ce3040-end sem-2012
TRANSCRIPT
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Department of Civil Engineering,
liT
Madras
CE
3040 Environmental Engineering
End Semester Examination Jan -
May
2012
Total marks: 100 Duration: 3hrs
Part A: Answer the following questions briefly 10 x 4 =40 marks)
1
Expand the following abbreviations
a) UASB
b)MBBR c)MBR d) SBR e) RBC f) ASP
g)
MLSS
h)CSTR
2.
Name the treatment
unit natural
system where the following process occurs
a) Compression settling e) root zone treatment
b)
Ionic layer compression f) Eutrophication
c)
Sloughing of biofilms g) Methanogenesis
d)
symbiotic metabolism h) Formation
of
chloroorganics
3.
Perform a mass balance around the secondary settling tank to arrive at an expression for
sludge recycle ratio.
If
the sludge wasted
is
1
of
the
total
wastewater
flow into
a Actiyated
sludge waste water treatment plant,
MLSS
maintained is 3000mg/1 and underflow
concentration is 10,OOOmg/I, determine the recycle ratio
4. Why are aeration devices a vital part of ASP treatment plants? Name
two
major aeration
techniques used in these plants. How is
the
aeration requirement assessed for a given level of
treatment?
5.
What is sludge from ASP composed of? How is
the
sludge generated from aerobic treatment
systems managed and disposed? Show with a flow diagram.What are the resources that can be
recovered from sludge?
6.
What are the steps involved in providing water supply infrastructure for a community
including planning, designing and construction? What percentage ofthe water suppHed is used
for approximate waste water quantity estimations?
7. A filter plant is to be constructed to process 75700 m3/d. Assuming 15m h as an acceptable
filtration ate, and a surface configuration of x8 m , how many filters units will be required.
Allow one unit
as
a standby during backwashing.
If
the depth
of
the sand bed is 1m and
porosity is 0.3
with
settling velocity of sand is 0.08m/s, determine the expanded bed depth.
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8. List the mechanisms
of
coagulation and factors affecting coagulation. Sketch the effect
of
suspended solids concentration and coagulant dosage on the effective mechanism
of
coagulation.
9. Define with sketches or equations and mention the name
of
the t reatment process
associated with these models
a)
Double layer model
b)
Chick s model
c)
Monod s model
d) Langmuir s model
10. List
four
biokinetic parameters and define each
of
them.
Part B Provide detailed answers and Solve
th
following problems 15 x 4= 60)
1 Sustainable water infrastructure is planned for IITMadras campus by using the water from
the lake, reusing part of the treated water for gardening and toilet flushing and recycling the
remaining treated wastewater back into the lake. .
a) List the standards set for drinking water quality with respect to total suspended solids, total
dissolved solids, nitrates and microbes
b) List the standards set for discharge of wastewater into a surface water body w.r.t. TSS, TDS,
nitrates,
BOD
and COD.
c)
Sketch the water treatment scheme
to
meet drinking water standards
d) Sketch the waste water treatment scheme which will meet the irrigation requirements
standards.
e) What additional
treatment is
required to meet discharge standards
so
that
it can
be recycled
into the lake
f) Is there any other problem you envisage in the long term
if
this system becomes operational.
If
so what is your suggestion to improvise the treatment.
2. Compare the area required
for
treating a wastewater flow of 3550 m
3
day by a waste
stabilization pond system
an
activated sludge system and a trickling filter system. The influent
BODs following primary clarification
is
200mg/L. Also design the power requirement for
aerators to meet the expected BOD removal
in
an
ASP.
Data provided: For pond system, the reaction rate coefficient at
30C
is 0.35/day. The operating
temperature
in
winter
is 10 Dc Assume a single cell pond system with 85 removal of soluble
BOD for a pond depth
of
2.0m. Assume 8=1.06
For activated sludge process, take Y=0.6kg/kg, kd=0.05 per day, 8
c
=15days(Ali estimated at 10 C
temp), MLVSS=3000mg/L, return-sludge concentration=10000mg/L
of
suspended solids (S5)
and tank depth
as
5 m
For a tricking filter system the treatability constant is 0.1 min-
1
at 10 C and packing coefficient is
0.5 with a tank depth of 6.5 m and recirculation ratio as 2.
2
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3.
