New filter tech improves performance of desalination systems
22 June 2015
EU-funded researchers develop a self-cleaning filter membrane for desalination plants that cuts their energy use, waste and maintenance costs.
The Intergovernmental Panel on Climate Change predicts that 60 percent of the world’s population will not have enough water by the year 2050. The shortfall will affect Europe as well as developing countries. To reduce the resulting pressure on fresh water resources, desalinated seawater will be a valuable source of drinking water.
However, the filters used by desalination plants come with their own problems: they get clogged up with microscopic sea life and mineral deposits, generate waste when they are cleaned, and need large amounts of energy to work properly.
The €4.5m, EU-funded 'NAWADES' project is developing a long-life desalination filter membrane that resists mineral deposits. Because it stays clean, the membrane should lower desalination energy and maintenance costs and cut down on the pollution the process creates.
“The focus for the consortium is to see how we can improve the water desalination process and the economics of desalination, reducing the energy and chemicals needed,” says Steffen Schütz director of new filtration applications at project member Mann+Hummel GmbH.
To do this, the project team looked at all aspects of seawater desalination, from the different processes involved to the structure of the filter membranes. “You have to consider all the single process steps together and their interdependencies; it makes no sense to focus on just one,” says Schütz.
The team developed new membrane materials and coatings that use nanotechnology to resist the build-up of residues and keep the filter clean. They also developed a modular filter design based on the new membranes.
One way in which the project team modified the membranes was to add a nano-scale titanium dioxide coating that reacts with sunlight to break down organic matter that settles on the membranes.
By keeping the filters clean and clear of blockages, treatment plants do not need such high water pressure to remove salt from water, thus saving energy. The self-cleaning technology also means that plant operators can reduce the amount of polluting chemicals needed to clean filters and can cut maintenance costs.
NAWADES estimates that its filters will last about three times longer than existing membranes – up to eight years – so that fewer filters end up in landfill. Further increasing sustainability, desalination with the filters will create solid salt residue, which is cheaper to dispose of and less polluting than the waste brine solution left over from current filtering.
As well as the energy-saving and ecological benefits of the project’s technology, the team expects to increase the profitability of desalination plants. Overall, costs could go down by about 20 percent to less than €0.30/m3 of water produced, according to project estimates.
The materials developed in the project’s R&D phase are now being tested in a prototype filter in a large desalination plant in Spain. “We can do laboratory experiments, but it is crucial to know the membrane’s long-term behaviour under real-world conditions,” says Schütz.
Tests will run for several months in different conditions to optimise the membrane and collect data on potential energy savings, reliability, overall cost and sustainability.
“If tests go well, we can adapt the whole process further for different local conditions,” adds Schütz.
And because the filter system is modular, plant operators can also add more membranes for higher volumes of water filtering.