Over the past few decades, air transport has emerged as the preferred mode of transport for the nation. The public has come to demand and expect continuous on-time service to and from virtually any point on the globe in all but the most extreme weather conditions. However, during that same time, environmental awareness has demonstrated that practices that make on-time winter air travel possible can have a detrimental effect on the environment. Can the public have it all: safety, convenience, and a clean environment?
After investigations of several winter weather accidents during takeoff, the Federal Aviation Administration (FAA) concluded that in some cases ice had been a contributing factor. According to the National Transportation Safety Board (NTSB) advisory dated December 29, 2004, “Research has shown that almost imperceptible amounts of ice on an airplane’s wing upper surface during takeoff can result in significant performance degradation.” Therefore, the FAA has ruled that no aircraft be cleared for takeoff with ice of any kind adhering to its wings or control surfaces. This policy mandates aircraft deicing procedures during the winter months, a practice that at some point must be performed at nearly every airport in North America.
It is the responsibility of flight operations personnel, such as airline pilots and ground crews from Fixed Base Operations, to ensure the aircraft is clear of ice, snow, or frost before takeoff. There are several means by which this can be accomplished. However, by far the predominant and most effective method of removing ice from aircraft before takeoff has been the spray application of aircraft deicing fluid (ADF) and aircraft anti-icing fluid (AAF). These freeze-point depressants, based upon either propylene glycol or ethylene glycol, are sprayed on the aircraft by ground crews just prior to takeoff. The ADF melts the ice and carries away the moisture, preventing new ice from forming. However, for a single jetliner, this procedure can send thousands of gallons of glycol-contaminated stormwater sloshing to the pavement. Airport engineers and environmental managers must find a means to deal with the millions of gallons of ADF-contaminated runoff that can be generated through the course of winter operations.
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Photo: Inland Technologies Inc. |
| A "block and pump" operation. The pump hose is inserted into a drain standpipe. |
Though ADF is often engineered to contain additives—in some cases toxic—that improve its performance on the aircraft, it is ADF’s major constituent, the glycol freeze-point depressants, that appear to cause the most damage to the environment. Although the glycols in spent deicing fluid are technically biodegradable, during the process of decomposing they generate a high biochemical oxygen demand (BOD). They can rapidly deplete the available oxygen in surrounding waterways, causing stress to aquatic species. Teresa Lush of Inland Technologies Inc., a company that provides glycol recycling services, says, “In some areas, depending on the volumes used, they can become quite an issue.”
A Developing Market
Todd Brinkel, general manager of EQ Resource Recovery Inc., says that, as with many other airports, Detroit Metropolitan Airport (DTW) had been reliant upon the local publicly owned treatment works (POTW) to treat its spent ADFs. However, that arrangement presented a set of drawbacks
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Photo: EQ Resource Recovery Inc. |
| EQ Resource Recovery uses a tractor-based GRV for glycol collection at Willow Run Airport. |
“The loading was too much for their treatment systems at the POTW. More to the point, because of the seasonal nature of the loading, they would go from having no glycol or BOD load coming into their system, to all of a sudden having large slugs of glycol and BOD load, which would kill their bugs. It was very difficult to keep their bugs alive and acclimated to deicing fluid.” Brinkel says ADF collection and recycling programs can offer airport environmental managers a viable alternative to hefty BOD surcharges from local POTWs.
According to Brinkel, the idea of recycling spent ADF was slow to catch on at first. He says the original concept was to put it back on the airplanes as ADF, but that there was too much risk involved. “There were no real specifications for recovered glycol that would go back into deicing fluid, and there were very few people who wanted to take that risk. As a result, we developed markets for recycled propylene glycol, as a replacement for virgin glycol, in several other markets. Typically, our fluid is sold to paint manufacturers and antifreeze manufacturers, as well as to specialty chemical manufacturers.”
