HYDRUS

WETLAND MODULE
VERSION 2

ManualbyGünter Langergraber1 and Jirka Šimůnek2
March 2011

1

Institute for Sanitary Engineering and Water Pollution Control
BOKU - University of Natural Resources and Life Sciences, Vienna
Muthgasse 18, A-1190 Vienna, Austria
2

Department of Environmental Sciences
University of California Riverside
Riverside, CA, 92521, USA

Abstract
Langergraber, G. and J. Šimůnek, HYDRUS Wetland Module, Version 2. Hydrus Software
Series 4, Department of Environmental Sciences, University of California Riverside,
Riverside, California, USA, p. 56, 2011.
This report documents version 2 of the HYDRUS wetland module. In version 2, two biokinetic
model formulations can be chosen: (1) CW2D (Langergraber and Šimůnek, 2005) and (2)CWM1 (Constructed Wetland Model #1) (Langergraber et al., 2009b). Aerobic and anoxictransformation and degradation processes for organic matter, nitrogen and phosphorus are
considered in CW2D, whereas aerobic, anoxic and anaerobic processes for organic matter,
nitrogen and sulphur are considered in CWM1.

DISCLAIMER
This report documents version 2 of the HYDRUS wetland module. The Wetland module wasdeveloped as a supplemental module of the HYDRUS software package, to model thebiochemical transformation and degradation processes in subsurface wetlands. The software
has been verified against selected test cases. However, no warranty is given that the program iscompletely error-free. If you do encounter problems with the code, find errors, or havesuggestions for improvement, please contact one of the authors at
Günter LangergraberTel: +43-(0)1-47654-5814
Fax: +43-(0)1-368 99 49
Email: guenter.langergraber@boku.ac.at
Jirka Šimůnek
Tel/Fax: 1-951-827-7854
Email: jiri.simunek@ucr.edu

Table of contents
1

Introduction ................................................................................................................ 1

2

Modeling of constructed wetlands ............................................................................ 33

2.1

Numerical models for SSF CWs ........................................................................ 3

2.2

The Constructed Wetland Model N°1 (CWM1)................................................. 4

Description of the CW2D and CWM1 biokinetic models....................................... 5
3.1

Principles ............................................................................................................ 5

3.2

Matrix format and notation ................................................................................. 5

3.3

Comparison of CW2D and CWM1 components and processes ......................... 7

3.4

CW2D biokinetic model ..................................................................................... 9
3.4.1 Stoichiometric matrix and reaction rates ................................................. 9
3.4.2 Model parameters .................................................................................. 12

3.5

CWM1 biokinetic model .................................................................................. 14
3.5.1 Stoichiometric matrix and reaction rates ............................................... 14
3.5.2 Model parameters .................................................................................. 17

3.6
4

When to use which biokinetic model? .............................................................. 18

Version 2 of HYDRUS GUI ..................................................................................... 19
4.1

Preliminary remarks.......................................................................................... 19

4.2

Pre-processing................................................................................................... 20
4.2.1 The "Solute Transport" window ............................................................ 20
4.2.2 The "Solute Transport Parameters" window ......................................... 21
4.2.3 The "Reaction Parameters" window ...................................................... 22
4.2.4 The "Constructed Wetland Model Parameters I" window .................... 23
4.2.5 The "Constructed Wetland Model Parameters II" window ................... 25
4.2.6 "Initial Conditions" on the Navigator Bar ............................................. 26

4.3

Post-processing ................................................................................................. 27
4.3.1 The "Results - Graphical Display" window .......................................... 27
4.3.2 The "Observation Nodes" window ........................................................ 28

5

Examples ................................................................................................................... 29
5.1

Pilot-scale vertical flow CW for wastewater treatment (Wetland 4) ................ 29

5.2

Pilot-scale horizontal flow CW for wastewater treatment (Wetland 5) ............ 35i5.2.1 System description and measured data .................................................. 35
5.2.2 Model set-up .......................................................................................... 35
5.2.3 Simulation results .................................................................................. 38
5.3
6

Input data.................................................................................................................. 42
6.1

7

Applications of the HYDRUS wetland module................................................ 41
The 'options.in' input file .................................................................... 42

Output data ............................................................................................................... 43
7.1

Format of the 'effluent.out' output file ............................................... 43

8

List of examples ........................................................................................................ 44

9References ................................................................................................................. 45ii

List of Figures
Figure 4.1: The "Domain types and Units" window. ....................................................................... 19
Figure 4.2: The "Solute Transport" window with a selection of the CW2D biokinetic model. ....... 20
Figure 4.3: The "Solute Transport" window with a selection of the CWM1 biokinetic model. ...... 21
Figure 4.4: The "Solute Transport Parameters" window for CWM1 (for length units in meters andtime units in days)........................................................................................................ 22
Figure 4.5: The "Solute Transport Parameters" window for CW2D (for length units in meters andtime units in days)........................................................................................................ 22
Figure 4.6: The "Reaction Parameters" window. ............................................................................. 23
Figure 4.7: The "Constructed Wetland Model (CW2D) Parameters I" window (for time units indays)............................................................................................................................. 24
Figure 4.8: The "Constructed Wetland Model No1 (CWM1) Parameters I" window (for time units
in days). ....................................................................................................................... 24
Figure 4.9: The "Constructed Wetland Model (CW2D) Parameters II" window (for time units indays)............................................................................................................................. 25
Figure 4.10: The "Constructed Wetland Model No1 (CWM1) Parameters II" window(for time units
in days). ....................................................................................................................... 25
Figure 4.11: "Initial Conditions" in the data tree of the Navigator Bar for CW2D (left) and CWM1
(right). .......................................................................................................................... 26
Figure 4.12: The "Import Initial Conditions" window for CWM1. ................................................. 26
Figure 4.13: The main window of HYDRUS GUI for CW2D with the "Results - Graphical
Display" section of the Navigator Bar open. ............................................................... 27
Figure 4.14: The main window of HYDRUS GUI for CWM1 with the "Results - Graphical
Display" section of the Navigator Bar open. ............................................................... 27
Figure 4.15: The "Observation Nodes" window for CW2D. ........................................................... 28
Figure 4.16: The "Observation Nodes" window for CWM1............................................................ 28
Figure 5.1: The "Copy Project" window. ......................................................................................... 29
Figure 5.2: Selection of the biokinetic model in the "Solute Transport" window............................ 29
Figure 5.3: Set up of diffusion coefficients in the "Solute Transport Parameters" window. ........... 30
Figure 5.4: Inflow concentrations in the "Time Variable Boundary Conditions" window. ............. 31
Figure 5.5: The "Default Domain Properties" window. ................................................................... 31
Figure 5.6: The "Time Information" window. ................................................................................. 32
Figure 5.7: Concentrations of fermentable, readily biodegradable soluble COD (SF) at 2 depths (theWetland 4 example). .................................................................................................... 32
Figure 5.8: Concentrations of nitrate nitrogen (SNO) at 3 depths (the Wetland 4 example). .......... 33
Figure 5.9: Concentrations of heterotrophic bacteria (XH) at 5 depths (the Wetland 4 example). .. 33iii

Figure 5.10: Concentrations of autotrophic bacteria (XA) at 5 depths (the Wetland 4 example). ... 34
Figure 5.11: Plan view of the HF CW showing sampling wells (left) and a cross-sectional view of
one of five intermediate sampling wells (right) (Headley et al., 2005). ...................... 35
Figure 5.12: BOD5 and NH4 concentrations measured along the flow path of the HF CW (Headley
et al., 2005). ................................................................................................................. 35
Figure 5.13: Material distribution (right: inlet distribution zone = Material 2). .............................. 36
Figure 5.14: Root water uptake distribution..................................................................................... 36
Figure 5.15: The "Time Variable Boundary Conditions" window................................................... 37
Figure 5.16: The Ammonia NH4 "Reaction Parameters" window. ................................................. 37
Figure 5.17: The Dissolved Oxygen "Reaction Parameters" window. ............................................ 37
Figure 5.18: Cumulative Root Solute Uptake for Dissolved Oxygen. ............................................. 38
Figure 5.19: Dissolved Oxygen concentrations in the two-dimensional domain. ............................ 38
Figure 5.20: Dissolved Oxygen concentrations in a vertical cross section through the HF bed 0.5 m
before the effluent. ....................................................................................................... 39
Figure 5.21: NH4-N concentrations along the flow path in a depth of 50 cm in the HF bed. ......... 39
Figure 5.22: Comparison of measured and simulated NH4-N concentrations along the flow path in a
depth of 50 cm of the HF bed. ..................................................................................... 39
Figure 5.23: Comparison of measured and simulated COD concentrations along the flow path in a
depth of 50 cm of the HF bed. ..................................................................................... 40iv

List of Tables
Table 3.1: Gujer matrix describing process kinetics and stoichiometry for heterotrophic bacterial
growth in an aerobic environment (adapted from Henze et al., 2000, using thenotations of Corominas et al., 2010) .............................................................................. 6
Table 3.2: Comparison of CW2D and CWM1 components............................................................... 7
Table 3.3: Definitions of CW2D and CWM1 components in the liquid and solid phases................. 7
Table 3.4: Comparison of CW2D and CWM1 processes. ................................................................. 8
Table 3.5: Stoichiometric coefficients for ammonium nitrogen. ....................................................... 9
Table 3.6: Stoichiometric coefficients for inorganic phosphorus. ..................................................... 9
Table 3.7: Stoichiometric matrix of reactions in CW2D (Langergraber and Šimůnek, 2005; see
Table 3.10 for definitions of the stoichiometric coefficients)...................................... 10
Table 3.8: Reaction rates in CW2D (Langergraber and Šimůnek, 2005). ....................................... 11
Table 3.9: Kinetic parameters in the CW2D biokinetic model (Langergraber and Šimůnek, 2005).
..................................................................................................................................... 12
Table 3.10: Temperature dependences, stoichiometric parameters, composition parameters andparameters describing oxygen transfer in the CW2D biokinetic model (Langergraberand Šimůnek, 2005). .................................................................................................... 13
Table 3.11: Stoichiometric matrix of reactions in CWM1 (Langergraber et al., 2009; see Table 3.16
for definitions of the stoichiometric coefficients)........................................................ 14
Table 3.12: Stoichiometric coefficients for ammonia nitrogen. ....................................................... 15
Table 3.13: Reaction rates in CWM1 - part 1 (Langergraber et al., 2009). ..................................... 15
Table 3.14: Reaction rates in CWM1 - part 2 (Langergraber et al., 2009). ..................................... 16
Table 3.15: Kinetic parameters in the CWM1 biokinetic model (Langergraber et al., 2009b). ....... 17
Table 3.16: Temperature dependences, stoichiometric parameters, composition parameters andparameters describing oxygen transfer in the CW2D biokinetic model (Langergraber
et al., 2009b). ............................................................................................................... 18
Table 3.17: Application of the biokinetic models for different applications ................................... 18
Table 4.1: Units of concentrations in the liquid and solid phases and of the bulk density, ............. 19
Table 4.2: Default values of diffusion coefficients for CW2D and CWM1 components (for length
units in meters and time units in days). ....................................................................... 22
Table 5.1: COD influent fractionation for organic matter components in CW2D and CWM1for a
total COD of 300 mg/L (values in mg/L). ................................................................... 30
Table 5.2: Influent concentrations (values in mg/L). ....................................................................... 30
Table 5.3: Parameters for root water and solutes uptake. ................................................................ 36
Table 6.1: Description of variables used in the 'options.in' input file. .................................. 42v

