Constructed wetlands for the treatment of airport de-icer

253 Pages·2007·9.89 MB·English

Constructed wetlands for the
treatment of airport de-icer
Klaus M. Richter
This thesis is submitted in partial fulfilment of the requirements for the
Degree of Doctor of Philosophy
University of Sheffield
Department of Civil and Structural Engineering
November 2003
DECLARATION
I declare that the work in this thesis has been composed by myself and no portion of the work
hasbeensubmittedinsupportofanapplicationforanotherdegreeorqualificationofthisorany
other university or other institute of learning. The work has been my own except where
indicated and all quotations have been distinguished by quotation marks and the sources of
informationhavebeenacknowledged.
ii
ABSTRACT
Airports are facing the dual challenge of maintaining public safety and protecting the
environment. De-icerand anti-icercontainingglycol basedagentsareusedtoensure wintertime
flight safety. These fluids have the potential to impose enormous oxygen demands on receiving
waters, leading to degradation of the resources. Due to tighter discharge consent standards and
an increase in the public awareness of environmental pollution, many airport operators are
examiningalternativemethodsformanagingde-icingfluidwastewater.
Thisthesis deals with a novel wayof treatingthe airportrunoff. British AirportAuthorities
(BAA) commissioned a gravel type subsurface flow reed bed system to treat the glycol-laden
runoff at Heathrow Airport. Constructed wetlands act as an efficient water purification system
and nutrientsinkand remove efficientlyBOD, COD and other pollutants. Duetothe movement
towards sustainable, environmental engineering relying on natural ecologic processes, such
artificial systems are being increasingly used rather than traditional energy and chemical
intensivetreatmentprocesses.
In this thesis the performance of the subsurface reed beds at Heathrow Airport is assessed
at the very beginning of operation and after one year of operation. Since no data of real scale
applicationsofsubsurfacereedbedsisreporteduptonow,thecollecteddataandthesubsequent
assessment has a significant importance for further designs of constructed wetland based
treatmentapplications.
In this thesis the hydraulics of the beds were examined by means of fluorescent tracer
studies to gain insight in the residence time distribution of pollutants entering the constructed
wetland. A framework for modelling pollutant transport in wetlands is developed and pollutant
transport models based on multi-order Aggregated Dead Zone cells and the Advective
DispersiveEquationarepresented.
iii
ABSTRACT iv
The treatment performance was studied in several tests. The overall removal of glycol as
well as the removal of glycol within the constructed wetland was examined. Total removal of
glycol was dependent on the influent concentration and measured up to a level of 45 mg
COD/L. The removal of glycol within the wetland follows a first order reaction rate. The main
removal of glycol was detected within the first half of the constructed wetlands. Short wetlands
with a relatively high hydraulic load were found to have the most efficient layout in terms of
removedglycolmassperarea.
A pollutant removal model that incorporates the findings from the assessment of the
hydraulics and the treatment performance is developed for the constructed wetland system and
verifiedwithrealdata.
