Reac ve Transport Modeling of Subsurface Flow Constructed Wetlands Using the HYDRUS Wetland Module

Constructed wetlands (CWs) are engineered water treatment systems designed to remove various types of contaminants. A large number of processes simultaneously contribute to water quality improvement in CWs. During the last decade, there has been a wide interest in the understanding of complex “constructed wetland” systems, including the development of numerical process-based models describing these systems. A number of process-based numerical models for subsurface fl ow (SSF) CWs have been developed during the last few years; however, most of them are either in an early stage of development or are available only in-house. The HYDRUS wetland module is the only implementa on of a CW model that is currently publicly available. Version 2 of the HYDRUS wetland module includes two biokine c model formula ons simula ng reac ve transport in CWs: CW2D and CWM1. In CW2D, aerobic and anoxic transforma on and degrada on processes for organic ma er, N, and P are considered, whereas in CWM1, aerobic, anoxic, and anaerobic processes for organic ma er, N, and S are taken into account. We simulated horizontal fl ow CWs using both biokine c models. Compared with the CWM1 implementa on in the RETRASO code, the HYDRUS implementa on was able to simulate fi xed biomass, which is of high importance for obtaining realis c predic ons for the treatment effi ciency of CWs. We also compared simula on results for horizontal fl ow CWs obtained using both CW2D and CWM1 modules that showed that CWM1 produces more reasonable results because it also considers anaerobic degrada on processes. The infl uence of wetland plants on the simula on results was also inves gated. Simulated biomass profi les in the fi lter were completely diff erent when considering O2 release from roots, thus indica ng the importance of considering plant eff ects.