1

Introduction

Constructed Wetlands (CWs) are engineered water treatment systems that optimize thetreatment processes found in natural environments. CWs are popular systems whichefficiently treat different kinds of polluted water and are therefore sustainable
environmentally friendly solutions. A large number of physical, chemical and biologicalprocesses are simultaneously active and mutually influence each other (e.g., Kadlec andWallace, 2009). As complex systems, CWs for a long time have been considered as "blackboxes". Only little effort has been made to understand the main processes leading tocontaminant removal. Only recently, efforts have been made to understand the processes in
CWs in more detail, and modern tools from environmental microbiology, plant biology,
ecology, and molecular biology have been used for this purpose (e.g., Faulwetter et al.,2009).
During the last few years, models of different complexities have been developed fordescribing processes in SubSurface Flow (SSF) CWs. The main objective of numericalmodeling of CWs is to obtain a better understanding of the processes governing thebiological and chemical transformation and degradation processes, to provide insights into
these "black box" systems, and last but not least, to evaluate and improve existing design
criteria (Langergraber, 2008).
This report documents version 2 of the HYDRUS wetland module. Version 2 of the
HYDRUS wetland module includes two biokinetic model formulations: (1) the CW2D
module (Langergraber and Šimůnek, 2005), and/or (2) the CWM1 (Constructed Wetland
Model #1) biokinetic model (Langergraber et al., 2009b). In CW2D, aerobic and anoxictransformation and degradation processes for organic matter, nitrogen and phosphorus aredescribed, whereas in CWM1, aerobic, anoxic and anaerobic processes for organic matter,
nitrogen and sulphur are considered. CWM1 has been developed with the main goal toprovide a widely accepted model formulation for biochemical transformation anddegradation processes in SSF CWs. The HYDRUS wetland module is the only
implementation of a CW model that is currently publicly available.
Chapter 2 gives a brief overview of available numerical models for SSF CWs. Chapter 3
describes the CW2D and CWM1 biokinetic models, whereas Chapter 4 describes theirimplementation into HYDRUS. Chapter 5 describes two additional examples: Wetland 4shows the startup of a simulation using the CWM1 biokinetic model and Wetland 5 thesimulation of the effects of wetland plants. A description of additional input and output
files is then provided in Chapters 6 and 7, respectively.
For detailed information about the CW2D and CWM1 biokinetic models, the reader isreferred to the original papers, i.e., Langergraber and Šimůnek (2005) and Langergraber etal. (2009b), respectively. For detailed information on how to set-up models for SSF CWs
in HYDRUS, the reader is referred to the manual of version 1 of the HYDRUS wetland
module (Langergraber and Šimůnek, 2006). For general information on HYDRUS thereader is referred to Šimůnek et al. (2008), for detailed information on the software to thetechnical manual (Šimůnek et al., 2011).

12Modeling of constructed wetlands

2.1

Numerical models for SSF CWs

No free water level is visible in SSF CWs and water flows either horizontally or verticallythrough the porous filter media. Horizontal Flow (HF) systems can be simulated when only
water flow saturated conditions are considered. A series or network of continuously stirredtank reactors (CSTRs) is most frequently used to describe the hydraulics of these systems,
and reactions are modeled with various complexities. For modeling vertical flow (VF)CWs with intermittent loading, transient variably-saturated flow models are required. Dueto the intermittent loading, these systems are highly dynamic, adding to the complexity
needed to model the overall system. Models applicable to VF CWs use either the Richards
equation or other simplified approaches to describe variably-saturated flow.
The following list (Langergraber, 2011) summarizes process-based numerical models
available for subsurface flow CWs, whereby only models with minimum complexity indescribing water flow and/or biochemical processes are listed. More information on themodels can be found in recently published review papers (Langergraber, 2008, 2010; andLangergraber et al., 2009a) and in the original references, respectively.
1. Complex flow models with transport of a single solute• Schwager and Boller (1997): finite-element flow model, simulating tracer andoxygen transport in intermittent sand filters.
• Forquet et al. (2009): two-phase flow numerical model (based on finite-elements),
simulating the parallel movement of air and water in a VF filter.
2. Reactive transport models for saturated flow conditions• Reactive transport models applicable only for constant flow rates:- Mashauri and Kayombo (2002): only carbon transformation processes.
- Mayo and Bigambo (2005): only nitrogen transformation processes.
- Wang et al. (2009): only nitrogen transformation processes.
• Reactive transport models with a tanks-in-series approach for water flow:- Chen et al. (1999): only carbon transformation processes.
- Wynn and Liehr (2001): carbon and nitrogen transformation processes.
- Marsili-Libelli and Checchi (2005): carbon and nitrogen transformation
processes.
- Rousseau (2005): carbon and nitrogen transformation processes; a reaction
model in matrix notation based on the mathematical formulation of the
Activated Sludge Models (ASMs; Henze et al., 2000).
• Reactive transport models coupled to a complex groundwater flow model:- PHWAT (Brovelli et al., 2009a,b): carbon and nitrogen transformation
processes; a reaction model in the matrix notation based on ASMs, coupledwith the groundwater flow model MODFLOW; an extension of MODFLOW
for unsaturated zones is on the way to be implemented.

33. Reactive transport models for variably-saturated flow
• Reactive transport models with simplified approaches for simulating variablysaturated water flow:- McGechan et al. (2005): different horizontal layers to describe variablysaturated water flow; considers pools of organic matter, ammonium, nitrate andoxygen; microbiologically controlled transformations between these pools.
- FITOVERT (Giraldi et al., 2010): different horizontal layers to describe
variably-saturated water flow; a reaction model in the matrix notation based on
ASMs describing carbon and nitrogen transformation processes, implemented
in Matlab®.
- Freire et al. (2009): combination of CSTRs and dead-zones to describe
variably-saturated flow; description of the removal processes for the dye AO7
only.
• Reactive transport models coupled with flow models that use the Richards equation
to describe variably-saturated water flow:- CW2D (Langergraber, 2001; Langergraber and Šimůnek, 2005): implemented
in the HYDRUS software; a reaction model in the matrix notation based on
ASMs describing carbon, nitrogen, and phosphorous transformation processes,
it has most published applications.
- Ojeda et al. (2008): implemented in the RetrasoCodeBright (RCB) flow model,
simplified description of organic matter, nitrogen, and sulphur transformation
processes.
- Wanko et al. (2006): considers organic matter removal and oxygen transport in
VF filters.
- Maier et al. (2009): implemented in the MIN3P flow and transport code;
describes processes in CWs for the remediation of contaminated groundwater.

2.2

The Constructed Wetland Model N°1 (CWM1)The Constructed Wetland Model N°1 (CWM1) is a general model describing biochemicaltransformation and degradation processes for organic matter, nitrogen, and sulphur in SSF
CWs (Langergraber et al., 2009b). CWM1 has been published with the main goal toprovide a widely accepted model formulation for biochemical transformation anddegradation processes in CWs that can then be implemented in various simulation tools.
CWM1 describes all relevant aerobic, anoxic, and anaerobic biokinetic processes occurringin HF and VF CWs that need to be considered in order to predict effluent concentrations oforganic matter, nitrogen, and sulphur. 17 processes and 16 components (8 solute and 8
particulate components) are considered.
Version 2 of the HYDRUS wetland model provides the first available implementation of
CWM1.

4

3

Description of the CW2D and CWM1 biokinetic models

3.1

Principles

In version 2 of the HYDRUS wetland module, two biokinetic models for describing thetransformation and degradation processes are implemented:
1. CW2D (Langergraber and Šimůnek, 2005) was mainly developed for modeling VF
systems and therefore includes only aerobic and anoxic transformation anddegradation processes. These processes are described for the main constituents ofwastewater, i.e., organic matter, nitrogen, and phosphorus.
2. CWM1 (Constructed Wetland Model #1, Langergraber et al., 2009b) was
developed as a general model describing biochemical transformation anddegradation processes for organic matter, nitrogen, and sulphur in HF and VF CWs.
CWM1 describes all relevant aerobic, anoxic, and anaerobic biokinetic processes
occurring in HF and VF CWs required to predict effluent concentrations of organic
matter, nitrogen, and sulphur.
As the wastewater constituents considered in the CW2D and CWM1 biokinetic models aredifferent, it has to be noted that no direct conversion between model components ispossible and therefore provided by the HYDRUS GUI. The user is responsible for thecorrect use of the two biokinetic models.

3.2

Matrix format and notation

It is a common practice to present biokinetic models using the matrix notation introducedby the IWA (International Water Association) for ASMs (Henze et al., 2000). The Gujer
matrix consists of 3 parts representing:
1. stoichiometry,
2. kinetic rate expressions, and
3. composition.
A simple model representing aerobic heterotrophic bacteria growth and decay (adaptedfrom Henze et al., 2000) is chosen as an example to illustrate the use of the Gujer matrix.
Table 3.1 describes two processes (growth and decay of heterotrophic bacteria) and threecomponents (biomass, substrate, and dissolved oxygen). Bacteria need energy to integrate
their carbon substrate and produce new biomass. Heterotrophs (XOHO) find their energy
and their carbon source in an organic substrate (SB) and use dissolved oxygen (SO2) as anelectron acceptor under aerobic conditions. Consequently, only part of the substrate usedby bacteria will directly contribute to biomass growth (1/YOHO), whereas the other part isoxidized to produce energy (1-1/YOHO).
In this example, the growth rate depends on the maximum growth rate of the heterotrophic
biomass (μOHO,Max), the biomass concentration (XOHO), the availability of the substrate forthe bacteria (SB/(KSB,OHO+SB) where KSB,OHO is the half-saturation coefficient for SB), andthe availability of electron acceptors (SO2/(KSO2,OHO+SO2) where KSO2,OHO is the halfsaturation coefficient for SO2). The ratios SB/(KSB,OHO+SB) and SO2/(KSO2,OHO+SO2) are theMonod equations used as a switching function for substrate, nutrients, alkalinity, and5

electron acceptors. Similarly, when a process occurs only when a component is absent(e.g., dissolved oxygen in anoxic processes), the switching function takes the following
form: KO2, OHO/(KO2,OHO+SO2) .
The continuity check for every process is calculated by multiplying the stoichiometriccoefficients by the correlated term in the composition matrix for every component andsumming up for different processes (recalling that oxygen is negative COD, its coefficientmust thus be multiplied by -1).

