CFD Predictions in Large Mechanically Aerated Lagoons

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CFD Predictions in LargeMechanically Aerated
Lagoons
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Contents

• Introduction
• Aerated Lagoon CFD Model
• Lagoon Hydraulics
• RTD Predictions
• Biological Model
• Application
• Weyerhaeuser Grande PrairieIndustrial
  Application
• Conclusions

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Introduction
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Introduction
Motivation Improvement of lagoon performance
through a deeper understanding of the hydraulics.
Development of Residence Time Distribution (RTD)
curves without dye studies. Goal Develop a 3-D
Computational Fluid Dynamics (CFD) hydraulic
model of a large aerated industrial lagoon.
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Introduction
Performance Factors Incorporated in Model

• Basin shape
• Inflow rate and position
• Aerators Number, position, HP
• Baffles/Curtains
• Sludge accumulation profile
• Biology

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Aerated Lagoon CFD Model
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Aerated Lagoon Geometry
Inlets
Aerators
Baffles
Outlet
CFD Grid
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Bottom Sludge Profiles
Measurement Data
Surface Generation Algorithm
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RTD Prediction Methods
MeanAge
Particlevs.Dye
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Biological Model
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Biological Model
Rate Equations
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Applications
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Weyerhaeuser Grande Prairie
Grande Prairie is a gt850,000 m3, two cell lagoon
5.29m deep (18ft) with an operating water depth
of 4.57m (15ft) when clean. Cell 1 is 326m x
323m, and cell 2 is 326m x 312m. Cell 2 has two
flow baffles. The 1997 volume flow rate is 622
l/s from the south inlet, and the 2005 flow is
632 l/s from the north inlet. Each floating
aerator is 75HP and circulates 1286 l/s of
liquid. The 1997 configuration has 25 aerators
(18 in cell1 and 7 in cell2). The 2005
configuration has 27 aerators (19 in cell 1 and 8
in cell 2).
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2005 Hydraulic Flowfield
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1997 Grande Prairie Field Study Comparison
Model sludge profile estimated. Unknown at time
of dye study.
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Grande Prairie Aerator Optimization
Initial
Optimized
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Biological Model
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Biological Model
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Conclusions

• A three dimensional CFD model has been developed
  for predicting detailed hydraulic performance
  (including RTD curve prediction) in large
  mechanically aerated lagoons.
• Using this model, wastewater engineers can
  combine their existing knowledge and expertise
  with the established power of CFD. The operation
  of an existing aerated lagoon can be fully
  analyzed over a range of operational parameters
  (aerator numbers, positions, and capacities
  baffle installation influent flowrate and
  location bottom sludge profile, etc.) without
  running field dye studies. The method
  constitutes an efficient and powerful tool for
  improving lagoon performance and optimizing lagoon

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Conclusions

• A simplified aerobic biological model has been
  developed and coupled into the hydraulic CFD
  model. Through this coupling, three dimensional
  variation and evolution of the biological
  processes can be predicted within the lagoon.
  Prediction of BOD removal is a natural
  consequence of the three dimensional interplay
  (including deposition and feedback) between
  bacteria solids, BOD, and nutrients, and also of
  the dissolved oxygen supplied through individual
  aerators. Initial results show promise and
  provide a pathway towards a deeper understanding
  of the wastewater treatment in these lagoons.