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Combined sewer overflows and their contribution to legacy faecal pollution in rivers

   School of Biological & Environmental Sciences

About the Project

We are seeking a highly motivated candidate to carry out interdisciplinary PhD research combining water quality science, catchment management and applied environmental microbiology. The supervisory team links expertise at University of Stirling (Dr David Oliver, Prof Richard Quilliam) and the UK Centre for Ecology & Hydrology (Dr Andrew Singer) with additional CASE support from the Scottish Environment Protection Agency (Dr Ruth Stidson).

Recently, sewage discharges into UK surface waters have received significant media attention with increased recognition of the frequency and magnitude of combined sewer overflow (CSO) spills raising public awareness of the risks posed to water quality and downstream ecological and public health. To date, much of the debate concerning CSOs has focused on the immediate impacts of sewage spills to the hygienic status of the receiving water, but a secondary issue is the accumulation of solid fractions of untreated human sewage in riverbed sediments. Discharges from CSOs also deliver faecal indicator organisms (FIOs), such as E. coli, and potential pathogens into suspension in river drainage networks and, depending on factors such as, e.g., river flow, microbial-particle associations, and sedimentation rates, a proportion of faecally-derived microbial pollutants will become incorporated along with solids in the riverbed. Consequently, there is potential for legacy stores of FIOs to build up over time in riverbed sediments near to where CSOs discharge. The presence of legacy stores of FIOs in riverbed sediments can therefore provide a potential in-stream source of microbial pollution, resulting in delayed impairment of water quality. However, we know very little about how such potential legacy FIO stores in riverbeds vary in terms of their spatial and temporal characteristics or how the survival and resuspension of FIOs from these hotspots can contribute to subsequent downstream risk, including the potential for impacting on bathing water quality.

The overarching aim of this studentship, therefore, is to provide critical data on the importance of legacy stores of FIOs in riverbed sediments that accumulate in response to CSO discharges. Specifically, the research objectives are to:

1.      Evaluate how legacy stores of FIOs in riverbed sediments vary in space and time downstream of CSOs;

2.    Characterise FIO die-off in sewage-contaminated riverbed sediments under different environmental conditions;

3.    Determine and quantify the factors controlling FIO resuspension from hotspots of sewage-contaminated riverbed sediments; 

4.    Develop a risk-based approach to predict microbial pollution of the wider environment from hotspots of sewage-contaminated riverbed sediments.

The project will involve fieldwork in river and catchment environments, controlled laboratory experiments and GIS mapping of river drainage networks to help contextualise the relative risk of legacy FIO stores in riverbed sediments contaminated by CSO discharges across case study catchments. Following an initial critical literature review, the studentship will comprise of three core components: (1) detailed characterisation of persistence profiles of FIOs (and potential pathogens) in sewage contaminated riverbed sediment under a suite of environmental conditions; (2) quantification of mobilisation and resuspension potential of FIOs entrained in sewage-contaminated riverbed sediment across a range of environmental/hydrological scenarios; and (3) an integrated programme of targeted catchment monitoring and GIS-supported risk modelling, drawing on outputs from (1) and (2), to deliver new understanding of the longer-term risks posed by sewage-contaminated riverbed sediment stores in catchment systems.

The entry qualification for this PhD studentship is a first class or upper second class honours degree and/or a relevant postgraduate degree, in biological/environmental sciences. Whilst experience in microbiology would be useful, it is certainly not essential as the student will receive full laboratory training.

The application deadline is Friday 6th January 2023 at 12:00 noon. By this time applicants must have submitted an application through the IAPETUS DTP online application system (open from 1st November 2022) further details are here: However, serious applicants should contact Dr Oliver () well before the deadline to discuss their application.

Initial shortlisting will take place immediately after the 6th January deadline. Those candidates who are successful in shortlisting will be required to attend an IAPETUS interview on Tuesday 28th February or Wednesday 1st March 2023.

UKRI eligibility rules enable a small proportion of IAPETUS PhD studentships to be awarded to non-UK applicants from overseas and for successful international candidates we will apply to Stirling University to waive overseas fee costs; applicants from overseas should contact to discuss this.

Funding Notes

This is a competitively funded PhD studentship as part of the NERC Doctoral Training Partnership IAPETUS (View Website). The studentship has CASE (Co-operative Awards in Science and Engineering) support from SEPA, providing additional resource and training opportunities.


Further information on the project, skills and training opportunities can be found here:

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