A Q&A with Richard Stover, executive VP of Desalitech, discussing a reverse osmosis (RO) innovation that greatly increases recovery rates and overall efficiency, while also enhancing flexibility and reliability.
Lofty claims abound in the world of water technology, especially among startup companies. However, when a technology is adopted by an internationally known, pioneering municipality, it’s definitely worthy of attention and consideration. Such is the case with Desalitech’s Closed Circuit Desalination (CCD), which Singapore PUB is piloting as a means to further enhance the efficiency of its RO treatment system for water reuse. The technology, which increases efficiency by returning water to the front of the process in a closed loop, is also being used for industrial operations in Israel and in the U.S.
To explain the patented technique and the benefits it can provide (and to whom), I spoke with the executive VP of Desalitech, Richard Stover. What I encountered weren’t just lofty claims, but proven results — at PUB and elsewhere. Though still up-and-coming, this innovation could very well be the future of RO.
How exactly does Closed Circuit Desalination (CCD) work?
It's a semi-batch approach. The CCD system recycles or recirculates the membrane reject through a unique configuration of standard RO equipment. The batches charge and discharge on the fly, so to speak, with continuous operation of the pumps and production of the product permeate. The result is up to 97 percent recovery, with substantially less energy consumption and greater flexibility and reliability.
Every 10 to 30 minutes, depending on the water being treated, how it's operated, and how much recovery you want, the system is emptied of all the concentrate and filled with new incoming feed water. By completely flushing the system out and starting over again, you don't get the accumulation and precipitation of unwanted elements that can cause fouling or scaling. This frequent flushing is really beneficial for long-term, sustained performance of the membrane elements.
Can you briefly describe RO system cross-flow? How does it work in a conventional sense, and how is CCD different?
With cross-flow filtration, you send the water past the membrane instead of driving into the membrane. What that does is sweep away the accumulated material from the surface. The filter just works as a surface barrier. Nothing gets into the filter — it's all stopped right on the outside active layer, literally one molecular layer on top of the RO membrane. If you don't have a pretty substantial flow going past, salt accumulates right at the surface and the membrane essentially shuts down. They call it concentration polarization. It stops working, so that’s the necessity of cross-flow.
The way we do cross-flow in the CCD system is primarily through recirculation. You're actually using the concentrate and bringing it back around and combining it with the feed so you have very good cross-flow. There's a pump in that loop that's dedicated to supplying that cross-flow. If you didn't have that, then you would have to supply cross-flow with your main feed pump. This requires that most of the feedwater is left in the feed channels at the last membrane, so that the last membrane can function. Whatever is left after the last membrane leaves the membrane vessels as brine waste. That's why, with conventional RO, recovery is limited to about 50 percent per stage.
For our process, we've got cross-flow by virtue of the circulation. As long as you can keep pumping water into this system and recirculating, you can keep getting more and more recovery.
What water/wastewater market segments would benefit most from CCD technology?
Our motivation is the need for water, the increasing demand, and the decreasing resources to meet that demand. What we're trying to do is introduce a more efficient water purification technique. And by efficiency I mean everything: higher energy efficiency, more productive systems, less waste, and a higher recovery rate — to get more out of the water resource you have, whether it's wastewater, fresh water, groundwater, or seawater.
We have plants that have been running for close to five years now, but it’s only been two years since we've brought the technology out of Israel into new applications. What we’ve found is that there are certain markets where our value proposition just really hits home — those that benefit greatly from higher recovery and energy efficiency. Hence the markets we're going after: industrial water treatment and water reuse. Agriculture is a particularly strong focus area because it pulls all these needs and benefits together.
What have you learned since expanding outside of Israel and into new applications?
The basic engineering techniques used to design and build RO systems, they work. So you don't see a lot of piloting or testing of RO systems to make sure that specific project designs will perform correctly before you go to full scale. You pretty much just jump right into full scale. We're able to leverage the same experience and fast-track the implementation process because we’re using the same engineering tools. We’re ready to go right into big plants.
At Singapore PUB, we demonstrated improved recovery from 75 percent to 90 percent and increased output by 20 percent. We've been running a unit in Massachusetts for a good part of this year. All together we have about 20 plants running now. What we found is that our design tools, which are conventional RO design tools, correlate very well with real systems. That's just the way it is in RO.