← Mass balance

Component (i)

1

2

3

Process (j)

XOHO

SB

SO2

1. Growth1

2. Decay-1−

Stoichiometric parameters:
Kinetic parameters:

1
YOHO

−

(-mg COD/ L)

Dissolved
oxygen(mg COD/ L)

Substrate

Continuity →(mg COD/L)

Heterotrophic
biomass

Table 3.1: Gujer matrix describing process kinetics and stoichiometry for heterotrophic bacterial
growth in an aerobic environment (adapted from Henze et al., 2000, using the notations ofCorominas et al., 2010)

Process rate ρj

1 - YOHOYOHOμ OHO,Max-1

bOHO XOHO

SB
SO2
X OHO
K SB,OHO + SB K SO 2,OHO + SO2

YOHO = Heterotrophic yield coefficientµOHO,Max = Maximum heterotrophic growth rate
KSB,OHO = Half-saturation coefficient for substrate
KSO2,OHO = Half-saturation coefficient for oxygen
bOHO = Heterotrophic decay rate

The reaction rates for the three components are calculated by summing up the products ofthe stoichiometric factor and the process rate over the different processes. For the example
described above the reaction rates are calculated as follows:μ OHO,Max

rX OHO = μ OHO,maxrSB = −

1
YOHO

S O2

SB

K SB,OHO + S B K SO 2,OHO + S O2

μ OHO,max

SB

X OHO − b OHO X OHO

S O2

K SB,OHO + S B K SO 2,OHO + S O2

X OHO

 1 − YOHO S O2
SBμ OHO,maxrSO = −X OHO − b OHO X OHO
K SB,OHO + S B K SO 2,OHO + S O2
 YOHO 

6

(3.1)

3.3

Comparison of CW2D and CWM1 components and processes

Table 3.2 compares the components defined in the CW2D and CWM1 model formulations.
As described before, both biokinetic models describe processes affecting organic matterand nitrogen. Additionally, CW2D also describes processes affecting phosphorus, whereas
CWM1 describes processes affecting sulphur.
Table 3.2: Comparison of CW2D and CWM1 components.
CW2D (Langergraber and Šimůnek, 2005)

CWM1 (Langergraber et al., 2009b)

Organic matter, nitrogen, phosphorus

Organic matter, nitrogen, sulphur

CW2D components
1. SO: Dissolved oxygen, O2.
2. CR: Readily biodegradable soluble COD.
3. CS: Slowly biodegradable soluble COD.
4. CI: Inert soluble COD.
5. XH: Heterotrophic bacteria
6. XANs: Autotrophic ammonia oxidizing bacteria(Nitrosomonas spp.)
7. XANb: Autotrophic nitrite oxidizing bacteria(Nitrobacter spp.)
8. NH4N: Ammonium and ammonia nitrogen.
9. NO2N: Nitrite nitrogen.
10. NO3N: Nitrate nitrogen.
11. N2: Elemental nitrogen.
12. PO4P: Phosphate phosphorus

Soluble components
1. SO: Dissolved oxygen, O2.
2. SF: Fermentable, readily biodegradable soluble
COD.
3. SA: Fermentation products as acetate.
4. SI: Inert soluble COD.
5. SNH: Ammonium and ammonia nitrogen.
6. SNO: Nitrate and nitrite nitrogen.
7. SSO4: Sulphate sulphur.
8. SH2S: Dihydrogensulphide sulphur.
Particulate components
9. XS: Slowly biodegradable particulate COD.
10. XI: Inert particulate COD.
11. XH: Heterotrophic bacteria.
12. XA: Autotrophic nitrifying bacteria.
13. XFB: Fermenting bacteria.
14. XAMB: Acetotrophic methanogenic bacteria.
15. XASRB: Acetotrophic sulphate reducing bacteria.
16. XSOB: Sulphide oxidizing bacteria.

Organic nitrogen and organic phosphorus are modeled
as part of the COD.
Nitrification is modeled as a two-step process.
Bacteria are assumed to be immobile.
It is generally assumed that all components except
bacteria are soluble.

Organic nitrogen and organic phosphorus are modeled aspart of the COD.

Contrary to version 1 of the HYDRUS wetland module, organic matter components aredefined in both liquid and solid phases, i.e., adsorption/desorption processes of organic
matter components can be modeled in version 2. Table 3.3 summarizes in what phases(i.e., liquid and/or solid) the CW2D and CWM1 components are defined. It has to be notedthat the number of components in Table 3.3 for both CW2D and CWM1 is increased by
one to that given in Table 3.2. In both models, a non-reactive tracer that is independent ofother components is added. This non-reactive tracer is defined in both liquid and solid
phases.
Table 3.3: Definitions of CW2D and CWM1 components in the liquid and solid phases.
Component 1 2
3
4
5
6 7 8
9
10
11 12
13
14 15 16
L L+S L+S L+S S
S S L+S L
L
L L+S L+S CW2D
L L+S L+S L+S L+S L L L
L+S L+S S
S
S
S
S
S
CWM1
L = defined in the liquid phase only; S = defined in the solid phase only; L+S = defined in both liquid andsolid phases

Table 3.4 compares the processes defined in the CW2D and CWM1 model formulations.
In CW2D only aerobic and anoxic processes are defined. Two main types of bacteria are

7

17
L+S

modeled, heterotrophic and autotrophic bacteria. One special feature of CW2D is thatnitrification is modeled as a two-step process, from ammonia over nitrite to nitrate.
Since in CWM1 anaerobic processes are also defined, 6 different types of bacteria needs tobe described. Besides heterotrophic and autotrophic bacteria, also fermenting, acetotrophic
methanogenic, acetotrophic sulphate reducing and sulphide oxidising bacteria are definedin order to describe mainly anaerobic processes.

Table 3.4: Comparison of CW2D and CWM1 processes.
CW2D (Langergraber and Šimůnek, 2005)

CWM1 (Langergraber et al., 2009b)

Heterotrophic bacteria:
1. Hydrolysis: conversion of CS into CR.
2. Aerobic growth of XH on CR(mineralization of organic matter).
3. Anoxic growth of XH on CR (denitrification
on NO2N).
4. Anoxic growth of XH on CR (denitrification
on NO3N).
5. Lysis of XH.

Heterotrophic bacteria:
1. Hydrolysis: conversion of XS into SF.
2. Aerobic growth of XH on SF (mineralization of organic
matter).
3. Aerobic growth of XH on SA (mineralization of organic
matter).
4. Anoxic growth of XH on SF (denitrification).
5. Anoxic growth of XH on SA (denitrification).
6. Lysis of XH.
Autotrophic bacteria:
7. Aerobic growth of XA on SNH (nitrification).
8. Lysis of XA.
Fermenting bacteria:
9. Growth of XFB (fermentation).
10. Lysis of XFB.
Acetotrophic methanogenic bacteria:
11. Growth of XAMB: Anaerobic growth of acetotrophic,
methanogenic bacteria XAMB on acetate SA.
12. Lysis of XAMB.
Acetotrophic sulphate reducing bacteria:
13. Growth of XASRB: Anaerobic growth of acetotrophic,sulphate reducing bacteria.
14. Lysis of XASRB.
Sulphide oxidizing bacteria:
15. Aerobic growth of XSOB on SH2S: The opposite process toprocess 13, the oxidation of SH2S to SSO4.
16. Anoxic growth of XSOB on SH2S: Similar to process 15 butunder anoxic conditions.
17. Lysis of XSOB.

Autotrophic bacteria:
6. Aerobic growth of XANs on SNH(ammonium oxidation).
7. Lysis of XANs.
8. Aerobic growth of XANb on SNH (nitriteoxidation).
9. Lysis of XANb.

8

3.4

CW2D biokinetic model

3.4.1 Stoichiometric matrix and reaction rates
Table 3.5 and Table 3.6 show stoichiometric coefficients for ammonium nitrogen andinorganic phosphorus, respectively. Table 3.7 shows the stoichiometric matrix of reactions
in CW2D, whereas Table 3.8 shows the reaction rates.
Table 3.5: Stoichiometric coefficients for ammonium nitrogen.

ν1,N =
ν2,N =
ν3,N =
ν4,N =
ν5,N =
ν6,N =
ν7,N =
ν8,N =
ν9,N =

iN,CS - (1- fHyd,CI) . iN,CR - fHyd,CI . iN,CI
1/YH . iN,CR - iN,BM
1/YH . iN,CR - iN,BM
1/YH . iN,CR - iN,BM
iN,BM - (1 - fBM,CR - fBM,CI) . iN,CS - fBM,CR . iN,CR - fBM,CI . iN,CI- 1/YANs - iN,BM
iN,BM - (1 - fBM,CR - fBM,CI) . iN,CS - fBM,CR . iN,CR - fBM,CI . iN,CI- iN,BM
iN,BM - (1 - fBM,CR - fBM,CI) . iN,CS - fBM,CR . iN,CR - fBM,CI . iN,CI

See Table 3.10 for definitions of the composition and stoichiometric parameters.

Table 3.6: Stoichiometric coefficients for inorganic phosphorus.

