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Wyoming Department of Environmental Quality DivisionLagoon Aeration – Theory & Design
Tuesday, February 28, 2012
Kevin Rood, P.E., BCEE
Just when you know the answers, they’re to
the wrong questions
Overview
1) Lagoons in general2) Decision process to determine if the aerated lagoons
are the right answer3) Facultative lagoons4) Partially mixed aerated lagoons5) Mixed aerated lagoons completely6) Equipment 7) Questions (at any time)
Community Goals
1) Meet treatment requirements
2) Lowest possible capital costs
3) Lowest possible operating costs
4) Be trouble-free
Lagoons
Surface Water DischargeLand Application
ContinuousIntermittent
Discharging Non Discharging
Lagoon Systems are a Combination of these Process Types
Storage Facilitative Aerobic Anaerobic
Community Needs
• Population
• Flows
• Loads
• Type of waste
• Water quality issues
• Available land
• Size of lagoons• Separation distances• Available stream• Discharge requirement• Distance from the
community• Topography• Geology
Lagoons
Mechanical Plant Available Land
Community Needs
NO YES
NO
Adequate
Non Discharge
NPDES Permit Required
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
Land Application
Evaporation
Retention
Retention
1. Storage = Water Gain – Weight Loss2. Water Gain = Water Loss
– Hydraulics problem– Evaluation organic loading– Construction controlled by geology– Design controlled by topography and other physical constraints– Weather
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
RequiredLand Application
Evaporation
Retention
Land Application
Industrial • Manufacturing• Mining• Fracking
Agricultural• Grain Crops• Livestock Food• Silviculture• Wetlands
• No discharge to surface water• Catch basins needed• Control application • Sampling and monitoring• Beneficial reuse
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
RequiredLand Application
Evaporation
Retention
Intermittent Discharge to Surface Water• Regulatory issues• Effluent quality• Down stream issues• Sizing control / by influent water• Sampling and monitoring
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
RequiredLand Application
Evaporation
Retention
Continuous Discharge
• Sizing control by water quality in and out• Most treatment • Sampling and monitoring
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
RequiredLand Application
Evaporation
Retention
Treatment Storage
Facilitative Aerobic Anaerobic
Natural With Air
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
Required Land Application
Evaporation Retention
Storage Treatment
Anaerobic• Without oxygen• High strength waste• Energy recovery• Odor issues
Treatment Storage
Facilitative Aerobic Anaerobic
Natural With Air
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
Required Land Application
Evaporation
RetentionStorage Treatment
Aerobic• With oxygen• Physically smaller• More equipment• Completely mixed• Highest quality effluent
Treatment Storage
Facilitative Aerobic Anaerobic
Natural With Air
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
Required Land Application
Evaporation
RetentionStorage Treatment
Facilitative
Anoxic Anaerobic
Aerobic
• Conventional• Supplemental Air• Partial Mixed
Treatment Storage
Facilitative Aerobic Anaerobic
Natural With Air
Adequate
Non Discharge
NPDES Permit
Lagoons
Mechanical Plant
Available Land
Community Needs
NO
YESNO
Discharge
NO
YES
YES
Continuous Intermittent
Required Land Application
Evaporation
RetentionStorage Treatment
FacultativePreliminary Treatment
Treatment Cell #1 Treatment
Cell #2
Storage Cell Polishing Cell
Stream
* Optional
*
*
• Wyoming Requirement• Max Loading 40 lbs/Acre/Day• 180 HDT Outfall
The Operation of the Facultative Pond
o2
o2
