Son Olarak Bitiyooo

7/31/2019 Son Olarak Bitiyooo

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TABLE OF CONTENTS

EXECUTIVE SUMMARY 2

SLUDGE TREATMENT IN WASTEWATER TREATMENT 3

SLUDGE TREATMENT IN PAAKY 7

RETURN SLUDGE PUMPING STATIONS .............................................................................................................7

EXCESS SLUDGE PUMPING STATIONS ..............................................................................................................7

DISSOLVED AIR FLOATATION UNIT ...................................................................................................................7

SLUDGE STORING TANK ........................................................................................................................................8

SLUDGE DEWATERING BUILDING ......................................................................................................................8

FILTRATE PUMPING STATION ..............................................................................................................................9

AS IS DESIGN 10

PROCESS CALCULATION ......................................................................................................................................10

HYDRAULIC CALCULATIONS .............................................................................................................................15

COST ANALYSIS ........................................................................................................................................................26

MODIFIED DESIGN 27

CALCULATIONS ........................................................................................................................................................27

COST ANALYSIS ........................................................................................................................................................27

NEW DESIGN 28

ANAEROBIC DIGESTION 32

DESIGN CRITERIA FOR ANAEROBIC DIGESTION ......................................................................................33

DESIGN OF ANAEROBIC DIGESTER 34

PROCESS CALCULATION ......................................................................................................................................34

COST ANALYSIS ........................................................................................................................................................49

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EXECUTIVE SUMMARY

his report is prepared to present the design of sludge treatment in Paaky

Wastewater Treatment Plant and Anaerobic digestion. The flowrate is taken

as 100,000 m3 / day and the peak flowrate is 125,000 m3 / day. It includes an

as is, a modified and a new design of the sludge lines and a new design

for anaerobic digestion.TIn as is design of sludge treatment units of Paaky Wastewater Treatment Plant all

process and hydraulic calculations are done for the DAF, sludge storage tank and centrifuge

units. The approximate cost of this project is 4,300,000 $.

In modification of Paaky Wastewater Treatment Plant, sludge storage detention time

is minimized and tank is reconstructed according to chosen storage day. The approximate cost

of this project is 10,000 $.

In new design of Paaky Wastewater Treatment Plant is average flowrate is taken as

100,000 m3 / day. This new design is performed to adapt the range of design criteria. The

approximate cost of this project is 4,700,000 $.

Anaerobic digestion has been designed according to Paaky influent wastewater

parameters. All calculations were done including dimensioning, amount of gas production, heat

requirements. The approximate cost of this project is 10,000,000 $.

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SLUDGE TREATMENT IN WASTEWATER TREATMENTSLUDGE TREATMENT IN WASTEWATER TREATMENT

Wastewater treatment objectives are accomplished by concentrating impurities into solid form

and then separating these solids from the bulk liquid. These concentration of solids, referred to

as sludge, contains many objectionable materials and must be disposed ofproperly. The sludgeresulting from wastewater treatment operations and process is usually in the form of a liquid or

semisolid liquid that typically contains from 0.25 to 12 % solids by weight, depending on the

operations and processes used. Of the constituents removed by treatment, sludge is by far the

largest in volume, and its processing and disposal is perhaps the most complex problem facing

the engineer in the field of wastewater treatment. Sludge disposal facilities usually represent 40

to 60 % of the construction cost of wastewater treatment plants, account for as much as 50 %

of the operating cost, and are the cause of a disproportionate share of operating difficulties. [1]

[2]

Gravity Thickening

Gravity thickening is accomplished in a tank similar in design to a conventional sedimentation

tank. Normally, a circular tank is used. Dilute sludge is fed to a center - feed well. The feed

sludge is allowed to settle and compact, and the thickened sludge is withdrawn from the bottom

of the tank. Conventional sludge - collecting mechanisms with deep trusses or vertical pickets

are used to stir the sludge gently, thereby opening up channels for water to escape and

promoting densification. The supernatant flow that results is returned to the primary settling

tank or to the headworks of the treatment plant. The thickened sludge that collects on the

bottom of the tank is pumped to the digesters or dewatering equipment as required; thus, storage

space must be provided for the sludge. Gravity thickening is most effective on primary sludge.

A photo of gravity thickener is shown below.

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Gravity thickeners used dewatering the treatment sludge are designed on the basis of solids

loading. To maintain aerobic conditions in gravity thickeners, provisions should be made for

adding 24 to 30 m3/m2.day of final effluent to the thickening tank. Typical concentrations of

unthickened and thickened sludges and solids loadings for gravity thickener are shown below.

[3]

[4]

An operating variable, sludge volume ratio normally range between 0.5 and 20 day; the lower

values are required during warm weather. For operation, alternatively, sludge - blanket depth

should be measured. Blanket depths may range from 0.6 to 2.4 m; shallower depths are

maintained in the warmer months.

Flotation Thickening

There are three basic variations of the flotation thickening operation ; dissolved - air flotation

(DAF), vacuum flotation, and dispersed - air flotation. Dissolved - air flotation is being

widely preferred for especially waste activated sludge. Air is introduced into a solution that is

being held at an elevated pressure. When the solution is depressurized, the dissolved air is

released as finely divided bubbles carrying the sludge to the top, where it is removed. Photos of

DAF are shown below. [5]

[6]

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[7]

Activated sludge solids from the secondary clarifiers which are not returned to the aerators are

wasted. The DAF (Dissolved Air Flotation) thickener tanks receive the wasted solids. Solids

enter the DAF tank where they are mixed with water and compressed air. As the air and water

mix, solid particles are lifted to the surface by rising air bubbles in the tank.

The floating solids are then collected by a series of tank skimmers while the water is recycled

back to the raw sewer to be processed through the plant. The solids from the DAF are pumped

to the anaerobic digesters. [8]

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[9]

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SLUDGE TREATMENT IN PAAKYSLUDGE TREATMENT IN PAAKY

RETURN SLUDGE PUMPING STATIONSRETURN SLUDGE PUMPING STATIONS

Return sludge from the clarifiers is pumped back to the distribution chamber before the Bio-P

Tanks.