ν1,P =
ν2,P =
ν3,P =
ν4,P =
ν5,P =
ν6,P =
ν7,P =
ν8,P =
ν9,P =

iP,CS - (1- fHyd,CI) . iP,CR - fHyd,CI . iP,CI
1/YH . iP,CR - iP,BM
1/YH . iP,CR - iP,BM
1/YH . iP,CR - iP,BM
iP,BM - (1 - fBM,CR - fBM,CI) . iP,CS - fBM,CR . iP,CR - fBM,CI . iP,CI- iP,BM
iP,BM - (1 - fBM,CR - fBM,CI) . iP,CS - fBM,CR . iP,CR - fBM,CI . iP,CI- iP,BM
iP,BM - (1 - fBM,CR - fBM,CI) . iP,CS - fBM,CR . iP,CR - fBM,CI . iP,CI

See Table 3.10 for definitions of the composition and stoichiometric parameters.

9

Table 3.7: Stoichiometric matrix of reactions in CW2D (Langergraber and Šimůnek, 2005; see
Table 3.10 for definitions of the stoichiometric coefficients).

10

Table 3.8: Reaction rates in CW2D (Langergraber and Šimůnek, 2005).
R Process / Reaction rate rcj
Heterotrophic organisms
1

Hydrolysis

Kh ⋅2c CS c XH⋅ c XHK X + c CS c XH

Aerobic growth of heterotrophs on readily biodegradable COD

µH ⋅
3

cO 2
c CR
⋅
⋅ f N , Het ⋅ c XH
K Het ,O 2 + c O 2 K Het ,CR + c CR

NO3-growth of heterotrophs on readily biodegradable COD

K DN ,O 2µ DN ⋅
4

K DN ,O 2 + c O 2

K DN , NO 2
c NO 3cCR⋅⋅⋅ f N , DN ⋅ c XH
K DN , NO 3 + c NO 3 K DN , NO 2 + c NO 2 K DN ,CR + cCR

NO2-growth of heterotrophs on readily biodegradable COD

K DN ,O 2µ DN ⋅
5⋅

K DN ,O 2 + c O 2⋅

c NO 2c CR⋅⋅ f N , DN ⋅ c XH
K DN , NO 2 + c NO 2 K DN ,CR + c CR

Lysis of heterotrophsb H ⋅ c XH
Autotrophic organisms 1 – Nitrosomonas
6

Aerobic growth of Nitrosomonas on NH4µ ANs ⋅7

cO 2
c NH 4c IP⋅⋅⋅ c XANs
K ANs ,O 2 + c O 2 K ANs , NH 4 + c NH 4 K ANs , IP + c IP

Lysis of NitrosomonasbHANs ⋅ c XANs
Autotrophic organisms 2 – Nitrobacter8

Aerobic growth of Nitrobacter on NO2µ ANb ⋅9cO 2
c NO 2⋅⋅ f N , ANb ⋅ c XANb
K ANb ,O 2 + c O 2 K ANb , NO 2 + c NO 2

Lysis of NitrobacterbHANb ⋅ c XANb
Conversion of solid and liquid phase concentrations

c XY =

ρ⋅ s XY , where Y = H , ANs, ANbθ

Factor for nutrientsf N ,x =c NH 4c IP⋅, where x = Het , DN , ANb
K x , NH 4 + c NH 4 K x , IP + c IP

See Table 3.9 for definitions of rate coefficients.

113.4.2 Model parameters
Table 3.9 shows the kinetic parameters, and Table 3.10 the temperature dependences,
stoichiometric parameters, composition parameters and parameters describing oxygen
transfer for the CW2D biokinetic model as described in Langergraber and Šimůnek (2005).
Table 3.9: Kinetic parameters in the CW2D biokinetic model (Langergraber and Šimůnek, 2005).
Description [unit]
Hydrolysis
Khhydrolysis rate constant [1/d]KX
saturation/inhibition coefficient for hydrolysis [g CODCS/g CODBM]
Heterotrophic bacteria (aerobic growth)maximum aerobic growth rate on CR [1/d]µHbHrate constant for lysis [1/d]Khet,O2
saturation/inhibition coefficient for SO [mg O2/L]
Khet,CR
saturation/inhibition coefficient for substrate [mg CODCR/L]
Khet,NH4N
saturation/inhibition coefficient for NH4 (nutrient) [mg N/L]
Khet,IPsaturation/inhibition coefficient for P [mg N/L]
Heterotrophic bacteria (denitrification)
maximum aerobic growth rate on CR [1/d]µDN
KDN,O2saturation/inhibition coefficient for SO [mg O2/L]
KDN,NO3N
saturation/inhibition coefficient for NO3 [mg N/L]
KDN,NO2N
saturation/inhibition coefficient for NO2 [mg N/L]
KDN,CRsaturation/inhibition coefficient for substrate [mg CODCR/L]
KDN,NH4N
saturation/inhibition coefficient for NH4 (nutrient) [mg N/L]
KDN,IPsaturation/inhibition coefficient for P [mg N/L]
Ammonia oxidising bacteria (Nitrosomonas spp.)
maximum aerobic growth rate on SNH [1/d]
µANs
bANs
rate constant for lysis [1/d]KANs,O2
saturation/inhibition coefficient for SO [mg O2/L]
KANs,NH4N
saturation/inhibition coefficient for NH4 [mg N/L]
KANs,IPsaturation/inhibition coefficient for P [mg N/L]
Nitrite oxidising bacteria (Nitrobacter spp.)
maximum aerobic growth rate on SNH [1/d]
µANb
bANb
rate constant for lysis [1/d]KANb,O2
saturation/inhibition coefficient for SO [mg O2/L]
KANb,NO2N
saturation/inhibition coefficient for NO2 [mg N/L]
KANb,NH4N
saturation/inhibition coefficient for NH4 (nutrient) [mg N/L]
KANb,IPsaturation/inhibition coefficient for P [mg N/L]
* Langergraber (2007)

12

Value
for 20°C (10°C)
3 (2)0.1 (0.22) *6 (3)0.4 (0.2)
0.2
2
0.05
0.01
4.8 (2.4)
0.2
0.5
0.5
4
0.05
0.01
0.9 (0.3)
0.15 (0.05)
1
0.5
0.01
1 (0.35)
0.15 (0.05) *
0.1
0.1
0.05
0.01

Table 3.10: Temperature dependences, stoichiometric parameters, composition parameters andparameters describing oxygen transfer in the CW2D biokinetic model (Langergraber and Šimůnek,2005).
Parameter
Description [unit]
Temperature dependences (activation energy [J/mol] for Arrhenius equation)
Tdep_het
Activation energy for processes caused by XH [J/mol]
Tdep_aut
Activation energy for processes caused by XA [J/mol]
Tdep_Kh
Activation energy Hydrolyses [J/mol]
Tdep_KX
Activation energy factor KX for hydrolyses [J/mol]
Tdep_KNHA
Activation energy for factor KNHA for nitrification [J/mol]Stoichiometric parameters
fHyd,CI
production of CI in hydrolysis
fBM,CR
fraction of CR generated in biomass lysis
fBM,CI
fraction of CI generated in biomass lysis
YHetyield coefficient for XH
YANs
yield coefficient for XANs
YANb
yield coefficient for XANb
Composition parameters
iN,CR
N content of CR [g N/g CODCR]
iN,CS
N content of CS [g N/g CODCS]
iN,CIN content of CI [g N/g CODCI]iN,BMN content of biomass [g N/g CODBM]
iP,CRP content of CR [g P/g CODCR]
iP,CS
P content of CS [g P/g CODCS]
iP,CIP content of CI [g P/g CODCI]iP,BMP content of biomass [g P/g CODBM]OxygencO2_sat_20
saturation concentration of oxygen [g/m³]
Tdep_cO2_sat
activation energy for saturation concentration of oxygen [J/mol]
rate_O2
re-aeration rate [1/d]* Langergraber (2007)

Value
47800
69000
28000
-53000 *-160000 *
0.0
0.1
0.02
0.63
0.24
0.24
0.03
0.04
0.01
0.07
0.01
0.01
0.01
0.02
9.18
-15000
240

13

3.5

CWM1 biokinetic model

3.5.1 Stoichiometric matrix and reaction rates
Table 3.11 shows the stoichiometric matrix of reactions in CWM1, Table 3.12
stoichiometric coefficients for ammonium nitrogen, and Table 3.13 and Table 3.14 thereaction rates.
Table 3.11: Stoichiometric matrix of reactions in CWM1 (Langergraber et al., 2009b; see
Table 3.16 for definitions of the stoichiometric coefficients).

14

Table 3.12: Stoichiometric coefficients for ammonia nitrogen.
ν 5,1 = iN,XS – (1-fHYD,SI) * iN,SF - fHYD,SI * iN,SI
ν 5,2 = ν 5,3 = iN,SF/YH – iN,BM
ν 5,4 = ν 5,5 = ν 5,11 = ν 5,13 = ν 5,15 = ν 5,16 = – iN,BM
ν 5,6 = ν 5,8 = ν 5,10 = ν 5,12 = ν 5,14 = ν 5,17 = iN,BM – fBM,SF * iN,SF – (1 – fBM,SF – fBM,XI) * iN,XS – fBM,XI * iN,XI
ν 5,7 = - i N, BM −1
YA

ν 5,9 = iN,SF/YFB – iN,BM
See Table 3.16 for definitions of the composition and stoichiometric parameters.

Table 3.13: Reaction rates in CWM1 - part 1 (Langergraber et al., 2009b).
R

Process / Reaction rate rcj

Heterotrophic organisms
1

Hydrolysis
X S ( X H + X FB )kh * 
 * ( X H + η h * X FB )
 K X + ( X S ( X H + X FB )) 2

Aerobic growth of XH on SF (mineralization)   SF  
 
SO
S NH
K H 2 SHSF * X H
 * 
 * 
 * 
 * 
K
S
S
S
K
S
K
S
K
S
+
+
+
+
+
F   F
A  
OH
o  
NHH
NH  
H 2 SHH 2S*  SF
µ H * 3

Aerobic growth of XH on SA (mineralization)
 SF  S F   K OH  
 
 

S NO
S NH
K H 2 SH * 
 * 
 * 
 * 
 * X H
 * 
η g * µ H * 
 K SF + S F   S F + S A   K OH + S o   K NOH + S NO   K NHH + S NH   K H 2 SH + S H 2 S * 

4Anoxic growth of XH on SF (denitrification)   SA  
 
SO
S NH
K H 2 SHSA * X H
 * 
 * 
 * 
 * 
 K SA + S A   S F + S A   K OH + S o   K NHH + S NH   K H 2 SH + S H 2 S * µ H * 5

Anoxic growth of XH on SA (denitrification)  S A   K OH  
 
 

S NO
S NH
K H 2 SHSA * 
 * 
 * 
 * 
 * X H
 * 
+
+
K
S
S
S
K
S
K
S
K
S
K
S
+
+
+
+
A   F
A  
OH
o  
NOH
NO  
NHH
NH  
H 2 SHH 2S*  SA

η g * µ H * 6

Lysis of XH

bH * X H
Autotrophic bacteria
7

Aerobic growth of XA on SNH (nitrification)  SO  S NH
K H 2 SA * X A
 * 
 * 
µ A * 
 K NHA + S NH   K OA + S o   K H 2 SA + S H 2 S * 

8Lysis of XAbA * X A

Fermenting bacteria
9Growth of XFB (fermentation)   K OFB   
K H 2 SFBK NOFBS NH
SF
 * 
 * 
 * 
 * 
 * X FB
+
+
+
+
+
K
S
K
S
K
S
K
S
K
S
F  
H 2 SFBH 2S*  
OFB
O  
NOFB
NO  
NHFB
NH 
 SFB

µ FB * 10

Lysis of XFB
b FB * X FB

See Table 3.15 for definitions of rate coefficients.

