ACEE 434ACEE 434ACEE 434ACEE 434Environmental Systems DesignEnvironmental Systems Design

Week 6October 7 2009

ACEE 434 Fall 2009 HDP 1

October 7, 2009

Flow EqualizationFlow Equalization

2ACEE 214 Fall 2009 HDP

IntroductionIntroductionIntroductionIntroduction

• Objective: give a relatively constant flowrate to the downstream operations and processes

• Functions:- Dampen the daily variation in flowrate and loadings- Reduce the required size of the downstream treatment facilitiesq- feasible dry weather flows in separate sewer system and sometimes for storm

water flows

• Type: in-line or side-line facilities

• Effects:- 10-20% of BOD entering is stabilized in the equalization basin- 23-47% of SS is further removed in the primary clarifier- reduce shock load on biological process

ACEE 434 Fall 2009 HDP 3

LocationLocationLocationLocation

In-line equalization basin

Side-line equalization basin

ACEE 434 Fall 2009 HDP 4

Reynolds and Richards Figure 7-17Equalization basins

DesignDesignDesignDesign

Average hourly flow rate

Reynolds and Richards Figure 7-19Fluctuating volume determined by hydrograph

Reynolds and Richards

ACEE 434 Fall 2009 HDP 5

Design ExampleDesign ExampleDesign ExampleDesign Example• Determine the fluctuating volume required volume for an in-line flow• Determine the fluctuating volume required volume for an in-line flow equalization basin.

ACEE 434 Fall 2009 HDP 6

Average hourly flow rate = 6687 liters/min Reynolds and Richards Design Example 7-5

Design ExampleDesign ExampleDesign ExampleDesign Example10000

Time Flow Delta

0 6590 97Required volume =

8000

9000

0 6590 -97

1 6170 -517

2 5260 -1427

3 4470 -2217

4 3940 -2747

5 3440 -3247

q1,140,540 liters

6000

7000

(lpm)

Average flow =6687 lpm

6 3440 -3247

7 3480 -3207

8 5790 -897

9 7870 1183

10 8590 1903

11 8820 2133

4000

5000

Flow

 rate ( 88 0 33

12 8820 2133

13 8820 2133

14 8670 1983

15 8400 1713

16 8400 1713

17 8140 1453

2000

300017 8140 1453

18 7610 923

19 7340 653

20 7340 653

21 7120 433

22 6170 -517

0

1000

1 2 3 4 5 6 7 8 9 101112131415161718192021222324

23 5900 -787

24 6590 -97

6687.2 1140540

Average flow Fluctuating volume

ACEE 434 Fall 2009 HDP 7

Time (hour)Average flow Fluctuating volume

Primary SedimentationPrimary Sedimentation

8ACEE 214 Fall 2009 HDP

IntroductionIntroductionIntroductionIntroduction

• Objective: remove readily settable solids and floating materials and thus reduce the suspended solids content.

• Removal rate: 50-70% of suspended solids and 25-40% of BOD

• Numbers of tank: generally more than twog y

• Type: rectangular or circular tanks

ACEE 434 Fall 2009 HDP 9

Rectangular TankRectangular TankRectangular TankRectangular Tank

Chain-and-flight sludge collector Traveling bridge sludge collector

http://www.incineratorsystem.com/chain_and_flight_type_sludge.htm

ACEE 434 Fall 2009 HDP 10

http://www.hitachi-pt.com/products/es/purification.html

Rectangular TankRectangular TankRectangular TankRectangular Tank

MetCalf and Eddy Figure 5-40Typical rectangular primary sedimentation tank (a) plan and (b) section

ACEE 434 Fall 2009 HDP 11

section

Circular TankCircular TankCircular TankCircular Tank

http://www.cityoffortwayne.org/images/stories/Primary%20clarifier%20dedication%209-26-08/Primaryclarifierdedication%20006.jpg

ACEE 434 Fall 2009 HDP 12

Circular TankCircular TankCircular TankCircular Tank

Center feed Peripheral feed

ACEE 434 Fall 2009 HDP 13

MetCalf and Eddy Figure 5-41Typical circular primary sedimentation tanks: (a) center feed and (b) peripheral feed.