For each two clarifiers a Return Sludge Pumping

Station is constructed. Each pumping station is

equipped with 5 return sludge pumps, 2 for each

clarifier plus a common stand by. The pumps are

submersible pumps. The pumps are automatically

operated, controlled by the inlet flow meter in order to

achieve a constant return sludge rate.

EXCESS SLUDGE PUMPING STATIONSEXCESS SLUDGE PUMPING STATIONS

Excess sludge is taken from channel 4 and 2 in each of the Process Tank. A total number of 3

eccenter screw pumps are used. Each has a capacity of 167 m/h, 3rd is stand-by. The pumps are

controlled by a timer to remove a preset amount of excess sludge every day. The starting order

of the pumps is alternated once a day to distribute the running time of pumps as equally as

possible.

DISSOLVED AIR FLOATATION UNITDISSOLVED AIR FLOATATION UNIT

The excess sludge is concentrated in dissolved air flotation unit (DAF Unit). The sludge is

mixed with recycled reject water, which is over saturated with atmospheric air under pressure.

When this mixture enter the DAF Unit, fine air

bubbles will from and carry the sludge to thesurface of the DAF Unit, where it is scraped off.

In the unit two pumps are in operation and one

is stand-by. The pumps are operated at the same

time and with the same capacity as the excess

sludge pumps. The starting order of the pumps

alternated once a day to distribute the running

time of pumps as equally as possible.

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Each pressure tank is equipped with a pressure transmitter for the pressure tank in the tank a

pressure switch to activate the compressor.

SLUDGE STORING TANKSLUDGE STORING TANK

The concentrated sludge from the DAF Unit gratitates to a Sludge Storage Tank. The tank is

equipped with slow moving mixers to keep the sludge homogenized and bottom air diffusors to

keep it aerobic. The blowers for the diffusors are controlled by the oxygen transmitter in the

tank. One blower is on duty one is stand-by. The starting order of the blowers is alternated

weekly to distribute the running time of blowers as equally as possible.

Sludge Storage tank before dewatering (centrifuge)

SLUDGE DEWATERING BUILDINGSLUDGE DEWATERING BUILDING

The sludge is dewatered in 2 centrifuges. The sludge is fed into each centrifuges with a 2 step

eccenter screw pump. Each pump has a capacity of 10 m/h. Polymer is added by 2 step

eccenter screw pumps working in parallel with the feeding pumps. The polymer is added on the

suction side of the feeding pumps and mixed with the sludge in the pipe using in line static

mixer.

The sludge pumps and dosing pumps are automatically operated controlled by the pressure in

the centrifuges. The dewatered sludge is transported by a system of eccenter screw pump to an

outside container area situated at the backside of the Sludge Dewatering Building.

The centrifuges and the Sludge Storage Tank are interconnected so that centrifuge cannot be

started unless sufficient amount of sludge is available in the storage tank.

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FILTRATE PUMPING STATIONFILTRATE PUMPING STATION

Filtrated water from the centrifuge is sent to the collection distribution chamber. There are 2

submersible pumps one is stand-by.

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AS IS DESIGNAS IS DESIGN

PROCESS CALCULATIONPROCESS CALCULATION

DISOOLVED AIR FLOATATION

( )( )1.3 1a

a

s f P RA

S S Q

=

A/S = Air to solids ratio, ml(air)/mg (solids)

0.005 0.06 [13]

sa = air solubility, ml/l

f = fraction of air dissolved at pressure P, usually 0.5 [13]

P = pressure ,atm

p = gage pressure, kPa ( 275-350 kPa) [15]

Sa = influent suspended solids, g/m3 (mg/L)

R = pressurized recylce, m3/d

Q = mixed-liquor flow, m3/d

Temp., oC 0 10 20 30

sa, mL/L 29.2 22.8 18.7 15.7

[13]

sa = 18.7 mL/L

P =101.35

101.35

p +=

275 101.35

101.35

+= 3.71 atm

( )( )1.3 18.7 0.5 3.71 10.05

300 1600

R =

R = 1385.6 m3/d

Velocity of the solids = 8 160 L/m2.min

Surface Area =3 3 3

2

1385.6 / 10 /

8 / .min 1440min/

m d L m

L m d

= 120.3 m2

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A =2

4

D= 120.3 => D = 12.5 m => A = 122.7 m2

Solids Loading = 1.2 3 kg/m2hr [13]

Solids Loading = ( ) ( ) 21600 1385.6 4 4 / .122.7

RQ Q x kg m hr A

+ + = = (NOT N THE RANGE)

DAF detention time =3

3

6000.37 9

1600 /

md hr

m d= =

SLUDGE STORAGE TANK

Diameter = 27 m

Depth = 4.3 m

Volume =2 2

327 4.3 24604 4

Ddepth m

= =

Sludge storage tank detention time =3

3

246015.4

160 /

md

m d= (NOT IN THE RANGE) [13]

SLUDGE MASS BALANCE

Input Parameters;

BODinfluent = 320 g/m3

SSinfluent = 300 g/m3

Organic N = 10 g/m3

NH4 = 17 g/m3

TN = 27 g/m3

TP = 5 g/m3

Waste Activated Sludge

Biomass Production;

,

1000000,4(240 135) 0,15 0,081 100000 0,4(240 135)9,23 100000 0,12 20

1 (0,081 9,23) 1 (0,081 9,23) 1 (0,081 9,23)

