Postgraduate research opportunities

Improved Water Treatment via Densification of Flocs

This modelling and simulation study will investigate the processes by which an aggregate or floc within a solid-liquid wastewater suspension densifies (i.e. becomes more compact) as the suspension is subjected to shear, such densification facilitating the wastewater treatment separation process.

Number of places



29 January 2019


3 years


Students applying should have (or expect to achieve) a minimum 2.1 undergraduate degree in a relevant engineering/science discipline, and be highly motivated to undertake multidisciplinary research.

The project will suit a student with a background in chemical engineering or a cognate discipline (e.g. physics, applied mathematics, mechanical engineering).

Applications will be considered up to 21 January 2020. Those received before 21 September 2019 will be given priority. The proposed start date for the project is 01 February 2020.

Project Details

Water, whether it is required for domestic consumption, for industry or for agriculture, is essential for life. Increasingly however many parts of the world are facing issues of water stress and/or water scarcity. To address such issues, a new approach to water management is called for, not just attempting reduce first-pass water consumption in existing processes, but also innovating to promote water treatment and re-use.

At the heart of the treatment of any wastewater suspension, a solid-liquid separation step needs to be performed. The separation step can be sped up when tiny particulate solids in the suspension manage to group together into larger aggregates or flocs. The process can be sped up further still if the flocs can be made to densify (i.e. bind together more tightly). Empirically it has been found that such densification can be achieved by applying shear to the flocs e.g. by raking the suspension.

Despite this empirical observation of densification that can subsequently improve wastewater treatment, the details of exactly how flocs densify are still largely unknown. This makes it impossible to design a particular shearing regime that can optimise the treatment of any given wastewater suspension.

This project under the supervision of Dr Paul Grassia ( is aimed at obtaining detailed mechanistic understanding by simulating wastewater flocs on a microstructural level. Treating a floc as a randomly oriented chain of sticky beads, this project will use Stokesian dynamics simulations to investigate quantitatively how the topology and geometry of such a chain evolves under the application of shear. As the chain reconfigures due to shear, and more and more of the beads within it stick to one another, it is expected to become more topologically constrained, and these topological constraints should subsequently be reflected in geometric constraints also, leading to a more compact structure.

The insights thereby gained from this study will enable the structure of sheared flocs to be determined as a function of their shear history, and the consequent implications for optimising wastewater treatment processes will then be explored.

In addition to undertaking cutting edge research, students are also registered for the Postgraduate Certificate in Researcher Development (PGCert), which is a supplementary qualification that develops a student’s skills, networks and career prospects.


Usher, S. P., Spehar, R., Scales, P. J., 2009. Theoretical analysis of aggregate densification: Impact on thickener performance. Chem. Engng J.  151, 202--208.

Funding Details

This PhD project is initially offered on a self-funding basis. It is open to applicants with their own funding, or those applying to funding sources. However, excellent candidates will be eligible to be considered for a University scholarship.

Contact us

Ms Jacqueline Brown

+44(0) 141 574 5319

James Weir Building, 75 Montrose Street, Glasgow, G1 1XJ

How to apply

Apply for this PhD project here.

Please quote the project title in your application.