Membranes could lead to water-tight investments

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Last month delegates from governments, industry, universities and non-governmental organisations convened in Stockholm, Sweden, for World Water Week. As they debated water policy issues, industrialised countries were finally facing up to the fact that access to stable supplies of clean water is now a concern for them, as much as for developing nations.  

Water shortages currently affect 88 countries that are home to half the world’s population. Over the next 25 years, population growth and increased industrial production could cause the number of people affected by severe water shortages to increase by a factor of four.

Many western countries are looking to enhance water supplies by adopting technologies such as desalination, which are more commonly used in regions such as the Middle East that have always suffered from shortages. This trend will become more pronounced, as water shortages become more widespread and the membrane-based technologies used for obtaining water from unconventional sources such as sea water, salty groundwater and industrial effluent, become more efficient.

Investment in desalination takes off in developed countries

Towards the end of last month, Degrémont, the water treatment subsidiary of French water giant Suez Environment, signed a €159 million contract to design, build and operate a desalination plant in Barcelona, Spain.

This followed agreements to build similar desalination plants in El Atabal, Spain, and Perth, Australia. The utility company Thames Water was also planning to build one in London, until London’s mayor, Ken Livingstone, blocked its application, arguing that it should concentrate instead on fixing leaks.

These new plants will utilise reverse osmosis, which has now overtaken the older thermal process in which seawater is evaporated and then distilled, to transform sea water into drinking water. The technique involves extracting salt by forcing seawater through a membrane that allows the passage of water molecules but blocks salt molecules. To overcome the natural tendency of water to travel from low-salt solutions to high-salt solutions via osmosis, this process has to be conducted at high pressures, of around 80 bar.

Similar membrane-based techniques can also be used to extract drinking water from dirty and polluted water sources. The reverse osmosis market is now worth over $1 billion and growing by 10 per cent a year.

The first generation of desalination plants used membranes made of cellulose acetate, but these were replaced by more efficient polyamide membranes in the 1980s and then thin-film composite membranes in the mid-1990s.

But still better membranes are required because obtaining water by desalination continues to require huge amounts of energy, making it two to three times more expensive than conventional water treatment.

“The main areas of R&D for desalination by reverse osmosis are in the pre-treatment of the seawater to limit membrane clogging and the effort to reduce energy consumption,” explains Michel Dutang, head of research and development at Veolia Environment, a French company that builds desalination plants.

For instance, the Australian company Orica Watercare has developed a novel magnetic resin that removes organic matter from water and thereby reduces membrane clogging. Meanwhile, Nick Hankins, a researcher in water treatment technologies at Oxford University, has developed a technique for removing organic matter by getting it to bind with special bubbles, known as micelles. Various research groups are developing membranes with pores made of carbon nanotubes.

European water treatment research needs central direction

But at present research into membrane-based technologies is disparate and uncoordinated, while hardly any spin-off companies have been established in Europe to commercialise water treatment research, says Hankins “So, basically, I think the field is wide open - I don’t believe there is a lot of activity in spin-off companies at the moment, but I do think that they’ll be a huge interest in the future.”

Membranes also form the centrepiece for a novel desalination technology known as forward osmosis, which could be the successor to reverse osmosis. Forward osmosis works by utilising osmotic pressure rather than fighting against it, and therefore has the potential to be highly energy efficient.

A semi-permeable membrane separates sea or river water from a specially prepared solution containing a high concentration of a salt-like molecule. This concentrated solution generates an osmotic pressure, which naturally draws water molecules from the sea or river water through the membrane. The trick then is to extract the salt-like molecules from the clean water.

“Our scheme is to have a material which is magnetically separable,” explains Barnaby Warne, technical director of Apaclara, a Bristol-based company that is one of the early pioneers of forward-osmosis. “So you will have a nanoscale magnetic particle, and attached to this will be an osmotic agent, which at a high concentration will draw water across the membrane.”

Apaclara is currently developing a prototype small-scale forward-osmosis unit for use by soldiers out in the field. The company has received a grant from the US Office of Naval Research and expects shortly to receive another from a UK development agency, but it is also looking for venture capital investors.

But there is no doubt that major practical advances in water treatment will need a more co-ordinated research effort. To this end, in 2004 the European Commission set up the Water Supply and Sanitation Technology Platform, which includes Suez Environment and Veolia Environment as members, to set out European water research priorities for the next 25 years. These priorities will feed into Framework Programme 7, which is due to start in 2007.

On a smaller scale, Hankins is looking to co-ordinate research activities by establishing a centre for water research at Oxford University. This will provide a platform for liaising with industry and should eventually be a launch pad for spin-off companies.

“Membrane technology will play a significant role in the centre’s research activities,” Hankins says. “They’re gaining greater acceptance and use, particularly for potable water treatment.”