PhD project: Controlling the microbial generation of nitrous oxide in wastewater treatment; a pathway to reduce greenhouse gas emissions

Project description

The wastewater treatment (WWT)  process is arguably the most important biotechnological application in the modern world. Each day, large volumes of influent wastewater are processed in municipal WWT plants so that safe effluent is returned to the water cycle. Although WWT plants tend to have lengthscales on the order of kilometres, it is the metabolic activity of flocculating bacteria with lengthscales on the order of micrometres that make this process work. In short, the bacteria degrade dissolved pollutants in the wastewater whilst forming compact flocs (or aggregates), which are then subsequently separated from the liquid under gravity (settling).

Nitrous oxide, N2O, is the 3rd most important greenhouse gas (GHG) after carbon dioxide (CO2) and methane (CH4). A strong GHG, N2O is ~300 times more potent per mass than CO2, and its average concentration in the atmosphere has increased 2% per decade over the last 150 years (with t­­he rate doubling over the last 30 years). It is also the main contributor to the depletion of the ozone layer. N2O is generated in the WWT process during nitrogen removal steps. These steps are essential to protect waterways from eutrophication and thus preserve precious ecosystems. Nitrogen removal relies on the activity of nitrifying and denitrifying bacteria in the WWT tanks, but these processes also produce N2O. Developing a systematic understanding of N2O generation, however, is highly nontrivial owing to the large complexity of the microbial communities in WWT, which can vary between geographical locations.  There is therefore a pressing need to develop simple experimental systems to model N2O generation in WWT.

Veolia, the multinational waste management company, manage WWT facilities around the world, including several in Scotland with two here in Edinburgh. They are committed to tackling grand challenges posed by the climate crisis and have identified the control and regulation of N2O in WWT as one of these challenges. Detection and analysis of N2O are essential, but impactful innovation will involve manipulating the nitrifying and denitrifying bacteria to consume N2O.

In this project, we will adopt a multiscale approach to this problem, combining plant-scale detection/analysis with an experimental model system for understanding microbial production and consumption of N2O in WWT. The student will initially use Comamonas denitrificans as a potential model system for understanding N2O production (source) and consumption (sink) in WWT bacteria.  C. denitrificans, an important heterotrophic denitrifier in WWT with rapid denitrifying ability, is easy to culture and forms aggregates in suspension and on surfaces.  The cells within these aggregates form interconnected space-spanning networks with fascinating mechanical properties and so are excellent systems with which to study from a soft matter and biological physics perspective.

Depending on the conditions, denitrifying bacteria like C. denitrificans, can act as a net source or net sink for N2O, and here we will promote the latter by manipulating conditions to enhance its ability to consume N2O. We will use a combination of chromatographic (e.g., gas chromatography) and amperometric (e.g., sensors) techniques to monitor N2O concentrations in suspended flocs and biofilms of  C. denitrificans, and complemented with a suite of imaging techniques, assess how the N2O metabolism influences the structure and mechanics of the aggregated bacterial community. The project will involve simple batch culture experiments, some flow cell work, and will progress to more complicated bioreactor experiments that provide systematic control of operation conditions. The student will also spend time at Veolia's WWT plants, here in Edinburgh,  gathering data on N2O emissions, and perform experiments (in the on-site labs) on biological samples isolated from the WWT plant.

Edinburgh is a core partner of the National Biofilm Innovation Centre (NBIC), which means that you will be embedded in a wider network of PhD students and researchers interested in bacterial communities and biofilm formation.

This is a fully-funded PhD position joint  between the School of Physics & Astronomy and the School of Engineering,  and comprises a tax-free stipend of £16,062 pa, paid for 3.5 years: plus, fees and additional programme costs.

Potential applicants should contact Gavin Melaugh (g.melaugh [at] or Efthalia  Chatzisymeon (e.chatzisymeon [at] for further information.

Students should hold a 2.1 Hons degree or above, or equivalent, in physics, chemistry, engineering, biology,  or a related discipline.  A Master’s degree in one of the above fields would be advantageous.  Applicants should submit their degree certificate, transcripts, a covering letter, CV, English language certificate (if required) and two academic references using the following link:

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