Membrane distillation technology: The new way to go

Technological breakthroughs are quickly rising to the fore.

Dr Prince with the International Association of Advanced Materials Scientist Medal (IAAM Scientist Medal). Photo credit: EWTCOI, Ngee Ann Polytechnic


Dr J Antony Prince, the Senior Manager who heads the Membrane Technology team at the Environmental and Water Technology Centre of Innovation (EWTCOI), Ngee Ann Polytechnic, led a team in pioneering ground breaking developments in membrane technology. “Membrane technology, that’s my passion, my interest, and what I’m working for,” he said with a smile. For his passion and achievements, Dr Prince was recently awarded the prestigious International Association of Advanced Materials Scientist Medal (IAAM Scientist Medal).

Water & Wastewater Asia was privileged to speak to Dr Prince, who earned his PhD from the Newcastle University (UK), to better understand the research breakthroughs in membrane technology.

One of the most prevalent issues facing the world today is the lack of access to clean, drinkable water and sanitation. The United Nations (UN) has cautioned time and again that by 2025 – less than a decade away – an estimated 1.8 billion people around the world will be living in regions afflicted by complete water scarcity, and the United Nations International Children’s Emergency Fund (UNICEF) has warned that by 2040, up to 600 million children, about a quarter of the total children’s population, will be forced to live in environments without sanitised water, and an estimated 2,000 children under the age of five die every day because of bad water hygiene.

With the increasing demand for high quality, potable water, many new technologies for water purification are being conceptualised and developed for both non-potable and potable use. “Apart from reverse osmosis, there is membrane distillation, forward osmosis, and electrodeionisation for desalination. It depends on the application and what kind of water you want to treat,” Dr Prince commented.

While Dr Prince accepts that membrane technology is well-developed, he considers it inefficient. The present rate of recovery using sea water reverse osmosis (SWRO) stands at only 45% to 50%. Another critical issue is that membranes are highly vulnerable to fouling. He also believes that the market for membrane-based filtration systems is oversaturated, owing in a large part to their dependability, easy availability and straightforward process. “We have microfiltration, ultrafiltration, nanofiltration, and reverse osmosis (RO) for water treatment,” he pointed out.

It was these factors that spurred him on to explore and concentrate his efforts on other avenues in membrane technology. “Now, the innovation is focussed on the materials. I question how we can design the materials to reduce the pressure and how can these materials absorb more water. Can we focus on surface charge and hydrophilicity? Studies have shown that bio-inspired membranes – like functionalised graphene and aquaporin based membranes – can perform 100 times better than the commercial membranes in the market right now. It comes down to understanding the science related to the material,” he elaborated.

Already, Dr Prince and his colleagues, Dr Gurdev Singh and Mr Shanmugasundaram, have patented two recent technologies, one of them being Distil™.  “Distil™ is the combination of a patented Vacuum Air Gap Membrane Distillation (VAGMD) process and a unique nanofibre-based triple layer membrane. It can be used for various industrial applications including desalination, product concentration, precious metal recovery etc, and is ready for commercialisation. Capable of recovering more water than the RO system, it can be operated completely based on solar-powered energy. Unlike the RO system, it does not need high pressure to operate. Solar thermal energy (STE) is used to heat the water, and solar photovoltaic (PV) energy is used to operate the pump. The driving force is the vapour pressure gradient and the temperature difference across the membranes,” he explained.

Membrane Distillation (MD) has been around since 1963, and holds many notable advantages. This includes its ability to use heat to function, thus lowering operational costs, protracted periods of time in between necessary maintenance, capability of working even when exposed to a high concentration of salt, and increased economic viability. However, MD has never been used on a large scale, owing to the limitation of the membranes.

But while the Distil™ was initially created for desalination, Dr Prince and his colleagues gradually expanded its applications into different areas, such as treating wastewater generated by various industries, like nickel electroplating and agricultural industries, to create not only reusable water, but also recover valuable resources from water. The technology will be implemented on a full scale soon.

Another patented technological breakthrough that may be seen in the market soon is the NF-Star™, an electrospinning device used for the production of flat sheet nanofibres. Nanofibres are not new products; they have been around for approximately the past two decades. They are used in the energy industry, in batteries as separators as well as in tissue engineering, where they are utilised as scaffolding. Only recently have nanofibres made the leap into the water industry, where they can be found in the microfiltration, ultrafiltration and micro porous hydrophobic membranes for membrane distillation. Nanofibres can even be used as a porous substrate to develop nanofiltration and forward osmosis membranes.

Dr Prince has big plans for the NF-Star™. “The technology can be used for a broad range of applications; it can produce nanofibres, highly porous membranes with the highest permeability. But as mentioned before, its limitation is that it cannot be used for nanofiltration or forward osmosis unless you modify it further. There are other scientists looking at this field, but we are focusing on a different area. We are looking into vapour transfer membranes, meaning we want the hydrophobic or water-repelling surface property. We are using the lab-scale nanofibre production machine to produce water-repelling membranes for vapour transportation in our Distil™ system. The novel nanofibre based triple layer membrane provides up to six times higher permeability compared to other currently available membranes for distillation.

Nanofibres are notoriously difficult to produce on a large scale, which often leads to an increase in costs, but if the development goes well, the NF-Star™ has the potential to address that problem. It can not only produce nanofibres on a larger scale, it can do so at a much lower cost. “We’re always looking at how we can translate ideas to the market. When we think of an idea, we’re always thinking of how we can scale up the production capacity while also reducing the costs for production,” Dr Prince said. NF-Star™ has been licensed to a local SME, Nanoflux Pte Ltd, who intends to sell the machine this year.

Dr Prince is confident that his technology will not only be accepted in the conservative water treatment industry, but that there will also be huge demand, especially with the impending price hike in Singapore as well as the looming global water crisis. “This price hike has really gotten companies thinking about recycling water. With the number of companies approaching us, we have started integrating technologies in order to solve the problem, and MD is one of the solutions. We are also looking into other applications of our MD to help conserve water. There is definitely a lot more interest in reducing, recycling and recovering water.”

But beneath the technological achievements and world standing lies a caring, humanitarian heart. Dr Prince harbours very high hopes of his technology benefitting other nations around Singapore and further the global water cause. “Countries like Singapore that are quite developed, can offer to help underdeveloped countries, but the huge challenge is high operating costs. Some NGOs (non-governmental organisations) are serving the regions, but they cannot offer to take on the burden of the operating costs. So, actually, our aim is to reduce the operating costs. By doing so, we can better serve society.”

 

This article was published in Water & Wastewater Asia’s May/June 2017 issue.