Reverse osmosis desalination is playing an increasingly important role in the bid to meet the Middle East's growing thirst for water.
Rapid population growth and industrial development are putting heavy demand on water supplies in the Middle East, and the construction of artificial islands is throwing up new challenges for water providers.
But utility companies are finding that reverse osmosis (RO) desalination technology can provide a quick and cost-effective solution to these problems, and as a result this method of desalination is gaining market share in the region.
In the RO desalination process, high pressure is used to push saline water through semi-permeable membranes to remove the dissolved salt content.
It does not require heat, unlike the thermal distillation methods, such as multi-stage flash (MSF) and multi-effect distillation (MED), which vaporise the water to remove the salts. This means the facilities can be built independently from power plants and be connected to the electrical grid instead.
Bad image
RO is not a new technology; it has been around for more than 30 years. For sometime, though, water firms in the Middle East were wary of experimenting with RO desalination because one of the early projects constructed in Bahrain during the 1970s famously suffered many complications as a result of its inadequate pretreatment system.
Other plants dating from the same era also experienced operational problems and some continue to suffer, as Paul Buijs director of Global Membrains consultancy explains: "RO requires a good pre-treatment. In the UAE and other areas in the Gulf there are some installations that are facing problems. You can bring most of the problems back to the fact that the buyer has gone for the lowest possible investment cost instead of the lowest cost of operation.
"If you apply a very rudimentary system of filtration you will get the particles out, but you won't get the bugs out, and they start fouling and clogging up the membranes, reducing their efficiency. With sufficient pretreatment, especially when applying ultra-filtration, you will have a trouble-free RO system. Normally manufacturers would recommend a cleaning once every three months, however, we are involved in a system in Belgium which is cleaned once every year and even then it is a very limited cleaning.
It shows that with a good pre-treatment you get a very stable situation. And you can do that on any type of water - there are even ROs for industrial applications that are run on municipal effluent, which obviously has a very high biofouling tendency. With a good pretreatment there is no problem with RO.
A growing understanding of the chemistry behind the technology and the need for daily pH control, along with improvements in membrane design have enabled RO desalination to shed its bad image in the region over the past few years.
The fall in the cost of RO desalination has also helped it to gain in popularity, as Aqualyng's Eric Jankel explains: "The economics of the technologies now favours RO, when all other things are equal.
The price for the end-user has come down, hitting a bottom about four or five years ago. The technology has also improved and the membranes are more productive. If you spend US $500 for an eight inch by forty inch element you are producing more water from that element today than you would have done five or ten years ago."
Energy recovery
Another important driver in the shift towards this technology has been the improvement in the efficiency of energy recovery devices, which have significantly reduced the cost of operating of RO desalination units.
"Energy is about 25% of the cost of producing water on a lifecycle basis," states Jankel. "If you save a marginal amount on energy you can make significant savings on the cost of production."
The most energy-intensive part of the RO process is the initial pressurisation of the feedwater.
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