With its recycling facility two miles from the Detroit Metropolitan Airport, EQ has held the contract for glycol recovery and recycling at the airport since 1997, when the DTW ADF recycling project began. During the deicing season, from October through April, EQ assigns a staff of five to the airfield to work directly with the airport’s environmental department.
DTW has four centralized deicing pads that drain to a series of collection tanks. Brinkel says most aircraft deicing operations are conducted on these pads. “We collect 96 to 97% of our fluid from the pads. The other 3% is collected by Glycol Recovery Vehicles [GRVs] from the areas around the gate,” where he says deicing is sometimes permitted.
Foremost, Brinkel says, an ADF recycling project requires a team effort, which he begins before the first aircraft arrives at the gate. According to Brinkel, meteorologists from Northwest Airlines, the airport’s leading tenant, share their weather data with the airport. These data are used to plan for both deicing and subsequent collection of the spent fluid. Brinkel says during the winter, “We actually have morning operations meetings with Northwest Airlines to coordinate deicing schedules.” This allows EQ to deploy the GRVs in an efficient manner. The cooperative arrangement allows the airline the convenience of deicing some of its larger planes at the gate.
However, Brinkel says, “It’s a fairly complicated dance. After each plane leaves the gate, the GRV is dispatched to clean up. They can spray a lot of fluid on those jumbo planes, and with drain inserts in place, once that plane backs out you’re left with a large puddle of fluid on the ground that isn’t draining anywhere. It’s best that it be collected at that point so workers don’t have to walk or drive through it.”
Brian Wagoner, environmental administrator for the Wayne County Airport Authority, says he is an advocate of the pads as part of the recycling scheme. “The more planes you get to the pads, the less dirty snow you have at the gates. If you’ve seen a gate deicing operation, you just get a mess; there are unbelievable amounts of sloppy, slimy, orange-pink snow. That stuff has a pretty substantial load associated with it. So if you can minimize that quantity, you can help yourself out.” He says the airport has found ways to make the deicing pads more attractive to carriers with changes as simple as “adjusting the width of the slots, which involves taking the paint off, putting new paint on, and putting out new airfield diagrams.” And he says it’s working. “Our quantity of contaminated snow has steadily gone down as we moved more and more planes to the pads.”
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Photo: Inland Technologies Inc. |
| The recycling plant at St. John's Airport in Newfoundland |
The Dilution Equation
Pure Type I ADF is 88% glycol, and Type IV is 60% glycol; when sprayed on an aircraft as part of a deicing procedure, each gallon of ADF can mix with several gallons of melted snow and ice. If there is active precipitation during the deicing procedure, the mixing continues in puddles on the ground, and some very dilute mixtures can result.
The DTW project uses a Misco handheld refractometer to determine propylene glycol concentrations in the field. Under EQ’s contract with DTW, the airport receives monetary compensation for streams of spent ADF it collects that are more than 5% propylene glycol. For streams between 2% and 5%, the airport pays EQ a fee for processing the material. According to Wagoner, however, this fee is “nothing compared to what it would cost to dispose of it at a POTW.”
As feedstock for the recycling process, Brinkel says, EQ aims for a target average glycol concentration of 15% from the mix of effluent streams. This, he says, ensures the economic feasibility of the recycling process. “Over the years, our average concentration from DTW has worked out to be about 17%.” Sweetening the deal for the airport, he says, is that “for every 100,000 gallons of pure glycol we extract from the system, we will take another 50,000 gallons of 2% to 5% material. When you mix it all together, the average concentration is better than 15%.”
Moving the Water
“A lot of times our bigger challenge is moving clean water, rather than handling spent deicing fluid,” Wagoner says. “If it starts out raining and you have a whole collection system that’s full of water, and then things turn to freezing rain, somehow you’ve got to move an awful lot of water and get ready to start moving spent deicing fluids.”
