1JCI 11

Energy can be neither created nor destroyed, but only converted from one form to another.

First Law of ThermodynamicsKarl Friedrich Mohr

In a closed system the mass of the system must remain constant over time.

Law of Conservation of Mass Antoine Lavoisier

2

CEE 426Wastewater Treatment Plant Design

October 23, 201312:05 pm Room 1213 Engineering Hall

Thomas E. JenkinsPresident JenTech Inc.

6789 N. Elm Tree RoadMilwaukee, WI 53217

414-352-5713tom.jenkins.pe@gmail.com

J enTec h Inc .

3

• Calculating Air Rates

• Types of Aerators and Processes

• Blower Selection

Aeration and Energy

3

4

Aeration is the Most Significant Energy Use in a WWTP

Aeration and Energy

4

34%

11%

55%Pumping and OtherHVACAeration

55

Rates vary with:• Time of Day

•On-peak, Off-Peak• Day of Week• Size of Costumer• Demand (kW) and Consumption (kWh)

The First Goal of an ECM (Energy Conservation Measure) is to Reduce Cost

Energy Consumption ≠ Energy Cost

66

BOD RemovalOxygen Required for metabolismAmount of O2 is proportional to Organic LoadUtilization Approximately 1.1 lb. O2/lb BOD5

Types of Processes

77

Nitrification NH3 NO3

Oxygen Required to convert Ammonia to Nitrate

Amount of O2 is proportional to Ammonia Concentration

Utilization 4.6 lb. O2/lb NH3 ConvertedHydraulic Residence Time and SRT (Solids

Retention Time) Determine if Nitrification Will Occur

Types of Processes

88

Denitrification NO3 N2 and O2

Anoxic ReactionCarbon Source RequiredApproximately 25% of O2 Used for Nitrification Can be Recovered

• Only if raw wastewater is used as carbon source

Types of Processes

99

MechanicalFine PoreCoarse BubbleJet Aeration

All work by creating contact between air and the mixed liquor. All require the transfer of mass across the liquid/gas boundary.

Types of Aerators

10

Horizontal Mechanical Aerator (Brush Aerator)

Mechanical Aerators

10

11

Vertical Shaft and Aspirating Mechanical Aerator

Mechanical Aerators

11

1212

Calculating O2 Transfer

Cperature liquor tem mixed:

1.024:factor correction etemperatur:conditions standard and processat DO saturation:,

solids dissolved for total correction:rclean wate water toprocess Ratio:

rclean wate DO, ppm 2.0 psia, 14.7 C,20

hr/hplbO RateTransfer Oxygen Standard:

20

2

20

20

T

CC

SOTR

CCCSOTRAOTR T

• Typical aerator SOTR 2.0 to 4.5 lbO2/hp-hr

1313

Determining Power Required for Mechanical Aerators:

Calculating Air Rates and O2 Transfer

hr/hp2lbO RateTransfer Oxygen Actual:AOTR

000,16_

AOTRVtOURhpaerator

Note that hp USED is a function of design!

• Mixing Limits:• 1 ft/sec velocity• 0.5 hp/1,000 ft3

1414

Proportional to Immersion• Reduced Immersion < OTR and < hp• Variable Weir Level Control

Proportional to Speed• Lower Speed < OTR and < hp• Variable Frequency Drives, Two Speed Motors

Proportional to Actual DO Concentration• Lower is Better• DO Control Significant

Mechanical Aerator Energy

1515

Mechanical Aerator EnergyLower speed = lower power

30 40 50 60 70 80 900.0

0.5

1.0

1.5

2.0

2.5

Power

rpm

bhp/

ft. ro

tor l

engt

h

1616

Mechanical Aerator EnergyLower speed = lower oxygen transfer

30 40 50 60 70 80 900.0

0.5

1.0

1.5

2.0

2.5

Power

rpm

bhp/

ft. ro

tor l

engt

h

30 40 50 60 70 80 900

1

2

3

4

5

6

7

8

SOTR

rpm

SOTR

lb/h

r/ft

roto

r len

gth

1717

Mechanical Aerator EnergyNet result is lower efficiency

30 40 50 60 70 80 900.0

0.5

1.0

1.5

2.0

2.5

Power

rpm

bhp/

ft. ro

tor l

engt

h

30 40 50 60 70 80 90012345678

SOTR

rpm

SOTR

lb/h

r/ft

roto

r len

gth

30 40 50 60 70 80 900.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

SAE

rpm

SAE

lb/h

p hr

Does It Matter?

