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By Pete Hildebrandt
Koch Membrane Systems is one of the pioneers in membrane technology, according to James Vecchio, marketing director. “Our fluid systems division is largely responsible for development of the spiral-wound membranes,” says Vecchio. “We created really the first spiral-wound, reverse-osmosis membranes many years ago—before they were part of Koch. This system is commonly used to treat water and wastewater for reuse and is frequently used in desalination plants.”
Koch works with the metal-finishing industry for oily-waste applications involving both straight ultra-filtration and ultra-filtration followed by reverse osmosis (RO). It has worked with the food industry extensively in the area of suspended-solids removal, and oil and grease treatment associated with mayonnaise and salad-dressing plants and bakeries.
Its latest product for the food industry is its membrane bioreactor (MBR). This particular item, launched within the last year, is a Puron submerged hollow-fiber membrane in conjunction with biological treatment to reduce BODs, CODs and suspended solids, and, therefore, to generate water usable for a lot of industrial applications.
Submerged hollow fiber membrane filtration systems featured in Puron modules are made up of clumps of extended strawlike hollow fibers. These fibers have tiny pores of approximately 0.05 microns that operate as a blockade to bacteria and suspended solids.
The hollow fibers are attached at the bottom but otherwise move freely their whole length. The top ends of the fibers are sealed to prevent clogs from hair or other fibers. In order for the system to operate, hollow-fiber bundles mounted vertically within the modules are submerged into activated sludge. With application of slightly negative pressure inside the fiber, water is drawn under vacuum through the fiber wall from the outside to the inside. Filtered materials remain outside, analogous to the coffee grounds left behind in the filter.
Under pressure, air bubbles shake the membranes, scouring the outside of the hollow fibers and removing accumulated debris. This type of membrane works well in a membrane bioreactor, including treatment of both municipal and industrial wastewater. These industrial wastewater sources include paper mills, breweries, food processors, chemical plants, and textile manufacturers.
Koch’s Magnum features a length longer than the standard 40-inch RO or nano-filtration elements. It has been especially effective in water softening as well as RO for brackish and seawater desalination applications.
“Being 60 inches long, fewer elements may be used in a pressure vessel with a Magnum; this means there are fewer O-ring seals and less costly replacements because you are buying fewer elements, installation is easier, and there is less of a chance for leakage due to fewer seals involved,” says Vecchio. “The Magnum can be a way of reducing costs, handling, and storage, for instance.”
Efficient Cleaning Is Key
“Industrial process water is a big market for us, and another is industrial wastewater,” says Vecchio. “That means treating the wastewater before it goes out to the sanitary sewer or for use in a closed-loop system where you recycle all of the wastewater, separating the water from the wastewater and reusing the water in the process for such things as power-plant cooling or boiler feed. The idea is, rather than sending the water down the drain, remove the contaminants and then send the water back in for reuse.”
Most of the Koch tubular products are used for wastewater applications because they can deal with high concentrations of solid waste or suspended solids in the water.
One of the big advantages of the tubular membranes is that the high concentrations of solids can be dealt with.
If a buildup of contaminants on the membrane surface occurs, the tubes can be cleaned mechanically. Most membranes are cleaned by soaking them in chemicals.
With the Koch tubular product, cleaning can be done using sponge balls: tiny sponges fed into the hollow tubes under pressure that wipe the surface of the membrane clean. “Chemicals in conjunction with the sponge balls make for a much more effective cleaning,” says Vecchio. “Under pressure the balls find their way into the opening of the tubes, and the pressure from the re-circulating pump forces the balls through the tubes.”
Historically, the industries looked at for industrial wastewater treatment have been businesses such as metal-bashers and heavy industry manufacturing plants, according to Imran Jafrey, Koch Membrane Systems business manager for industrial water and wastewater.
“Therefore, we’ve done a lot more with them in the area of ultra-filtration for suspended-solids, oil, or grease removal; but we’ve also done work for food manufacturers with oily wastes.
“In the past, most municipalities have been in a position where they could accept the BOD, but [the compounds listed above] were the problem items. Their bacteria could not handle the oil and grease being sent down.
“But they could handle the extra sugars and dissolved proteins coming from food-processing waste; conventional membrane technology has problems retaining those things, and they must be treated biologically. Most municipalities were happy with that kind of wastewater, as they could blend it in with their sanitary waste and give the bugs something to eat.”
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| Over the years, a push for cleaner effluents and the development
of new technologies has driven the improvement
of membranes. |
In the 1970s Koch began working with companies to treat oily waste with ultra-filtration, generating an effluent free of waste. “As we move forward we really see the growth being on the MBR side,” says Jafrey. “With membrane-bioreactor technology, starting in the late 1980s to the mid-1990s there was a push to use membranes instead of clarifiers to produce a cleaner effluent.”
Two things driving the continuous improvement in membrane technology over the years were a push for cleaner effluent and, simply, the development of new products.
Since then there have been vast improvements in membrane technology right up to the present time, according to Jafrey. It is an evolving product line.