6235.23 /

x bio

x x x x xP

x x x

kgVSS d

= + +

+ + +=

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31 16235.23 / 1558.8 /1000 0,004

kg d m day =

% Total Solids is assumed 0,4

WASN =

3 3 1 12.21558.8 / (1 8) / 6235.23 0.8 622.56 /1000 100

m day g m kgN d + + =

BOD in WAS = [ ]6235.23 0.65 1.42 0.68 3913.3 /kg d =

NDN =

3 3

3

1 1100,000 27 / 100,000 9 / 622,56

1000 1000

1177.44 /

kg kg g m g m

g g

kgNO N day

=

NDN = (QIR+ QR)NO3.N effluent

1177.44 = (QIR+ 100,000) x 8

QIR= 47,180 m3/day

IR = 0,47

WASP =( )3 3 3100,000 / 5 / 2 / 300 /m d g m g m kg day =

% TP in SS =

300 /4.8%

6235.23 /

kg day

kg day=

% TP in in VSS =

300 /6%

6235.23 / 0.8

kg day

kg day=

P release = ( )6% 2.3% (6235.23 0.8) 184.55 /kg day =

WAS : C60 H81 O23 N12 P mw = 1374 g

TN = (12 x 14) / 1374 = 12.2 %

TP = 31g / 1374g = 2.26 %

Dissolved Air Floatation

Biomass Production;

,

1000000,4(240 135) 0,15 0,081 100000 0,4(240 135)9,23 100000 0,12 20

1 (0,081 9,23) 1 (0,081 9,23) 1 (0,081 9,23)

6235.23 /

x bio

x x x x xP

x x x

kgVSS d

= + +

+ + +=

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31 16235.23 / 155.88 /1000 0, 04

kg d m day =

% Total Solids is assumed 4%

DAFN =

3 3 1 12.2155.88 / (1 8) / 6235.23 0.8 609.93 /1000 100

m day g m kgN d + + =

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Sludgeamount(kg/d) 6235,23

% solid 0,4solid

sludge(m3/d) 1558,81

EFFLUENT




% solid 4 % solid 4 % solid 25

solidsludge(m3/d) 154,337



AERATION

CENTRIFUGEDAF SLUDGESTORAGE

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HYDRAULIC CALCULATIONSHYDRAULIC CALCULATIONS

Headloss through Pipe from Secondary Clarifiers to RAS Pumping Station

Q = 100,000 m3/d / 4 = 25,000 m3/d

D = 500 mm

L = 27.53 m

Assume % 1 sludge

Kentrance = 0.5

Kexit = 1

e (roughness coefficient) = 0.045mm = 0.000045m for steel

= 1.14x10-3N.sec/m2 for 15 C

= 1000 kg/m3

00009.05,0

000045.0

104.6sec/.1014.1

)/47.1()5.0()/1000(Re

/47.14/)5.0(

/28.0/

5

23

3

2

3

==

=

==

===

D

e

mN

smmmkgDV

smsm

AQV

f = 0.020 (from Moody Diagram)

H = Hmajor + Hminor

mg

smg

smm

mH

g

VKKK

g

V

D

LfH exitentrance

23.02

)/47.1()15.0(2

)/47.1(5.053.27020.0

2)2(

222

2

90

2

=++=

+++=

RAS Pumping Station

There are 4 + 1 pump:

Type: Submercible

Flowrate: 3.6 m3/h

Head: 10m

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Power: 2.4 kW

Rotation: 2830 d/d

Brand: Flyt/CD 3085 HT 250

Cost: 2.4 kW x 4 x 0.07$ x 365 x 24 = 5,887 $ / year

Headloss through Pipe from RAS Pumping Station (Clarifiers 1 & 2) to CDC 2

Q = 100,000 m3/d / 2 = 50,000 m3/d

D = 700 mm

L = 391 m

Assume % 1 sludgeFind yield stress from Figure 14-6, (a) (Ref: M&E, 2003)

sy = 0.05 N/m2

Find coefficient of rigidity from Figure 14-6, (b) (Ref: M&E, 2003)

= 0.001 kg/m/s

smsm

V

A

QV

/50.1

4

)7.0(

/58.02

3

==

=

Reynolds Number:

VDNR =

where:

NR: Reynolds number, dimensionless

: density of sludge, kg/m3 = 1000 kg/m3

V: average velocity, m/s

: coefficient of rigidity, kg/m/s

63

101//001.0

)7.0)(/5.1)(/1000(xsmkg

msmmkg

NR ==

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Hedstrom Number:

2

2

ysDHe=

9

2

332

1047.1)//001.0(

)/1000)(/03.0()7.0(x

smkg

mkgmNmHe ==

where:

He: Hedstrom number, dimensionless

sy: yield stress, N/m2

Find friction factor from Figure 14-6, (c) [13]

f = 0.0025

D

LVfP

22 =

223

/4189)7.0(

)/5.1)(391)(/1000)(0025.0(2mN

m

smmmkgP ==

msmmkg

mN

P 42.0)/81.9)(/1000(

/418923

2

==

Hminor =g

VKKKK exitent

2)2(

2

9045 +++

Hminor = mg

x 41.02

)5.1()275.06.015.0(

2

=+++

HT = 0.42m + 0.41m = 0.83m

Headloss through Pipe from RAS Pumping Station (Clarifiers 3 & 4) to CDC 2

Q = 100,000 m3/d / 2 = 50,000 m3/d

D = 700 mm

L = 468 m

Assume % 1 sludgeFind yield stress from Figure 14-6, (a) [13]

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sy = 0.05 N/m2

Find coefficient of rigidity from Figure 14-6, (b) [13]

= 0.001 kg/m/s

smsm

V

A

QV

/50.1

4

)7.0(

/58.02

3

==

=

Reynolds Number:

VDN

R

=

where:





1050000//001.0

)7.0)(/5.1)(/1000( 3==

smkg

msmmkgNR

Hedstrom Number:

