About the Project
Membrane fouling – the deposition of organic and inorganic matter on the membrane surface – is a major technical obstacle affecting membrane-based water treatment processes. Fouling results in decreased membrane permeance, selectivity, and shorter useful life due to irreversible fouling. Despite significant efforts to mitigate fouling through, e.g., low-fouling membrane coatings, fouling is inevitable due to the high convective fluxes driving foulants to the membrane surface. Consequently, physical and chemical cleaning strategies, known collectively as cleaning-in-place (CiP) protocols, are indispensable to ensure the sustainable use of membrane technology in water treatment.
Most CiP formulations entail proprietary mixtures of buffered surfactants and chelants that dissolve organic foulants and disperse colloidal metal-organic complexes. Application of CiP solutions often follows manufacturer-specified cleaning conditions, including cross-flow velocity, duration and frequency of cleaning cycles. Such operating conditions, however, are not optimised for specific feed water and foulant chemistries. Moreover, the important influence of CiP solution temperature is often neglected. Solution temperature plays a key role in membrane cleaning, as the interactions responsible for foulant adhesion to the membrane become weaker with rising temperature1. However, the role of temperature in CiP has not been studied systematically. Incomplete knowledge about the influence of operating conditions has hindered development of efficient CiP protocols.
This PhD project will formulate tailored CiP strategies for membranes in Scottish Water (SW) treatment plants. The overarching goal is twofold: i) to identify the CiP temperature resulting in optimal membrane performance; ii) to identify CiP formulations (or mixtures thereof) suitable for application at ambient feed water temperatures (i.e., in cold water). Considering that CiP at SW membrane plants is often carried out at ambient water temperature (Tamb = 10 °C or lower), we anticipate significant improvements in cleaning efficiency if CiP were carried out at slightly higher temperatures. The cost of CiP operations at above-ambient temperatures will be weighed against the improvement in process performance (stemming from mitigated fouling) by a technoeconomic analysis. Lastly, we will perform a life cycle assessment of CiP protocols to identify CiP candidates meeting SW’s sustainability goals.
Training and mentoring
This project offers a unique training opportunity in the fundamentals of colloid and interface science, as well as membrane-based processes for water quality control. The student will be mentored by a supervisory team with complementary expertise, who will provide training in a wide variety of experimental techniques. In addition, the student will acquire industrial experience through a three-month placement at a Scottish Water membrane plant.
*** Please note that funding for this project is only available to UK citizens and landed permanent residents (including EU citizens with settled status).
Research Plan. The research programme is structured along the following four work packages (WPs).
WP1. Elucidate cleaning mechanisms and optimal cleaning conditions. To elucidate optimal CiP conditions and identify the most effective formulations for a given foulant matrix, we will investigate the response to shear of foulant layers, the surface tension of the various CiP formulations, as well as foulant adhesiveness to the membranes. To this end, we will employ state-of-the-art rheology, tensiometry, SEM and AFM-based force spectroscopy to gain fundamental insights into CiP mechanisms to optimize efficiency.
WP2. What is the optimal temperature for CiP? To address this question, experiments simulating fouling and cleaning will be carried out in a pilot-scale unit at Edinburgh University (UoE). Experimental insights obtained in our lab will inform experiments in a SW facility, where optimal cleaning strategies will be identified in an industrial-scale system.
WP3. What is the cost of fouling (and cleaning) in SW plants? We will determine the economic impact of fouling and cleaning in tubular and spiral wound membrane operation. To this end, we will quantify the costs of CiP, at ambient and above-ambient temperature, and compare them to the cost of fouling.
WP4. Life-cycle assessment (LCA) of membrane CiP protocols. To evaluate the sustainability of CiP protocols, LCA will be conducted on selected formulations showing optimal cleaning performance.
References
(1) BinAhmed, S.; Hozalski, R. M.; Romero-Vargas Castrillón, S. Feed Temperature Effects on Organic
Fouling of Reverse Osmosis Membranes: Competition of Interfacial and Transport Properties. ACS ES&T
Eng. 2021, 1 (3),
591–602. https://doi.org/10.1021/acsestengg.0c00258.
(2) Porcelli, N.; Judd, S. Chemical Cleaning of Potable Water Membranes: The Cost Benefit of
Optimisation. Water Res. 2010, 44 (5), 1389–1398.
https://doi.org/10.1016/j.watres.2009.11.020.
Funding Notes
Tuition fees + stipend are available for Home/landed EU students (International students not eligible)
References
Further information about the supervisor (Dr S Romero-Vargas):
https://www.research.ed.ac.uk/en/persons/santiago-romero-vargas-castrillon
Further information about the co-supervisor (Prof A Lips):
