Modelling Pollution transport in Constructed Wetlands

Project Highlights:
- Development of robust model capable of simulating solute and microplastic transport processes, nutrient removal efficiency, and hydraulic efficiency in constructed wetlands.
- Development of a machine learning-based Bayesian approach uncertainty quantification methodology to investigate the key modelling parameters, and inversely quantify and reduce the uncertainties of the numerical modelling tool developed within this study. We will use existing field-based data for validation and calibration processes.
- Undertaking scenario modelling to Investigate the effects of climate variability, seasonal and interannual variation in vegetation composition, as well as the geometrical design of the pond on the performance of the constructed wetlands and their pollution removal efficiency.

Overview:
Constructed wetlands (CWs) are ecologically engineered systems that use soil, vegetation, and organisms to treat water and remove solute and solid pollution. It is the interplay between water-vegetation-soil that governs the wetland physical, chemical, and biological treatment processes. These 'Natural Capital' assets are one of the most effective measures to treat municipal and industrial wastewater, greywater, and storm-water runoff. Dynamics of water movement plays a key role in the removal of pollutants, as it influences the hydraulic residence time for treating the pollutants. Plant communities have a prominent effect on the wetland hydrodynamics and performance, as they generate flow resistance, changes the velocity field, and affect mixing characteristics, enabling suspended material to fall to the wetland bed. Seasonal variation in vegetation growth and die-back influences the performance of the system. In addition, the microbial community will respond over time to the organic and metal pollutants that are constituents of the effluents. In recent years, several studies investigated the pollution transport mechanisms in constructed wetlands. However, critical knowledge gaps remain in modelling the physical, biological processes affecting solute and solid transport in wetlands.

The main aim is to develop a robust numerical simulation tool capable of accurately modelling pollution transport and storage processes in the constructed wetlands to quantify the nutrient removal efficiency, and the hydraulic efficiency of constructed wetlands. Development of such model is critical for optimal and efficient design, operation, and maintenance of these natural capital assets. The model validation and fine-tunning with be undertaken using field-based tracer study data from our existing project in collaboration with the Norfolk Rivers Trust. This project will also investigate and quantify the effects of climate variability and seasonal and interannual variation in vegetation composition on the performance, mixing and dispersion processes within the CWs to inform the design and operation of CWs. Hence, this project will provide a step change in environmental protection and integrated catchment management by modelling and optimising the performance of constructed wetland natural capital assets, and significantly, be influential at a time of considerable investment in these systems by the water industry.