Adapting RO Plants for New Membranes

John Walp, commissioning manager of the Brackish Groundwater National Desalination Research Facility in Alamogordo, talked to Chamber of Commerce Water Committee members Monday [8/11/08] about new technologies.

The article mentions something about the speed and direction of membrane evolution.

Technological development and innovation are also taking place in membranes used to filter water in reverse osmosis. Large diameter membranes have been found to reduce capital costs. Also, pre-filtration technology development is gaining momentum because it extends the life of expensive membranes.

“If you want to keep replacing membranes, then let raw water through,” Walp said. “If you want expensive membranes to last, you have to treat the water first.”

Pump and energy recovery development is taking place to improve efficiency and reduce energy consumption, Walp said.

In short, the cost of reverse osmosis technology is going down with an influx of new innovation, Walp said.

Today the average cost of water processed by reverse osmosis is $2.27 to $3.03 a gallon. Within five years the cost will be closer to $1.89 a gallon and within 20 years, the cost will drop to and average of 50 cents a gallon

As I’ve mentioned before–I think costs will drop faster. But there will be intermediate steps. These intermediate steps, however, promise to cause quite a headache for planners.

“The California Coastal Commission has cast an historic vote to approve Poseidon Resources’ Carlsbad Desalination Project….The project is on schedule to begin construction the first half of 2009 and delivering drinking water in 2011. ”

Great. That plant may incorporate the latest RO pump developed by Energy Recovery Inc.

But its only great luck that the pump comes along at the same time as the plant is in its planning stages.

What happens when an RO technology comes along that goes against the latest engineering model. Notice above that pretreatment is getting more traction as a way to extend the life of membranes?

Likely, Poseiden’s new Carlesbad project will adopt some kind of pretreatment. A popular pretreatment is to chlorinate water before its passed through the membrane. The chlorine kills the wee beasties & algae that foul membranes. But then the chlorine is also removed–before it passes throught the membrane — because chlorine also tends to degrade membranes faster.

Doesn’t that look like a complicated cad.

What happens if you get a membrane that requires plant design changes.

Well, as it happens, a new chlorine tolerant membrane from the University of Texas at Austin has been developed. However, its not clear as to whether this is an improvement on the membrane designed by UCLA’s Eric Hoek announced two years ago. The chlorine tolerant membrane would cut step two out of the process. But Eric’s membrane might cut steps one and two out of the process. The chlorine membrane is not ready for prime time–nor has any date been set for it to go into commercial production. Eric Hoek’s membrane is further along. It is slated for commercial production in late 2009/early2010.

As of now Poseiden can’t cad either into current engineering specs.

But since the new membranes cut out a step or two of pretreatment — there should be a way to write this into the specs for the plant. Likely Poseiden has the tools for this. I would suggest two. I mentioned both here a couple years back. The first by Autodesk “enables customers to create designs based on the functional requirements of a product before they commit to complex model geometry, allowing designers to put function before form.” The second tool developed by MIT would enable you to cost out retooling the Poseiden plant for a new membrane. According to the article I posted here back in 2006 “The model allows companies and organizations to develop more accurate bid proposals, thereby eliminating excess “cost overrun” padding that is often built into these proposals.”

Of course the sort of plant design changes caused by teams at UT Austin and UCLA will pale in comparison to the LLNL membranes–but that’s for another year.

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3 Comments on “Adapting RO Plants for New Membranes”

  1. nick2 Says:

    VV emailed to say that:

    You refer to a new pump by ERI. It is not actually a pump. It is an energy recovery device that recovers energy from the high pressure concentrate leaving the RO system. It is a standard practice to recovery energy from the concentrate in seawater RO system. In the past, turbine based devices were used. Now, devises based on positive displacement are being used (such as the one made by ERI). With these new generation devices, such as the one by ERI, you can recover 95% or higher energy that is in the concentrate stream. However, ERI is not the only manufacturer making devices based on positive displacement principle. There are others – Calder makes DWEER which essentially uses the same principle and has comparable efficiencies. And many others are also entering the field including KSB, Aqualyng, etc.

    As for the RO feed pumps, no major breakthroughs. The efficiency has been 85 to 88% for a while now.

    And there are some projects where it might be preferable to use the older turbine based energy recovery technology (for small plant where there is limited space and reliability and ease of operation take precedence over slightly higher efficiency).

  2. Tobi Steamer Says:

    nice post. imho you may be able to optimize current generation membranes by introducing micro bubbles to them by way of electrolysis. current research suggests that micro bubbles make the surfaces of confined spaces very slick. Slick enough to overcome osmotic pressure? good question. don’t know. but the question is worth addressing with an experiment because if true then you might be able to substitute expensive pumps for electrolysis machines. the next question is would the electrolysis be cheaper than pumping.


  3. […] the problem that evolving membrane technology creates for deal plant designers like Posiden. I mentioned this a couple blogs ago. They’ll need to be able to design new desal plant in such a way that they […]


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