CONTENTS
Abstract........................................................................................................................................iii
Contents.........................................................................................................................................v
AbbreviationsandNotations........................................................................................................vi
ListofTables................................................................................................................................x
ListofFigures.............................................................................................................................xii
1 Introduction...........................................................................................................................1
1.1 AimsandObjectives.....................................................................................................2
1.2 Structureofthethesis....................................................................................................3
2 Literaturereview...................................................................................................................4
2.1 Constructedwetlands....................................................................................................4
2.1.1 Introduction...........................................................................................................4
2.1.2 Typesofconstructedwetlands..............................................................................7
2.2 Pollutantremovalprocessesinconstructedsubsurfaceflowwetlands....................... 12
2.3 AirportRunoff............................................................................................................26
2.3.1 PollutantsattheMayfieldFarmConstructedWetland.......................................27
2.3.2 Biodegradationofglycol..................................................................................... 29
2.4 Hydrologyandpollutanttransport.............................................................................. 34
2.4.1 Hydraulicpropertiesofsubsurfaceflowwetlands.............................................. 34
2.4.2 Flowthroughsaturatedmedia............................................................................. 36
2.4.3 Openchannelflow.............................................................................................. 37
2.4.4 Laminarandturbulentflow................................................................................. 38
2.4.5 Advectivetransport............................................................................................. 39
2.4.6 Advectivedispersivetransportinasaturatedmedium........................................39
v
CONTENTS vi
2.4.7 Advectivedispersivetransportinopenchannelflow......................................... 42
2.4.8 Solutionsforthemixingequations..................................................................... 43
2.4.9 Non-Fickiandispersionmodels .......................................................................... 47
2.5 Degradationratekinetics............................................................................................53
3 Modellingofsolutetransport.............................................................................................. 57
3.1 Introduction................................................................................................................. 57
3.2 ParameterestimationfortheADE-Model.................................................................. 59
3.3 ParamterestimationfortheADZ-Model....................................................................64
3.3.1 HigherorderADZ-models.................................................................................. 64
3.3.2 NumericalalgorithmsfortheparameterestimationofADZ-models................. 66
3.3.3 DecompositionofhigherorderADZ-models..................................................... 76
3.4 Sensitivityanalysisanduncertaintyofparameters..................................................... 77
3.4.1 Sensitivityanalysis.............................................................................................. 77
3.4.2 Uncertaintyofparameters................................................................................... 79
3.5 Designofexperiments................................................................................................83
3.5.1 Aspectsoftracerinjection................................................................................... 83
3.5.2 Samplingrateandfilteringofdata...................................................................... 88
4 TheHeathrowconstructedwetlands................................................................................... 93
4.1 Runofftreatmentdesignconcept................................................................................93
4.2 Thesubsurfaceflowreedbedsystem......................................................................... 94
5 Experimentalresults............................................................................................................99
5.1 Generaltests................................................................................................................99
5.1.1 Dischargetests....................................................................................................99
5.1.2 Testfordeterminationoftheporosity...............................................................101
5.1.3 Testfordeterminationofthehydraulicconductivity........................................101
5.1.4 Determinationoforganicmatter.......................................................................101
5.2 Fieldtestforhydraulicperformance.........................................................................102
5.2.1 Dyeadsorption..................................................................................................103
5.2.2 Determinationofdispersivities.........................................................................104
5.2.3 Temporalobservations......................................................................................110
5.3 Treatmentperformancetestsforglycolremoval......................................................117
