Applications of HYDRUS Based CW2D Wetland Module: a Review

Constructed wetlands are becoming increasingly popular around the world to remove nutrients, organics, trace elements, pathogens, and other contaminants from wastewater and/or runoff water. Generally constructed wetlands can be built considering several designs connected to the flow which can be either saturated or unsaturated, vertical or horizontal, surface or subsurface and all the possible combinations. The CW2D (Constructed Wetlands 2D) multi-component reactive transport module was developed as an extension of the Hydrus-2D. CW2D was created to simulate biochemical transformation and degradation processes for organic matter, nitrogen and phosphorus in constructed wetlands with subsurface flow. The IWA Activated Sludge Models, which use monod-type expressions to describe the process rates, serve as the foundation for the mathematical structure of CW2D. All process rates and diffusion coefficients are temperature dependent. The biochemical components included in CW2D are dissolved oxygen, three fractions of organic matter (readily- and slowly-biodegradable, and inert), four nitrogen compounds (ammonium, nitrite, nitrate, and dinitrogen), inorganic phosphorus, and autotrophic and heterotrophic micro-organisms. Considering the background knowledge, the review provides recent applications of CW2D module with HYDRUS for simulation of wastewater treatment performance of constructed wetlands and suggests the possibility of addition of more features in CW2D module for more realistic simulation outcomes.