15

Table 3.14: Reaction rates in CWM1 - part 2 (Langergraber et al., 2009b).
Acetotrophic methanogenic bacteria
11

Growth of XAMB   K OAMB   K NOAMB 

K H 2 SAMB
S NH
SA * 
 * 
 * 
 * 
 * X AMB K SAMB + S A   K H 2 SAMB + S H 2 S *   K OAMB + SO   K NOAMB + S NO   K NHAMB + S NH µ AMB * 12

Lysis of XAMBb AMB * X AMB

Acetotrophic sulphate reducing bacteria
13

Growth of XASRB


 
 
  K OASRB   K NOASRB S SO 4
K H 2 SASRB
S NH
SA * 
 * 
 * 
 * 
 * 
 * X ASRB
+
+
+
+
+
+
K
S
K
S
K
S
K
S
K
S
K
S
A  
SOASRBSO 4  
H 2 SASRB
H 2S*  
OASRB
O  
NOASRBNO  NHASRBNH 
 SASRBµ ASRB * 14

Lysis of XASRBb ASRB * X ASRB

Sulphide oxidizing bacteria
15

Aerobic growth of XSOB on SH2S


 
 

SH 2S
SO
S NH
 * 
 * 
 * X SOB K SSOB + S H 2 S   K OSOB + SO   K NHSOB + S NH 

µ SOB * 

16

Anoxic growth of XSOB on SH2S
   K OSOB  

SH 2S
S NO
S NH
 * 
 * 
 * 
 * X SOB
+
+
+
+
K
S
K
S
K
S
K
S
H 2S  
NOSOB
NO  
OSOB
O  
NHSOB
NH 
 SSOBµ SOB *η SOB * 17

Lysis of XSOBb SOB * X SOB

See Table 3.15 for definitions of rate coefficients.

163.5.2 Model parameters
Table 3.15 shows the kinetic parameters in the CWM1 biokinetic model as described inLangergraber et al. (2009b).
Table 3.15: Kinetic parameters in the CWM1 biokinetic model (Langergraber et al., 2009b).
Parameter
Hydrolysis
Kh
KX

Description [unit]hydrolysis rate constant [1/d]saturation/inhibition coefficient for hydrolysis [g CODSF/g CODBM]
correction factor for hydrolysis by fermenting bacteria [-]ηH
Heterotrophic bacteria (aerobic growth and denitrification)
maximum aerobic growth rate on SF and SA [1/d]µH
correction factor for denitrification by XH [-]ηgbHrate constant for lysis [1/d]KOH
saturation/inhibition coefficient for SO [mg O2/L]
KSF
saturation/inhibition coefficient for SF [mg CODSF/L]
KSA
saturation/inhibition coefficient for SA [mg CODSA/L]
KNOH
saturation/inhibition coefficient for SNO [mg N/L]
KNHH
saturation/inhibition coefficient for SNH (nutrient) [mg N/L]
KH2SH
saturation/inhibition coefficient for SH2S [mg S/L]
Autotrophic bacteria
maximum aerobic growth rate on SNH [1/d]µAbA
rate constant for lysis [1/d]KOA
saturation/inhibition coefficient for SO [mg O2/L]
KNHA
saturation/inhibition coefficient for SNH [mg N/L]
KH2SA
saturation/inhibition coefficient for SH2S [mg S/L]
Fermenting bacteria
maximum aerobic growth rate for XFB [1/d]µFB
bFB
rate constant for lysis [1/d]
KOFB
saturation/inhibition coefficient for SO [mg O2/L]
KSFB
saturation/inhibition coefficient for SF [mg CODSF/L]
KNOFB
saturation/inhibition coefficient for SNO [mg N/L]
KNHFB
saturation/inhibition coefficient for SNH (nutrient) [mg N/L]
KH2SFBsaturation/inhibition coefficient for SH2S [mg S/L]
Acetotrophic methanogenic bacteria
maximum aerobic growth rate on for XAMB [1/d]
µAMB
bAMB
rate constant for lysis [1/d]KOAMB
saturation/inhibition coefficient for SO [mg O2/L]
KSAMB
saturation/inhibition coefficient for SA [mg CODSA/L]
KNOAMBsaturation/inhibition coefficient for SNO [mg N/L]
KNHAMBsaturation/inhibition coefficient for SNH (nutrient) [mg N/L]
KH2SAMBsaturation/inhibition coefficient for SH2S [mg S/L]
Acetotrophic sulphate reducing bacteria
maximum aerobic growth rate for XASRB [1/d]
µASRB
bASRB
rate constant for lysis [1/d]
KOASRBsaturation/inhibition coefficient for SO [mg O2/L]
KSASRBsaturation/inhibition coefficient for SA [mg CODSA/L]
KNOASRB
saturation/inhibition coefficient for SNO [mg N/L]KNHASRB
saturation/inhibition coefficient for SNH (nutrient) [mg N/L]
KSOASRB
saturation/inhibition coefficient for SSO4 [mg S/L]
KH2SASRB
saturation/inhibition coefficient for SH2S [mg S/L]
Sulphide oxidizing bacteria
maximum aerobic growth rate for XSOB [1/d]µSOB
correction factor for anoxic growth of XSOB [-]ηSOB *bSOB
rate constant for lysis [1/d]
KOSOB
saturation/inhibition coefficient for SO [mg O2/L]
KNOSOBsaturation/inhibition coefficient for SNO [mg N/L]
KNHSOBsaturation/inhibition coefficient for SNH (nutrient) [mg N/L]
KSSOB
saturation/inhibition coefficient for SH2S [mg S/L]

Value
for 20°C (10°C)
3 (2)0.1 (0.22)
0.1
6 (3)
0.8
0.4 (0.2)
0.2
2
4
0.5
0.05
140
1 (0.35)
0.15 (0.05)
1
0.5 (5)140
3 (1.5)
0.02
0.2
28
0.5
0.01
140
0.085
0.008
0.000256
0.0005
0.01
140
0.18
0.012
0.0002240.0005
0.01
19
140
5.28
0.8
0.15
0.2
0.5
0.05
0.24

* typing error in the original CWM1 publication.

17

Table 3.16 shows temperature dependences, stoichiometric parameters, composition
parameters and parameters describing oxygen transfer as described in Langergraber et al.
(2009b).
Table 3.16: Temperature dependences, stoichiometric parameters, composition parameters andparameters describing oxygen transfer in the CW2D biokinetic model (Langergraber et al., 2009b).
Parameter
Description [unit]
Temperature dependences (activation energy [J/mol] for Arrhenius equation)
Tdep_HyKh
Activation energy Hydrolyses [J/mol]
Tdep_HyKX
Activation energy factor KX for hydrolyses [J/mol]
Tdep_H
Activation energy for processes caused by XH [J/mol]
Tdep_A
Activation energy for processes caused by XA [J/mol]
Tdep_KNHA
Activation energy for factor KNHA for nitrification [J/mol]
Tdep_mueFB
Activation energy for XFB growth [J/mol]
Tdep_bFB
Activation energy for XFB lysis [J/mol]
Tdep_AMB
Activation energy for processes caused by XAMB [J/mol]
Tdep_ASRB
Activation energy for processes caused by XASRB [J/mol]
Tdep_SOB
Activation energy for processes caused by XSOB [J/mol]Stoichiometric parameters
fHyd,SI
production of SI in hydrolysis
fBM,SFfraction of SF generated in biomass lysis
fBM,XI
fraction of XI generated in biomass lysis
YH
yield coefficient for XH
YA
yield coefficient for XA
YFB
yield coefficient for XFB
YAMB
yield coefficient for XAMBYASRByield coefficient for XASRBYSOByield coefficient for XSOBComposition parameters
iN,SF
N content of SF [g N/g CODSF]
iN,SI
N content of SI [g N/g CODSI]iN,XSN content of XS [g N/g CODXS]iN,XIN content of XI [g N/g CODXI]iN,BMN content of biomass [g N/g CODBM]OxygencO2_sat_20
saturation concentration of oxygen [g/m³]
Tdep_cO2_sat
activation energy for saturation concentration of oxygen [J/mol]
rate_O2
re-aeration rate [1/d]

3.6

Value
28000
-5440047800
75800-160000
47800
0
0
0
0
0.0
0.05
0.1
0.63
0.24
0.053
0.032
0.05
0.12
0.03
0.01
0.04
0.03
0.07
9.18
-15000240

When to use which biokinetic model?

Table 3.17 provides hints which biokinetic model (i.e., CW2D or CWM1) to use fordifferent types of CWs and for what type of processes.
Table 3.17: Application of the biokinetic models for different applications
Biokinetic modelCW2D(Langergraber and Šimůnek, 2005)

Type of CW

•
•
•
•

Processes

18

VF CWsLow loaded HF beds
Modeling P retention in CWs
Modeling nitrification as a 2-stepprocess

CWM1(Langergraber et al., 2009b)• VF and HF CWs• Modeling anaerobic processes• Modeling transport and fate ofsulphur

4

Version 2 of HYDRUS GUI

4.1

Preliminary remarks

As described already in Langergraber and Šimůnek (2006), concentrations units in theliquid and solid phases, as well as units of the bulk density, are fixed after choosing thelength unit. In version 2 of HYDRUS this is done in the "Domain types and Units" window(Figure 4.1). The resulting concentration units are shown in Table 4.1.

Figure 4.1: The "Domain types and Units" window.