5.3.1 Parameters,methodsofanalysisandsamplepreparation.................................117
5.3.2 Fieldtests,Series1,February2002...................................................................118
5.3.3 Fieldtests,Series2,November2002................................................................122
5.3.4 Laboratorytests.................................................................................................131
CONTENTS vii
6 Discussion......................................................................................................................... 134
6.1 Introduction...............................................................................................................134
6.2 PartA:pollutanttransportinconstructedwetlands..................................................134
6.2.1 Assessmentofthecollecteddata......................................................................134
6.2.2 Pollutanttransportmodelwithanaggregateddeadzoneapproach..................142
6.2.3 Pollutanttransportmodelwithanadvective-dispersiveapproach....................175
6.2.4 Summaryofpollutanttransportmodelling.......................................................188
6.3 PartB:treatmentperformanceofglycol...................................................................189
6.3.1 Assessment of the pollutanttransport modelfortheevaluation ofpollutantdecay
constants............................................................................................................189
6.3.2 Laboratorytestofglycoldegradationinagravelmatrix..................................194
6.3.3 TemporalBODobservations ............................................................................196
6.3.4 Temporalglycolobservations...........................................................................198
6.3.5 Derivation of glycol degradation performance from temporal COD observations
...........................................................................................................................199
6.3.6 DerivationofglycoldegradationconstantsfromspatialCODobservations....207
6.3.7 Summaryoftheevaluationofglycoltreatmentperformance...........................215
6.4 PartC:AModelforglycolremovalintheSSFconstructedwetland.......................216
6.4.1 Development of a temporal glycol removal model and application to observed
data....................................................................................................................216
6.4.2 Summaryofmodellingglycolremovalinsubsurfacewetlands.......................221
7 Conclusions.......................................................................................................................222
7.1 Introduction...............................................................................................................222
7.2 Conclucions...............................................................................................................223
8 Recommendationsforfurtherwork..................................................................................225
8.1 Extensionofthecurrentstudy..................................................................................225
8.2 Otherpointsofinterest..............................................................................................226
9 References......................................................................................................................... 227
ABBREVIATIONS AND NOTATIONS
Abbreviations
BOD biochemicaloxygendemand
BOD ,BOD fivedayorultimatebiochemical oxygendemand
5 u
cBOD carbonaceousBOD
COD chemicaloxygendemand
DEG diethyleneglycol
DOC dissolvedorganiccarbon
EG ethyleneglycol
PG polyethyleneglycol
ThOD theoreticaloxygendemand
ThTOC theoreticaltotalorganiccarbon
TOC totalorganiccarbon
ADE advectivediffusionequation
ADZ aggregateddeadzone
AIC Akaikeinformationcriterion
EE equationerror
FWS freewatersurfacewetland
HF horizontalflow
IV instrumentalvariable
LS leastsquare
SRIV simplifiedrefinedinstrumentalvariable
SSF subsurfaceflowwetland
VF verticalflow
YIC Younginformationcriterion
viii
ABBREVIATIONSANDNOTATIONS ix
Mathematical Notation
^ the"hat"-signindicatesanestimatedvalueofaparameters
* the"star"-signindicateapre-filteredparametervector
-
the"overbar"-signindicateatimeaveragedparameter
d, derivativeofaparameter
dA elementalcross-sectionalareaofthecontrolelement
dh/dx hydraulicgradient
c t changeofconcentrationwithtime
grad(c) gradient of the concentration, (the gradient is pointing into the direction of
the greatest increase of the concentration and its magnitude is the rate of
increaseinconcentrationperunitlengthintothatdirection)

transferfunctionforthecontinuoustimeADZmodel
s
bz
transferfunctionforthediscretetimeADZmodel
1az1
Latin Letters
a parameterorparametervector
a ,a ,... 1st,2nd,...parameterofvectora
1 2
A cross-sectionalarea
A wetlandsurfacearea
A(z-1) transferfunctionpolynom A
b parameterorparametervector
b ,b ,.. 0st,1st,...parameterofvector b
0 1
B(z-1) transferfunctionpolynom B
c concentrationofpollutantatithsample
i
C concentrationofthesinglereactant
C* backgroundconcentration
C(x,t) concentrationatlocation x attimet
i i i i
d averagegraindiameter
D hydraulicradius
D dispersioncoefficientinx direction
x
D* coefficientofmoleculardiffusion
e turbulentdiffusionfactorin xdirection
x
e(k) whitenoise
ET evapotranspirationrate
h waterdepth
i indexfortheithsampleofobservation
ABBREVIATIONSANDNOTATIONS x
I infiltrationrate
k thereactionrateconstant
k dispersionfactorinxdirection
x
K hydraulicconductivity
L length
m numberofparametersoftheA polynomofatransferfunction
n numberofparametersoftheB polynomofatransferfunction
n effectiveporosity
nM MANNING’Snconstant
n reactionorderinreactionkinetics
N numberofobservations
P precipitationrate
P wettedperimeterofachannel
P(k) inverseoftheinstrumentalcovariancematrix
q areahydraulicloadingrate
A
q volumetrichydraulicloadingrate
V
Q flowrate
R 2 coefficientofdetermination
T
t time
t timeofithsample
i
t traveltime,thedifferenceintimebetweenthecentroidsofthedistributions
T ADZ-cellresidencetime
c
u fluidvelocity
u(k),u kthelementofvectoru
k
U meanvelocity
v fluidvelocity
v specificdischarge
V reactorvolume,ADZ-cellvolume
V waterstorageinwetland
W width
x(k), x kthelementofvectorx
k
X datavector
X sensitivitycoefficient
i,k
y(k), y kthelementofvectory
k