GY232 Environmental Pollution & Control
School of Environment & Technology
Semester 1 Examinations January/February 2011
GY232
ENVIRONMENTAL POLLUTION
AND CONTROL
Instructions to Candidates:
Time allowed: ONE and a HALF hours
Answer any TWO questions
All questions carry equal marks
24 January–4 February 2011
Page 1 of 5
GY232 Environmental Pollution & Control
Question 1
(a)
Compare and contrast the likely physical, chemical and biological
characteristics of groundwater abstracted as a source of drinking water from
the chalk aquifer in southern England, with those characteristics of water
abstracted from a lowland river in the same region.
(20 marks)
(b)
Discuss how the characteristics of the two water sources described above will
influence the design and operation of appropriate drinking water treatment
plants for each source of water.
(30 marks)
Question 2
(a)
Outline how Stokes’ Law describes the settling of discrete particles in an ‘ideal
settling tank’ (class I settling) and, with reference to the behaviour of
suspended particles in a real water treatment plant settling tank, describe how,
in practice, settling differs from this law.
(30 marks)
(b)
A settling tank is designed to remove spherical discrete particles with 0.5 mm
diameter and specific gravity (Sp) 1.02, from water at 20°C.
Assuming ideal settling conditions and laminar flow, and using the equation
given below, determine the percentage removal of spherical discrete particles
with a diameter of 0.25 mm and a specific gravity (Ss) of 1.01, in this tank.
Show the stages of your calculation.
Kinematic viscosity (μ) of water at 20°C is 1.01 x 10-6 m2/s and the specific gravity
of water is 1.00.
D 2 g ( Sp  Sf )
Vs 
18
Where:
Vs
D
g
Sp
Sf
μ
=
=
=
=
=
=
settling velocity of the particle in ms-1
diameter of the particle in m
acceleration due to gravity in ms-2 (9.81)
specific gravity of the particle
specific gravity of the fluid
kinematic viscosity of the fluid in m2 s-1
(20 marks)
Page 2 of 5
GY232 Environmental Pollution & Control
Question 3
(a)
With reference to the incomplete graph below (Figure 1), describe what
happens when chlorine is added to drinking water that contains organic matter
and ammonia.
D
B
A
C
Figure 1. A simplified breakpoint chlorination curve
(30 marks)
(b)
Using the equation given below, compare the contact times required to give E.
coli (a faecal indicator bacterium) kill rates of 99.9 % in water with (i) a free
chlorine residual of 0.2 mg/l, and (ii) a combined chlorine residual of 1 mg/l, k
values for these two scenarios are 10-2/s and 10-5/s respectively.
The required contact time for chlorine to give a stated kill of bacteria is
described by the following equation:
2
 No 
t2
=
. log10  
k
 Nt 
Where
t
k
N0
Nt
=
=
=
=
contact time in seconds
reaction constant
number of organisms originally
number of organisms at time t
(20 marks)
Page 3 of 5
GY232 Environmental Pollution & Control
Question 4
(a)
With reference to the ‘Monod growth curve’ for microorganisms, describe the
roles of oxidation, auto-oxidation and biosynthesis in the breakdown of
organic matter in secondary biological treatment of wastewaters in (i) a
trickling filter (attached growth); and (ii) activated sludge system (suspended
growth).
(30 marks)
(b)
Give the land area requirements (in m2) for trickling filter (BOD loading 0.1
3
kg/m3/day) and conventional activated sludge (BOD loading 0.6 kg /m /day)
provision for a town of 40,000 people that has a daily dry weather flow (DWF)
of 200 litres per person, and a mean wastewater strength of 220 mg/l BOD.
Assume a trickling filter depth of 1.8 m and aeration tank depth of 3 m.
Primary sedimentation removes 55% of the applied BOD. State all
assumptions made.
(20 marks)
Question 5
(a)
Giving suitable examples, discuss the major sources of (i) gaseous; and (ii)
particulate air pollutants in urban environments, and outline their potential
negative impacts on human health and the environment.
(40 marks)
(b)
Eight separate sources of sound, when measured in isolation, give the
following values for sound pressure level (SPL), measured in decibels (dB):
77; 122; 88; 69; 80; 112; 120 and 77
Using the information provided in Table 1 below, determine the resulting
sound pressure level when all the sources occur at the same time.
Table 1. Difference table for adding dB
Difference between two levels in dB
Add to the higher level
0
1
2 or 3
4
5 to 7
8 or 9
10 or more
3
2.5
2
1.5
1
0.5
0
(10 marks)
Page 4 of 5
GY232 Environmental Pollution & Control
Question 6
(a)
With reference to Figure 2 (below), describe the processes that lead to the
stabilisation of municipal solid waste (MSW) in an effectively designed and
managed landfill facility.
Figure 2. Changes in gas and leachate composition during stabilisation of
municipal solid (MSW) in a landfill facility.
(35 marks)
(b)
A town in southwest England (with a population of approximately 180,000)
requires a new landfill facility. This facility must process all municipal solid
waste from the town for the next 30 years. Average household size is
currently 2.3 persons. Recycling policy has reduced the MSW per household,
that will go to landfill each week, to 7 kg. Assume the density of waste to be
350 kg m-3. A planning restriction limits the height of the landfill to 10 m.
Calculate the approximate land area required for this facility, stating all the
assumptions that you have made, and describe the limitations of your answer.
(15 marks)
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