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9210-202
Level 7 Post Graduate Diploma in Civil Engineering
Environmental Engineering
You should have the
following for this examination
• one answer book
• pen, pencil, ruler
• non-programmable calculator
No additional data are
attached
General instructions
• This paper consists of eight questions.
• Answer any five questions.
• A non-programmable electronic calculator may be used but candidates must show
sufficient steps to justify their answers.
• Drawings should be clear, in good proportion and in pencil.
• All questions carry equal marks. The maximum marks for each section within a
question are shown.
© The City and Guilds of London Institute 2014
ST00043505 H1 PO4500104010 10179809
1
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2
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3
a)
i)
What is meant by biogeochemical cycles? Discuss some impacts resulting
from the disruption of biogeochemical cycles.
ii) Why is species diversity essential for a stable ecosystem?
iii) Water pollution causes the reduction of dissolved oxygen level in the water.
Explain briefly its impact on the ecological balance.
iv) Discuss the impacts of global warming, especially on ecosystems.
PCBs are a group of organic industrial chemicals that become very persistent
contaminants when released into the environment. How will it impact on human
health if PCBs are released into a river? Explain briefly.
i)
Pathogens are not always bacteria. Name two pathogenic bacteria and
viruses sometimes found in water supplies.
ii) What is an indicator organism? List the characteristics of the ideal pathogen
indicator. Indicate which organism most nearly exhibits these characteristics.
iii) A microbiological test showed that the total coliform count of a river water
sample is 48 MPN/100 ml. Comment on the suitability of this water for drinking.
What are the dominant hardness producing ions and how does hardness
affect potable water?
ii) What is methemoglobinemea and discuss it as water related illness.
iv) List 3 reasons which cause tastes and odours in a water supply?
i)
Why is aeration used in water treatment plants? Discuss the applicability of
aeration in groundwater and surface water.
ii) A town with a population of 150,000 has an average per capita demand of
140 litres/day. Design a sedimentation tank for supplying water considering
maximum demand as 1.5 times the average demand. Assume the detention
period is 5 hours for the settling tank and overflow rate is 900 litres/hour/m2.
State any assumptions made.
iii) It is proposed that a wide and shallow sedimentation tank is more effective
than a deep and narrow tank in removing suspended solids. Explain your view.
The rapid mixing tank will blend 24 – 40 mg/l of alum with the flow, which varies
with the characteristics of the river water quality. Estimate the minimum quantity
(Kilogram per day) of alum added and maximum storage of alum to be kept in
stores for a week. Consider the maximum demand found in Q2 b) ii) as the
daily flow.
i)
i)
ii)
iii)
c)
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i)
ii)
b)
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(1 mark)
i)
ii)
iii)
The rapid filtration unit in a water treatment plant is to be constructed to
process 100,000 m3/day. Pilot plant analysis showed that a filtration rate of
20 m/h will be acceptable. Estimate the number of filter units which will be
required assuming that the approximate surface configuration of a filter unit
is 7 m x 10 m. Allow one unit out of service for backwashing.
The backwash velocity for cleaning filtration units of the above plant is 40 m/h.
Each backwash period requires 20 min, and the first of each filter run takes
10 min from each run where water is wasted. Estimate the net production of
clean water of each filter if it is backwashed once a day.
What percentage of the total flow is used to clean the cleaning filter?
Explain why chlorination is considered necessary even when filtration
is provided.
What are the disinfecting agents that kill bacteria when chlorine is added
to water?
List two methods other than chlorination that can be used to disinfect
water supplies.
What are the two basic methods used for desalinization of water?
How can activated carbon improve drinking water quality? What are two
important properties of activated carbon?
List the advantage of microfiltration in water intakes.
2
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4
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b)
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Discuss the sources and impacts of nitrogen and phosphorus in water bodies.
What are the key physical parameters affecting water quality in lakes?
List the major physical processes involved in self-purification of watercourses.
What is an oxygen sag curve? How does it help in understanding the
effects of organic pollution?
A wastewater outlet discharges water into a natural stream. Determine the
flow, and dissolved oxygen in the stream at a downstream point as shown
in Figure Q4.
(2 marks)
(2 marks)
(2 marks)
(3 marks)
(5 marks)
Figure Q4
c)
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ii)
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5
a)
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ii)
Oxygen demanding wastes such as BOD is a major contaminant of surface
waters. A laboratory test was carried out to determine 5-day BOD of a
surface water sample. Why is the experiment carried out for 5 days?
Why are the BOD bottles stoppered and experiment run in the dark?
If 3 day 15ºC BOD is 85 mg/l, what will be its 5 day 20ºC BOD?
