Design Calculation Sewage Pit

EA for the Proposed STP

Dindigul Municipality Pure Enviro 108

ANNEXURE III

DESIGN CALCULATION

Present Sewage Flow : 13.65 MLD

= 569 m3/hr

Peak Factor : 2.25

Peak Flow : 30.71 MLD

= 1279.58 m3/hr

Design Characteristics:

BOD : 170 – 370 mg/l

Total Suspended Solids : 250 mg/l

Fecal Coliform : 5 x107 MPN/100ml

Total Sewage Characteristics:

pH : 5.5 – 9.0

BOD : ≤ 20 mg/l

COD : ≤ 250 mg/l

Oil & Grease : ≤ 5 mg/l

Total Suspended Solids : ≤ 30 mg/l

Nitrate Nitrogen (as NO3) : ≤ 5 mg/l

Ammonia Nitrogen (as N) : ≤ 50 mg/l

Total Phosphorous (as PO4) : ≤ 5 mg/l

Total Coliform : ≤ 1000 no/100 ml



Receiving Chamber – 1 No

Average Flow : 13.65 MLD

Design Flow (Considering Peak factor) : 30.71 = 1279.58 m3/hr

Detention Time : 120 sec

Volume Required : (1279.58 / (60 x 60)) x 120

= 42.65 m3

Provide receiving chamber of size : 6.0 m x 3.0 m x 2.5 m (SWD) + 0.5 (FB)

Provide Volume : 45 m3 > 42.65 m

3, OK

2. Coarse Screens – 2 Nos (1 Mechanical + 1 Manual) 1 Working + 1 Standby:

Design Flow : 30.71 MLD

= 1279.58 m3/hr

= 0.36 m3/sec

Design Velocity at peak flow : 0.6 m/sec

Clear Opening between bars : 25 mm

Size of Bars : 75 mm x 10 mm

Screen area required : 0.36 / 0.6 = 0.6 m2

Width of Channel provided : 1.0 m

Velocity through screens at peak flow : 1.2 m/sec

Clear Area : 0.6 / (1.2 x Sin 600) = 0.58 m2

Clear Opening between bars : 25 mm, 0.025m

No. of clear openings : 24

Dimension of bar : 75 mm x 10 mm

Width of channel : (24 x 25) + (25 x 10)

= 850 mm, 0.85m

Width Provided : 1000 mm



Provide a screen channel of size 1 m wide x 0.7 m (SWD) + 0.5 m (FB)

Check for Approach Velocity at Average Flow

Average Flow : 13.65 MLD = 0.158 m3/sec

Channel Area : 1 m wide x 0.7 m SWD = 0.7 m2

Velocity : 0.158 / 0.7 = 0.23 m/sec < 0.3 m/sec, ok.

3. Fine Screens – 2 Nos (1 Mechanical + 1 Manual) 1 working + 1 standby


= 0.36 m3/sec

Design Velocity at ultimate flow : 0.6 m/sec

Area required at Ultimate flow : 0.36 / 0.6

= 0.6 m2

SWD provided : 0.7 m

Width of channel : 1.0 m

Velocity through screen : 1.2 m/sec

Clear Area : 0.36 / 1.2

= 0.3 m2

Angle of inclination : 400

Net inclined screen area required : 0.3 / (1.2 x Sin 400)

= 0.39 m2

SWD provided : 0.8 m

Net Clear width of channel : 0.39 m

Clear opening between bars : 6mm = 0.006 m

No. of clear openings : 0.39 / 0.006

= 65

No. of bars : = 66

Dimensions of bar : 75 mm x 10 mm



Width of channel : (65 x 6 + 66 x 10) / 1000

= 1m

Width provided : 1000mm

Provide a screen channel size 1m wide x 0.8m SWD + 0.5m free board

Check for Approach Velocity at Average Flow

Average Flow : 13.65 MLD

= 0.158 m3/sec

Channel Area : 1m wide x 0.8m SWD

: 0.8 m2

Velocity : 0.158/0.8

: 0.20 m/sec < 0.3m/sec

• Degritting tank 2 nos ( 1w + 1 s ):