2

2

ysDHe=

24500)//001.0(

)/1000)(/05.0()7.0( 2

332

==smkg

mkgmNmHe

where:




f = 0.002

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D

LVfP

22 =

223

/6017

)7.0(

)/5.1)(468)(/1000)(002.0(2mN

m

smmmkgP ==

msmmkg

mNP 45.0

)/81.9)(/1000(

/601723

2

==

Hminor =g

VKKKK exitent

2)3(

2

9045 +++

Hminor = mg

x 5.02

)5.1()375.06.015.0(

2

=+++

HT = 0.45m + 0.50m = 0.95m

Headloss through Pipe from 4th Aeration Tank to Excess Sludge Pumping Station

Q = 1558.8 m3/d

D = 400 mm

L = 99 m

Assume % 0.4 sludge

Kentrance = 0.5

Kexit = 1


= 1.14x10-3N.sec/m2 for 15 C

= 1000 kg/m3

0001125.04,0

000045.0

1026.5sec/.1014.1

)/15.0()4.0()/1000(Re

/15.04/)4.0(

/018.0/

4

23

3

2

3

==

=

==

===

D

e

mN

smmmkgDV

smsm

AQV


H = Hmajor + Hminor

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mg

sm

g

sm

m

mH

g

VKKK

g

V

D

LfH exitentrance

094.02

)/15.0()5.115.0(

2

)/15.0(

4.0

99021.0

2)2(

222

2

90

2

=+++=

+++=

Excess Sludge Pumping Station

Type: monopump

Flowrate: 167 m3/h

Pressure: 3 bar

Head: 20m

Power: 30 kW

Rotation: 270 d/d

Brand: CB 12 K AC IRS/monopumps Dresser

Cost = 30kW x 2 x 365 x 24 x 0.07$ = 36792$/year

Headloss through Pipe from Excess Sludge Pumping Station to DAF Unit

Q = 1558.8 m3/d

D = 400 mm

L = 62.15 m

Assume % 0.4 sludge

Kentrance = 0.5

Kexit = 1


= 1.14x10-3N.sec/m2 for 15 C

= 1000 kg/m3

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0001125.04,0

000045.0

1025.5sec/.1014.1

)/15.0()4.0()/1000(Re

/15.04/)4.0(

/018.0/

4

23

3

2

3

==

=

==

===

D

e

mN

smmmkgDV

smsm

AQV


H = Hmajor + Hminor

mg

sm

g

sm

m

mH

g

VKKK

g

V

D

LfH exitentrance

064.02

)/15.0()75.015.0(2

)/15.0(

4.0

15.62021.0

2)(

222

2

90

2

=+++=

+++=

Headloss through Pipe from DAF Unit to Sludge Storage Tank

Q = 155.88 m3/d

D = 200 mm

L = 120.65 m

Assume % 4 sludge

Find yield stress from Figure 14-6, (a) [13]

sy = 5.5 N/m2

Find coefficient of rigidity from Figure 14-6, (b) [13]

= 0.012 kg/m/s

smsm

V

A

QV

/057.0

4

)2.0(

/018.02

3

==

=

Reynolds Number:

VDNR =

21


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where:





10.2//5.5

)2.0)(/057.0)(/1010( 3==

smkg

msmmkgNR

Hedstrom Number:

2

2

ysDHe=

1543055)//012.0(

)/1010)(5.5()2.0(2

32

==smkg

mkgmHe

where:




f = 1

D

LVfP

22 =

223

/122

)2.0(

)/01.0)(65.120)(/1010)(1(2mN

m

smmmkgP ==

msmmkg

mNP 012.0

)/81.9)(/1000(

/12223

2

==

Hminor = negligible

HT = 0.012m

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Headloss through Pipe from Sludge Storage Tank to Centrifuge

Q = 155.8 m3/d

D = 200 mm

L = 22.5 m

Assume % 4 sludge

Kentrance = 0.5

Kexit = 1


= 1.14x10-3

N.sec/m2

for 15 C = 1000 kg/m3

000225.04,0

000045.0

101sec/.1014.1

)/057.0()2.0()/1000(Re

/057.04/)2.0(

/018.0/

5

23

3

2

3

==

=

==

===

D

e

mN

smmmkgDV

smsm

AQV


H = Hmajor + Hminor

mg

sm

g

sm

m

mH

g

VKKK

g

V

D

LfH exitentrance

006.02

)/057.0()15.0(

2

)/057.0(

2.0

5.22021.0

2)2(

222

2

90

2

=++=

+++=

Headloss through Pipe from Centrifuge to CDC 2 for Supernatant

Q = 130.93 m3/d

D = 300 mm

L = 129.3 m

Kentrance = 0.5

Kexit = 1

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= 1.14x10-3N.sec/m2 for 15 C

= 999 kg/m3 for 10 C

00015.03,0

000045.0

1052.5sec/.1014.1

)/021.0()3.0()/999(Re

/021.04/)4.0(

/0015.0/

3

23

3

2

3

==

=

==

===

D

e

xmN

smmmkgDV

smsm

AQV


H = Hmajor + Hminor

mg

sm

g

sm

m

mH

g

VKKK

g

V

D

LfH exitentrance

004.02

)/021.0()5.115.0(

2

)/021.0(

3.0

3.129036.0

2)2(

222

2

90

2

=+++=

+++=

Supernatant Pumps

# of pumps: 2:

Type: submercible

Flowrate: 360 m3/h

Head: 6m

Power: 8.8 kW

Brand: Flyt/CP 3140 LT 610

Headloss through Pipe from DAF Unit to CDC 2 for Supernatant

Q = 1402.2 m3/d

D = 300 mm

L = 24.34 m

Kentrance = 0.5

Kexit = 1

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= 1.14x10-3N.sec/m2 for 15 C

= 999 kg/m3 for 10 C

000015.03,0

000045.0

1095.5sec/.1014.1

)/22.0()3.0()/999(Re

/22.04/)4.0(

/016.0/

4

23

3

2

3

==

=

==

===

D

e

mN

smmmkgDV

smsm

AQV


H = Hmajor + Hminor

mg

sm

g

sm

m

mH

g

VKKKK

g

V

D

LfH exitentrance

011.02

)/22.0()75.06.015.0(

2

)/22.0(

3.0

34.24020.0

2)(

222

2

9045

2

=++++=

++++=

Centrifuges

There are 2 centrifuges.