Assume k20 = 0.1/day.
Sketch a flow diagram that shows the overall preliminary and primary
sewage treatment processes.
What is the basic purpose of tertiary treatment of sewage? Describe three
occasions where tertiary treatment is needed in wastewater treatment.
In biological wastewater treatment the most commonly used system is the
activated sludge system. What is the main design parameter in activated
sludge plants? Why should the activated sludge process be operated in the
starvation (Low F/M) stage?
A community based completely mixed activated sludge process is to be
used to treat a wastewater flow of 1000 m3/hr having a BOD of 250 mg/l.
Design criteria are as follows: Yield = 0.4, Sludge age = 5 days, and
MLSS = 2000 mg/l. If the substrate exit concentration is 7.75 mg/l calculate
the period of aeration and the volume of the tank. Retention time is given
by
= Y. (So –Se)/ X (1+ c kd)
with usual notations.
What is the purpose of recirculation in a trickling filter? How does temperature
affect a trickling filter operation?
A trickling filter removes BOD5 with 80% efficiency and the efficiency of the
primary treatment that precedes it is 35%. If the raw sewage BOD5 is 288 mg/L,
Determine the BOD5 of secondary effluent. What is the overall removal
efficiency of BOD5?
3
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(4 marks)
(2 marks)
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See next page
6
a)
i)
ii)
The use of oxidation ponds or lagoons has proved very effective for the
treatment of domestic wastewater. Design an oxidation pond to treat
5000 m3/day of municipal wastewater. The average influent BOD5 is
150 mg/l and it is desired to have an average effluent BOD5 of 5.0 mg/l.
Assume that the detention period is 30 days.
BOD5 loading rate should be 15-90 kg/ha-day.
Oxidation Ditches are used for secondary treatment in wastewater treatment.
Figure Q6 a) shows the plan view of an oxidation ditch. A curved vertical wall
has been constructed at the two ends of the Oxidation Ditches. Explain the
purpose of this wall.
(5 marks)
(3 marks)
Figure Q6 Plan View of the Oxidation ditch
b)
c)
7
a)
A town with a population of 10,000 is designing a sewage treatment plant to
handle both domestic and industrial wastes from a dairy plant, a packing plant,
and a cannery plant.
A sanitary survey revealed the following:
Dairy plant 2.5 x 106 l/d waste with BOD of 1200 mg/l
Packing plant 3.2 x 106 l/d waste with BOD of 500 mg/l
Cannery plant 4.6 x 106 l/d waste with BOD 420 mg/l
Domestic sewage is 250 litres per capita per day with BOD of 50 mg per capita
per day. An expansion factor of 20% is to be provided.
Find (a) design population equivalent for the plant
(b) BOD loading
(c) hydraulic loading.
i)
Discuss three options available for land treatment of wastewater.
ii) What factors are important in planning and designing of on-site sub-surface
wastewater disposal systems? Provide three examples or such systems.
i)
ii)
b)
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c)
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ii)
What is the most important factor in integrated solid waste management?
Explain briefly.
Effective solid waste management is essential for any nation. Solid waste
management will not take place effectively if the society does not carry out
its duties and responsibilities. Discuss the duties of individual persons, Local
Authorities and policy makers towards sustainable solid waste management.
What are the problems associated with E-waste? Provide three examples.
Discuss the importance of informal sector participation in e-waste
management in a developing country.
Waste substances are hazardous if they possess four characteristic attributes.
List them.
What is ‘bioremediation’? Briefly describe how it is accomplished for VOCs
and for chlorinated hydrocarbons. What is ‘natural bioremediation’?
4
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8
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In addition to those on human health, what are some other harmful effects
of air pollution?
Briefly describe photochemical smog and how it forms. Is it a primary
pollutant? Why?
An air quality standard limit hourly ozone (O3) levels to 0.12 ppm. Express this
concentration in terms of µg/m3 at 25°C and 1 atm pressure? Molecular
weight of O is 16.
Terms of Reference (ToR) is a guideline document to be used in EIA or IEE
Process for an EIA report. List the items to be described in a ToR.
Quantifying impacts are important in recommending alternatives for a
proposed development project by doing an EIA. What are the methods
available to quantify impacts of the projects and alternatives?
Rapid urban development including illegal construction causes flooding.
How does rainwater harvesting reduce urban flooding? Explain briefly.
What is base flow? Identify the base flow in the following hydrographs.
(2 marks)
(2 marks)
Explain return period or recurrence interval in terms of probability that an
event will take pace.
(3 marks)
5
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(2 marks)