A water treatment plant is to process 30,000 cum/d.
The
rapid mixing tank will blend
35mg/1
of alum with the flow and is to have a detention time of 2 minutes. The tank is to have a square
crosssection. This
unit
will be followed by
four
flocculators with a maximum width
of
10m
and
depth of 4m to connect to the sett ling basin.
Determine
a)
quantity of alum added per day b) Dimensions
of
the two units c) Flocculator
paddle area d)Power input
for
the two units in KW
for
a Gvalue of 900
sec-
1
for rapid mixer
and Gt value of 3.5 x 10
4
and G of 30 S 1 for flocculator
Compare the designs of a circular set tling tank and a rectangular tank, perform the necessary
checks and recommend one of them based on operational criteria.
The settling basins will be constructed of reinforced concrete and the cost of forming and
pouring circular walls is 1.25 times the cost of forming and pouring straight walls. What will be
your final recommendation including cost criteria?
4. Estimate the total quantity of brackish(salty) groundwater
that
must be processed and the
quantity
and quality
of
waste streams from a
RO
facility required
to
produce 4000 cum/d
of
water for a village. Assume both recovery (water) and rejection rates (solute) are equal to 90
and
the
concentration
of
feed water is 4000g/m
3
.
The RO takes care
of
disinfection b u ~ some
residual disinfection has to be provided based on the following
data
Sample No Chlorine dosage mg/I Residual chlorine after 10 min contact (mg/I)
1 0.2 0.19
2 0.4
0.36
3 0.6 0.50
4 0.8
0.48
5 1.0 0.2
6
1.2 0.4
7
1.4
0.6
8
1.6 0.8
Sketch a 'chlorine demand curve'. What is the break point dosage and what is the ~ t u l
chlorine dosage
if
residual requirement
is
O.4mg/l?
Alternatively if the dissolved solids are mainly composed
of
Iron, Manganese, bicarbonates and
chlorides of Calcium, Magnesium, what will be you suggestion
for
treatment and the reactions.
No quantification is necessary.
3
.
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Design Criteria for water treatment units
1. Rapid mixer: Range of G = 700 to 1000 S-l
2. Flocculation basin
Gt
= 10
4
-
10
5
3. Surface loading rate: 12-18m
3
/day/m
2
Depth discrete: 2.5 to
3m
Use 1000-
S
)
Use 10
5
)
Horizontal flow velocity,
Vh
s 36 rnlhr Heavy discrete)
Weir overflow rate,
Vw s 14
m
3
/hr/m
length Heavy discrete)
4. Slow sand filters rate 100 to 200
Ilhlm
2
Rapid sand filters rate 3000 to 6000 1Ih1m
2
~ s e 5 Vh/m2)
Pressure sand filters rate 6000 to 15,000 llhlm
Constants
Ilw = Viscosity of water = 1.139 x 10-
3
Ns/m2
pw
=
Density
of
water @25C
=
981
kg/m
3
R = Universal Gas Constant = 8.3144 llmole.K
E
=
Activation Energy for
Cb @pH
7 =34,340
llmole
Formulae
1.
G =
PNIl)112
4. / = 150(1-
e
1.75
Re
_ JO.
6
e
b
-
. VI
8
q =
b
e
e
1 bCe)
QpC
p
11. F = kl: .C
I I A
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Design
Criteria
for Waste
water treatment
Activated sludge
plant
(conventional):
Volumetric loading rate : 0.3-0.6
kgBOD5 cum
Air supply : 45-90 cum kgBOD5
FIM
ratio : 0.2-0.4
Mean cell res. Time : 4-15 days
Hydraulic retention
time
4-8 hrs
Formulae:
x
=
}cY So -
S
()
(1
+ kd }J
Trickling filters (
Medium
rate):
Organic loading rate : 0.24 - 0.32
kgBOD5 m
3
.day
Hydraulic loading rate 4-10 m
3
/m
2
.day
Power reqd: 2-8 kw l000m
3
Formulae
Se e kDIQn
So 1 +
R
-
Re kDIQn
Waste stabilization pond:
Formulae
S 1
kT k20
= <l>T-20 where <1>=1.03-1.12
Oxygen requirement = 2 kg Ikg
of
BOD5
Oxygen transfer efficiency =
lkg
oxygen kw.h
I