1818

Coarse Bubble

Diffused Aeration

1919

Fine Pore (Fine Bubble)

Diffused Aeration

2020

Calculating OTE and O2 Transfer

Cperature liquor tem mixed:

1.024factor correction etemperatur:conditions standard and processat DO saturation:,

correction altitude:7.14

saturationfor correction etemperatur::

typical0.95 solids dissolved for total correction:1_with_age new, 1 :factor Fouling:

rclean wate water toprocess Ratio:rclean wate DO, ppm 2.0 psia, C,14.720

hr/hplbO EfficiencyTransfer Oxygen Standard:

20

20

2

20

20

20

T

CC

PCC

F

SOTECC

CCCSOTEFOTE

barometric

S

Tf

2121

Calculating Air Flow Rates

ationdenitrificfor credit includenot does - typical6.4

ppm nitirfied NH:

value typicalis 1.1ppm removed BOD:

mgd flow wastewater:

6.41.1335.0

33

3

NH

BODQ

NHBODOTE

QSCFM

rem

remf

2222

• Proportional to Submergence• Deeper is Better• Also Requires Higher Blower Power

• Proportional to Air Flow per Diffuser• Flux Rate (1 to 10 SCFM/ft2 Typical)• Lower is better

• Proportional to Actual DO Concentration• Lower is Better• DO Control is Significant

Diffused Aeration Energy

2323

Calculating Air Rates and OTE

• Typical OTEf ≈ 50% SOTE• SOTE Fine Pore ≈ 2% per foot submergence• SOTE Coarse Bubble ≈ ¾ % per foot

submergence• Mixing Limits:

• Fine Pore: 0.12 to 0.08 CFM/sq ft• Coarse Bubble: 20 CFM/1,000 cu ft

2424

OTE Increases with Higher SubmergenceOTE Decreases with Higher Air Flow per Diffuser

Diffused Aeration

7.6m = 25’ 6.1m = 20’ 4.6m = 15’ 3.0m = 9.8’ 1.5m = 5’1m3/hr = 0.58 CFM 5m3/hr = 2.94 CFM 9m3/hr = 5.30 CFM

2525

Excess DO means significantly more aeration power.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

Nom

inal

Pow

er M

ultip

lier

Actual DO Concentration, ppm

Blower Power Ratio (Compared to 2.0 ppm DO)

Based on 500' ASL, 55 °F, 9.9 ppm Csat

actual

actual

CCC

QQ

*

20

*20

0.2

0.2

Diffused Aeration

2626

• Miscellaneous Aeration Processes

• Aerobic Digestion

• Sludge Holding

• Post-Aeration

• Channel Aeration and Equalization

Types of Processes

27

Energy use varies with time of dayOTE, α, Organic Load, Hydraulic Load, All Vary with Time of Day

Aeration and Energy

27

12:00 AM 03:59 AM 07:59 AM 11:59 AM 03:59 PM 07:59 PM 11:59 PM0%

20%

40%

60%

80%

100%

120%

140%

Time of Day

% A

vera

ge D

aily

Flo

w

2828

• Efficiency• Control• Turndown• Design Parameters

Blower Selection Considerations

29

Efficiency Varies with Blower TypeRange is 60% to 80%

Aeration and Energy

29

30

• Blower Power is a Function of Pressure and Flow Rate

• Efficiency Varies Flow Rate for a Given Blower

• Efficiency Drops as Flow is Decreased

• Good Turndown (>50%) is Desirable

Aeration Blower Power

30

31

Aeration Blower Power

31

3232

Aeration Blower Power

feet diffusers, of at top water ofdepth :

diffusers and pipingon distributi through loss head :,psia pressure barometric :

psia pressure discharge:

31.2

psia pressure,inlet :F TempInlet :

Minuteper Feet Cubic QInlet :

7.14528

460

dif

diffpiping

bar

dis

diffpipingdif

bardis

i

i

i

i

D

pppp

ppD

pp

pT

ICFM

pTSCFMICFM

Ignoring Relative Humidity

3333

Aeration Blower Power

rate flowe Maximum and Minimum:,

100%

decimal ,efficiencyBlower :horsepower brakeBlower :

85,64

minmin

max

minmax

283.0717.0

QQ

QQQTurndown

effbhp

pppeffICFMbhp

b

indisinb

3434

Aeration Blower Power

Blower System Qmax:Qmin = 8:1

Specify Blower System for Turndown• Four with Design Flow at 33% Max Q

• Two with Design Flow at 50% Max Q Plus Two with Design Flow at 25% Max Q

• 50% Turndown Each Blower

35

Design Specifications Identify Worst Case Operating ConditionsFor Discharge Pressure

• Max Temperature• Max Relative Humidity• Max System Flow Rate and ΔP

For Motor Power• For Throttled Centrifugal bhp at Min Temperature• For Variable Speed Centrifutal bhp at Max Temperature

Evaluation Conditions do not Equal Design Conditions

Aeration Blower Power

35

36

Process Requirements Come First!

Systems should be justified by payback

Aeration and Energy

36

ngsAnnualSaviostEquipmentCyearsPayback,

37

Over Life of Equipment: Energy Cost is more Significant than Equipment, Installation, or Maintenance Costs

Aeration and Energy

37

3838

http://www.sanitaire.com/3117803.asphttp://www.stamfordscientific.com/http://www.wastewater.com/http://www.eimcowatertechnologies.com/http://www.water.siemens.com/en/about_us/legacy_brands/Pages/envirex.aspxhttp://rootsblower.com/http://water.epa.gov/scitech/wastetech/upload/Evaluation-of-Energy-Conservation-Measures-for-Wastewater-Treatment-Facilities.pdf

Internet References

39

Aeration and Energy

Questions?

39