Can the CCD configuration be retrofitted to current RO operations? What are the space implications?
We do retrofits. We prefer to build new systems because we can optimize the selection of the pumps, the plant layout… everything, for best performance. When we do a retrofit, we have to re-plumb it and move things around to get the configuration that we want. For example, we use short membrane arrays. We use three or four membrane elements in a line. That's enough for us to achieve high recovery because we're recirculating. There are performance benefits of having just a few membranes in line. In a conventional system with standard RO, you have to put as many membranes in a line as you can to get maximum recovery — you might see 7, 14, 21, or even more membranes in a line. But it's all the same equipment. We have several retrofit-type systems working, and they deliver most of the benefits.
What is the initial capital cost of a new or retrofitted CCD system, and what is the return on investment (ROI)?
For the systems that we're selling in the U.S., cost is comparable to conventional RO. It's the same number of membranes, the exact same high-pressure pump. That cost is really a pretty broad variation, depending on the amount of pretreatment and the size of the system. There's some economy of scale where larger systems are less dollars per gallon of output than smaller systems.
The ROI comes down to lower cost of ownership. If you're saving energy, producing less waste that you have to pay to get rid of, and experiencing less downtime for maintenance, there's obvious savings and benefits. If you're coming in at the same initial price point, then it's an immediate return on investment because you're operating less expensively.
If it’s a retrofit, how long it takes to pay for the retrofit really depends on what you started with. Nobody really moves if you're talking about more than a five-year ROI. We're well under that. There are some cases where the ROI is much less than a year.
Where the energy prices are very high, or the brine disposal cost is very high, it really pays to do a retrofit. In a lot of cases it makes sense to just tear out the existing system and put in the new system, but that's not usually the way it's done. Usually you need the water, so you put a new system in parallel with the old system and decommission the old system later.
What specific industrial markets do you serve?
Oil and gas is big with natural gas extraction. You get a lot of water out of the ground when you extract natural gas — it's something like a 10-to-1 ratio of water-to-gas. By and large that water is salty. To discharge it to the environment, you need to desalinate it. You're trying to clean it up and concentrate it to minimize disposal cost. That’s the waste treatment side.
On the process side, a lot of companies use steam or water to enhance recovery. You need to control the water’s composition for it to be the most effective when it's down in the formation. Both in the U.S. and Canada, you see a lot of enhanced oil recovery techniques that use desalinated purified water.
These O&G markets are pretty good for us. In some instances the salinity is just too high for RO; but if you can use RO, you do — it's by far less expensive and less energy-intensive than alternative techniques, especially with the Desalitech process.
We serve food and beverage, both on the wastewater side and on the water supply side, as well as power plants, which are actually the biggest industrial consumer of fresh water in the world.
If you've got any kind of steam turbine or boiler, then you need highly purified water. And again, if you can use RO, it's a step in that water purification process you absolutely do. It's so much more cost-effective than any other technique. We add to that. The Desalitech process is substantially more economical.
Do you foresee increased adoption of CCD in the U.S. market?
Very much so. We have the three essential ingredients for going to market. The first is well-established demonstration and reference plants. Most of ours are in Israel, but now we've got a couple of plants running in the U.S. The CCD process has been proven to work; that’s important because nobody really wants to be an early adopter.
The second ingredient is a good staff. We hired really experienced people from the market — experienced RO people. They're spread out across the country.
The third essential ingredient is money. In the last year and a half, we've taken in $10 million in private equity investment, which lets us do things like hire experienced people, build pilot systems, and finance build-own-operate performance contracts. You don't have to pay us anything up front, just pay us for the benefit you get from it. These are all coming into play and we're getting a tremendous amount of momentum. It's been a lot of fun.
Richard Stover, Ph.D., is the executive VP of Desalitech, Inc., which aims to reduce waste, reduce energy consumption, and increase reliability in water purification and wastewater treatment applications with its patented reverse osmosis process. With more than 25 years of professional experience in water technologies, Dr. Stover has numerous patents and won the Sidney Loeb award for innovation. He serves on the board of the International Desalination Association (IDA).
Image credit: "IMGP0946," © 2008 kurtiselton, used under an Attribution 2.0 Generic license: http://creativecommons.org/licenses/by/2.0/