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Cloudcroft, NM, becomes the first in the nation to install the first potable water reuse system using reverse osmosis and membrane bioreactor technology in tandem.
By Amy Sorkin Kurland
Continuing drought conditions. An elevation of 9,000 feet. A relatively remote location. These are the big water supply challenges faced by the village of Cloudcroft, in south-central New Mexico. In order to overcome the locale’s inherent problem of attaining and sustaining a water supply, the village chose to install the nation’s first potable water reuse system designed to utilize reverse osmosis (RO) and membrane bioreactor (MBR) technology in tandem.
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Photo: Sanitaire |
| A water reuse system can meet the needs of an entire community. |
“We’ve had a prolonged drought in the Southwest,” begins Mike Nivison, the village of Cloudcroft administrator. “Not only is the village located on a high elevation, but it’s at the top of the watershed, so there’s very limited supply to accumulate water in our aquifer. In addition, because the village is not on a flat surface, we don’t have a water table. So you can’t just drill down X number of feet to find water. You have to find it from the ground. But it runs through crevasses as opposed to being in a known place, so it’s not an easy process.”
In the past five years, the demands faced by the village in attaining and sustaining water have become particularly heightened. In fact, one summer the village was forced to haul water in from an outside source—a solution at once expensive and impractical, and one that could not be relied on in the long term. Ultimately, the events of that summer served to accentuate the need for a long-term water solution to be enforced as soon as possible.
In addition to providing water to its residents, the village needs water to sustain tourism, which is the backbone of its economy. As a result, the pressure to find a viable solution has been intense because the future existence of the village depends on it.
After years of involved analysis and a series of short-term quick fixes, Cloudcroft and the state recently came up with a long-term solution, which can be broken down into three parts. The first part involves making sure the village is not losing a lot of water in leaks and that consumers aren’t being frivolous with the water supply. This first step also involves making sure that all the incoming water, or “wet water,” is being used to maximum benefit and that the maximum amount of this water is being collected.
The second part of the solution requires the installation of a water reuse system (using RO and MBR technology) to supply the village with potable water. In the past, there was much talk throughout the country of creating such a system. When the Cloudcroft project is completed, the village will become the first city in the nation to actually put its money where its mouth is by following through on the development and implementation of such a dual water treatment project.
The final part of the Cloudcroft solution required the village to find an outside water source that would allow them to draw water in an economically sound way. This third step was perhaps the most challenging aspect, due to Cloudcroft’s elevated and relatively secluded location. The difficulty in finding a water source is not unique to Cloudcroft. In fact, city and state officials—along with some engineers—are still putting their heads together to identify a viable solution for the entire state of New Mexico.
In the meantime, installation of the new water reuse system in Cloudcroft continues. Construction of the project began in May ’06 and was scheduled to be completed in early 2007. The reuse system was chosen as a solution partly because it’s the most viable alternative and partly because the village really doesn’t have any other choice if it wants to continue to grow economically.
In a Nutshell
The reuse system design was created by Eddie Livingston of Livingston and Associates, an engineering firm hired by the village. In short, it consists of an MBR, an RO system, and a UF membrane system.
Instead of throwing the treated effluent back into a lake or river, as would be the case in most situations, the treated water is added to the existing raw water source, which for Cloudcroft includes rainfall as well as spring and well water.
“They’re using an MBR for wastewater treatment combined with RO,” begins John Koch, product manager–MBR at ITT/Advanced Water Treatment, the wastewater treatment equipment supplier involved with the Cloudcroft reuse project. “The treated wastewater that results is then combined with Cloudcroft’s raw water source. After the two are combined, the water is then taken to another membrane step, ultrafiltration. This takes out particulate and reduces viruses and bacteria. Then it’s ready to be disinfected and sent out for drinking.”
The original thought was to build upon Cloudcroft’s existing retention basins, which would have required upgrading the whole system and enabled the recycled water to be used at golf courses and other secondary water systems.
“This way we wouldn’t have to deplete our drinking water any more than we had to,” says Nivison. “But as the drought progressed over 2000, our wells were going down. So we started the process of drilling wells and looking for other solutions. We realized eventually that we wouldn’t be able to supply drinking water. And then it kind of hit us all at once, like a cannonball: By adding another step to the treatment process, we could turn this indirect reuse water into drinking water too.”
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Photo: Sanitaire |
| Because Cloudcroft, NM, has no water table, water reuse supplements its supply. |
Reuse for Drinking
In general, there are two types of reuse: direct reuse and indirect reuse. Direct reuse entails turning wastewater into drinking water. Although direct reuse is being used overseas, people in the US just aren’t ready for the concept yet. Indirect reuse, on the other hand, is what is being done at Cloudcroft. It’s a more digestible way of introducing the idea of water reuse into the American public. Indirect reuse is basically a “diluted” version of direct reuse: The treated wastewater is mixed with the raw water source and then put through an additional treatment step before it’s supplied back to homes and businesses to be used as drinking water.