During daylight hours
Co2
Co2 + NH3 + H2S + CH4
Bottom sludge
Organic wastesOrganic acids
alcohols
H2S + 202 + H2S04
Algae
Dead Cells
Bacteria
Dead Cells
Wastewater
Reaeration
Sunlighto2Wind
C02
H2S
New CellsNutrients
New Cells
Design Considerations
• Solids loading rate to primary cells
• Hydraulic detention time
• Temperature
• Minimize short circuiting
• Predominant wind direction
Solids Loading
• Models can be used to predict loading rates• Regulatory agency usual sets max. rate
Average Winter Temperature
lbs/ac/day
Greater than 15 C 40-80
0-15 20-40
Less than 0 10-20
Wyoming Regulations = Max 40 lbs/pc/day
Hydraulic Detention Time
• BOD reduction and Coliform reduction are generally modeled as 1st order kinetic
BOD
BOD (eff) = BOD (Inf)1 + Ke(T)
T = Time (days)Ke = K20 THETA (t-20)
K20 = 0.276 per day
THETA = 1.07 range (1.05 – 1.09)
95% BOD Removal Days
TempDays
Deg C Deg F
5 41 190
10 50 135
15 59 96
20 68 68
25 77 66
Coliform
• Ne = Ni
1 + Kt (T)
Ni = Influent Coliforms
Ne = Effluent Coliforms
Kt = removal constant per day
T = time daysKt = 2.6 (1.19) (t-20)
t = Temperature C
Hydraulic Detention times range 30-180 daysWyoming regulation = 180 days
99% Removal in Days
TempDays
Deg C Deg F
5 41 521
10 50 216
15 59 90
20 68 38
25 77 16
Treatment Cell No. 1 Treatment
Cell No. 2
Storage Cell
Polishing Cell
2’
• Treatment cells: 2’ to 6’ deep• Storage cell: 6’ to 10’ deep• Polishing cell: approx. 2’ deep
Facultative Lagoon
• Seepage– Wyoming limits - 1/8-inch day max– Common 2.6x10-9 cm/sec/ft depth - approx. 0.1 inch/day– Common - no seepage, use impervious liner
Compacted Soil 95% Standard Proctor, MR O, + 3%
1 ft select cover material Erosion Control (RIP RAP)
Impervious Liner
Leak Detection System
Partial Mixed Aerated Lagoon• Satisfy oxygen requirement but not mixing requirements
• Wyoming requirements loading for treatment• Cells less than 2 lbs/1000 cft• Minimum D.O. = 2 mg/l• HDT = 7 day for treatment
• Storage to provide• 30 days overall• HDT
*Optional
Stream
Outfall
Preliminary Treatment
*****
* * *
AeratedCell No. 1
Aerated Cell No. 2
Storage Cell
Polishing Cell
*
*
Partial Mixed Aerated Lagoon
• Upgrade of overloaded lagoons• Reduce the footprint of lagoon to fit specific location• Good for BOD removal less effective in other areas• Add oxygen to shorten treatment time
Mixing and Oxygenation
• How much is the question• Complete mix is considered 10-50 Hp/MG• Partial mix is considered 5-15 Hp/MG• Complete mix with air 0.15-0.3 scfm/sft fine bubble• Complete mix with air 0.15-1.0 scfm/sft course bubble
BOD lb needs 1.2-1.5 lbs of oxygenLb Ammonia to nitrate needs 4.6 lbs of oxygenMechanical aerators 2.5-3.5 lbs of O2/hp-hour
Diffused aeration 6.0-6.5 lbs O2/hp-hour
Oxygen
1. Flow (mgd) x BOD (mgll) x 8.34 lbs/gal = lbs BOD/Day2. Flow (mgd) x TKN (mgll) x 8.34 lbs/gal = lbs TKN/Day
Oxygen (lbs/day) = 1.5 (lbs BOD/Day) + 4.6 (lbs TKN/Day)at 20 C & 1 ATMAir contains approximately 21% oxygen and weighs approximately 0.0749 lbs/cft
Oxygen (cont)
• Standard oxygen required equal lbs of oxygen to meet the applied load
• Actual oxygen required accounts for temperature, wastewater characteristic, and dissolved oxygen residualAOR = Alpha (SOR (beta x Csw – C) 1.024 (t-20)
Csalpha = oxygen-transfer correction factor
alpha = 0.8-0.85 (surface aerator)alpha = 0.6-0.65 (diffused aerator)
Beta = salinity correction factor B = 0.9-0.95 TypicalCSW = Oxygen saturation for water at temperature & elevation
Cs = oxygen saturation at 20 C and sea level (9.17 mg/l)C = residual dissolved oxygent = temperature in Degrees C
Elev. Cheyenne Wyoming ~ 6,100 ft elevation
Temp. Solubility of Oxygen
5 C 41 F 10.2 mg/l
10 C 50 F 9.1 mg/l
15 C 59 F 8.1 mg/l
20 C 68 F 7.3 mg/l