Table 4.1: Units of concentrations in the liquid and solid phases and of the bulk density,
Length Units
Concentrations in the liquid phase
Concentrations in the solid phase
Bulk density

m
g.m-3
g.t-1
t.m-3

cm
µg.cm-3 = µg.mL-1µg.g-1g.cm-3mm
ng.mm-3 = ng.µL-1
ng.mg-1
mg.mm-319

The HYDRUS user interface does not provide conversion of mass units and thus thedefault values of CW2D and CWM1 must be interpreted based on Table 4.1. Therefore
units of concentrations in the liquid and solid phases and of the bulk density are fixedaccording to Table 4.1 once the length units are chosen.

4.2Pre-processing

4.2.1 The "Solute Transport" window
To activate the HYDRUS wetland module in the GUI in the "Solute Transport" window(Figure 4.2), the "Wetland Module" box has to be checked. The Mass Units have to be set
according to the chosen length units (Table 4.1). If the CW2D biokinetic model is chosen
in Figure 4.2, the Number of Solutes is equal to 13 (12 CW2D components and one nonreactive tracer, independent of the other 12 compounds). If CWM1 is selected (Figure 4.3)
the Number of Solutes is set to 17 (16 CWM1 components and one non-reactive tracer). If
the Wetland Module is chosen, the "Attachment/Detachment Concept" (used in thestandard HYDRUS to simulate the transport of particles, such as colloids, viruses, andbacteria) cannot be used and the Initial Conditions cannot be given in Total
Concentrations. Initial Conditions need to be given in liquid or solid phase concentrations.

Figure 4.2: The "Solute Transport" window with a selection of the CW2D biokinetic model.

20

Figure 4.3: The "Solute Transport" window with a selection of the CWM1 biokinetic model.

Please note that the Iteration Criteria in the "Solute Transport" window are used to adapt
time steps based on the maximum allowed change in the dissolved oxygen concentration(∆c < cabs + crel.c) during a particular time step when using the Wetland module (despite
the text in the window stating that the iteration criteria are defined for Nonlinear
Adsorption only). When this criterion is not fulfilled, the next time step will be reduced(see the dMul2 variable in the HYDRUS technical manual, Šimůnek et al., 2011).
Dissolved oxygen is the critical component in both CW2D and CWM1 with respect to theirnumerical stability as its reaction rates are fastest.
4.2.2 The "Solute Transport Parameters" window
Figure 4.4 and Figure 4.5 show the "Solute Transport Parameters" windows for CWM1and CW2D, respectively. In the "Solute Transport Parameters" window the generaltransport parameters are set (i.e., bulk density, longitudinal and transverse dispersivities,
and diffusion coefficients in the liquid and gaseous phases; for the description of chemicaland physical non-equilibrium transport parameters Fract and ThImob see the HYDRUS
manual, Šimůnek et al., 2011).

21

Figure 4.4: The "Solute Transport Parameters" window for CWM1 (for length units in meters andtime units in days).

Figure 4.5: The "Solute Transport Parameters" window for CW2D (for length units in meters andtime units in days).

Table 4.2 summarises the diffusion coefficients suggested for CW2D and CWM1
compounds. For a comparison with literature data see Langergraber and Šimůnek (2006).
The same diffusion coefficient is used for all organic compounds, as well as for all
nitrogen compounds. Due to the lack of data, diffusion coefficients for inorganic
phosphorus and sulphur compounds are assumed to be the same as for nitrogen.
Table 4.2: Default values of diffusion coefficients for CW2D and CWM1 components (for length
units in meters and time units in days).
Compound
Dissolved oxygen
Organic matter
Ammonium nitrogen
Nitrite nitrogen
Nitrate nitrogen
Elemental nitrogen
Phosphate phosphorus
Sulphate sulphur
Dihydrogensulphide sulphur

CW2D
SO
CR, CS, CI
NH4N
NO2N
NO3N
N2
PO4P
-

Liquid
1.73E-04
1.09E-04
1.92E-04
1.92E-04
1.92E-04
1.92E-04
1.92E-04-

Gaseous
1.85
-

CWM1
SO
SF, SA, SI, XS, XI
SNH
SNO
SSO4
SH2S

Liquid
1.73E-04
1.09E-04
1.92E-04
1.92E-04
1.92E-04
1.92E-04

Gaseous1.85-

4.2.3 The "Reaction Parameters" window
Figure 4.6 shows the "Reaction Parameters" window for dissolved oxygen. One "Reaction
Parameters" window is shown for each defined compound. All CW2D and CWM1 kinetic
reactions are implemented as zero-order rate equations separately from the reactions

22

defined in these HYDRUS windows. Therefore all reaction rates in these windows shouldbe zero. Only parameters for the following processes need to be set in these windows:
1. Adsorption and desorption parameters (Kd, Nu, Beta, Alpha)2. Uptake of compounds via roots (cRoot)
For the description of these parameters the reader is referred to the HYDRUS manual(Šimůnek et al., 2011).

Figure 4.6: The "Reaction Parameters" window.

4.2.4 The "Constructed Wetland Model Parameters I" window
The "Constructed Wetland Model Parameters I" and "Constructed Wetland Model
Parameters II" windows show the parameters of the biokinetic models, depending on
which one is chosen. Figure 4.7 and Figure 4.8 show the kinetic parameters of the CW2D
and CWM1 biokinetic models as listed in Table 3.9 and Table 3.15, respectively.

23

Figure 4.7: The "Constructed Wetland Model (CW2D) Parameters I" window (for time units indays).

Figure 4.8: The "Constructed Wetland Model No1 (CWM1) Parameters I" window (for time units
in days).

24

4.2.5 The "Constructed Wetland Model Parameters II" window
Figure 4.9 and Figure 4.10 show the temperature dependences, stoichiometric parameters,
composition parameters, and parameters describing oxygen transfer for the CW2D and
CWM1 biokinetic models as listed in Table 3.10 and Table 3.16, respectively.

Figure 4.9: The "Constructed Wetland Model (CW2D) Parameters II" window (for time units indays).

Figure 4.10: The "Constructed Wetland Model No1 (CWM1) Parameters II" window(for time units
in days).

25

4.2.6 "Initial Conditions" on the Navigator Bar
Figure 4.11 shows the "Initial Conditions" part of the data tree of the Navigator Bar (theleft sidebar of the HYDRUS GUI) for CW2D and CWM1. Names of all components arelisted here, with the "L" letter denoting the initial concentration in the liquid phase and "S"
the initial concentration in the solid phase. The names of the same components also appear
when importing initial conditions from previous simulation runs, as shown in Figure 4.12
for CWM1.

Figure 4.11: "Initial Conditions" in the data tree of the Navigator Bar for CW2D (left) and CWM1
(right).

Figure 4.12: The "Import Initial Conditions" window for CWM1.

26

4.3

Post-processing

4.3.1 The "Results - Graphical Display" window
Figure 4.13 and Figure 4.14 show the main window of the HYDRUS GUI with the"Results - Graphical Display" section of the Navigator Bar open for CW2D and CWM1,
respectively. In both figures the concentration of heterotrophic organisms is shown.
Similarly as when defining the initial conditions, the names of all components are listed inthis section of the Navigator Bar.

Figure 4.13: The main window of HYDRUS GUI for CW2D with the "Results - Graphical
Display" section of the Navigator Bar open.

Figure 4.14: The main window of HYDRUS GUI for CWM1 with the "Results - Graphical
Display" section of the Navigator Bar open.

27

4.3.2 The "Observation Nodes" window
Figure 4.15 and Figure 4.16 show the "Observation Nodes" window for CW2D and
CWM1, respectively. Again names of all variables are displayed, including all biochemicalcompounds.

Figure 4.15: The "Observation Nodes" window for CW2D.

Figure 4.16: The "Observation Nodes" window for CWM1.

28

5

Examples5.1

Pilot-scale vertical flow CW for wastewater treatment (Wetland 4)

The Wetland 4 example is the same as the Wetland 1 example described in Chapter 5.1 of themanual for version 1 of the HYDRUS wetland model (Langergraber and Šimůnek, 2006),
except evaluated using the CWM1 model instead of the CW2D biokinetic model. In thefollowing text, the steps needed to set-up Wetland 4 from Wetland 1 are shown. To ensurethat all other factors (e.g., transport domain, FE-mesh, water flow) of this project remain thesame and only the reactive transport parameters are changed we start by copying the
Wetland 1 project and rename it Wetland 4 (Figure 5.1). Note that in Wetland 1 the length
units were centimeters and the time units were hours and that they remain the same in
Wetland 4. After opening the project, we change the biokinetic model from CW2D to CWM1
in the "Solute Transport" window (Figure 5.2).

Figure 5.1: The "Copy Project" window.

Figure 5.2: Selection of the biokinetic model in the "Solute Transport" window.

29

In the next step the diffusion coefficients must be specified in the "Solute TransportParameters" window (Figure 5.3), e.g., to default values as shown in Figure 4.4.

Figure 5.3: Set up of diffusion coefficients in the "Solute Transport Parameters" window.

In Wetland 1, adsorption was considered for phosphorus and the tracer compound (CW2D
components 12 and 13, respectively). In the "Reaction Parameters" window (Figure 4.6) the
adsorption parameters have to be checked and the parameters Kd and Alpha have to be set to 0
for CWM1 components 12 through 16.
The next step is to specify the influent concentrations in the "Time Variable Boundary
Conditions" window. The COD fractionation, i.e., the distribution of the total COD between
individual COD model fractions, has to be done. A comparison between organic mattercomponents in CW2D and CWM1 is shown in Table 5.1. It is assumed that CI = SI + XI (theinert fraction is the same); CS = XS; and CR = SF+SA (mostly SF) (Table 5.1).
Table 5.1: COD influent fractionation for organic matter components in CW2D and CWM1 for a total
COD of 300 mg/L (values in mg/L).
CW2D components

CR

CS

CI

Value

160

120

20

CWM1 components

SF

SA

SI

XS

XI

Value

155

5

10

120

10

Table 5.2 shows the influent concentrations used for the Wetland 4 example. Figure 5.4 showswhere and how to specify the influent concentrations of individual components (note thatcomponent 17 is an independent tracer; also note that in cValx-y, x is the BC number and y is
the component number). Similarly as in Wetland 1, cValue2, i.e., the 2nd vector of the timedependent solute concentrations, is used in Wetland 4 as well.
Table 5.2: Influent concentrations (values in mg/L).
Components

SO

SF

SA

SI

SNH

SNO

SSO4 SH2S XS

XI

Value

1

155

5

10

60

0.1

20

10

30

0.1

120

Figure 5.4: Inflow concentrations in the "Time Variable Boundary Conditions" window.

