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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
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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
J enTec h Inc .
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3
• Calculating Air Rates
• Types of Aerators and Processes
• Blower Selection
Aeration and Energy
3
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Aeration is the Most Significant Energy Use in a WWTP
Aeration and Energy
4
34%
11%
55%Pumping and OtherHVACAeration
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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
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BOD RemovalOxygen Required for metabolismAmount of O2 is proportional to Organic LoadUtilization Approximately 1.1 lb. O2/lb BOD5
Types of Processes
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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
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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
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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
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Horizontal Mechanical Aerator (Brush Aerator)
Mechanical Aerators
10
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Vertical Shaft and Aspirating Mechanical Aerator
Mechanical Aerators
11
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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
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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
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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
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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
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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
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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?
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Coarse Bubble
Diffused Aeration
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Fine Pore (Fine Bubble)
Diffused Aeration
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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
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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
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• 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
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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
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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
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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
*
20
*20
0.2
0.2
Diffused Aeration
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• Miscellaneous Aeration Processes
• Aerobic Digestion
• Sludge Holding
• Post-Aeration
• Channel Aeration and Equalization
Types of Processes
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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
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• Efficiency• Control• Turndown• Design Parameters
Blower Selection Considerations
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Efficiency Varies with Blower TypeRange is 60% to 80%
Aeration and Energy
29
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• 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
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Aeration Blower Power
31
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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
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3333
Aeration Blower Power
rate flowe Maximum and Minimum:,
100%
decimal ,efficiencyBlower :horsepower brakeBlower :
85,64
minmin
max
minmax
283.0717.0
QQQTurndown
effbhp
pppeffICFMbhp
b
indisinb
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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
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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
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Process Requirements Come First!
Systems should be justified by payback
Aeration and Energy
36
ngsAnnualSaviostEquipmentCyearsPayback,
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Over Life of Equipment: Energy Cost is more Significant than Equipment, Installation, or Maintenance Costs
Aeration and Energy
37
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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
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Aeration and Energy
Questions?
39