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7/23/2019 CE3040-END SEM-2012 http://slidepdf.com/reader/full/ce3040-end-sem-2012 1/5 / 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. -\ 1

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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.

-\

1

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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