The next step is to set initial conditions for the CWM1 components (note that this Table, i.e.,"Default Domain Properties", is available only for simple rectangular geometries and that for
general geometries, one needs to define initial conditions graphically). A simple approach to
set the initial conditions is chosen: all liquid and solid phase concentrations are set to 1 if thecomponent is considered or to 0 if not, i.e. for Wetland 4 this results in: L1-L10 =1; L11L16 =0; L17 =1; S1-10 =0 and S11-17 =1 (Figure 5.5). Although 13 or 17 components are
displayed in this table for CW2D and CWM1 modules, initial values need to be specified only
for those, which are needed as shown in Table 3.3.

Figure 5.5: The "Default Domain Properties" window.

Finally, since we want to run the simulation for 10 days we have to adjust the Final Time inthe "Time Information" window (Figure 5.6). Since we want to repeat the same loading31

pattern each day, the Number of times to repeat the same set of BC records is therefore set to
10. The Maximum Time Step is 60 seconds. Together with the settings for iteration criteria inthe "Solute Transport" window (Figure 5.2), the Maximum Time Step defines the stability of
the numerical solution (see before). For Wetland 4 with a Maximum Time Step of 60 seconds,
an Absolute Concentration Tolerance of 0.01 mg/L is a setting that avoids numericalinstabilities.

Figure 5.6: The "Time Information" window.

Figure 5.7 through Figure 5.10 show the simulation results at 5 observation nodes during thefirst 10 days for fermentable soluble COD (SF), nitrate nitrogen (SNO), heterotrophic bacteria(XH), and autotrophic bacteria (XA), respectively. The observation nodes have been set at
depths of 1, 5, 10, 25, and 60 cm in the vertical flow filter. The observation node at the 60-cm
depth (#1) represents the effluent concentration. Please note that simulation results obtained
by CWM1 for this example have not been verified using measured data.

Figure 5.7: Concentrations of fermentable, readily biodegradable soluble COD (SF) at 2 depths (theWetland 4 example).
32

Figure 5.8: Concentrations of nitrate nitrogen (SNO) at 3 depths (the Wetland 4 example).

Figure 5.9: Concentrations of heterotrophic bacteria (XH) at 5 depths (the Wetland 4 example).

33

Figure 5.10: Concentrations of autotrophic bacteria (XA) at 5 depths (the Wetland 4 example).

34

5.2

Pilot-scale horizontal flow CW for wastewater treatment (Wetland 5)

5.2.1 System description and measured data
The Wetland 5 example is based on the experiments for a HF CW described by Headley et al.
(2005). The experimental site consisted of a 1 m deep HF CW planted with Schoenoplectus
tabernaemontani (soft stem bulrush) and was designed to treat primary settled municipal
wastewater in sub-tropical New South Wales, Australia. Water samples were collected fromthe upper (0.17 m), middle (0.5 m), and lower (0.83 m) depths at five equally-spaced sample
points along the longitudinal axis of the 8.8 m² bed (Figure 5.11). Figure 5.12 shows measured
data for BOD5 and NH4 concentrations measured along the flow path of the HF CW obtained
at a hydraulic loading rate of 40 mm/d.

Figure 5.11: Plan view of the HF CW showing sampling wells (left) and a cross-sectional view of oneof five intermediate sampling wells (right) (Headley et al., 2005).

Figure 5.12: BOD5 and NH4 concentrations measured along the flow path of the HF CW (Headley etal., 2005).

5.2.2 Model set-up
The width of the transport domain was 5.5 m, its depth was 1.1 m (1 m bed depth and 0.1 m
free board are simulated), and the slope of the domain was 0.1°. The transport domain itself
was discretized into 37 columns and 26 rows. This resulted in a structured two-dimensional
finite element mesh consisting of 926 nodes and 1800 triangular finite elements. As describedby Headley et al. (2005), the first 0.5 m on the right part of the domain is a distribution zone
(a right part of Figure 5.13) that consists of a different material than the main bed. An
atmospheric BC is used at the inlet point (a top right part in Figure 5.13) and a constantpressure head BC (a constant head of 95 cm at a node 5 cm above the bottom of the domain)at the outlet point (bottom left in Figure 5.13) of the system. This guarantees that the waterlevel in the HF bed is maintained at 1 m. Calculations for Wetland 5 have been carried out

35

using the CW2D biokinetic model. Using instead the CWM1 biokinetic model can be done as
described in Wetland 4.

Z

X

Figure 5.13: Material distribution (right: inlet distribution zone = Material 2).

Headley et al. (2005) reported that the root biomass was very dense in the upper 25 cm of HF
bed, decreased rapidly with depth, and only very few roots were observed at depths greaterthan 40 cm below the surface. The root distribution was set up accordingly (Figure 5.14).
Note that no roots are present in the inlet distribution zone.

Z

X

0.000 0.091 0.182 0.273 0.364 0.455 0.545 0.636 0.727 0.818 0.909 1.000, Min=0.000, Max=1.000

Project Head1_fin - CWHeadley et al. (2005) - hydr.0.02 - Disp = 0.1 - O2 = 4g
Domain Properties, Root Water Uptake

Figure 5.14: Root water uptake distribution.

Parameters for root water and solutes uptake are shown in Table 5.3 and the settings in the
GUI in Figure 5.15 through Figure 5.17. The negative value of cRoot for Dissolved Oxygen isused to model oxygen release from the plant roots.
Table 5.3: Parameters for root water and solutes uptake.
Parameter

Value

Unit

Window

Potential transpiration rate

0.0115m/hTime Variably Boundary Conditions (Figure 5.15)

cRoot (Ammonia NH4)

50

g/m³

Reaction Parameters for NH4 (Figure 5.16)

cRoot (Dissolved Oxygen)

-800

g/m³

Reaction Parameters for Oxygen (Figure 5.17)

36

Figure 5.15: The "Time Variable Boundary Conditions" window.

Figure 5.16: The Ammonia NH4 "Reaction Parameters" window.

Figure 5.17: The Dissolved Oxygen "Reaction Parameters" window.

37

5.2.3 Simulation results
Figure 5.18 shows the cumulative oxygen release by plant roots for a simulation time of 1day. The simulated cumulative release is 20 g/m (a minus value for uptake indicates a releaseof oxygen). This results in a specific oxygen release of 2.5 g/m²/d (the total area covered byplants is 8 m² (5 m length of the bed times 1.6 m width), a rather conservative value.
However, this oxygen release resulted in dissolved oxygen concentrations of about 0.1 mg/L
in the root zone near the outlet of the bed (Figure 5.19 and Figure 5.20). Note that the contour
levels in Figure 5.19 were adjusted to emphasize small values. Only by considering oxygen
release by plant roots it was possible to simulate the decrease of NH4-N concentrations along
the flow path in the HF bed (Figure 5.21). Figure 5.22 and Figure 5.23 show that thesimulation results are in good agreement with measured data for NH4-N and COD
concentrations, respectively.

Figure 5.18: Cumulative Root Solute Uptake for Dissolved Oxygen.

Z

X

0.000 0.025 0.050 0.100 0.250 0.500 0.750 1.000 2.000 4.000 7.000 10.000

Dissolved Oxygen - L1[-], Min=0.000, Max=9.813

Figure 5.19: Dissolved Oxygen concentrations in the two-dimensional domain.

38

Figure 5.20: Dissolved Oxygen concentrations
in a vertical cross section through the HF bed
0.5 m before the effluent.

Figure 5.21: NH4-N concentrations along theflow path in a depth of 50 cm in the HF bed.

40

35

NH4-N (mg/L)

30

25

20

15

Simulated data

10

Simulated inlet/outlet
Measured data

5

0
0

1

2

3

4

5

Distance from the inlet (m)Figure 5.22: Comparison of measured and simulated NH4-N concentrations along the flow path in a
depth of 50 cm of the HF bed.

39

200

COD (mg/L)

180
160

Simulated data

140

Simulated inlet/outlet

120

Measured data

100
80
60
40
20
0
0

1

2

3

4

5

Distance from the inlet (m)Figure 5.23: Comparison of measured and simulated COD concentrations along the flow path in a
depth of 50 cm of the HF bed.

40

5.3

Applications of the HYDRUS wetland module

The following list gives an overview of different applications, in which the HYDRUS wetland
module was used:•

CWs for treating combined sewer overflow (compare example "Wetland 3" asdescribed in chapter 5.3 of Langergraber and Šimůnek, 2006): Dittmer et al. (2005),
Henrichs et al. (2007, 2009), and Meyer et al. (2008).

•

CWs treating effluents of the wastewater treatment plant for irrigation purposes:
Toscano et al. (2009).

•

Simulating run-off from agricultural sites and the effect of streamside managementzones: Smethurst et al. (2009, 2010).

41

6

Input data

6.1

The 'options.in' input file

An additional option, namely limited effluent flow rates, can be specified in the additional
input file 'options.in'.
The 'options.in' input file is not supported by the graphical user interface of the
HYDRUS software. It needs to be created manually and placed in the temporary working
directory created by HYDRUS (Šimůnek et al., 2011). If this input file does not exist, thenHYDRUS does not consider this additional option (note that this file was more extensive inthe past, but a lot of the special options in version 1 have become standard features in version
2).
The definition of variables used in 'options.in' is given in Table 6.1, and an example ofthe file is given below:

Input file "Options.in"lSeepLimitqSLimit (positive)f0.

Table 6.1: Description of variables used in the 'options.in' input file.
Variable name

Type

Unit

Description

lSeepLimit

logical-= true: use the maximum effluent flow rate for a seepage face BC;= false: normal seepage face BC

qSLimit

float

[L/T]

Maximum allowed seepage face flux (positive)42

7

Output data

7.1

Format of the 'effluent.out' output file

An additional output-file 'effluent.out' is created that contains information about
effluent concentrations along the outflow boundary. If multiple outflow boundaries exist, only
the concentration value for the first boundary from this list (free drainage boundary, seepage
face boundary, variable flux boundary, and constant flux boundary) is printed. This file isprinted during the simulation run.
All solute fluxes and cumulative solute fluxes are positive out of the regionTimecEff(1)cEff(2)...

cEff(12)cEff(13).0000010.0009541.0033000::.870194E+01.870195E+01.870198E+01.227306E+00.227296E+00.227269E+00

...
...
...