“We use the RO membrane combined with an MBR to make it drinking water,” elaborates Nivison. “This takes out all the impurities. Then we blend it 50-50 with our existing drinking water.” Contrary to popular belief by those outside the industry, the quality of this water is actually higher and safer than that of typical tap water. “Once it goes through this process, it’s much better-quality water than that taken out of wells, springs, and lakes. And the finished water still has to meet the drinking-water standards set forth by the regulating agency,” adds Koch.
The Lowdown on the Layout
Instead of building an entirely new system, Cloudcroft’s existing wastewater treatment facility is simply being modified to accommodate the upgraded system. Constructed in 1952, the original system consists of a primary clarifier, a trickling filter, and a secondary clarifier followed by a chlorine contact chamber for disinfection. Current upgrades will include the addition of an influent screen, grit removal, and an equalization basin that will accommodate fluctuating flows. In short, the existing system will be upgraded to incorporate both MBR and RO technologies, with chloramines, UV, and hydrogen peroxide as part of the disinfectant process.
The wastewater treatment plant, which is around the edge of the village, houses the MBR, the first step in the treatment process. The water treatment plant, which is about 2 to 3 miles away from downtown Cloudcroft and where the UF will take place, is adjacent to it where the RO will be installed. The wastewater treatment plant and the water plant are about 5 to 6 miles apart from each other.
At Cloudcroft, the RO plant was strategically located adjacent to the water treatment plant. Typically it doesn’t really matter where the RO is located, but in this case it made the most sense because of the elevation between the wastewater plant and the water plant. This elevation allows gravity to be used for the transportation of effluent from the wastewater plant to the water plant, reducing operation costs. To achieve this transport, the village had to add over 3 miles of conduit between the two treatment sites.
The First Stage of Treatment
Although there are many different steps involved in the Cloudcroft system, it can be divided down into three main steps: MBR, RO, and UF. Let’s start with first things first: MBR.
One of the reasons the MBR technology was chosen for Cloudcroft was because it’s a compact system that delivers high-quality effluent while requiring minimal operator attention. It also meets pretreatment requirements for RO. Using MBR for treating wastewater is relatively new, having been used for about the last 10 years. Usually it’s employed to produce reuse-quality water. “Up until Cloudcroft it’s been unconventional to use reuse water to supplement raw drinking-water sources,” begins Koch. “Usually it’s used for boiler water, irrigation, waterscaping, making snow, et cetera, not for public consumption. But there are a lot of areas in the country where there’s not enough potable water, so wastewater treatment plants are now preparing to provide reuse-quality water to reduce potable water demand.”
The MBR, like conventional wastewater treatment systems, uses the activated sludge process. The bacteria utilize waste. Conventional systems, however, rely on gravity to separate the liquids from the solids. The MBR relies on a perforated membrane to do the trick: The membrane, whose pores typically range from 0.05 to 0.1 meter, provides a positive barrier and prevents suspended solids from passing to the effluent. At the same time this removes some bacteria, pathogenic microorganisms, and viruses.
Because the MBR does not rely on gravity, it can operate at a much higher mixed liquor suspended solids (MLSS) level in the aeration tank in comparison to conventional activated sludge (CAS) systems. Because the membrane allows for such high MLSS and a consolidation of process steps, the MBR has a more compact footprint than CAS systems—a nice added perk.
MBR systems can utilize two types of membrane configurations: low-pressure immersed membranes or high-pressure external membranes. The latter is commonly used at municipal wastewater treatment plants and is what was selected for Cloudcroft. Two of the big benefits of using this system is reduced operating costs and a less frequent need for cleaning, which means less maintenance and a lower operation cost.
Treatment Step #2
Once the MBR process is complete, the effluent will be directed to the RO plant and other reclaimed water storage tanks. “The main purpose of RO is to reduce the total dissolved solids, such as minerals, calcium, magnesium, et cetera,” says Koch. “Since these elements will be recycling the water, they tend to increase in time. This is undesirable for drinking.” The RO removes such things as dissolved solids, disinfectant products, endocrine disrupting compounds, pharmaceuticals, and personal care products. Although many of these substances are not currently regulated in wastewater discharge permits, they are becoming a concern as the popularity of water reuse grows.
Reverse osmosis systems use pressure vessels to house the RO membrane. The RO membrane has pores much like the MBR does. The pore size with RO, however, is even smaller than it is with the MBR—it’s at the molecular level. When the feed water passes through the RO membrane, the water that is retained is called reject or concentrate. This will be used for fire control in the Cloudcroft area. The stream from the RO system is high-quality effluent, and it will be blended with the spring and well water to be further treated to become potable tap water.
“There are other systems that take treated water and put it back into the ground. From there it goes into an aquifer and then into the water treatment plant for drinking. But here we’re not putting it into the ground, it’s stored and later mixed with raw water drinking source,” says Koch.
The Final Cleansing
UF is very similar to the membrane process used by the MBR system. Its purpose is to remove any particulars that might still be there, including bacteria. “At Cloudcroft it’s used to address the fact that their spring and well water—now mixed with the water that comes from the RO process—has not been treated yet,” says Koch.
