Stronger and fouling resistant membranes

Leader

Challenge

Biofouling on membranes can be described as an irreversible deposition and accumulation of organic matter on the membrane surface. This type of fouling is caused by the attachment of microorganisms and the subsequent growth of colonies on the surface. The microorganisms and their secretions of extracellular polymeric substances form a biofilm that is stabilised by weak physico-chemical interactions. The biofilm increases the fluid friction resistance and the overall hydraulic resistance of the membrane. This leads to a reduction in water flux, requiring higher pressures to maintain flow, demanding increased energy usage.

Membranes used for reverse osmosis (RO) desalination have a dense barrier layer in the polymer matrix, which requires high pressures to be exerted on the high concentration side of the membrane, usually 600‐1000 psi for seawater. Polyamide thin film composites are the state‐of‐the‐art membrane technology used for seawater RO desalination however, there are three key problems that exist with the current membrane technology; (1) it is not resistant to biofouling (2) not resistant to chlorine treatment and (3) not resistant to compaction.

Investigation 

Develop a polymeric coating material with reduced bacterial affinity and the method for its deposition onto a variety of desalination membranes. Additionally, develop a membrane that is resistant to mechanical degradation.

Outcomes

A novel anti-biofouling, anti-microbial coating was successfully developed and tested. The coating was specifically designed to adhere to commercial membrane surfaces and when applied to RO membranes there was at least a four times reduction in biofouling, compared to commercially available membranes. While the coated membrane was significantly more hydrophilic, it maintained competitive permeation flux and rejection properties. The effect was not as pronounced when tested on ultrafiltration (UF) and microfiltration (MF) membranes as the coating procedure needed to be longer and this had the effect of reducing performance.

UF and MF membranes were fabricated incorporating a novel polysulfone polymer end capped with polyhedral oligomeric silsesquioxane (POSS) nanoparticle, which is bulky and causes regions of local, high free volume in the solid state. This property is particularly desirable for separation materials as any intrinsically high free volume increases the selective solubility of the membrane material in the separation process, while reducing the importance of diffusion, selection and increasing separation efficiency. Under testing, those membranes with 5% wt/wt POSS afforded greater mechanical strength without compromising pure water flux. Increasing POSS content above 5% decreased membrane thickness and suppressed the macrovoid size in the membrane.

Future Direction 

An alternative approach to the coating may be to develop additives that display anti-biofouling properties which can be added into the interfacial polymerisation process to produce desalination membranes in the first instance. This has many benefits in terms of cost, processability and lifetime of membranes. In this sense and provided the additive has the correct characteristics and these can be synthesised in the lab, a broad range of characteristics could be imparted onto the membranes surface, such as anti-fouling, anti-microbial, boron capture, increase salt rejection, etc. There are a large number of new natural anti-biofouling compounds being discovered and synthesis of these would be a focus with the aim of preparing appropriate additives.

Partners

Ellis partners


 

Total Value: $1,925,689 (cash and in-kind contributions)

Principal Investigator: Professor Amanda Ellis

Title: Development of universally applicable coatings and additives for state-of-the-art reverse osmosis and pre-treatment membranes

Length: 36 months

Personnel: 11 collaborators contributing 5.6 FTE

Related Project: Mitigation of membrane biofouling using natural polysaccharide surface coating (Phase 1 and Phase 2)

Further Information

FR2 FLINDERS Coatings Summary Poster

Project Summary Poster – fouling resistant membranes

WP-Backgrounds Lite by InoPlugs Web Design and Juwelier Schönmann 1010 Wien