In this thesis microfiltration (MF) membranes are studied with a focus on the removal of viral pathogens.
‘This is a promising step for safe drinking water in the future,’ says Terica Sinclair. ‘Microfiltration membranes can be modified to remove bacteria (some microns in size) and even viruses which are 20-30 nm in size.’
Apart from being small, viruses are robust and very persistent in aquatic environments, making them a serious and persistent problem. ‘We showed MF membranes to be a worthy alternate approach to ultrafiltration (UF) membranes for virus removal,’ Terica says. ‘This is very hopeful news for people in resource limited regions of the world, as UF membranes require higher pressures to operate. They can’t do without pumps and electricity, making them impossible to incorporate in the most simple, decentralized, and cheapest point of use systems.’
After a systematic literature search, in this thesis, commercially available MF membranes were modified using a cationic polymer, polyethyleneimine (PEI), as a coating. ‘This polymer was chosen as it demonstrates antimicrobial activity against a range of pathogens,’ Terica says. ‘Using various characterization techniques, we monitored the PEI coating and correlated the performance of the membrane before and after coating.’
With most viruses being net negatively charged, the positively charged active antiviral layer acted as adsorbent and reduced the viral titre. ‘We were able to maintain relatively high fluxes in a gravity driven process,’ Terica writes.
Subsequently, Terica focused on finding suitable antiviral moieties, to further enhance the reduction capability of the optimised membranes. Silver and silver nanoparticles (AgNPs) were used as antimicrobial agents with five capping or stabilising polymers, on MS2 bacteriophages. Also copper nanoparticles (CuNPs) were investigated, as an economical alternative to silver.
At last, the modification process was further enhanced using covalent layer-by-layer deposition techniques to the coated MF membranes.
‘The stability and viral reduction could be further improved,’ Terica says. ‘We were very happy to meet WHO standards for virus removal by household water treatment and safe storage (HWTS) systems (5 log10-units removal) . This result, in the latter stages of my PhD, is very encouraging for future research on modified MF membranes for drinking water purification. Two follow-up projects are now started from my work, on finding the best antiviral tools and to further develop the membranes and membrane systems.’
The unique combination of application driven research, in combination with adding nanoparticle techniques, proved very rewarding in this PhD work.
‘We won several prizes including the Suez Water and Health Award,’ Terica says. ‘The project was very multidisciplinary in its approach, including virology, nanotechnology and membrane engineering. Also rewarding was the recognition I received at international conferences in which virology experts welcomed the results coming from this, not very broadly known, membrane technology. They saw the great importance of this approach for future drink water treatment strategies. The first steps I was able to take, may mean some giant leaps for virus treatment in the future.’
Terica started the PhD after her successful master work at the Universidad Zaragoza. Terica: ‘Here I focused on bacteria removal with modified MF membranes. This work was part of the European EM3E Erasmus Mundus Master program in Membrane Engineering for a Sustainable World. By virtue of Professor Kitty Nijmeijer and Erik Roesink, I was able to proceed on this project, as Wetsus European Centre of Excellence for Sustainable Water Technology had this important water challenge as a topic.’
Within the research group Membrane Science & Technology, Terica was supervised by Professor Erik Roesink, Assistant Professor Wiebe de Vos and Professor Ana Maria de Roda Husman. ‘Also we collaborated with Wageningen University & Research. There, Aldrik Velders of the BioNT Group was very helpful in performing microscopy experiments using our samples as an input.’
In her future job, Terica is attracted to R&D in an industrial setting. ‘I would like to perform more applied research now,’ she says. ‘I imagine to work on membrane development in food and beverage first, working on my research skills and deepen my knowledge of the field. After that, I will most certainly return to drinking water as my main topic of research. It is my passion to contribute to safe and safely accessible drinking water, being a main topic worldwide, now and in the decades to come. From an early age on, I was involved in volunteering projects, as my father is active in UN regions which are in crisis. Also with my sisters, who work as international doctors, I collaborated by volunteering alongside with them.’