Capacity: 255 kg solid/h

Nominal velocity (Va): 3500d/d

Nominal Power: 30kW

Boul diameter: 340mm

Brand: Guinard/D3LLC 30C HP

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COST ANALYSISCOST ANALYSIS

UNIT UNIT COST COST

Construction 1,000,000 $

Excess Sludge Pumps 3 20,000$ 60,000$

Compressors (250 l / day) 2 50,000$ 100,000$

Mixers 4 50,000$ 200,000$

Diffusers (9) 340 200$ 68,000$

Sludge Blender 2 10,000$ 20,000$

Sludge feeding pumps 2 5,000$ 10,000$

Polyelectrolyte feeding

pumps2 3,500$ 7,000$

PE ring pump 1 5,000$ 5,000$

Exit sludge pump 2 5,000$ 10,000$

Centrifuges 2 1,000,000$ 2,000,000$

Liquid PE feeding pump 1 10,000$ 10,000$

TOTAL COST

4,300,000$

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MODIFIED DESIGNMODIFIED DESIGN

Storage should be provided to smooth out the fluctuations in the rate of solids and biosolids

production and to allow solids to accumulate during periods when subsequent processing

facilities. Storage is particularly important in providing a uniform feed rate ahead of the

following processes; mechanical dewatering, lime stabilization, heat drying and thermal

reduction.

Sludge tanks may be sized to retain the sludge for a period of hours to a few days. If sludge is

stored longer than 2 to 3 days, it will deteriorate, become odorous, and be more difficult to

dewater.

In as is design sludge retention time is too long (15 days). Therefore diameter of the tank isreduced by constructing inner sidewall.

CALCULATIONSCALCULATIONS

Sludge Retention Time is assumed 4 days

Required Volume of storage tank = (4days) x (154,337 m3/day)

[ (D2) / 4] x 4,3 m = 617 m3

D= 13.5 m

Diameter is taken 13.5 m.

Sludge Retention Time = 4 days


COST

Construction 10,000$

TOTAL COST

10,000$

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NEW DESIGNNEW DESIGN

MECHANICAL SLUDGE THICKENER

In wastewater treatment plants, the sludge cannot be or is not desired to be directly taken into

the dewatering equipment as the sludge content is too low. The solids content of sludge has to

be brought to a higher level, in other words, the sludge has to be thickened prior to dewatering

to obtain maximum efficiency form the dewatering equipments.

Various mechanical thickening devices have started to be frequently utilized in treatment plants

in the last years, including pre-dewatering belts. The pre-dewatering belts can either be used as

a compact unit together with the beltpress, or be used separately as an independent unit.

Advantages;

No separate building

construction is required.

When utilized as a compact

unit with the beltfilterpress,

it does not take up any extra

land, it only causes an

increase in height.

Even in cases where it is

used as a separate unit, it

requires less land than a

DAF thickener or a gravity

thickener of the same capacity.

The initial investment costs are low.

It requires lower polymer and energy consumption compared to other mechanical

thickeners.

The selection of the most suitable pre-dewatering belts is based on the properties of the sludge

to be thickened and the capacity.

The pillow blocks used in the pre-dewatering belt allow effective contact between the sludge

and the belt surface, and thus maximize the efficiency of the equipment. The number of and thespace between the pillow blocks are determined based on the process.

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Comparison of Capacity of Mechanical Thickeners

models Hydraulic capacity (for sludge with a solid content of %0.4-0.8)m3

/h

PDWB-

L

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105

10 X X X X

15 X X X X X

20 X X X X X X X

25 X X X X X X X

Belt width m 2

width m 2.32

Length m 4.5

Height m 1.3

Filtration length m 3.6

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Motor power kW 0.75

Belt speed m/min 3.7-10.9

Washing water requirement m3/h 7

Air requirement lt/min 50

Belt tension Mechanical

Belt aligment Pneumatic

Sludge scraping Mechanical

Belt protection With proximity limit sensor

Washing nozzles Manually cleaned

COST ANALYSES

UNIT UNIT COST COST

Construction 800,000 $



Mixers 4 50,000$ 200,000$

Diffusers (9) 200 200$ 40,000$


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pumps2 3,500$ 7,000$

PE ring pump 1 5,000$ 5,000$


Centrifuges 2 1,000,000$ 2,000,000$


Mechanical Sludge

Thickener1 1,000,000$ 1,000,000$

TOTAL COST

4,700,000$

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ANAEROBIC DIGESTIONANAEROBIC DIGESTION

Anaerobic digestion is among the oldest process used for the stabilization of solids and

biosoldis.In the anaerobic digesters another group of bacteria begin to digest and dissolve the

solids to their basic components. This process uses bacteria which do not need atmospheric

oxygen to survive, so therefore, no air is bubbled into the tanks. In fact, air mixed with the

gasses may be explosive, so we strive to keep all air out. The anaerobic digesters produce a

stable sludge which is readily dewatered. The process is also a source of methane gas, which is

used as a fuel source for heating the digesters, heating several buildings, and fueling the engine

generator to produce electricity. The digester is kept at an optimum temperature of between 90-

95 degrees F. About 40,000 cubic feet of methane gas is produced per day. [10]

[11]

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Flow Diagram of a Basic Anaerobic Digester

DESIGN CRITERIA FOR ANAEROBIC DIGESTIONDESIGN CRITERIA FOR ANAEROBIC DIGESTION

PARAMETER UNITS VALUE

Solids Loading Rate kgVSS/m3.d 1,6 4,8

Solids Retention Time days 15 20

VS destroyed m3/kg 0.75-1.12

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DESIGN OF ANAEROBIC DIGESTERDESIGN OF ANAEROBIC DIGESTER

The purpose of this project was to design and build an anaerobic digester to meet the following

criteria.

