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Dynamics of pollution transport in constructed wetlands: identification and quantification of underlying physical mechanisms of solute and solid (microplastic) transport

   School of Life Sciences

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  Dr S Abolfathi, Dr J M Pearson  No more applications being accepted  Competition Funded PhD Project (European/UK Students Only)

About the Project

Project Highlights:
• Generation of fundamental knowledge of the performance of natural capital waste-water treatment systems – constructed wetlands – that will underpin significant investment by the water industry from 2020-2027.
• Developing novel methods to track and analyse behaviour of solute and microplastics transport under the impacts of constructed treatment wetland processes
• Identify and quantifying key underlying physical transport mechanisms that govern movement of solute and microplastics (of different density, size and shape) in the constructed wetland ecosystem and understand the potential for microplastics to cause ecotoxicity in biological organization within a wetland ecosystem.


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 (contact and activity 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. However, critical knowledge gaps remain in sources and fate of pollutants in wetland ecological systems.
The main aim is to identify and quantify key mechanisms that govern the transport and fate of pollutants using laboratory and field-based data from wetlands located within the Norfolk Rivers Trust. This project will also explore the interaction of microplastics with soil and ecological systems within wetlands to understand the potential for ecotoxicity in biological organizations. These mixing and transport mechanisms will be investigated using state of the art fluorometric and experimental fluid dynamics methods as well as our innovative technology for microplastic staining. The new insights offered by this project will enable understanding the dynamics of pollutant transport in wetland systems. The algorithms which will be developed within this project will be coupled with existing multi-phase flow models in order to simulate pollutant transport under various hydro-climates. Hence this project will provide a step change in environmental protection and integrated catchment management by understanding 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.

This project will undertake laboratory-based physical modelling measurements and fieldwork data collection to understand the dynamics of pollutant transport in wetlands. We will create an interacting mesocosm wetland environment using the world class experimental facility at Warwick Water Laboratory. Fluorometric tracing along with novel particle staining techniques will be applied, alongside planar laser-induces fluorescence(PLIF) and particle image velocimetry(PIV/PTV), with the aim of identifying and quantifying underlying physical transport mechanisms of pollutants and the impact of hydraulic conditions on the transport and fate of the pollutant. The experimental and fieldwork investigations will explore the interactions of microplastics with sediment bed of fluvial systems with the aim of identifying and quantifying the hyporheic exchange processes governing pollutant interactions with the wetland sediment bed. A comprehensive set of tests will be conducted to quantify transport and fate of different types of microplastic polymers (varying in density, shape and size), across a wide range of environmental flows.

Training and skills:

Training will be provided in a wide range of numerical tools to process and analyse experimental fluid dynamics data. Training on particle staining technique will be provided for microplastics tracer measurement. The student will be trained in cutting-edge hydrodynamic and fluorometric measurement techniques including, Particle-Image-Velocimetry and Laser-Induced-Fluorescence. Through our industrial partners a range of training will be provided on catchment planning and management, pollution risk management, habitat improvement, communication and public understanding of science. In addition, the researcher will be able to work closely with the wetland design and creation team, ensuring that their science will be applied and validated at full field-scale.

Funding Notes

This funding provides full tuition fees at the Home/EU rate, pays an annual tax free stipend in line with UK Research Councils (£15,285) and provides a research training support grant (RTSG) of £8,000.


Further reading:

Rillig, M.C. (2012) ‘Microplastic in terrestrial ecosystems and the soil?’, Environmental Science and Technology 46, 6453-6454.
Ballent, A., Pando, S., Purser, A., Juliano, M.F. and Thomsen, L. (2013) ‘Modelled transport of benthic marine microplastic pollution in the Nazaré Canyon’, Biogeosciences 10(12), 7957-7970.
Besseling, E., Quik, J.T.K., Sun, M. and Koelmans, A.A. (2017) ‘Fate of nano- and microplastic in freshwater systems: A modeling study’, Environmental Pollution 220, 540-548.
Web page:
Norfolk Rivers Trust.
Norfolk Rivers Trust have created innovative natural treatment plant for over a million litres of water a day to help improve the quality of water that is returned to the River Ingol, one of Norfolk’s precious chalk streams.
Frogshall: Creating an Integrated Constructed Wetland (ICW)
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