Constructed Wetland Module
Constructed wetlands are becoming increasingly popular worldwide for removing nutrients, organics, trace elements, pathogens, or other pollutants from wastewater and/or runoff water. This manual describes a multi-component reactive transport module CW2D (Constructed Wetlands 2D, Langergraber, 2001, Langergraber and Šimůnek, 2005), that was developed as an extension of the Hydrus-2D (Šimůnek et al., 1999) and HYDRUS (Šimůnek et al., 2006) variably-saturated water flow and solute transport program. CW2D was developed to model the biochemical transformation and degradation processes in subsurface-flow constructed wetlands. The biochemical degradation and transformation processes for organic matter, nitrogen and phosphorus are considered. The mathematical structure of CW2D is based on the IWA Activated Sludge Models (Henze et al., 2000). Monod-type expressions are used to describe the process rates. All process rates and diffusion coefficients are temperature dependent. The biochemical components defined in CW2D include dissolved oxygen, three fractions of organic matter (readily- and slowly-biodegradable, and inert), four nitrogen compounds (ammonium, nitrite, nitrate, and dinitrogen), inorganic phosphorus, and heterotrophic and autotrophic micro-organisms. Organic nitrogen and organic phosphorus are modeled as part of the COD. Heterotrophic bacteria are assumed to be responsible for hydrolysis, mineralization of organic matter (aerobic growth) and denitrification (anoxic growth). Autotrophic bacteria are assumed to be responsible for nitrification, which is modeled as a two-step process. All micro-organisms are assumed to be immobile. Lysis is considered to be the sum of all decay and loss processes.
The manual provides a short overview of the constructed wetland technology, describes internal details of the reactive transport CW2D module, its main principles, its mathematical formulations, and a set of default parameters based on the literature review. It also describes how CW2D is implemented into HYDRUS, what modifications were made in the original code, and how the new module can be run using the HYDRUS graphical user interface. Finally, it presents several illustrative and verification examples of the use of CW2D, and description of additional new input and output files.
Download the manual: Hydrus_CW2D_Manual.pdf (1,5 MB)
Langergraber, G. and J. Šimůnek, Modeling Variably-Saturated Water Flow and Multi-Component Reactive Transport in Constructed Wetlands, Vadose Zone Journal, 4, 924-938, 2005.
Langergraber, G., and J. Šimůnek, The Multi-component Reactive Transport Module CW2D for Constructed Wetlands for the HYDRUS Software Package, Manual – Version 1.0, HYDRUS Software Series 2, Department of Environmental Sciences, University of California Riverside, Riverside, CA, 72 pp., 2006.