Modeling Variably Saturated Water Flow and Multicomponent Reactive Transport in Constructed Wetlands

Constructed wetlands (CWs) are becoming increasingly popular worldwide for removing organic matter (OM), nutrients, trace elements, pathogens, or other pollutants from wastewater and/or runoff water. We present a multicomponent reactive transport model CW2D (i.e., Constructed Wetlands 2D), as an extension of the HYDRUS-2D variably saturated water flow and solute transport software package. CW2D was developed to model the biochemical transformation and degradation processes in subsurface-flow CWs. Such wetlands involve a complex mixture of water, substrate, plants, litter, and a variety of microorganisms to provide optimal conditions for improving water quality. The water flow regime in subsurface-flow CWs can be highly dynamic and requires the use of a transient variably saturated flow model. The biochemical components defined in CW2D include dissolved oxygen (DO), three fractions of OM (readily and slowly biodegradable, and inert), four N compounds (ammonium, nitrite, nitrate, and dinitrogen), inorganic P, and heterotrophic and autotrophic microorganisms. Organic N and organic P were modeled as part of the OM. The biochemical degradation and transformation processes were based on Monod-type rate expressions. All process rates and diffusion coefficients were assumed to be temperature dependent. Heterotrophic bacteria were assumed to be responsible for hydrolysis, mineralization of OM (aerobic growth), and denitrification (anoxic growth). Autotrophic bacteria were assumed to be responsible for nitrification, which was modeled as a two-step process. Lysis was considered to be the sum of all decay and sink processes. We demonstrate the performance of the model for one- and two-stage subsurface vertical flow CWs. Model simulations of water flow, tracer transport, and selected biochemical compounds are compared with experimental observations. Limitations of the model are discussed, and needs for model improvements are summarized.

[1]  Philippe C. Baveye,et al.  Microbial Clogging of Saturated Soils and Aquifer Materials: Evaluation of Mathematical Models , 1995 .

[2]  C Boutin,et al.  How to treat raw sewage with constructed wetlands: an overview of the French systems. , 2005, Water science and technology : a journal of the International Association on Water Pollution Research.

[3]  Andreas Schwager,et al.  Transport phenomena in intermittent filters , 1997 .

[4]  Enrico Tronci.  1997 , 1997, Les 25 ans de l’OMC: Une rétrospective en photos.

[5]  K. Loague,et al.  Development and testing of a compartmentalized reaction network model for redox zones in contaminated aquifers , 1998 .

[6]  N. E. Edlefsen,et al.  A SEDIMENTATION TUBE FOR ANALYZING WATER‐STABLE SOIL AGGREGATES , 1935 .

[7]  S. Yates,et al.  Modeling colloid attachment, straining, and exclusion in saturated porous media. , 2003, Environmental science & technology.

[8]  Robert H. Kadlec,et al.  The inadequacy of first-order treatment wetland models , 2000 .

[9]  F. Schwartz,et al.  Modeling the removal of metals from groundwater by a reactive barrier: Experimental results , 1994 .

[10]  P. Vanrolleghem,et al.  Estimating (combinations of) Activated Sludge Model No. 1 parameters and components by respirometry , 1999 .

[11]  Raimund Haberl,et al.  Constructed wetlands for the treatment of organic pollutants , 2003 .

[12]  R. Carsel,et al.  Developing joint probability distributions of soil water retention characteristics , 1988 .

[13]  Gerald N. Flerchinger,et al.  Intercode comparisons for simulating water balance of surficial sediments in semiarid regions , 2002 .

[14]  D Goetz,et al.  The impact of sewage composition on the soil clogging phenomena of vertical flow constructed wetlands. , 2003, Water science and technology : a journal of the International Association on Water Pollution Research.

[15]  J. Šimůnek,et al.  Geochemical Transport , 2018, SSSA Book Series.

[16]  A. Walter,et al.  Modeling of multicomponent reactive transport in groundwater-2 , 1994 .

[17]  G Langergraber.  Simulation of subsurface flow constructed wetlands--results and further research needs. , 2003, Water science and technology : a journal of the International Association on Water Pollution Research.

[18]  Robert H. Kadlec,et al.  Wetland residence time distribution modeling , 2000 .

[19]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[20]  P. Engesgaard,et al.  Numerical analysis of biological clogging in two-dimensional sand box experiments. , 2001, Journal of contaminant hydrology.

[21]  Stewart W. Taylor,et al.  Biofilm growth and the related changes in the physical properties of a porous medium. 3. Dispersivity and model verification. , 1990 .

[22]  G Langergraber,et al.  The role of plant uptake on the removal of organic matter and nutrients in subsurface flow constructed wetlands: a simulation study. , 2005, Water science and technology : a journal of the International Association on Water Pollution Research.

[23]  Barbara A. Bekins,et al.  Simulation of aerobic and anaerobic biodegradation processes at a crude oil spill site , 1995 .

[24]  M. V. Genuchten,et al.  Integrated modeling of vadose-zone flow and transport processes , 2005 .

[25]  G Langergraber,et al.  Simulation of a subsurface vertical flow constructed wetland for CSO treatment. , 2005, Water science and technology : a journal of the International Association on Water Pollution Research.

[26]  Karel J. Keesman,et al.  Identification of activated sludge and wastewater characteristics using respirometric batch-experiments , 1998 .

[27]  John S. Selker,et al.  Considerations for modeling bacterial-induced changes in hydraulic properties of variably saturated porous media , 2002 .

[28]  Guenter Langergraber,et al.  Constructed wetlands for rehabilitation and reuse of surface waters in tropical and subtropical areas ? first results from small-scale plots using vertical flow beds , 1999 .

[29]  Jeanne M. VanBriesen,et al.  Chapter 7. MICROBIOLOGICAL PROCESSES IN REACTIVE MODELING , 1996 .

[30]  Klaus Mauch,et al.  Soil clogging in vertical flow reed beds – mechanisms, parameters, consequences and.......solutions? , 1997 .

[31]  Graham B. McBride,et al.  Effect of water level fluctuation on nitrogen removal from constructed wetland mesocosms , 1999 .

[32]  M. V. Genuchten,et al.  Mass transfer studies in sorbing porous media. I. Analytical solutions , 1976 .

[33]  W. Parton,et al.  Dynamics of C, N, P and S in grassland soils: a model , 1988 .

[34]  H. Bork.  Methods of soil analysis , 1988 .

[35]  P. Magnico.  Impact of dynamic processes on the cloupling between fluid transport and precipitate deposition , 2000 .

[36]  T. M. Wynn,et al.  Development of a constructed subsurface-flow wetland simulation model , 2001 .

[37]  Hari S. Viswanathan,et al.  A reactive transport model of neptunium migration from the potential repository at Yucca Mountain , 1998 .

[38]  R. I. Mackie,et al.  The Role of Particle Size Distribution in the Performance and Modelling of Filtration , 1993 .

[39]  W. Gujer,et al.  A Mathematical Model for Rotating Biological Contactors , 1990 .

[40]  Jeanne M. VanBriesen,et al.  Multicomponent transport with coupled geochemical and microbiological reactions: model description and example simulations , 1998 .

[41]  Karl Svardal,et al.  The dynamic behaviour of nitrifying activated sludge systems influenced by inhibiting wastewater compounds , 1995 .

[42]  A Pressl,et al.  Evaluation of substrate clogging processes in vertical flow constructed wetlands. , 2003, Water science and technology : a journal of the International Association on Water Pollution Research.