Viewpoint: Are ceramics set to take over from PVDF membranes?

A year has passed since the EU restriction proposal for PFAS were published. At the time, there was concern that the industry’s preferred membrane material, PVDF, might fall foul of the proposals. Dr Graeme Pearce discusses whether PVDF membranes have any long-term prospects and, if not, whether ceramics will benefit from the restrictions.

VDF is in the PFAS family

In the membrane industry, the most common material used is PVDF. However, PVDF is deemed to be a PFAS and does not seem to qualify for one of the potential exemptions.  

Recent pronouncements show that not much has changed either for supporters or opponents of continuing to use PVDF. However, as far as the right to manufacture and use PFAS in water treatment products, the prospects do not look encouraging.  

The complications of balancing different perspectives from the side of the business and user, and also for environmental/health issues for all 27 EU member states will continue to cause headaches. However, as things stand, it is likely that PVDF membranes will fall foul of EU restrictions. 

Market already moving toward ceramics

PVDF has established itself as a key material in membranes for water treatment and in some applications is clearly market leading. Are there signs that ceramics will take advantage of the PVDF uncertainty? The answer seems to be yes and no!

Some markets set their sights away from polymerics some time ago, prior to the PFAS discussion. For example, about half of the UK municipal market now specifies ceramics, and the world’s largest ceramic drinking water plant will be commissioned near Birmingham within a year. 

As early adopters of polymerics, a few bad experiences for some UK users have meant that decision makers in these firms have now said ‘never again’. Although those early-stage development problems from first generation products are, in reality, firmly in the past, the emotional scars have been translated into an unmoveable opinion.

Comparing ceramics vs PVDF in an open market

Most markets demand a level playing field comparison when evaluating polymeric and ceramic options. The early days of reverse osmosis allowed engineers to compare newly standardised products across the board in terms of flow, rejection and price. 

When ultrafiltration came along, comparison became even easier since particle removal could be taken for granted and the only parameters considered were flux and price. Arguably, with the existence of different formats, this was a step too far, but the desire to compare meant that this simple comparison methodology achieved traction.

The advent of ceramics has put the comparison method of focusing on flux and price into question. Ceramics have much higher flux but are also more expensive. Surely there are other issues of suitability, or system and operational knock-on effects that come into play when looking at a project? 

Herein lies the difficulty for ceramics in making the big breakthrough in markets still open to both options. It can be misleading to try to compare across a broad spectrum with such different performance and price points. Maintaining the status quo is clearly less risky.

Level playing field holding ceramics uptake back

Ceramics have done best in industrial markets where the end user doesn’t care about flux and price comparisons between different membrane suppliers, but solely on the value that the membrane system will provide to their application and the payback achieved. Industrial applications often have a degree of difficulty which ceramics are well suited for, such as fouling and/or aggressive feed streams.

What can ceramics do to strengthen their appeal in the wider market? Can the discussion be moved along so that ceramics can focus on issues that are difficult for polymerics? Perhaps it is the level playing field approach that has done least favours for ceramics, since the full gamut of water applications can have broad requirements.

Where do ceramics outperform PVDF membranes

As an example, ceramics are better with challenging feeds because aggressive physical or chemical cleaning can be used to recover the membrane. Our newsfeeds these days are full of stories of extreme weather events and localised flooding, turbidity spikes, and algal blooms.  

The events are a long-predicted outcome of climate change that is now becoming a reality. Ceramic membrane systems that could be recovered if the feed envelope goes out of specification would be a much better option for the end user than a piece of paper with an irrelevant warranty written on it.

Another issue is that ceramic systems take up less space. Fluxes are high, which has an immediate impact on footprint. Also, a ceramic treatment train is often simpler, which makes it compact.

Advantages of ceramics likely to spell end of PVDF membranes

Ceramics are certainly placing themselves to take advantage of travails in the polymeric market. In all likelihood, restrictions on the use of PVDF membranes will take some years to come into place. However, although fluoro-carbons in general and specifically PFAS have had an incredible positive impact on society, the environmental and health downsides will ultimately mean that their use will be restricted to areas in which they are truly essential. 

Membranes for use in water treatment are unlikely to qualify as one of those essential uses since ceramics could cost effectively replace them. 

As an industry, we need to consider the option of using ceramics more widely and accelerate their adoption. This would ensure that we learn the undoubted application lessons in a timely fashion and have a better experience than in the early days of polymerics.

Dr Graeme K Pearce is a membrane technology specialist with 40 years’ experience in the membrane industry. He is the principal of Membrane Consultancy Associates.