The design should

Attempt to maximize the amount of biogas produced per unit time,

Be simple and easy to understand so that the average person is able to grasp the function

and theory behind each component of the design with only a small amount of guidance.

The idea here is to encourage people looking at the design to think and understand the

requirements for controlled anaerobic digestion and the continuous flow model.

Be a durable, compact, versatile design which is capable of being shifted around if

necessary to be displayed.

Be operated with a minimum of monitoring, regulating, and adjusting (in other words,

be easy to operate).

Attempt to reduce time and money costs associated with maintenance

Attempt to minimize the cost of setting up and running the digester without

compromising the performance of operation or the other specifications of the brief

PROCESS CALCULATIONPROCESS CALCULATION

Observed Yield for BOD Removal

51

5

,

/24.0)25)(06.0(1

/60.0

1kgBODkgTVSS

dd

kgBODkgTVSS

k

YY

CBODd

BOD

obs =+=

+=

Observed Yield for Nitrogen Removal

NkgNHkgTVSSdd

kgBODkgTVSS

k

YY

CNd

Nnobs =+

=+

= + 4/088.0)25)(05.0(1/20.0

1 15

,

,

Soluble BOD in the Effluent

Total Soluble

BOD in the =Total BOD in the effluent BOD exerted by TSS in the effluent

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effluent(S)

BOD exerted

by TSS in = 30 mg/l x (0.65 biodeg.solids/kg TSS) x 1.42 BODL/solid

the effluent x 0.68 kg BOD5/kg BODL

= 18.83 mg/l

S = 20 18.85

= 1.17 mg/l

Biological Solids increase due to BOD5 Removal

TSS increase = dkgSSQY effOobs /7172)17,1300(000,10024.0)( ==

Biological Solids increase due to Nitrogen Removal

TSS increase = dkgSSQY effOobs /140)117(000,100088.0)( ==

Total TSS increase

Ratio of TVSS/TSS is assumed as 0.8

Total TVSS increase = dkgdkgdkg /7312/140/7172 =+

Total TSS increase = dkgkgTSSkgTVSS

dkg/9140

/8.0

/7312=

TSS loss in the effluent = 30 mg/l x 110,000 m3/day = 3000 kg/d

TSS in the WAS = 9140-3000 = 6140 kg/d

Volume of WAS

TSS increase = 3/5/8.0

/4000 mkgkgTSSkgTVSS

LmgTVSS =

Volume of WAS = daymmkgdkg /1228/5//6140 33 =

Total BOD in the WAS

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BOD exerted by TSS=

dkgkgBODkgBOD

solidskgbiokgBODkgTSSsolidkgbiodkg

L /7.3853/68.0

.deg/42.1/.deg65.0/6140

5

5

=

Soluble BOD5 = 1.17g/m3x 1228 m3/day /1000 = 1.44 kg/day

Total BOD5 = 3853.7 kg/day + 1.44 kg/day = 3855.14 kg/day

Return Sludge

10,000 g/m3 x (QR m3/day) = 5000 g/m3 x [(Q+QR) m

3/day]

10,000 g/m3 x (QR m3/day) = 5000 g/m3 x [(99,676+QR) m

3/day]

QR = 99,676 m

3

/day

WASN (Total Nitrogen in WAS)

Org.N = 0.122 kg Org.N/kg TSS x 6140 kg TSS/day x 0.8 kg TVSS/TSS = 599.3 kg/d

NH4+-N = 1 g NH4+-N/m3 x 1228 m3/d x (kg/1000 g) = 1.23 kg/d

NO3N = 8 g NO3

N/m3 x 1228 m3/d x (kg/1000g) = 9.8 kg/d

Total N = 610 kg/day

NDN = TN in the influent to the biological system TN lost in the effluent

TN in WAS

= 24.57 x 99,676/1000 897kg/day -610 kg/day

= 942 kg/day

WASP (Total Phosphorus in WAS)

WASP = 99,676 x (5-2)/1000 = 299.028 kg/day

% TP in SS = 299.028 / 6140 = 4.87 %

% TP in VSS = 299.028 / (6140 x 0.8) = 6.08 %

PO4P Release = ( 6.08-2.3) x (6140 x 0.8) = 185,7 kg/d P

ALUM ADDITION

TSS caused by Al3+ precipitation as AlPO4

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TSS increase = (molar wt. of Al / molar wt. of P ) x (amount of PO43P precipitated or

released )

=27

185.7 / 209 /

31

x kg d kg d=

TSS caused by precipitation as Al(OH)3

TSS increase = (molar wt. of Al(OH)3 / molar wt. of P ) x (amount of PO43P precipitated or

released ) in primary sludge

=78

185.7 / (2.5 1) 701 /31

x kg d kg d =

TSS increase = 910 kg/d

Total TSS increase = 6140 kg/d + 910 kg/d = 7050 kg/d

Total amount of Al3+ applied = (amount of PO43P precipitated / molar wt. of P ) x applied

AL3+/P molar ratio x molar wt. of Al

=185.7

2.5 27 404.3 /31

x x kg d= kgAL3+/day

Volumeof liquid alum solution =

Total amount of Al3+ applied x molar wt. of Al2(SO4)

2 x molar wt. of Al x 0.25 x 1300 kg/m3

=3

3

404.3kg/d x 3427.88 /

2 x 27 x 0.25 x 1300 kg/mm d=

Total volume of WAS = 1220.12 + 7.88 = 1228 m3/day

Characteristics of combined and blended sludge

Total TSS increase = 7050 kg/d + 15,000 kg/day = 22,050 kg/day

Total Volume of combined sludge = 324 m3/day + 1228 m3/day = 1552 m3/day

BOD5 in combined sludge = BOD5 in WAS + BOD5 in primary sludge

= 9600 kg/day + 3855,14 kg/day = 13,553 kg/day

Thickener Area =2

2

22050 kg/d470

46,9 kg/d/mm=

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Volume of dilution water =3

3

29.8 470 1552 3054 /

.