Custom Development Of Membrane Solutions
GEA Filtration, a German-owned process-solutions company with a North American office in Hudson, WI, has been involved with various aspects of membrane work since the 1970s. Currently GEA is mainly involved with process water being treated onsite. GEA Filtration is part of GEA, an international process-engineering company with more than 150 companies operating worldwide.
As a team member with technology leaders like Niro, Westfalia Separator, GEA Wiegand, and Tuchenhagen specializing in liquid and powder processing systems, GEA Filtration provides both customized membrane filtration plants as well as complete process lines specifically tailored to each customer’s specific needs and requirements. As with other membrane manufacturers, GEA offers a wide range of system and membrane types to allow for completely optimized specific separation. The range includes a number of both polymeric and inorganic membranes.
“GEA is involved with numerous filtration applications. If a plant is trying to conserve water inside its production facility, GEA will work with it on that,” says Doug Emerson, sales engineer with GEA Filtration. “Often this involves such processes as caustic recovery. When equipment is washed in a plant, there will be a desire to recoup both the water and the chemical at the same time.”
The company started out more involved with the food manufacturing end of things, including work in the dairy industry. Nowadays a great many filtration membranes are used to produce dried whey or milk products, according to Emerson. “We work in a number of other industries beyond the dairy industry as well,” says Emerson.
“What type of membrane an operation should use depends on what the manufacturer’s trying to accomplish: It could be micro, nano, ultra, or RO. It depends on what the target chemical or parameter is. Our operations are a bit different; we don’t actually manufacture a membrane, but instead work with a client on an individual basis to come up with a process solution and select the best membrane for the application.
“Companies typically approach us wondering what membrane technology can do for them. We in turn come up with a solution that works for them.”
GEA Filtration has a pilot facility on the premises as well as pilot units it can send out to clients in order for them to do their own research on various applications. But the company prefers to work with clients themselves in collecting data so it can come up with the membrane or technology that will work.
Membranes For Testing And Monitoring
3M Corp., in St. Paul, MN, manufactures some 10 different types of membranes regularly. It chiefly places them in different configurations to accomplish different objectives during their monitoring functions.
3M also has the Empore product, which is a membrane composed of particles having an active surface, PTFE, or basically Teflon. The particles and the PTFE are mixed together. The membrane consists of 90% particles and 10% PTFE material. The PTFE is fibrous and attaches to the particles to form a web. The size of the particles generally ranges from 45 to 50 microns, while the membrane itself has a thickness of 0.75 millimeters.
Next it can be rolled out to form a flexible membrane acting as a chromatography column. Material passing through it is absorbed by particles and either removed from the liquid or absorbed and released later for purposes of quantification or purification. Typically, it is used in some of the EPA methods for monitoring certain compounds in wastewater, such as in the chemical industry.
There are methods for monitoring volatile organics, and the EPA also has lists of compounds that are applicable for the different methods. This is applicable to any industry that has effluent, petroleum, food, wastewater, or runoff from farm fields. They are used to monitor pesticide levels, and 3M also has a product used in determining the quantity of oil and grease in effluent. Membranes are used in many other monitoring studies as well.
“This is not usually used for filtering, but usually for selectively absorbing and then releasing various samples to do a quantization of what’s there,” says Jennifer Heitkamp, senior chemist with 3M.
“If people get their well water tested and they’re looking for nitrates, this is something used in that analysis. A lot of times these membranes are used in the pharmaceutical industry for monitoring drug levels and in development during animal studies.”
Though the technology has been around for 20 years or more, there are different particles being developed that have diverse properties allowing for more selective desorption of things, according to Heitkamp. 3M also has a disk using activated carbon, particularly valuable with some of the problems involved with the chemistry of nitrosoamine.
One California study looked at treated wastewater and found that the actual treatment processes were resulting in elevated levels of nitrosoamines, which are also possible carcinogens. “Our membranes allowed the nitrosoamines to be captured in order to reveal how much of these compounds were present,” says Heitkamp. “The use of our product as an active filter has not been studied extensively until now, but this is something we are looking into.”
Heading Off The Need For Cleaning Through Membrane Design
TriSep Corp., of Goleta, CA, has been involved with membrane technology for a number of industries for some 15 years. Its membranes are spiral-wound: the only such available membrane on the market, with its own unique characteristics.
“Our membrane—which is not a fiber-based membrane—because of its spiral construction has much greater integrity, is much more robust and is 100% air-scoured and 100% back-flushed,” says Robert Brown, North American director of sales for TriSep.
Some of the factors driving advanced development of this technology include pressures to deal with microbial contamination by the dialysis, beverage, and pharmaceutical industries, according to Brown.
“This requirement to deal with bacterial contagion has always been in the dairy industry. But the problem that’s also developed is that these three market segments are now nervous about the quality of water treatment being provided by municipal water treatment facilities. In the dialysis industry, contaminated water can lead to patient illness or death; in the beverage industry, it can result in contamination of their syrup or their actual drinks, which has happened at times in the bottled-water industry. Likewise, in pharmaceutical manufacturing they’re always alert to problems with potential contamination with their products.”
