flow equalization 1. to overcome operational problems caused by flowrate variations to improve the...
TRANSCRIPT
Jae K. (Jim) ParkDept. of Civil and Environmental EngineeringUniversity of Wisconsin-Madison
Flow Equalization
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Flow Equalization
To overcome operational problems caused by flowrate variations
To improve the performance of the downstream processes
To reduce the size and cost of downstream treatment facilities
Principal Applications Dry-weather flows Wet-weather flows from separate sanitary sewers Combined stormwater and sanitary wastewater flows
http://10statesstandards.com/wastewaterstandards.html 2
Principal Benefits
Enhanced biological treatment because of reduced shock loadings, dilution of inhibiting substances, and stable pH
Improved effluent quality and thickening performance of secondary sedimentation tanks due to constant solids loading
Reduced effluent-filtration surface-area requirements, improved filter performance, and uniform filter-backwash cycle
Improved chemical feed control and process reliability by damping mass loading
Attractive option for upgrading the performance of overloaded treatment plants
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Theoretical Analysis Location of equalization facilities Type of equalization flow sheet Required basin volume
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Equalizationbasin
Primarytreatment
Secondarytreatment
Finaleffluent
Controlled-flowpumping station Flow meter and
control devices
Gritremoval
Gritremoval
Equalizationbasin
Primarytreatment
Secondarytreatment
Finaleffluent
Controlled-flowpumping station
Off-line equalization
In-line equalization
Volume Requirement
Cum
ulat
ive
infl
ow v
olum
e, f
t3
Average daily flowrate
Inflow massdiagram
Required equalization
volume
Flowrate Pattern A
Required equalization
volume
Average daily flowrate
Inflow massdiagram
Time of dayM M MNN
Design volume = 1.1~1.2 Theoretical volume5
Flowrate Pattern B
Basin Construction Construction materials: earthen, concrete, or steel
Basin geometry: a complete-mix reactor Operational appurtenances: facilities for flushing any
solids and grease, emergency overflow in case of pump failure, a high water takeoff for the removal of floating materials and foam, and water sprayer
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Operation Mixing: aeration or mechanical equipment
along with corner fillets and hopper bottoms Aeration: DO - min. 1 mg/L; air supply rate -
min. 1.25 cfm/1000 gal of storage capacity (0.16 L/m3∙sec); air supply isolated from other treatment plant aeration requirements
Controls: Inlets and outlets suitably equipped with accessible external valves, stop plates, weirs, or other devices to permit flow control and the removal of an individual unit from service; devices for liquid level and flow rate measurements
Electrical: National Electrical Code for Class I, Division 1, Group D locations
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Snapfinger Plant (GA) Equalization Tank
Capacity: 20 million gallons
Cost: $6.9 million
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Equalization Tank
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Mixing
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Mixing and Air Requirement To minimize mixing requirement, install grit chamber
ahead of equalization basins where possible. Mixing requirements for medium-strength municipal
wastewater with SS of 220 mg/L: 0.02~0.04 hp/103 gal of storage (0.004~0.0088 kW/m3)
Air supply: 1.25~2 ft3/103 gal·min (0.01~0.015 m3/m3·min)
If equalization tanks are located after primary sedimentation tanks, aeration may not be required.
For mixing and aeration, use mechanical aerators. Min. operating levels for floating aerators: > 5 ft. Pumping facilities are required. Provide a flow-measuring device on the outlet
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