PerformancePerformancePerformancePerformance

The efficiency of the primary clarifier is reduced by

1. Eddy currents formed by the inertia of incoming fluid2. Wind-induced circulation cells formed in uncovered tanks3. Thermal convection currents4 C ld t i th f ti f d it t th t4. Cold or warm water causing the formation of density currents that move along the bottom of the basin and warm water rising and flowing across the top of the tank5 Thermal stratification in hot arid climates5.Thermal stratification in hot arid climates

ACEE 434 Fall 2009 HDP 14

BOD and TSS RemovalBOD and TSS RemovalBOD and TSS RemovalBOD and TSS RemovaltR =

timedetention nominalt efficiency removal expected R where,

btaR

==

+=

constants empirical b a, =

Typical values for the empirical constants

Item a b

constants

Item a b

BOD 0.018 0.02

TSS 0 0075 0 014TSS 0.0075 0.014

MetCalf and Eddy Figure 5-46Typical BOD and TSS removal in primary sedimentation

ACEE 434 Fall 2009 HDP 15

tanks. (Greeley, 1938)

Short CircuitingShort CircuitingShort CircuitingShort Circuiting

Ideal flow Effect of density flow or thermal stratification

Effect of thermal stratification Formation of wind-driven circulation cell

ACEE 434 Fall 2009 HDP 16

MetCalf and Eddy Figure 5-47Typical flow patterns observed in rectangular sedimentation tanks

Design ConsiderationsDesign ConsiderationsDesign ConsiderationsDesign Considerations1. Detention time

- Coalescence of a suspension of solids becomes more complete as time elapse- Provide 1.5-2.5 hr based on the average rate of wastewater flow

2. Surface loading ratesS t l h t ti f t f t k fl t- Set low enough to ensure satisfactory performance at peak flow rate

3. Weir loading rates4. Scour velocity

To avoid resuspension (scouring) of settled particles horizontal velocities- To avoid resuspension (scouring) of settled particles, horizontal velocities through the tank should be kept sufficiently low

18 ⎤⎡ − )gdk(s

(unitless)scouredbeingmaterialofon typedependshatconstant t(m/s)scour producejust that will velocity horizontal where,

18

==

⎥⎦

⎤⎢⎣

⎡=

kV

f)gdk(s V

H

H

( )i lfdid )m/s (9.81gravity todueon accelerati g

(unitless) particles ofgravity specific s (unitless)scouredbeingmaterialofon typedependshat constant t

2=

==k

ACEE 434 Fall 2009 HDP 17(unitless)factor friction Weisbach -Darcy f

(m)particlesofdiameter d ==

Design DataDesign DataDesign DataDesign Data

Unit Range Typical

Primary sedimentation tanks followed by secondary treatment

Detention time hr 1.5-2.5 2

Overflow rate

Average flow m3/m2∙day 30-50 40

Peak hourly flow m3/m2∙day 80-120 100

Weir loading m3/m∙day 125-500 250

Primary sedimentation tanks with activated sludge returnPrimary sedimentation tanks with activated sludge return

Detention time hr 1.5-2.5 2

Overflow rate

Average flow m3/m2 day 24 32 28Average flow m3/m ∙day 24-32 28

Peak hourly flow m3/m2∙day 48-70 60

Weir loading m3/m∙day 125-500 250

ACEE 434 Fall 2009 HDP 18

MetCalf and Eddy Table 5-20Typical design information for primary sedimentation tanks

Design DataDesign DataDesign DataDesign Data

Unit Range Typical

RectangularRectangular

Depth m 3-4.9 4.3

Length m 15-90 24-40

Width m 3-24 4.9-9.8

Flight speed m/min 0.6 0.9

Circular

Depth m 3-4.9 4.3

Diameter m 3-60 12-45

B tt Sl / 1/16 1/6 1/12Bottom Slope mm/mm 1/16-1/6 1/12

Flight speed r/min 0.02-0.05 0.03

ACEE 434 Fall 2009 HDP 19

MetCalf and Eddy Table 5-21Typical dimensional data for rectangular and circular sedimentation tanks used for primary treatment of wastewater

