Development and application of (functionalised) nanofibre membranes for water treatment

Door een toenemend gebruik van water en de vervuiling ervan, is waterbehandeling een belangrijk thema. Membraanfiltratie is een van de mogelijke technieken om de waterkwaliteit te verhogen en kan gebruikt worden voor het behandelen van bv. zeewater, regenwater of effluent tot zuiver water. In dit werk worden nanovezelmembranen met microfiltratie-poriën gebruikt voor experimenten in waterfiltratie. Nanovezelmembranen werden reeds gebruikt in onder meer luchtfiltratie, maar bieden een aantal interessante eigenschappen voor waterfiltratie. Onder meer hun hoge porositeit is een belangrijke factor om het gebruik van nanovezels in waterfiltratie te verkennen. Ook biedt de productietechniek de mogelijkheid om functionaliteit toe te voegen aan het membraanoppervlak en dus aan de filtratie. Dit werk toont het grote potentieel voor nanovezelmembranen in verschillende types van waterbehandeling, met focus op laaggeconcentreerde stromen. De nanovezelmembranen verwerken een erg hoog debiet aan water in vergelijking met commercieel beschikbare systemen. Daarnaast tonen verschillende functionalisaties van de nanovezelmembranen hun potentieel voor een verbeterde desinfectie, als zelfreinigende membranen of voor de verwijdering van organische stoffen

Performance assessment of functionalized electrospun nanofibres for removal of pathogens

Perfonnance Assessment of Functionalized Electrospun Nanofibres for Removal of PathogensKeywords: functionalised nanofibre, pathogen removal, membrane filtration. The c1ectrospinning technique is a process for making continuous nanofibrcs in a nonwoven fonn. This process spins fibres ranging from 80 om diameter to several hundred nanometers. The non-woven structure is produced by app lying a high voltage to the anode, submerged in a spinn ing solution. This produces a charged jet of fluid when the electrical force is highcr than the surface tension of the solution and the fibres are collected on a grounded aluminum plate. Nanofibres have a small pore size and a large surface area to volume ratio compared to nonwovens (this ratio for a nanofibre can be as large as 1000 times of that of a microfibre). This, together with their low density and interconnected open pore structure. make the nanofibre nonwoven appropriate for a wide variety of filtration applications (Huang et al.. 2003). Due to the large effective surface areas. nanofibres can carry functional agents with different properties. such as biocidcs. With microfiltration membranes it is possible to retain suspended solids and micro-organisms. The added value of the tested nanofibre microfiltration membranes functionalized with silver nanoparticles (nAg) or other biocides to pathogen removal was studied. The biocides used in this study are commercially available. WSCP for example. is used as a cooling tower biocide and is applied directly into the water. Silver nanoparticles are nowadays implemented in a wide variety of consumer products for antimicrobial controL The aim of the study is to examine the effectiveness of different biocides and the possibility to electrospin them in a steady state nanofibre membrane. The results show that due to the silver nanoparticles and the funct ionalisation with biocides in the functionalized membrane a higher efficiency (3.9 10giO - 5,5 10glO) could be achieved. Further, the removal of pathogens is a factor 100 (2 10g10) higher with a WSCP (5%) than conventional microfihration. Functionalisation with Ag nanoparticles gave a 4 10gi0 removal. It is generally known that these particles only have effect on gram negative bacteria such as E. coli. WSCP and bronopol are bactericides that can be applicd on c1ectrospun nanofibres and it has also effect on gram positive bacteria (Chen et aI., 2008). The removal with a non-functionalised membrane is not as good as other micro-filtration studies. With other commercial membranes a 2 log I 0 - 4 logl 0 removal is possible (Zodrow et al.. 2009)

Electrospun nanofiber membranes functionalized with antibacterial particles

Electrospinning is the most efficient method for the production of nanofibrous structures, which have unique characteristics such as high porosity, high absorption capacity, small pore size and high specific surface area. Thanks to this, they can be used as filtration membranes. Nanofiber membranes have high clean water permeability values, however the pathogen removal efficiency is currently not satisfactory. For this reason, we functionalized the membranes with antibacterial particles, such as silver nanoparticles and commercial biocides, by adding them into the spinning solution. Afterwards, the membranes were characterized to study the effect of the functionalization on the fiber diameter and pathogen removal efficiency. The distribution of the silver nanoparticles was studied with SEM and TEM images. TEM-images showed that the silver nanoparticles are trapped inside the nanofibers. SEM-images confirmed that the average fiber diameter is not affected by the functionalization. To evaluate the removal of pathogens, water samples were taken from waste water from a general hospital (107 – 108 colony forming units per 100 ml) and were filtered with different membranes. A non functionalized nanofiber membrane could not achieve the same reduction in culturable organisms as commercial membranes (2 log10 – 4 log10 removal). Higher reduction was reached when silver nanoparticles were added to the membrane. A 3 log10 – 4 log10 removal was reached by adding silver nanoparticles to the spinning solution. Nanofiber membranes with biocides as functionalization agents achieved even a much higher reduction, up to 5,5 log10, which is competitive with commercial membranes currently on the market. In conclusion, the electrospinning process allows the functionalization of nanofiber membranes with antibacterial particles. This highly improves the pathogen removal efficiency of the membranes

Structure changes and water filtration properties of electrospun polyamide nanofibre membranes

Nanofibre membranes are studied extensively in water treatment. Inappropriate storage, however, could alter their performance, e.g. regarding water filtration. This shows the need for investigating this effect in more detail so as to offer a solution for long-term behaviour and stability. In this study, polyamide nanofibre membranes were treated under different conditions, simulating the diverse storage conditions and to simulate their use in water filtration systems. Under all these different settings, nanofibre properties (scanning electron microscope pictures, dimensional changes, tensile strength) and water filtration performance (clean water permeability (CWP), bacterial removal) were investigated. The results demonstrate that, as soon as the dimensional change of a membrane is >2%, the CWP, tensile strength and bacterial removal significantly decrease. These dimensional changes occurred when the membrane became dry after it had been in contact with water. As such, it is important to keep the membrane either in dry or in wet conditions to store its unique properties. When heat-treated, the membrane had a higher tensile strength and kept its morphology and characteristics better during storage