Dave Stropky, Paul Nowak, Suqin DongProcess Simulations Ltd.

Konstantin Pougatch, Martha SalcudeanUniversity of British Columbia

P.S. Pagoria, W.A. Barkley, C.W. BryantWeyerhaeuser Paper Company

CFD Predictions CFD Predictions in Largein Large

Mechanically Aerated LagoonsMechanically Aerated Lagoons

ContentsContents

Introduction

Aerated Lagoon CFD Model Lagoon Hydraulics RTD Predictions Biological Model

Application Weyerhaeuser Grande Prairie

Industrial Application

Conclusions

Introduction

IntroductionIntroductionMotivation: 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.

IntroductionIntroduction

Performance FactorsIncorporated in Model

Basin shape

Inflow rate and position

Aerators: Number, position, HP

Baffles/Curtains

Sludge accumulation profile

Biology

Aerated LagoonCFD Model

Aerated Lagoon GeometryAerated Lagoon Geometry

Aerators

Inlets

Baffles

Outlet

CFD Grid

Bottom Sludge ProfilesBottom Sludge Profiles

Aerators #13 and #16

y = 5.118E-11x6 - 2.591E-08x5 + 4.587E-06x4 - 3.219E-04x3 + 6.469E-03x2 + 1.046E-01x

0.0

3.0

6.0

9.0

12.0

15.0

18.0

0 25 50 75 100 125 150

R (ft)

Slu

dg

e D

ep

th (

ft)

All Data Except 13 SW

Poly. (All Data Except 13 SW)

MeasurementData

Surface GenerationAlgorithm

RTD Prediction MethodsRTD Prediction Methods

days164.8meanT

Case Tmean Tpeak TmedianAge Equation

(exit)TCPU

Particle 8.244 4.336 6.969 0.92Dye 8.364 4.502 7.086

8.37757.0

Particlevs.Dye

0

0.03

0.06

0.09

0.12

0.15

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2t / tmean

E(t)

Dye

Particle

Gxvx Ddt2dt)(d

cD)c(t

c 2

v

t

tDVMean

Age

)0(SBOD

)0(LBOD

)0(4PO

)0(DO

)0(ZX

DO

SBOD

LBOD

4PO

XZ

dt

Xd

dt

POd

dt

LBODd

dt

SBODd

dt

DOd

Z

4

SBOD

4PO

ZX Ben

thal

Pha

se

Aeration

Biological ModelBiological Model

LBODLignin based BOD. LBOD, specific to pulp and paper, converts to SBOD at a given rate. It needs to be accounted for to correlate with measured SBOD concentrations in the effluent.

SBOD Soluble BOD

XZ Active biomass (viable bacteria)

DO Dissolved oxygen

PO4 Nutrient phosphorus

Biological ModelBiological Model

Rate Equations

LBODLBOD

Lkd t

d

feedbac kbenthalLBODXZ

SBOD

SBODXZOBRY

SBOD

SBODXZOBR

SBOD

conversion LBODfrom Production

XZ of deathfrom Production

Growth) ( nConsumptioEnergy) ( nConsumptio

)()(

1

LLdeath

SS

kYOBRk

Kk

KkY

d t

d

DepositionDeath

Growth

Equation SBOD

XZXZ(Grow th) nC ons umptioOBR

XZ depos itiondeath kk

d t

d 1

feedbac kbenthalD eathGrow thPO

Eq.XZEq.XZ

PXYd t

d )4(

AerationGrow th)(Energy nC ons umptioD O

EquationSBOD

d t

d )(

Throttled by DO (both) and PO4 (growth)

Applications

Weyerhaeuser Grande PrairieWeyerhaeuser Grande Prairie

Grande Prairie is a >850,000 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).

2005 Hydraulic Flowfield2005 Hydraulic Flowfield

Vertical magnification x10

1997 Grande Prairie Field Study Comparison1997 Grande Prairie Field Study Comparison

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 5 10 15 20 25 30 35 40

T(days)

E(t)

Measurement

Computation

T0 Tpeak Tmean Tmedian Theory Tmean

Measurement 1.1 5.7 11.3 9.5 11.6

Computation 1.3 7.9 12.0 10.3 11.6

Model sludge profile estimated.Unknown at time of dye study.

Grande Prairie Aerator OptimizationGrande Prairie Aerator Optimization

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 5 10 15 20 25 30 35 40

T(Days)

E(T

)

Optimized Layout

Initial Layout

T0 Tpeak Tmean Tmedian Theory Tmean

Initial 1.3 8.0 16.6 13.7 16.6

Optimized 3.4 12.4 17.1 15.9 16.6

Initial

Optimized

Biological ModelBiological Model

Biological ModelBiological Model

LBOD SBOD XZ DO PO4

Inlet Measurement 267 297 5.5 0 1

Mid Channel Measurement 25 128 4.3 0.7

Mid Channel CFD Prediction 186 33 102 1.1 0.1

Outlet Measurement 13 21 4.2 1.2

Outlet CFD Prediction 126 28 49 0.1 1.6

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

ConclusionsConclusions

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.

ConclusionsConclusions