Design ExampleDesign ExampleDesign ExampleDesign Example

• Conditions:- Average wastewater flowrate = 20,000 m3/d- Peak daily flow = 50,000 m3/dy- Overflow rate 40 m3/m2d at average flow- Side water depth = 4 m

• Design rectangular primary clarifiers with a channel width of 6 m (2 sets).• Estimate BOD and TSS removals at average and peak flow

MetCalf and Eddy Design Example 5-10

ACEE 434 Fall 2009 HDP 20

MetCalf and Eddy Design Example 5 10Design of a primary sedimentation basin

Design ExampleDesign ExampleDesign ExampleDesign Example1 C l l ti f1. Calculating surface area:

223

2

m 500d/mm40/dm 20,000

O/FQ A =

⋅==

Surface area = 250 m2

Q = 20,000 m3/dd/mm40O/F ⋅

2. Determining the tank length:2

4 m

6 m

42 m

Tank volume = 500 m2

,

m 42 m 41.7m 6 2

m500WAL

2

≈=×

==

3 Computing detention time and overflow rate @ average flow:3. Computing detention time and overflow rate @ average flow:3m 2016 m) 6 m 2(42 m 4 eTank volum =××=

/d20 000Q 3

d/mm 39.742m)2(6m

/dm20,000 AQ rate Overflow 23

3

⋅=×

==

hr2 4224hrm2016VolumeTank timeDetention3

Okay

Ok

ACEE 434 Fall 2009 HDP 21

hr2.42day/dm 20,000Q

timeDetention 3 =⋅== Okay

Design ExampleDesign ExampleDesign ExampleDesign Example4 Computing detention time and overflow rate @ peak flow:4. Computing detention time and overflow rate @ peak flow:

d/mm .29942m)2(6m

/dm 50,000 AQ rate Overflow 23

3

⋅=×

== Okay)(

hr 97.0day24hr

/dm 50,000m 2016

QVolumeTank timeDetention 3

3

=⋅== Okay

5. Calculating the scour velocity using the following values:

1 25sgravitySpecific0.05k constant Cohesion

==

m10100μm 100 d particles ofDiameter m/s 9.81 g gravity todueon Accelerati

1.25s gravity Specific

6

2

×==

=

=

−

0.025ffactor friction Weisbach -Darcy =

m/s0.063)10)(1000.25)(9.81(8)(0.05)(1)gd8k(sV1/26

H =⎥⎤

⎢⎡ ×

=⎥⎤

⎢⎡ −

=−

ACEE 434 Fall 2009 HDP 22

m/s0.0630.025f

VH ⎥⎦

⎢⎣

⎥⎦⎢⎣

Design ExampleDesign ExampleDesign ExampleDesign Example6 Computing the peak horizontal flow:6. Computing the peak horizontal flow:

m/s 0.01200s/h)(24h/d)(36

14m)2(6m

/dm 50,000 AQV

3

x

=⎥⎦

⎤⎢⎣

⎡⎥⎦

⎤⎢⎣

⎡×

==)( )()(x ⎦⎣⎦⎣

Horizontal flow < Scour velocity Resuspension would not happen

7. Calculating BOD and TSS removal rates:

36%42)(0.020)(2.0.018

2.42bta

t removal BOD =+

=+

=

58%42)(0.014)(2.0.0075

2.42bta

t removal TSS

42)(0.020)(2.0.018bta

=+

=+

=

++

0 97

@ average flow

%640.97tremovalTSS

26%97)(0.020)(0.0.018

0.97bta

t removal BOD

===

=+

=+

=

@ peak flow

ACEE 434 Fall 2009 HDP 23

%6497)(0.014)(0.0.0075bta

removalTSS =+

=+

=

Design using Settling ExpDesign using Settling ExpDesign using Settling Exp.Design using Settling Exp.

