Shockingly efficient water membranes

SHOCKING membranes used for water treatment could reduce fouling and improve wastewater and desalination plant efficiency.

New research uses electrolysis to generate microbubbles that effectively remove impurities and prolong membrane lifetime.

The treatment of wastewater and desalination of seawater is becoming more and more important to provide clean water, especially in areas of drought. During the last few decades, membranes have been key to pressure-driven processes such as reverse osmosis, microfiltration, ultrafiltration and nanofiltration. Aside from the need for clean drinking water, such processes are essential for biotechnology, the food industry and medicine.

The simplicity of membranes means they offer several advantages over alternative treatment processes. For instance, they do not require chemical additives and can be easily scaled up. Their major drawback, however, is that they are susceptible to fouling, which blocks the passage of liquid, reducing efficiency and increasing costs until replacement or cleaning is needed.

Cleaning processes such as ultrasound can increase energy costs while others require the use of harsh chemicals. This frequent cleaning deteriorates membrane polymers over time and can also lead to water treatment plants having to be shut down, costing millions of pounds in lost operational hours. Therefore, finding a way to quickly and easily clean fouled membranes makes financial and environmental sense.

And a promising self-cleaning technology using hydrogen bubbles to remove impurities could provide an answer. The technology was developed by researchers at Swansea University’s Centre for Advanced Technologies and Environmental Research (CWATER) in the UK and Abu Dhabi’s Masdar Institute of Science and Technology in the UAE.

Lead researcher, Swansea’s Nidal Hilal, described the first steps in developing the technology. He said: “The beauty about this work is we use electrolysis. What we initially did was make the membrane conductive – we put carbon nanotubes on the surface, but you can use other materials. You put a very small current through to generate microbubbles which clean the membrane surface.”

Since this original work, which was published in 2014 and led to the filing of a patent, the technology has been developed to adapt to commercial needs.

He said: “More recently, we were thinking that making a membrane conductive may not be best for the manufacturer, as it would require new investment and lines to be produced. So we looked at the membrane module itself. A lot of the fouling occurs under the spacers, and for the first time we applied this technique to make the spacers conductive – we got fantastic results.”

Effective cleaning was demonstrated using both titanium metal spacers and current industrial polymeric spacers, which were coated with a carbon-based ink comprised of graphene nanoplates.

Hilal believes that his work, accepted for publishing in Desalination, could significantly save energy and man-power, and that there is no comparable current technology.

He said: “For the industry this is revolutionary. You do not need chemicals at all and you do not need to shut down. You can clean while running the operation and we have not seen any deterioration of the membrane surface by applying our 3 V.

“The membranes these days last in industry about five years with low fouling feeds, but when you use things such as wastewater they will deteriorate much more. Depending upon the feed, I would say, personally, with our method you would get at least 20% more time – and this is very modest. Our next step for us is now to take this further up and scale it up to make membrane modules.'