Waste Water Engineering Multiple Choice Questions on “Characteristics of Industrial Wastewater”.
1. Which of the following is not a physical characteristic?
a) Colour
b) pH
c) Odour
d) Temperature
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.