0.61 m

1.22 m

3.05

m

1.22 m

1.83 m

2.44 m

3.05 m

Batch settling column details for type II settling

ACEE 434 Fall 2009 HDP 24

g yp gReynolds and Richards Figure 9-11Batch settling column details for Type II settling

Design using Settling ExpDesign using Settling ExpDesign using Settling Exp.Design using Settling Exp.

for trateoverflowVwhere

tHV

c0

=

=

axis- x theand curve R theofintercept t column theofheight H

for trateoverflow Vwhere,

cc

c0

===

DE1

CD2

T )R-(RHH)R-(RR ++=

HHRC

cCD2

cT

tduring settle wouldsize )R-(R of particles t theheight tha the for t removed solids of fractions theR where,

H

==

H

H

ACEE 434 Fall 2009 HDP 25

Reynolds and Richards Figure 9-12Settling diagram for Type II settling

Design ExampleDesign ExampleDesign ExampleDesign ExampleDesign a primary clarifier satisfying the following conditionsDesign a primary clarifier satisfying the following conditions

1. The design detention time and design surface loading rates if 65% of the suspended solids are to be removedsuspended solids are to be removed

2. The diameter and depth of the tank

Time(min) 0 61m 1 22m 1 83m 2 44m 3 05mTime(min) 0.61m 1.22m 1.83m 2.44m 3.05m0 0 0 0 0 010 28 18 18 12 a20 48 39 25 27 a30 68 50 34 31 a45 70 56 53 41 a60 85 66 59 53 a90 88 82 73 62 a

a Data showed an increase in solids concentration

ACEE 434 Fall 2009 HDP 26

Reynolds and Richards Design Example 9-1Primary clarifier

Design ExampleDesign ExampleDesign ExampleDesign Example

Reynolds and Richards Figure 9-17

ACEE 434 Fall 2009 HDP 27

0.27hr 0.55hr 0.77hr 1.13hr 1.60hrReynolds and Richards Figure 9-17Graph showing suspended solids removal (as a percent) at various depth and settling times.

Design ExampleDesign ExampleDesign ExampleDesign Examplemhr24m3 05H 2

Time Surface loading Fraction removed

t(hr) V0(m3/d∙m2) RT(%)

0.27 275 33.7

0.55 133 48.7

dm/m 275mm

dhr24

hr 0.27m3.05

tHV 22

2c

0 ⋅=⋅⋅==

0.55 133 48.7

0.77 95.3 56.7

1.33 64.8 63.8

1.6 45.6 68.6 33.7% 60)-)(70(0.24/3.05 50)-(0.40)(60 40)-)(50(0.61/3.05

30)-)(40(0.88/3.0520)-)(30(2.04/3.0520 R T

=+++

++=

Reynolds and Richards Table 9-4

65% 65%

Reynolds and Richards Table 9 4Reduced dat for 20, 30, 40, 50, and 60% curves

65% 65%

1.22 hr 58.0

ACEE 434 Fall 2009 HDP 28

Reynolds and Richards Figure 9-18 Reynolds and Richards Figure 9-19

Design ExampleDesign ExampleDesign ExampleDesign Example1 The design detention time and design surface loading rates if 65% of the1. The design detention time and design surface loading rates if 65% of the

suspended solids are to be removed

1.22 x 1.75 = 2.14 hr

Scale-up factor

2. The diameter and depth of the tank

58.0 x 0.65 = 37.7 m3/d·m2

m201/dm 7570QA 23

===

Scale-up factor

m 16201π4A

π4D

m201d/mm 37.7rate Loading

A 22

===

⋅

ACEE 434 Fall 2009 HDP 29

ππ

SummarySummarySummarySummaryFl li ti• Flow equalization

• Calculation of the fluctuating volume • Primary clarifier• Estimation of detention time and overflow rate on a design guideline• Estimation of detention time and overflow rate on a design guideline• Estimation of detention time and overflow rate based on a settling experiment

ACEE 434 Fall 2009 HDP 30