Surface loading rate : 960 m3/m2/d

Surface area : 30.71 x 1000/960

: 31.99 m2

Dimensions of the Tank : 5.4m X 5.7 m

Detention time : 60 sec

Volume required : (30.71 x 1000/24 x 3600) x 60

: 21.33 m3

Liquid depth required : 21.33 / 31.99

Hence provide a Degritting tank with mechanism to fit in RCC chamber of size

5.7 m x 5.7 m x 0.66m (SWD) + 0.5 m free board

5 Primary Clarifier ----- 1 no

Design flow : 13.65 MLD

Overflow Rate : 25 m3/m2/day

Clarifier area required : 13650/25

: 546 m2

Dia required : 26.4 m



Provided diameter : 27.0m

Clarifier Area provided : 572.3 m2

Retention time : 3 hrs

Volume required : 13650/24 x 3

: 1706.25 cum

SWD required : 1706.25/546 = 3.12, say 3 m

Provide secondary clarifier of 27m dia x 3m SWD + 0.5m free board

Check for overflow rate

Surface area : 546 m2

Overflow Rate : 13650/546

: 25 m3/.2m/day , OK

Check for Weir loading : 13650

-------------------------

3.1412 x 25

: 173.8 m3/day/m, <300

6 Aeration Tank...1 No

Design flow for each tank : 13.65 MLD = 569 m3/hr

: 0.158 m3/hr

Type of Aeration : Diffused Aeration System

Inlet BOD to Aeration Tank : 0.8 x 300

(20% BOD removal in Degritting tank is assumed associated with grit)

: 240 mg/l

Outlet BOD : 20 mg/l

Total BOD load removed : (240-20) x 13650

----------------------

1000

: 3003 kg/day



MLSS : 2800 mg/l

F/M Ratio : 0.4

Volume of the tank required : 13650 x220

--------------

2800 x 0.4

: 2681.25 m3

Size of the tank provided : 30m x 20m x 4.5m SWD + 0.5m FB

Volume provided : 2700 m3

Check for HRT : 2700/569

4.75 hrs, between 4 – 6 hrs,

• Air Blower -- 3 Nos(2w+1s)

Oxygen Requirement : 0.9 kg / kg BOD destroyed

BOD destroyed : 3003 kg/d

Oxygen required : 0.9 x 3003

: 2702.7 kg/d

Air required : 2702.7

-------------------------------------------

1.21 x 0.232 x 24 x 0.7 x 1 x (0.0625 x 4.5)

: 2037.62 m3/hr

OR

Air volume for mixing : 10 cum/min per 1000 cum of tank volume

Air requirement/compartment : 10/1000 x 2702.7

: 27.03 m3/min

: 1621.8 m3/hr

Capacity of each blower : Higher of (1) & (2),

i.e.,2037.62,say(2040/2)

: 1020 m3/hr

Provide 3 Nos (2+1) blower, each of capacity 1020 m3/hr at 0.6 kg/cm2



• Secondary Clarifier ----- 1 no

Design flow : 13.65 MLD

Overflow Rate : 25 m3/m2/day

Clarifier area required : 13650/25

: 546 m2

Dia required : 26.4 m

Provided diameter : 27.0m

Clarifier Area provided : 572.3 m2


Volume required : 13650/24 x 3

: 1706.25 cum

SWD required : 1706.25/546

: 3.12,say 3 m

Provide secondary clarifier of 27m dia x 3m SWD + 0.5m free board

Check for overflow rate

Surface area : 546 m2

Overflow Rate : 13650/546

: 25 m3/2m/day, OK

Check for Weir loading : 13650

-------------------------

3.1412 x 25

: 173.8 m3/day/m, <300

• Chlorine contact tank ---- 1 No

Flow : 13.65 MLD

Retention time : 30 min

Volume : (13650 x 30) / (24x60)

: 284.38 m3



Provide Chlorine contact tank of 12 m x 8 m x 3.0 m SWD + 0.5m free board

Provide Volume : 288 m3

Baffles shall be provided along length of the tank for better mixing

SLUDGE HANDLING SYSTEM:

A. Return Activated Sludge:

Total flow including recirculation : 1.5 x 13650 = 20475 m3/day

MLSS in Aeration Tank : 2800 mg/l

Solids in recirculated flow : ((2800/1000) x 20475)

: 57330 m3/day

Consistency of solids : 1%

Return Activated Sludge Quantity : 57330/10

: 5733 m3/day

: 238.88, say 240 m3/hr

B. Excess Secondary Sludge from Secondary Clarifier:

Quantity of waste activated sludge,Q w : V X / Oc Xs

MLSS concentration in Aeration Tank X : 2800 mg/L

MLSS concentration in waste activated sludge from secondary clarifier: 10000 mg/l

Sludge Retention Time, Qc : 6 day

Total Aeration Tank Volume V : 2700 m3

Qw : 2700 x 2800

---------------------

6 x 10000

: 126 m3/day

1 Sludge sump ---- 1 No

Total sludge to sludge sump : 126 m3/day

Size of the sump provided : 7m x 7m x 2.5 m SWD + 0.5 FB



Volume of the sump provided: 122.5 m3

b) Air Blowers for sludge Mixing ------ 2 nos (1w+1s)