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Photo: Inland Technologies Inc. |
GRVs in operation at Calgary International Airport. In the
spring, they are used to power wash the pavement. |
He says each of the airport’s deicing pads has about 100,000 gallons of belowground storage, augmented by another 100,000 gallons of aboveground storage. When a winter storm approaches, Wagoner says, “The first thing is to make sure the belowground systems and the aboveground storage areas are empty. Once the storm hits, we begin pumping as fast as we can, clearing clean water from the system while checking the concentration regularly. The minute we get to about 2% glycol, we start flipping valves,” he says, to capture the high-concentration runoff in the storage tanks. “That’s a tricky call, though, because you don’t want to end up collecting a lot of clean water.”
The runoff from the deicing pads collected in the storage tanks must be transported by truck to the recycling plant. “During big storms, we run trucks throughout the storm and pump directly from the underground vault into the trucks,” says Wagoner. “When the storm gets too big and we can’t keep up, we start filling the aboveground tanks.” From there, he says, “It’s a race against time. The trick is to have enough storage and enough transport capacity to handle a pretty nasty storm. The doomsday scenario is when you have a big storm on Monday, then another one on Wednesday, and you haven’t had time to move the stuff out. For most storms, we’ve got enough storage and transport capacity to hold the recyclable fluid and move it out in trucks after the storm has passed, so we’re pretty much empty within two or three days.”
Brinkel says the recycling process starts immediately. “We have 7.6 million gallons of surge storage a half mile from the airport. Obviously, we can’t process the glycol as fast as it’s being collected, so it all gets mixed together, which gives us our average concentration.”
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Photo: Denver International Airport |
| A fleet of aircraft deicing vehicles at Denver International Airport during mild weather |
Turning up the Heat
As the tankers arrive at the processing facility, samples from each transport are collected and sent to EQ’s lab for on-the-spot analysis. There, a gas chromatography assay determines the “final” propylene gylcol concentration. At this stage, the effluent is screened for contamination with ethylene glycol, which the airport prohibits, as even a small amount of ethylene glycol can jeopardize the economics of the recycling. According to Brinkel, it’s difficult to remove the ethylene glycol during the recycling process, and “There is no market for a mixed product.”
Once the material has been screened, it is introduced to a high-efficiency evaporator, which removes the bulk of the water, resulting in an effluent consisting of about 50% to 60% propylene glycol, 40% to 50% water, plus the additives. During the second stage of the procedure, a vacuum distillation process removes the rest of the water and distills the propylene glycol. Brinkel says the impurities, such as suspended solids, the mineral content of the water, and the ADF additives, are left behind in what is called “the heel.” Brinkel says these precipitates are sent to one of several waste treatment plants owned by EQ, to be stabilized before their ultimate disposal at a landfill. The water distilled from the effluent, he says, meets pretreatment standards and can be sent to the local POTW. And the product of the distillation process—99.5% pure propylene glycol—is ready for market.
Brinkel estimates that during the winter of 2004–2005, the recycling program collected 888,000 gallons of pure deicing fluid that otherwise would have required treatment at the POTW. “I believe our program saves the airport $2 to 3 million per year in BOD surcharges, while netting a valuable commodity that can be reused.”
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Photo:Denver International Airport |
| Denver International Airport’s deicing pad with glycol distribution stations |
From the Ground Up
“Denver International Airport was built with its environmental management system [EMS] first in mind,” says Brian Stierman. “They built the deicing system first, and then basically built the airport around it.” Stierman is facility manager for Inland Technologies’ glycol recovery and recycling plant at Denver International Airport (DIA).
Inland has a full-time staff of 12 people who manage glycol operations at the airport. During the winter, Inland hires between five and 12 part-time and temporary workers to staff DIA’s glycol recovery and recycling facility.
The unpredictable winter weather on the edge of the Rockies is legendary, Stierman says. “In a matter of an hour, you can go from sunny and 53 degrees to 10 below with complete white out. In January, when it’s 30 degrees out, it can start to snow without warning; we just go from one mode of operation to another without batting an eye. As long as I’ve got my core group here, it’s easy.”