One way to overcome these problems is through the use of sanitary membranes. “In a conventional membrane there is a brine seal. The brine seal precludes that there could be any turbulent flow between the outside wall of the membrane and the inside wall of the housing; that’s a stagnant area,” says Brown.
“You can clean and sanitize all day long and you’re never going to get anything into that annulus because the only water in there is seepage under the normal operating pressures. If you remove the brine seal you now have a bypass because some percentage of the feed is going to go into the annulus area.”
TriSep conducted a major test of all the membranes labeled “sanitary” on the market. “What we wanted to discover was: What is the true bypass?” says Brown. “We found manufacturer claims of 10%–15% were off; their actual bypass was closer to 40%–50%.
“What that does is compromise the efficiency of the throughput of the membrane because with such a situation, 100 gpm is going in, 60 gpm is going through, and 40 gpm is going by. For such a scenario, what do you get? You’re paying for the feed, and then you are going to pump the feed outside the membrane to the drain. And all you really receive for all that is a bill from your utility for the cost of the energy to pump the bypass.”
The TriSep Turbo Clean, a 3.8-inch standard dairy-configuration membrane that is a hard-shell polypropylene product, was tested and found to have a bypass of between 10% and 15%, according to Brown. TriSep is now testing an 8-inch membrane. So far, its bypass has tested out as being approximately 2%.
“We can save about 25%–30% of the energy costs of anyone running a sanitary system if they convert from the standard sanitary membrane to the Turbo Clean,” says Brown. “What has occurred in the dialysis industry is that all the major OEMs have standardized on TriSep’s Turbo Clean for sanitary operations, because there is a great concern in this industry that patients be protected from toxins and pathogens with a post-RO UF device.”
The latter UF device is sold by one major membrane company and is very costly, according to Brown. “We’ve convinced them they should protect or secure the entire system through sanitary membranes up front, prior to the post-RO treatment.
“That has been standardized now on the part of several of the major OEMs operating supporting the clinical management groups such as Fresenius, Gambro, and Renal Care Group. What’s happened with dialysis [in] the dairy industry is now beginning to move into the beverage industry.”
TriSep now has three Coca-Cola plants converted to its Turbo Clean sanitary membranes. Two plants are in Texas, and one is in Massachusetts. One of the Texas plants has replaced the conventional membranes with the Turbo Clean product.
TriSep has also received orders for four new plants across the United States. The company also recently received orders for supplying a major order for 500-gpm and 700-gpm UF SpiroSep systems, followed by two complementary RO systems for coal-bed methane extraction.
“This is a huge project for us; we’re not going after the drinking-water market, but rather industrial applications, such as effluent from a waste plant that is used for industrial applications,” says Brown. “When major industries start stepping up and asking for our product to protect their product, that’s a good sign,” says Brown.
“TriSep has a membrane with a really well-controlled bypass, or in other words, the water that flows outside the membrane,” says Del Martinez, director of sales with Doosan HydroTechnology Inc., in Tampa, FL. “To my knowledge it’s been a superior product to others with this type of construction. The Turbo Clean keeps down the biofouling aspect taking place in our type of application—that of treating process water for beverage production.”
Doosan HydroTechnology works largely in municipal water treatment and other industrial water treatment applications. Martinez has expertise in the beverage and bottled-water industry. Doosan is a manufacturer that designs, manufactures, and installs whole water treatment systems. Some of these systems can be quite large.
The TriSep Turbo Clean membranes are RO. They change the quality of the water, removing the minerals. The SpiroSep membrane is a UF membrane, spiral-wound; it doesn’t change the quality of the water by taking out minerals, but it does remove particulates.
“That type of membrane is used more for wastewater treatment or for pre-filtration for RO where there is a need to really clean the water so there are no particulates,” says Martinez. “They can place a high load of solids in that membrane, and it does back-flushing to keep it clean as well as using air to scrub off the materials it filters out.”
To form an RO spiral-wound membrane, a very large sheet of material is stretched out. A mesh spacer is placed over this before the sheet is rolled up very tightly. A tube is in the center.
Once this membrane is rolled up into an 8-inch diameter membrane, the outside is covered with fiberglass. Water is run into the outside through the mesh spacers. It is forced by high pressure through the membrane itself, ends up in the central tube and is now purified.
“With the RO elements, those membranes are very, very tight,” says Martinez. “Those take pressures of approximately 100-600 psi—depending upon the water—to force the water through. They are actually so tight that they force the removal of minerals—such as calcium, sodium and others—from the water.”
The SpiroSep is the same setup but is not wound so tight—not enough to take out the minerals, but it will take out suspended solids. It can be used for pretreatment for RO. This system is used particularly in municipal wastewater treatment.
Doosan HydroTechnology has built a test module in Tampa, and Martinez is looking forward to getting more tests done. “It would be great if this testing led to our getting this approved as a treatment process for water used in soft-drink production,” says Martinez. “Such processes as these do not require reverse osmosis or heavy treatment to remove the minerals, though they might need to work on changing alkalinity. But that can be done by the adding of lime.”
Pete Hildebrandt is a writer specializing in science and engineering topics.
OW - January/February 2007 |
