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Space-age water treatment less constrained by gravity

March 21, 2013
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Are water markets around the world getting serious about conservation and reuse?

“It depends where on earth you are,” Snehal Desai, global business director, Dow Water and Process Solutions, says. “Outside the developed world you don’t necessarily have a ‘municipal feed.’ Having a secure water supply may therefore be a real issue for companies involved in process production. Plus, in building new infrastructure the developing world has opportunities to apply the latest technologies.”

Dow Water and Process Solutions is a unit of Dow Chemical, headquartered in Midlands, Mich., and is said to enjoy annual revenues of more than $1 billion.

“In the developed world too,” Desai adds, “in Europe, it’s no longer just demonstration projects.”

Processors must constantly readjust the three key production parameters of product quality, chemical use and energy management, Desai says, given rapidly unfolding globalization and critical issues related to energy costs, water availability and environmental concerns. In this unique, 21st century environment, for both private and public water infrastructure, Dow is committed to applying its expertise in reverse osmosis, nanofiltration and ultrafiltration.

These filtration technologies aren’t necessarily brand spanking new. Some aspects of them have been in commercial use for more than half a century. Instead, innovation comes, says Desai, from an understanding of regulatory concerns and market demand, and with applications tuned to unique industry environments.

Defining basics

As is well known, reverse osmosis is a membrane-technology filtration method for removal of many types of large molecules and ions from solutions. This is done by applying pressure to the solution when it is on one side of a selective membrane. Solute is retained on the pressurized side and pure solvent passes to the other side.
In a normal osmosis process, the solvent naturally moves from an area of low solute concentration, through a membrane, to an area of high solute concentration. Reverse osmosis is best known for its role in desalination of seawater.

Ultrafiltration is a kind of membrane filtration in which hydrostatic pressure forces a liquid against a semi-permeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through. The primary industrial use is for purifying and concentrating macro-molecular and especially protein solutions.

Nanofiltration is a more recent technology. Its best use, it is said, is for applications “somewhere between ultrafiltration and reverse osmosis” and is most often used in treating low total dissolved solids water such as surface water and fresh groundwater.

Innovation application specific

Each process industry has its own set of priorities, Desai notes. For example, given the rapid development of U.S.-based shale gas resources there’s healthy demand for treatment of water used in hydraulic fracturing and for the “produced water” that comes out of the well mixed with oil and gas. And unlike a food or even chemical processing plant, upstream oil and gas production sites may be in some of the most remote corners of the world.

“What’s important here,” says Desai, “are mobile units that can be left to run without operators and maintenance-free for a period of time. Water generated at those sites can now be reused or at least cleaned before disposal.”

For centuries, water treatment primarily depended on gravity and time, or separation by weight, to do the work. But as water becomes a constrained resource on a global scale, a level of technology will be applied to its conservation and use heretofore unimagined. If 75 years ago there was no such thing as television, let alone PCs, devices and the cloud, who’s to say that the environmental, technological and political landscape related to drinking water won’t be utterly transformed in the next 100 years? Advances in materials science have already made huge contributions, with more sure to follow.  

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