During the deicing season, which runs from September through April, the variability in demand on the deicing system is striking. Keith Pass, DIA’s industrial stormwater permit coordinator, says that during the winter of 2004–2005, ground crews applied 867,178 gallons of ADF, of which 69% was collected for recycling. The next year, a comparable amount was spent, with a collection efficiency of 70%. However, stormy conditions during the winter of 2006–2007 required crews to more than double the amount of fluid used in the preceding year. During that season, Pass says, 1,851,460 gallons of ADF were applied at the airport, yet the system was able to maintain a collection efficiency in the range of 70%.
Keeping Track of Glycols
Unlike the weather along the Rocky Mountains, DIA’s glycol management system is subject to precise control. “The airport’s permit requires glycol to be tracked from the moment it is delivered,” says Pass.
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Photo:Inland Technologies Inc. |
| This GRV has just cleaned up a morning frost deicing event at Washington’s Reagan Airport. |
Stierman says the airport, along with Inland Technologies as the contractor, manages the distribution, the blending, the collection, the recycling, and the recordkeeping for glycols. He says the airport hands off responsibility for the glycol only briefly: “I keep track of what comes out of my nozzles to load the applicator’s trucks.” But, he notes, he doesn’t track the actual spraying, which is an operation under the responsibility of the air carriers and their service providers. “But once the trucks spray it and it comes down to me from the gravity-fed downcomers, then I take control of that inventory again. We keep track of every drop that comes onto the airport.” And the tracking continues throughout the glycol recycling process.
Janell Barrilleaux, director of environmental projects for DIA, says, “Full aircraft deicing is specified to be performed only on the five deicing pads situated around the runways.” The drainage design of the pads provides for sheet flow to trench drains. Each pad has its own multi-celled storage pond ranging in capacity from 4 million gallons to 10 million gallons.
“One of the unique things about DIA’s drainage system,” Barrilleaux says, “is that we have built in three separate dedicated systems. We have a wastewater system that supplies the POTW, we have a stormwater system, and we have a third system—a separate system—designed specifically to handle spent deicing fluid.”
This collection system, she says, “is gravity fed from the deicing pads to the recycling facility at the ‘bottom of the hill’ where five 420,000-gallon tanks store the spent ADF.”
Once a sufficient amount of spent fluid has been collected in these storage areas to begin the glycol reclamation process, the plant is fired up. Barrilleaux says at the end of the process, “the reclaimed glycol is stored in an additional set of tanks until a buyer can be found.”
Continual Improvement
The airport built and installed its own glycol reclamation distillation system. Stierman says the previous contractor was able to accept feed stock with a minimum glycol concentration of 8% to 10%. However, this forced the airport to send effluent that had 8% to 10% glycol or less to be treated at the local POTW. When Inland Technologies took over the collection and recycling project in 2004, it modified the recycling facility, installing a glycol concentrator at the front end and creating a two-stage reclamation process. According to Stierman, Inland’s patented technology now allows the plant to reclaim glycol from fluids with as low as 1% glycol. This, he says, “results in less load on the ponds, helps lower costs to treat runoff at the POTW, and helps with DIA’s EMS program.” Under the new arrangement, Inland collects from both the pads and the gates. Anything that has more than 1% glycol is recycled, and effluent with less than 1% is routed to the POTW.
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Photo: EQ Resource Recovery Inc. |
| Transport tankers carry spent ADF the two miles from Detroit Metropolitan Airport to EQ’s recycling facility. |
Barrilleaux says there is an ongoing plan for improvement. “Our newest pad opened during the winter of 2006–2007. It was designed with a concentric series of trench drains surrounding the pads. The drains closer in to the pad receive the higher concentrate, while those further out receive more dilute mixtures. Each ring of trench drains has a piping system, with inline refractometers to direct fluid of over 1% glycol to the recycling facility.”
Though Barrilleaux says there is currently no regulatory requirement stipulating collection of fluids as dilute as 1%, DIA plans to do everything possible to maintain that collection rate. “We think we’re one of the best in the country.” In 2006, Denver International became the first airport in the nation to join the EPA’s Performance Track program, which Barrilleaux says is an important distinction, and she believes the airport’s glycol recycling program played a role.
