colour
Answer: c
Explanation: Sludge from the primary clarifier is gray in colour. It is also slimy in appearance. Also it has an offensive odour.
42. How does the chemical sludge appear?
a) Gray in colour and not slimy
b) Brown and flocculant like appearance
c) Red/grayish brown
d) Black in colour
Answer: c
Explanation: In case the sludge contains iron it is red in colour. In case it is lime sludge, it is grayish brown in colour. This sludge also has an objectionable odour.
43. How does the activated sludge appear?
a) Gray
b) Red
c) Brown and flocculant like appearance
d) Greasy
Answer: c
Explanation: The activated sludge is brown in colour. It also has flocculant like appearance. If the colour is dark, then the sludge has approached septic condition.
44. What is the % of dry solids assumed for a primary sludge from a settling tank at the outlet?
a) 12%
b) 5-7%
c) 8%
d) 9-11%
Answer: b
Explanation: The percentage of dry solids for a primary sludge is assumed as 5-7% at the outlet. In most cases, it is considered as 6%. In the case of sludge is from the flocculator or clarifier the percentage of solids is considered as 2-4%.
45. What is the percentage of dry solids assumed for the sludge at the outlet of a centrifuge?
a) 10-15%
b) 1-3%
c) 4-8%
d) 9-12%
Answer: c
Explanation: The percentage of dry solids assumed for the sludge at the outlet of a centrifuge is 4-8%. In most cases, this is considered as 5%. Even for a Gravity belt thickener with the addition of polyelectrolyte the percentage of dry solids is considered as 4-8%.

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