SUPERVISOR: Günter LANGERGRABER

PROJECT ASSIGNED TO: Berhard PUCHER

With the HYDRUS software package the simulation of the water flow and solute transport in the vadose zone can be described very well. The ongoing development of additional modules to address specific scientific needs provides a constant growth of the capabilities of the software. One developed module based in the field of wastewater treatment, is the Wetland Module. It includes two biokinetic models to describe the biochemical transformation and degradation processes of wasterwater constituents and was developed for the simulation of subsurface flow treatment wetlands (SSF TW). With this model a process based understanding of the processes happening within the filter media can be reached as well as design and operational questions answered. Also, filter systems used within the framework of natural based solutions (NBS) to reactivate the local water cycle and treat runoff water for different uses like irrigation or groundwater recharge, highly benefit from simulation tools like the Wetland Module. One missing sub-model which is not implemented in HYDRUS is a clogging model providing an option to simulate the transport and deposition of suspended particulate matter, biofilm growth and, their influences on the hydraulic conductivity. This is from upmost importance as the main reason of failure states the clogging of the system. Furthermore, as water reuse for different purposes is more and more needed, the process understanding of the transport and fate of pathogens in filter materials (GI) and TWs is highly important in order to design and operate such systems with the focus of public health. Another important development addressed by this thesis should include the coupling of the dual porosity model available in HYDRUS and the HYDRUS Wetland Module, in which up to now only equilibrium water flow (matrix flow) is available. Therefore, it is not possible to take account for preferential flow paths leading to non-equilibrium conditions in the filter media dividing the liquid phase into mobile and immobile regions where different biokinetic reaction terms may occur.

Thus, the objectives of this PhD thesis are:

  1. Developing a sub-model for the HYDRUS Wetland Module to describe particle transport and deposition, and its effect on the hydraulic conductivity.
  2. Developing a sub-model for the HYDRUS Wetland Module to describe pathogen transport and removal.
  3. Coupling a non-equilibrium dual-porosity flow and transport model and the HYDRUS Wetland Module.

The development of named sub-models will be carried out based on literature review of existing mathematical descriptions of the different processes. For the implementation in the HYDRUS software package the final mathematical descriptions will be translated in FORTRAN and integrated within HYDRUS to be used as standalone models to investigate one specific process and also coupled together in one module. Based on this model formulation not only filter systems and TW as standalone infrastructure can be described. Within the framework of HR21 methods shall be developed in order to use the developed models to describe the transport, retention and degradation of particulates and solutes within the littoral zone. Based on modelled and measured data predictions of pollutant retention within the soil matrix as well as occurring surface and subsurface transport shall be made. Results will include data and needed parameters which can be used for catchment scale models and therefore contribute to the integrated multidisciplinary understanding of natural and anthropogenic pressures on the riverine landscape.