At Cloudcroft, a new, fully automated pressurized UF membrane system will replace the existing water treatment system. It will receive feed water from a feed pump. The UF membrane is operated in a “dead-end” mode, with hollow fiber membranes in an “inside-out” flow configuration.
All membranes—the MBR, the RO, and the UF—require vacuuming to varying degrees. RO requires the most push, MBR the least. At Cloudcroft, the MBR uses a vacuum, the UF is pressurized (pumped), and for the RO, the elevation difference between MBR and RO is such that the system can use just gravity.
“Usually putting processed water through RO requires a high-pressure pump. But the fact that it didn’t was one of the attractive things about this setup,” says Koch.
Attaining the C Notes
The pioneering aspect of the Cloudcroft reuse system makes it very important, and it is being closely watched to see if it can be duplicated. It will take the public’s acceptance for this vision to become a reality. The hope is that if Cloudcroft’s residents are happy with the system, residents of other cities with dwindling or scarce water supplies will be open to trying a similar solution.
Originally, the project price was estimated to be about $2.29 million, but now—mostly due to rising gas prices—the estimate has been adjusted to somewhere in the neighborhood of $3 million. The sum total of funds before January 2007 was $636,000 that came from Governor Richardson’s Innovative Fund, $500,000 from the Water Trust Board, and $1.2 million has been attained over the last three years from legislative requests the village made annually.
“So far it’s all been state money,” says Nivison. “The biggest thing that hit us was gas prices.”
This new system will produce 100,000 gallons a day, and this is expandable to 200,000 gallons a day. Before the current reuse system had been decided on, upgrades had already been done for future reuse of water and so $750,000 has already been with the implementation of those initial upgrades which turned out to be much more timely than anyone had expected—they were just what was needed to accommodate the current reuse system now being installed.
How did Cloudcroft manage to get so much funding? Nivison has a few ideas. “I think what we’ve learned from this process is that when you have a problem, you better talk about it and notify people early on. This includes local and statewide communication. Identify your solutions and discuss them publicly. We did a good job of doing this, and it helped us get our grants and funding.
“The other thing is,” he continues, “the people you’re asking for money from don’t know what your situation is. So you need to be able to express a good plan that includes all the hard facts. Telling them the problem is not enough. You need to present a plan of action.” Another reason Nivison feels that Cloudcroft was so successful in attaining funding was because when it had been given money in the past, it used it like it said it would. “But just as importantly, we did so in a timely fashion,” he adds.
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Photo: Sanitaire |
| Cloudcroft's RO plant is situated at a lower elevation than the wastewater treatment plant, allowing gravity to transport the effluent, reducing energy costs. |
The Many Advantages of Reuse
Koch feels the village’s project is important because it shows the willingness of Cloudcroft to recognize that it can reuse its wastewater in a multitude of ways. Not only will it reuse the water for drinking purposes; it’ll use it for other things such as irrigation and fighting fires. (Fighting fires is particularly important in Cloudcroft and Otero County, where 140 structures have been lost to fire since 2000.) “The community really recognizes the value of the water, and they will utilize just about every drop of it for different purposes.”
The high quality of the water that comes out of the reuse system will make it extremely versatile, opening up new options for longer-term uses. “When we filter this water, it comes out so pure that in a point in time we can actually get ahead of the water shortage curve. Then we can seek a permit to re-inject the treated water back into the ground near our wells,” says Nivison. “Then we can pump it like we do our normal wells. Also, if we re-inject this water into our well field, we’re not putting something in there that’s a detriment to the well field and to the Earth.”
Another boon is maintenance. Nivison says the village and the state believe that there will be less maintenance than they’ve been doing on the existing system. “There are smaller and more efficient motors and more things assigned to gravity feed instead of electricity. We believe the membranes are easy to clean, and we’ll also be eliminating aspects of the old system that had heavy maintenance on the cleaning and electrical end.”
Perhaps most importantly, as mentioned before, there are other communities faced with similar water challenges as that of Cloudcroft, and the new reuse system can provide a viable solution for those communities in the future.
Looking Ahead
The implications Cloudcroft’s potable reuse system can have on the future of the industry, society, and the environment are abundant. “It’s very apparent to me that this is the future of the way we’re going to have to go,” shares Nivison. “The bottom line is we’re a land-water–based society. But without the water, the land’s worth nothing. So how do you get the water? When you don’t have enough, you better figure out a way to minimize not only on the conservation side but on how you can best use the water that exists. When you don’t have a viable source of water within a viable distance, your only choice is to reuse it.
“The world has the same water it had when it started. So all the Earth is a big water reuse system.” Nivison sees the job of those in the industry as ensuring that we have the best system available so that when we return the water, it’s better than what we started with. “I’m not talking about wastewater; I mean better water than what we already have in the ground and lakes, et cetera. That’s how we have to start thinking on this Earth.” There are probably few people living on this Earth who, if they really think about it, would disagree.
Amy Sorkin Kurland is an LA-based journalist and copywriter who specializes in marketing communications.
OW - May/June 2007 |
