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GW4 FRESH CDT PhD Studentship: Chlorine reduction wetlands

Department of Chemical Engineering

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Dr Jannis Wenk No more applications being accepted Competition Funded PhD Project (European/UK Students Only)

About the Project

GW4 FRESH is a consortium of the UK’s top research intensive universities: Bath, Bristol, Cardiff and Exeter and research organisations, British Geological Society and the Centre for Ecology and Hydrology.

This project will be based at the University of Bath.


Lead supervisor:
Dr Jannis Wenk, University of Bath, Department of Chemical Engineering, email [Email Address Removed]
Professor Andrew Weightman, Cardiff University, School of Biosciences
Professor Gabriel Yvon-Durocher, University of Exeter, Environment and Sustainability Institute
Mr Liam Reynolds, Wessex Water


Water utilities are occasionally required to discharge larger quantities of finished drinking water directly into surface waters due to local circumstances or historical obligations. If such drinking water has been chlorinated, it contains residual disinfectant that should be removed before the water is released since residual chlorine harms the aquatic ecology.

Residual chlorine can be removed physically via activated carbon adsorption or chemically with SO2 or NaS2O5. Chemical removal of residual chlorine has been routinely performed in the US. In the specific situation of a Southwest UK watershed/drinking water distribution system, active treatment measures to remove the residual chlorine are difficult to implement due to the remote location and intermediate discharges.

An alternative possibility for chlorine attenuation could be to first pass the water through a specially designed buffering wetland, where the residual chlorine is degraded. Residual chlorine decays over time (days). The decay may be increased due to catalytic/reactive interaction of chlorine with sediment soil and wetland substrate, e.g. iron/iron oxide surfaces (possibly to hours). Depending on the design of the wetland, there can be atmospheric and sunlight interaction, which also increases chlorine decay. Both soil natural organic matter and wetland organic matter may lead to secondary formation of disinfection by-products, so residual chlorine is removed but more harmful products can be formed.

The goal of this PhD project is to investigate the feasibility and potential benefits of a residual chlorine removal wetland and to understand the ecological implications of the current practice. The project takes place in close cooperation and coordination with a local water utility. The work includes an experimental part in which the interaction of residual chlorine with various wetland substrates, as well as sunlight, will be tested to inform possible wetland design, including the size and the hydraulic retention time of the buffering wetland to achieve full residual removal. The experiments also include measuring the concentration of common disinfection by-products (e.g. trihalomethanes). The effect of residual disinfectant on wetland ecosystems can be tested in specifically designed mesocosms. Within the current water shed the development of the microbial community, plants and fauna will be determined. Unrelated surface waters, upstream and downstream samples of the same water shed (including data of previous monitoring campaigns by the utility) and other nearby constructed wetlands will serve as comparison.

The PhD student will be part of a highly motivated team consisting of members at different GW4 locations and the water utility. The team is already collaborating on similar projects, including two related Fresh PhD studentships (2018 intake) on constructed polishing wetlands for nutrients and pathogen removal.


Applicants must have obtained, or be about to obtain, a First or Upper Second Class Honours degree, or the equivalent qualifications gained outside the UK, in an area appropriate to the skills requirements of the project.

In order to apply, you should apply direct to the CDT using their online application form:

You do NOT need to apply to the University of Bath at this stage – only those applicants who are successful in obtaining an offer of funding from the CDT will be required to submit an application to study at Bath.


More information about the application process may be found here:

Anticipated start date: 28 September 2020.

Funding Notes

A GW4 FRESH CDT studentship is available covering Home tuition fees and providing a training support grant and a stipend (£15,285 p/a, 2020/21 rate) for a period of up to 3.5 years. To be eligible, applicants must be citizens of the UK or other EU country and have been residing in the UK for at least 3 years prior to the start of the PhD (apart from temporary or occasional absences).
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