25 C 76 F 6.7 mg/l
Oxygen (cont)
• Use corrected lbs of oxygen to mechanical• Use corrected lbs of oxygen to convert to cubic feet of
air per minute at standard condition SCFM• Size blowers based on SCFM corrected for
– Temperature – Elevation– Humidity– Corrected conditions call ICFM or inlet
cubic feet per minute
Oxygen (cont)
• Wyoming requirements– Surface aerator intervals 200 ft or less– Minimum of two aerators– Transfer oxygen needed with larger unit out of service– Diffused aerator minimum of two blowers– Transfer oxygen needed with largest blower out of service
Treatment Cell No. 1 Treatment
Cell No. 2
Storage Cell
Polishing Cell
• Depth in treatment cells: 4’ to 12’• Depth in storage cell: 6’ to 15’• Depth in polishing cell: approx. 2’
Partially Mixed Aerated Lagoon
Complete Mixed Aerated Lagoon
Preliminary Treatment
*****
* * *
• Wyoming requirements• Max loading treatment cell No. 1• 10 lbs/ BOD /1000 cft• HDT = 1.5 days
• Max loading treatment cell No. 2• 2lbs BOD/1000 cft• HDT-7days• DO level 2.0 mg/l minimum
• Increase storage to 30 days overall
Treatment Cell No. 1
Treatment Cell No. 2
Storage Cell
Polishing Cell
Out Fall
Complete Mix Lagoons
• Almost activated sludge• Significant amount of equipment• If we would add a clarifier and return it, it would be
activated sludge• Requires frequent solids removal depending upon the
size of the storage cell• Higher loading • Same oxygen calculations a partial mixing
Complete Mix Lagoon
• No sedimentation in process basin• Mixing = 30 – 50 hp/mg
= 0.15 – 0.3 scfm/ft2 fine bubble = 0.5 – 1.0 scfm/ft2 course bubble
• Wyoming Requirement— Surface aerator interval 200 ft or less (much less)— Minimum two aerators— Transfer oxygen needed with largest aerator out of service— Diffused aeration minimum of two blowers— Transfer oxygen needed with largest blower out of service
Treatment Cell No. 1 Treatment
Cell No. 2
Storage Cell
Polishing Cell
• Depth in treatment cells: 8’ to 18’• Depth in storage cell: 8’ to 18’• Depth in polishing cell: approx. 2’
Complete Mixed Aerated Lagoon
EQUIPMENT
Aeration Equipment
• Broadly classified into two categories based on location of operation:– Surface Aerators– Sub-surface Aerators
• Parameters used to measure system performance– OTR – Oxygen Transfer Rate, lb O2/h– SOTR – Standard Oxygen Transfer Rate (OTR @ STP*), lb O2/h– OTE – Oxygen Transfer Efficiency, %– SOTE – Standard Oxygen Transfer Efficiency (OTE @ STP), %– SAE – Standard Aeration Efficiency (AE @ STP), lb O2/KW.h
STP – Standard Temperature & Pressure of 70 F & 1 atm⁰
Surface Aerators• Surface aerators, as the name indicates, are stationed
(floating or fixed) and operate at the water surfaceTypes include:– Floating Mechanical Aerators– Aspirators– Reel Type/Paddle Wheel Aerators
• Aerators operating on renewable sources are further classified as:– Solar powered Aerators– Wind powered Aerators
• Surface aerators usually tend to have moderate OTRs and low SAEs
• Oxygen transfers rates of 1.5 to 3 lbs O2 / Hp-hr
Floating Mechanical Aerators
• Uses the principle of agitation and turbulence
• Uses electrical energy to create turbulence
• Can be moored in different ways to suit needs
Floating Mechanical Aerators
Aspirators• Utilizes both air injection and mechanical mixing• Units can be operated to suit the needs:
– Angle of mixing and air injection can be changed– Dentrification mode – only mechanical mixing– Nitrification mode– Both mechanical mixing and air injection
• No additional blower(s) required for operation• Can operate effectively during winter
Aspirators
Installation at Moorhead, MN
Aspirators
Paddle Wheel Aerators
Installation at Austin, TX