Air volume for mixing : 10 m3/min per 1000 m3 of tank volume

Air requirment/compartment : (10 / 1000) x 122.5

: 1.225 cum/min

: 73.5 cum/hr

Provide 2 nos.(1+1) blower,each of capacity 73.5 m3/hr at 0.4 kg/cm2

• Thickener Feed Pumps ---- 2 nos (1w + 1s)

Type : Horizontal, Centrifugal

Capacity : 60 cu.m/hr

Head : 10m

4. Return Activated Sludge Pumps --- 2 nos(1w + 1s)

Type : Submersible, Non-clog impeller

Capacity : 15.0 cu.m/hr

Head : 10m

5 Sludge Thickener --- 1 no

Quantity of sludge : 126 m3/day

Solids concentration in : 1%

Total Solids : 10000/1000 x 126

Total solids in underflow : 1260 kg/day

Quantity of thickened sludge : 0.95 x 1260/36

: 33.25 cum/day

Thickener Overflow : 126 – 33.25

= 92.75 m3/ day

Solids Loading Rate : 50 kg/m2/day

Thickening Area required : 1260/50

: 25.2 m2

Thickener dia required : 5.67m

Thickener dia provided : 5.7m

Thickener dimension : 5.7m dia x 3m SWD + 0.5 m free board

• Centrifuge Feed Sump --- 1 No

Thickened sludge consistency : 3.6%



Quantity of thickened sludge : 33.25 m3/day


Volume of the sump required : 13.85 m3

Sump provided : 3.5m x 2m x 2.0m SWD + 0.5m free

board

7 Centrifuge Feed Pump --- 2 Nos (1w + 1s)

Type : Progressive cavity screw

Capacity : 10 m3/hr

Head : 15 mwc

• Centrifuge --- 2 Nos (1w+1s)

Type : Solid bowl type,co-current

Capacity : 10 m3/hr

Inlet consistency : 3.6%

Outlet consistency : 20%

• Supernatant Collection Sump - 1 No

Sludge flow to centrifuge : 33.25 cum/day

Solids in the centrifuge feed : 1260 kg/day

Solids in the under flow of centrifuge: 1197 kg/day

Centrifuge sludge underflow : 5.43 cum/day

Centrate floe from centrifuge : 33.25 – 5.43

: 27.82 m3/day

Total supernatant from thickener&centrifuge: 92.75 + 27.82

: 120.57 m3/day

Provide Supernatant collection sump of size 3.5 m x 3.5 m x 3m SWD + 0.5m free

board

b)Supernatant transfer pumps ----- 2 nos(1w+1s)

Type : Submersible, Non clog impeller

Capacity : 10 m3/hr

Head : 10m

Chemical Handling System

Polelectrolyte

Dosing Tank------ 2 Nos(1w+1s)

Polyelectrolyte at centrifuge : 1.5kg/ton of dry solids at centrifuge

Dry Solids at the centrifuge inlet : 1260 kg/d

: 1.26 ton/d

Polelectrolyte required : 1.26 x 1.5 = 1.89 kg/d

Solution Strength : 0.1%



Volume : 1.89 / (0.1 x 10-2

) = 1890 lit/day

provide 2 nos(1+1) HDPE tank, each of 2000 lit

Dosing pumps ----- 2 nos(1w+1s)

Type : Diaphram type

Capacity : 90 LPH

head : 40 MWC

Chlorinator------ 2 Nos (1w+1s)

Chlorine Dose : 10 mg/L as 100% Cl2

Chlorine Requirment : 10/1000 x 13650

: 136.5 kg/day

Chlorinator capacity provided : 6 kg/hr

Booster water pump----- 2 nos(1w+1s)

Type : Centrifugal, Horizontal

Capacity : 10 cum/hr

Head : 30 mwc

Quantity of chlorine provided : 6 x 24 kg/d

Chlorine concentration desired in the outlet : 1500 mg/l

: 1.5 kg/cum

Quantity of water required : 144 /1.5 = 96 cum/day

: 4 cum/hr = say 5 cum/hr

MISCELLANEOUS UNITS:

• Centrifuge Shed – 1 No Size of the room – 9 m x 6 m

• Chlorination and Toner Room – 1 No Size of the room – 6.0 m x 5.0 m x 3.6 m (TH)

� Administration and Laboratory building – 1 No

Size of the room – 10.0 m x 6.0 m x 3.6 m (TH)

� Motor Control Center (MCC) Room – 1 No

Size of the room – 6.0 m x 4.0 m x 3.6 m (TH)

EA

for

the P

ropose

d S

TP

Dindigu

l Mun

icipality

Pure Enviro

119

ANNEXURE IV

Documents

Design Calculation Sewage Pit