.162806E+01.162805E+01.162804E+01.138496E+01.138496E+01.138496E+01

TempEff
20.0000
20.0000
20.0000

The 'effluent.out' output file can be found in the temporary working directory createdby HYDRUS (Šimůnek et al., 2011).

43

8

List of examples

For CW2D
For the description of the CW2D examples see Langergraber and Šimůnek (2006).
a) Wetland1
A pilot-scale vertical flow constructed wetland (PSCW, chapter 5.1 in Langergraber andŠimůnek, 2006); an example of flow and reactive transport simulations.
b) Wetland2
A two-stage vertical flow constructed wetland (SSP, chapter 5.2 in Langergraber andŠimůnek, 2006); an example of reactive transport simulations.
c) Wetland3
A lab-scale vertical flow constructed wetland for treatment of combined sewer overflow(CSOCW, chapter 5.3 in Langergraber and Šimůnek, 2006); an example for controlled
effluent rate.
d) Wetland5
An experimental HF CW described by Headley et al. (2005); an example for simulating theinfluence of wetland plants (see chapter 5.2 of this manual).
For CWM1e) Wetland4
Same as Wetland 1 but using the CWM1 biokinetic model; an example of how to start asimulation using the new CWM1 biokinetic model (see chapter 5.1 of this manual).

44

9References

Brovelli, A., Baechler, S., Rossi, L., Barry, D.A. (2009a): Comprehensive process-based modelling of sandfilters and subsurface flow constructed wetlands. In: Bayona, J.M., García, J. (Eds.): 3rd International
Symposium on "Wetland Pollutant Dynamics and Control – WETPOL 2009" – Book of Abstracts, 20-24
September 2009, Barcelona, Spain, pp. 293-294.
Brovelli, A., Malaguerra, F., Barry, D.A. (2009b): Bioclogging in porous media: Model development andsensitivity to initial conditions. Environ Model Softw 24(5), 511-25.
Chen, S., Wang, G.T., Xue, S.K. (1999): Modeling BOD removal in constructed wetlands with mixing cellmethod. J Environ Eng 125(1), 64-71.
Corominas, L., Rieger, L., Takács, I., Ekama, G., Hauduc, H., Vanrolleghem, P.A., Oehmen, A., Gernaey,
K.V., Comeau, Y. (2010): New framework for standardized notation in wastewater treatment modelling.
Water Sci Technol 61(4), 841-857.
Dittmer, U., Meyer, D., Langergraber, G. (2005): Simulation of a Subsurface Vertical Flow ConstructedWetland for CSO Treatment. Water Sci Technol 51(9), 225-232.
Faulwetter, J.L., Gagnon, V., Sundberg, C., Chazarenc, F., Burr, M.D., Brisson, J., Camper, A.K., Stein,
O.R. (2009): Microbial processes influencing performance of treatment wetlands: A review. Ecol Eng 35,
987-1004.
Forquet, N., Wanko, A., Mosé, R., Sadowski, A.-G. (2009): Diphasic modelling of vertical flow filter. Ecol
Eng 35(1), 47-56.
Freire, F.G., Davies, L.C., Vacas, A.M., Novais, J.M., Martins-Dias, S. (2009): Influence of operating
conditions on the degradation kinetics of an azo-dye in a vertical flow constructed wetland using a simple
mechanistic model. Ecol Eng 35(10), 1379-1386.
Giraldi, D., de’Michieli Vitturi, M., Iannelli, R. (2010): FITOVERT: a dynamic numerical model ofsubsurface vertical flow constructed wetlands. Environ Model Softw 25, 633–640.
Headley, T., Herity, E., Davison, L. (2005): Treatment at different depths and vertical mixing within a 1-m
deep horizontal subsurface-flow wetland. Ecol Eng 25(5), 567-582.
Henrichs, M., Langergraber, G., Uhl, M. (2007): Modelling of organic matter degradation in constructedwetlands for treatment of combined sewer overflow. Sci Total Environ 380(1-3), 196-209.
Henrichs, M., Welker, A., Uhl, M. (2009): Modelling of biofilters for ammonium reduction in combined
sewer overflow. Water Sci Technol 60(3), 825-831.
Henze, M., Gujer, W., Mino, T., van Loosdrecht, M.C.M. (2000): Activated sludge models ASM1, ASM2,
ASM2D and ASM3. IWA Scientific and Technical Report No.9, IWA Publishing, London, UK.
Kadlec, R., Wallace, S. (2009): Treatment Wetlands. 2nd edition, CRC press, Boca Raton, FL, USA.
Langergraber, G. (2001): Development of a simulation tool for subsurface flow constructed wetlands.
Wiener Mitteilungen 169, Vienna, Austria, 207p (ISBN 3-85234-060-8).
Langergraber, G. (2007): Simulation of the treatment performance of outdoor subsurface flow constructedwetlands in temperate climates. Sci Total Environ 380(1-3), 210-219.
Langergraber, G. (2008): Modeling of processes in subsurface flow constructed wetlands – A review.
Vadoze Zone J 7(2), 830-842.
Langergraber, G. (2010): Process based models for subsurface flow constructed wetlands. In: Vymazal, J.
(ed.): "Water and Nutrient Management in Natural and Constructed Wetlands", Springer Science +Business Media B.V., Dordrecht Heidelberg London New York, pp.21-36 (ISBN 978-90-481-9584-8).
Langergraber, G. (2011): Numerical modelling: A tool for better constructed wetland design? Water Sci
Technol, accepted for publication.
Langergraber, G., Šimůnek, J. (2005): Modeling variably-saturated water flow and multi-component
reactive transport in constructed wetlands. Vadose Zone J 4(4), 924-938.
Langergraber, G., Šimůnek, J. (2006): The multi-component reactive transport module CW2D for
constructed wetlands for the HYDRUS Software Package. HYDRUS Software Series 2, Department ofEnvironmental Sciences, University of California Riverside, Riverside, CA, USA, 72p.

45

Langergraber, G., Giraldi, D., Mena, J., Meyer, D., Peña, M., Toscano, A., Brovelli, A, Korkusuz, E.A.
(2009a): Recent developments in numerical modelling of subsurface flow constructed wetlands. Sci Total
Environ 407(13), 3931-3943.
Langergraber, G., Rousseau, D., García, J., Mena, J. (2009b): CWM1 - A general model to describe
biokinetic processes in subsurface flow constructed wetlands. Water Sci Technol 59(9), 1687-1697.
Langergraber, G., Tietz, A., Haberl, R. (2007): Comparison of measured and simulated distribution of
microbial biomass in subsurface vertical flow constructed wetlands. Water Sci Technol 56(3), 233-240.
Maier, U., DeBiase, C., Baeder-Bederski, O., Bayer, P. (2009): Calibration of hydraulic parameters forlarge-scale vertical flow constructed wetlands. J Hydrol 369, 260–273.
Marsili-Libelli, S., Checchi N..(2005): Identification of dynamic models for horizontal subsurface
constructed wetlands. Ecol Model 187(2-3), 201-218.
Mashauri, D.A., Kayombo. S. (2002): Application of the two coupled models for water quality
management: facultative pond cum constructed wetland models. Phys Chem Earth 27(11-12), 773–781.
Mayo, A.W., Bigambo. T. (2005): Nitrogen transformation in horizontal subsurface flow constructedwetlands I: Model development. Phys Chem Earth 30(11-16), 658-667
McGechan, M.B., Moir, S.E., Castle, K., Smit, I.P.J. (2005): Modelling Oxygen Transport in a Reedbedconstructed Wetland Purification System for Dilute Effluents. Biosyst Eng 91(2), 191-200.
Meyer, D., Dittmer, U., Schmitt, T.G. (2008): Modelling CWs for CSO treatment-reasonable balancing
between detailed description and practicable handling. In: IWA (eds., 2008): Proceedings of the 11th IWA
Specialized Group Conference on "Wetland Systems for Water Pollution Control" - Volume 2, 1-7
November 2008, Indore, India, pp.851-857.
Ojeda E., Caldentey, J., Saaltink, M.W., García, J. (2008): Evaluation of relative importance of different
microbial reactions on organic matter removal in horizontal subsurface-flow constructed wetlands using a
2D simulation model. Ecol Eng 34(1), 65-75.
Rousseau, D.P.L. (2005): Performance of constructed treatment wetlands: model-based evaluation andimpact of operation and maintenance. PhD thesis, Ghent University, Belgium.
Schwager, A., Boller, M. (1997): Transport phenomena in intermittent filters. Water Sci Technol 35(6), 1320.
Šimůnek, J., van Genuchten, M.Th., Šejna, M. (2008): Development and applications of the HYDRUS andSTANMOD software packages and related codes, Vadose Zone J 7(2), 587-600.
Šimůnek J., Šejna, M., van Genuchten, M.Th. (2011): The HYDRUS Software Package for Simulating theTwo- and Three-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated
Media. Technical Manual, Version 2.0. PC-Progress, Prague, Czech Republic, 254p.
Smethurst, P.J., Petrone, K.C., Baillie, C.C., Worledge, D., Langergraber, G. (2010): Streamside
management zones for buffering streams on farms: Observations and nitrate modelling. Final project
report, CSIRO, Hamilton, TA, Australia.
Smethurst, P.J., Langergraber, G., Petrone, K.C., Holz, G. (2009): Hillslope and stream connectivity:
simulation of concentration-discharge patterns using the HYDRUS model. In: Proceedings 18th WorldIMACS Congress and MODSIM09 International Congress on Modelling and Simulation, 13–17 July
2009, Cairns, Australia, pp.4057-4063 (http://www.mssanz.org.au/modsim09/I14/smethurst_I14.pdf).
Toscano, A., Langergraber, G., Consoli, S., Cirelli, G.L. (2009): Modelling pollutant removal in a pilotscale two-stage subsurface flow constructed wetlands. Ecol Eng 35(2), 281-289.
Wang, Y., Zhang, J., Kong, H., Inamori, Y., Xu, K., Inamori, R., Kondo, T. (2009): A simulation model ofnitrogen transformation in reed constructed wetlands. Desalination 235(1-3), 93-101.
Wanko, A., Mose, R., Carrayrou, J., Sadowski, A.G. (2006): Simulation of Biodegradation in Infiltration
Seepage - Model Development and Hydrodynamic Calibration. Water Air Soil Poll 177, 19–43.
Wynn, M.T., Liehr. S.K. (2001): Development of a constructed subsurface-flow wetland simulation model.
Ecol Eng 16, 519-536.

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