Doing It Small
Todd Brinkel says EQ, while managing glycol collection at DTW, it also manages ADF collection for nearby Willow Run Airport, which serves mainly cargo traffic. “It’s a much smaller operation. We send someone out there daily to do a site inspection to make sure there isn’t anything going on that shouldn’t be.” Brinkel says EQ has one tractor-mounted GRV stationed at the airport that “we operate during storm events only. It works out because of the proximity to Detroit Metro and our facilities. They call us to give us the heads-up that they’re going to be deicing, and if they give us an hour lead time, we can have somebody there within two hours to do the collection.” He says once the material is loaded on tanker trucks, it can be brought to the recycling plant at DTW.
“If it were a small airport out in the middle of Iowa,” Brinkel says, “it would become much more difficult for a vendor to provide recovery and recycling services.” But, he says, it could be done with the assistance of a Fixed Base Operation. In fact, he says, EQ does provide glycol recycling service for Grand Rapids Airport. According to Brinkel, Grand Rapids does its own recovery and collection, and “when they have enough material to be trucked to our facility for recycling, they call us, and we come get it.”
Meeting Canadian Standards
“In Canada we have a federal regulation called Canadian Environmental Protection Act [CEPA] that limits the discharge of glycols in any waterways draining an airport to 100 parts per million,” says Inland’s Teresa Lush; the company is based in Nova Scotia. Canada’s Fisheries Act goes further, she explains, prohibiting the deposit of a deleterious substance of any type in water frequented by fish.
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Photo: Inland Technologies Inc. |
| A technician doing a system check at Inland’s Denver recycling plant |
According to the Halifax International Airport Authority, a basic glycol recovery and recycling operation at that airport has enabled the facility to maintain compliance with both of these stringent Canadian regulations.
Gordon Duke, vice president of operations at Halifax Airport, says a key to the program is designating specific areas for deicing. ADF spraying is restricted to the airport’s four deicing pads “if any ground contamination whatsoever could be expected.” The pads are located on either side of the runway, and adjacent berms contain the spent fluid and channel it into the drains. Duke says Inland Technologies supplies a GRV, which “is brought in to pick up anything that doesn’t make it into the drain.”
“At the beginning of the season, Inland technicians install temporary pumping stations for the standpipes serving each of the pads,” says Lush. If there is snow in the forecast, she says, technicians close the drain blocks in the pad, diverting the water away from the storm drains. When an aircraft is deiced on the pad, the runoff gets pumped from the pad and is stored in one of two 59,400-gallon holding tanks situated nearby. The effluent from these tanks is sent to Inland’s onsite glycol recycling facility for processing. Although it varies based on the weather, Lush says, “The airport collects and recycles close to 1.6 million gallons of glycol-impacted stormwater every year.”
Although the costs for implementing a glycol recovery and recycling program vary from site to site, Lush says, “If you look at a small airport like Halifax, you can see it required very few changes to airport infrastructure to do recycling. It’s not necessarily a huge investment.” She adds, “You can get a lot of environmental benefit from a little bit of effort.”
Reusing the Molecule
For recycling to work well, Brinkel says, “Everybody needs to be on the same page: the airlines, the airports, and the contractors.” Furthermore, “Everybody needs to be working toward the same goal of not just recycling, but staying in compliance with their environmental permits.”
“When it can work,” Brinkel explains, “the recycling program is obviously better for everybody—you’re actually reusing the molecules and saving resources.” He acknowledges, “There are some cases when destruction of the molecule is the most cost-effective way to go, but we’d like to see everybody who can recycle, do so.”
Teresa Lush puts it another way: “When you’re able to pick something off the ground that was considered waste, and then within weeks you’re able to turn it around and put it into your car and reuse it as automotive coolant, that just seems to be a better environmental result.”