mm d

d m =

At 30 mg/L

TSS with dilution water = 3054 30 91.62 /1000

kg d =

LIME ADDITION

TSS caused by Ca2+ precipitation as Ca3(PO4)2

TSS increase = (molar wt. of Ca / molar wt. of P ) x (amount of PO43P precipitated or

released )

= 3/88.717.1853112 mkgx =

TSS caused by precipitation as Ca(OH)2

TSS increase = (molar wt. of Ca(OH)2 / molar wt. of P ) x (amount of PO43P precipitated or

released ) in primary sludge

= 3/3.413)15.2(7.18531

46mkgxx =

TSS increase = 485.2 kg/d

Total TSS increase = 6140 kg/d + 485.2 kg/d = 6,625 kg/d

Total amount of Cal2+ applied = (amount of PO43P precipitated / molar wt. of P ) x applied

Ca2+/P molar ratio x molar wt. of Ca

= 7.179125.231

7.185=xx kgCa2+/day

Specific gravity of Ca(OH)2=481 kg/m3

Volumeof hydrated lime = 3243

2

kg/m2509x0.25xCaofmolar wt.x2

)(POCaofmolar wt.xappliedCaofamounttotal +

= daym /86.2kg/m481x0.25x12x2

46kg/d179.7 33

=

Total volume of WAS = 1225.14 + 2.86 = 1228 m3/day

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THICKENER

*1 truck capacity = 10 m3

Thickener effluent = ( )22050 91.62 0.85 18820.4 /kg d+ =

Volume = 318820.4 /

304.5 /0.06 1030

kg dm d=

BOD5 = 11478 kg/d

VSS = 18820.4 / 0.72 13551 /kg d kg d =

VSS / SS = 0.72 [15]

13551 0.52 7046.5 /stabilized

VSS kg d = =

VSSdestruction = 52 % [15]

13551 7046.5 6504.5 /remaining

VSS kg d = =

18820.4 7046.5 11774 /remaining

SS kg d = =

Kg/d 18820.4

% TS 6

m3/d 304.5

Number of truck* 30

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ANAEROBIC DIGESTIONANAEROBIC DIGESTION

SUPERNATANTSUPERNATANT

304.5 m3/d

EFFLUENTEFFLUENT

11774 kg/d = Wsludge + Wsupernatant

sup tan3304.5 /0.05 1030 0.004 1000

sludge erna tW W

m d= +

Wsludge = 11774 kg/d - Wsupernatant

sup sup311774

304.5 /

0.05 1030 0.004 1000

W Wm d

= +

62727 = 47096 4 Wsup + 51.5 Wsup

Wsupernatant = 329 kg / d

3

sup tan

32982.25 /

0.004 1000erna t m d = =

Wsludge = 11774 kg/d - 329 kg/d

Wsludge = 11445 kg/d

m3/d 82.25

% TS 0.4

m3/d 329

(kg/m3) 1000

BOD5 3000

Org N 0.34

NH4N 0.05

m3/d 11445

% TS 5

m3/d 222.2

(kg/m3) 1030

BOD5 4344.45

Org N 848.3

NH4N 127.25

Truck 22

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311445 222.2 /0.05 1030sludge

m d = =

Total Mass of Other Components in Digested Sludge:Total Mass of Other Components in Digested Sludge:

BOD5 = ( )3

3

311478 / 1 0.6 3000 82.25 10 4344.45 /

g mkg d kg d

m d

=

BOD5 stabilized = 60 % [15]

Org N in the effluent of thickener = 18820.4 / 0.122 0.8 1837 /kg d kg d =

Org N = ( )11445 222.2

(1837) 1 0.1 0.15 (1837) 0.1 848.3 /

11774 304.5

kg d + =

Conversion of Org N into NH4-N = 15 % [15]

NH4-N =848.3 / 0.15 127.25 /kg d kg d =

Conversion of Org N into soluble org N = 10 % [15]

Conversion of non-precipitated phosphorus (NPP) into soluble P = 30 %

PP capture = 100 %

BOD5 in supernatant = 3000 mg/L

Org N sup = ( )329 82.25

(8.94) 1 0.1 0.15 (8.94) 0.1 0.34 /11774 304.5

kg d + =

NPP in the effluent of thickener = 91.62 / 0.122 0.8 185.7 /kg d kg d =

NPP = 185.7 kg /d

CentrifugeWsludge = 11445 kg/d

Centrifuge = % 30

3

3

sup

11445 /37 /

0.3 1030

up tan 222.2 37 185.2 /

11445 0.15 1716.7 /

11445 1716.7 9728.3 /sludge

kg dDewateredsludge m d

S erna t m d

W kg d

W kg d

= =

= == =

= =

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Kg/d (sludge) 9728.3

% TS 30

m3/d 3

Number of truck 4

Anaerobic Digestion Capacity & Dimensions:Anaerobic Digestion Capacity & Dimensions:

There are 4 methods to calculate digester capacity. According to below results suitable volume

will be chosen at worst conditions.

1) Qavg = 304.5 m3/d

Digestion period = 15 days

3

3304.5 15 4567.5m

Digester days md

= =

2) High rate digerter = 2.5 kg / m3.day

TVSS = 18820.4 / 0.72 13551 /kg d kg d =

3

3

13551 /5345

2.5 / .

kg dDigester m

kg m day = =

3) Volume per capita

Assume =

30.03m

capita [15]

Population served = 250000

3

30.03 250000 7500m

Digester mcapita

= =

4) Volume reduction method

( )2

3in in out t Q Q Q D =

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DT= Digestion period (d)

Qin = Sludge amount (m3/d) = 304.5 m3/d

Qout = Effluent sludge amount (m3/d) = 222.2 m3/d

( )32304 304 222.2 15 3744.5

3Digester m

= =

Chosen volume = 7500 m3

Provide a 1 m depth for grit accumulation in the bottom cone.

