Water Turns Green

Conservation efforts are becoming a sustainability imperative at plants.

By Seán Ottewell, Editor at Large

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GE Power & Water has dramatically decreased its own water usage. In 2008 the company set a goal of a 20% reduction (versus a 2006 baseline) by 2012. It achieved a 30% cut by the end of 2009 and is now working on the next benchmark.

"Each application is customized for each of our plants: there is no cookie-cutter solution. At the same time it is important to remember that some of these improvements are based on changing operations. For example, a simple re-routing of water pipes reduced usage at one site. So cold water flow redesign can be very important while not being a major capex [capital expenditure]."

Looking to the future, Messina points to the challenges posed by the need to remove heavy metals such as mercury. In some countries, the legal requirement is for five parts per trillion: "This is a very complex demand to deal with and there's no one magic solution: a combination of technologies will be needed to achieve this."

Dow Water & Process Solutions, Edina, Minn., is focused on the twin requirements of reduced costs and increased sustainability.

"Industry generally will have to be very, very much more efficient so that water use can be focused on using it for drinking and food production. Reducing water use and then reusing it in the system is therefore becoming more important for the formation of long-term, sustainable enterprises," says Snehal Desai, global marketing director.

One major technology focus for the company is a new fouling-resistant (FR) series of filters for waste treatment centers. "This is particularly important in the production of chloralkalis, which requires a lot of water. Standard RO technology was used by one customer to recycle the water, but they wanted to increase the times between filter cleanings," notes Desai.

Customers increasingly are talking about the net energy footprint to treat water (Figure 1), too, prompting Dow to develop low energy technologies that, for example, need less pressure drop across filters. A low energy FR technology is due to be launched later this year.

MBRs are finding greater use to reduce the organic and suspended load in water streams, which then can be polished further with an RO system. Desai points to the new M20 series of MBR technologies as being crucial for users that need to produce water that can be re-used again in the process stream.

He also cites geographic challenges. "Companies on the Houston Ship Canal have big issues with fouling because the surface water can be very dirty there. On the Gulf Coast, the challenge is to provide cost-effective desalination technology. In China it also depends on sector and location of the plant, but the government is being very aggressive now in pushing water cleanliness."

Dow Water & Process Solutions is focusing its R&D efforts on three main areas: improved rejection of salt from water, lower energy use and better fouling resistance.

Typically, required salt rejection is 99.5–99.7% but ultrapure water, which is a rapidly growing market, demands even better performance -- this often involves RO coupled with ion exchange. One of the big costs here is resin regeneration; the company now is actively working on this.

Work also is advancing on nanofiltration. This is important where divalent ions such as calcium and sulfate must be rejected. For example, in oil production, injecting water with a high sulfate level increases scaling in wells.

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