• Utilizes paddle wheels to agitate the surface of the water• Typically operates at lower speeds compared to other aerators• Induces more horizontal mixing than vertical• Can be installed as floating or fixed units
Paddle Wheel Aerators
Solar Powered Aerators/ Mixers• Utilizes solar power• Water is drawn from the depths and circulated at the
surface• For very deep waters (>10ft), multiple pipes/draft tubes may
be used
Installation at Richmond, CA Installation at Guatemala
Solar Powered Aerators
Wind Powered Aerators/ Mixers• Utilizes wind power• Can operate at wind speeds as low as 5 mph• Backup motors can be used during low wind speeds
Installation at Holkham, UK
Wind Powered Aerators
Subsurface Aerators/ Mixers
• Subsurface aerators are installed below the water surface and they operate by forcing/diffusing air bubbles through the water. Types of subsurface aerators are:– Coarse Bubble Systems– Fine Bubble Systems– Submersible Mechanical Aerators
• With the exception of subsurface mechanical aerators, all subsurface aerators require air blowers, air blowers are further classified into:– Centrifugal blowers– Positive displacement blowers
Coarse Bubble Systems
• Coarse bubble systems use pores/orifices to release air bubbles in the order of 50 mm (50,000 micron) in size
• Offers high OTR and low SAE (2 to 5.5 Kg O2 /KWh)
• Considered low maintenance• Types of coarse bubble systems are:
– Air spargers– Broadband diffusers (chicken feeders)– Static tube aerators– Snap cap/permacap aerators– Non-clog diffusers
Coarse Bubble Systems
Static Tube Aerators
Permacap Diffusers
Broadband Diffusers
Coarse Bubble Systems
Air Sparger System Tideflex Diffusers
Coarse Bubble Systems
• Fine bubbles are created by passing compressed air through a porous material (diffusers)or by mechanically shearing (e.g. Jet Aeration) large air bubbles into smaller ones– Jet aerators usually have lower SAEs, in the order of 2.6 – 4 lb O2 /Hp-hr– Fine pore diffusers have higher SAEs, in the order of 8 – 11 lb O2 /Hp-hr– Fine pore diffusers require periodic cleaning
• Based on diffuser geometry, fine bubble diffusers can be classified into:– Tube Diffusers– Membrane Diffusers– Ceramic Diffusers
Fine Bubble Systems
Biolac® process utilizes fine bubble diffusion
Fine Bubble Systems
Fine Bubble Tube DiffuserJet Aeration
Fine Bubble Ceramic Diffuser
Fine Bubble Diffuser Video
Biolac® Process• Activated sludge process invented by Parkson co• Required mixing and suspension achieved at 4
CFM/1000 Cu.Ft• Diffusers are suspended above the floor by means
of hanging chainsBiolac ® Process
Biolac® Process
Submersible Mechanical Aerators• Self aspirating• Blower assistance can be provided for deeper
installations
Installation at Groveland, FL Installation at Lake City, TN
Submersible Mechanical Aerators – Video
Blowers
• All sub surface aerators (except submersible aerators) require blowers
• Blowers are compressors that operate at low pressures• Offer limited “turn up” or “turn down” and are energy
hungry• Classified into:
– Positive Displacement (PD) Blowers - constant flow, variable pressure
– Centrifugal Blowers – constant pressure, variable flow
• Smaller plants use PD blowers or centrifugal blowers• Larger plants use centrifugal blowers
Centrifugal Blowers
• Newer centrifugal blowers can be throttled using variable inlet guide vanes and variable outlet diffusers
• Have an optimum range and outside of it their efficiency drops
Single Stage Centrifugal Blower Multi Stage Centrifugal Blower
PD Blowers• Due to mode of operation, PD compression is not as
efficient as centrifugal blowers , but achieve higher pressures for same air flow
• Variable Freq. Drives (VFDs) can be used to vary the flow• With VFDs, flow is proportional to blower rpm
Positive Displacement Blower
QUESTIONS