Provide 0.6 m depth for scum blanket.

Provide 0.6 m between the floating cover and max. digester level.

Total inactive cone depth = 1 m

Total inactive upper depth = 1.2 m

Active side water depth = 20 m

Number of digester = 2

37500 37502

EachDigester m = =

23750 187.520

EachDigesterArea m= =

Diameter of each digester =2

187.5 15.44

DD m

= =

15.4 0.4 = 15 m3

2

375021.2

154

mVerticalsidedepth m

= =

1.2 m

20 m

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2.5 m1 m

3.16 m1 m

3 m

1.5m

7.5 m

( )2

22 320 15 1 115 2.5 3 2 1 3672.24 3 4 3 4

ActiveDigester m = + =

33672.2 2 7344.4TotalActive m = =

( )2

2 31.2 15 1 3 2 1 221.44 3 4

TotalInactive m = + =

37344.4 221.4 7565.8Total m = + =

7344.40.97

7565.8Active ratio = = > 0.8 IT IS IN THE RANGE! [15]

7344.424

304.5DigestionPeriodatAverageFlow d= =

7344.4 15.1487.2

DigestionPeriodatExtremeHighFlow d= =

7344.438.6

190.3DigestionPeriodatLowFlow d= =

3

3

18820.4 /2.56 / .

7344.4

kg dSolidsLoading kg m d

m= = [it is in the range] [13]

Gas ProductionGas Production

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There are 4 different methods to calculate the amount of gas production. The less value of gas

production will be chosen.

1) BOD5 in thickened sludge = 11478 kg/d

11478 /16879 /

0.680.05 0.8 16879

392.5 /1 1 0.03 24

L

Ox

c

kg dBOD insludge kg d

Y E SP kg d

kd

= =

= = =

+ +

Y = 0.04 0.1 mg VSS /mgBOD utilized

( )3

30.35 0.8 16879 1.42 392.5 4531 /m

ofmethane m d kg

= =

If methane volume is % 66 of digester gas:

31

4531 6865 /0.66

Digestergasproduction m d= =

2) Gas production based on total volatile solids

30.50m

GasproductionratekgTVSS

=

30.5 18820.4 0.71 6681.2 /Gasproduction m d = =

3) Gas production based on TVS reduction

30.9m

GasproductionkgTVSreduced

= [13]

3

30.9 7046.5 6341.8 /m

Gasproduction m d kgTVSreduced

= =

4) Gas production based on TVS reduction

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30.032m

Gasproductionratepopulationbasedcapita

=

30.032 250000 8000 /Gasproduction m d = =

Gas production volume = 6341.8 m3/d

Digester Heating Requirements

( )2 1R pH flow C T T=

Cp = Specific heat of sludge = 4200 J / kgoC

T2 = Digestion Temp = 35 oC

T1 = Sludge Temp = 12 oC

( ) 1018820.4

4200 35 12 5.19 10 /0.035R

H J day= =

Heat Losses from digesters

( )2 1LH U A T T=

U = Heat transfer coefficent

A = Area in which heat losses occurs

T2 = Digestion Operating Temp = 35 oC

T1 = Outside Temp

Roof Area:

2

SlantlengthRoofArea D=

2 2

2

7.5 0.6 7.52

15 7.52177.2

2

Slantlength m

RoofArea m

=

= =

U = 0.90 J/sm2 oC

Heat losses from the cover & roofing

( ) 80.90 177.2 35 0 86400 4.8 10 /LH J d= =

Area of Side Walls:

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Assume 50 % below ground

exp

2

osedheightSidewallareaaboveground D=

215 21.2 4992

Area m = =

U = 0.68 J/sm2 oC

Heat losses from the side wall above the ground

( ) 90.68 499 35 0 86400 1.03 10 /LH J d= =

Heat losses from the side wall below the ground

U = 0.80 J/sm2 oC

( ) 90.80 499 35 0 86400 1.2 10 /LH J d= =

Roof Area:

2 2 2115 7.5 2.5 186.32

BottomArea m= + =

U = 0.62 J/sm2 oC

Heat losses from the bottom cone

( ) 80.62 186.3 35 5 86400 2.89 10 /LH J d= =

( ) 8 82.89 4.8 10.3 12 10 30 10 /LTotalH J d = + + + =

% 20 minor losses

% 25 emergency conditions

8 10 630 10 2 1.45 6.06 10 / 2.56 10 /L

H J d kJ hr= = =

Selection of Heating UnitsSelection of Heating Units

External heat exchanger

Provide 2 units each rated 2.3 x 106 kJ/hr with natural gas

Digester gas for heating purposes, %65 of heating value of natural gas

Each unit will be derated = 6 62.3 10 0.65 1.49 10 /kJ hr =

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Total heat provided by 2 uints = 6 61.49 10 / 2 3 10 /kJ hr kJ hr =

Extra available % =6 6

6

3 10 / 2.5 10 /%17

3 10 /

kJ hr kJ hr

kJ hr

= =

Digester gas requirement

% 75 efficiency of heating units

63 3

2

3 10 /164.6 / 3950.4 /

0.75 24300 /

kJ hr Digestergasneeded m hr m d

kJ m

= = =

Produced gas = 6341.8 m3/d

6341.8 m3/d > 3950.4 m3/d

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UNIT UNIT COST COST

Construction 800,000 $



Mixers 4 50,000$ 200,000$

Diffusers (9) 340 200$ 68,000$




pumps2 3,500$ 7,000$

PE ring pump 1 5,000$ 5,000$


Centrifuges 2 1,000,000$ 2,000,000$


Mechanical Sludge

Thickener1 1,000,000$ 1,000,000$

Primary Sedimentation 1 50,000$ 50,000$

Digester Tank 1 5,000,000$ 5,000,000$

Heat Exchanger 1 10,000$ 10,000$Circulation Pump 1 10,000$ 10,000$

Compressor 1 50,000$ 50,000$

TOTAL COST

10,000,000$

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