Glycol Removal Made Simple

The Ohio Environmental Protection Agency’s instructions to Akron-Canton (OH) Airport were simple: meet the stormwater discharge limits by fall 2007. Fortunately for CAK, certain kinds of bacteria find propylene glycol delicious. Following the example set by Albany International Airport, the only other airport in the United States with a similar treatment system, CAK’s new deicing system is cleaning up the water, producing methane, and being good for the Akron environment.

“Quite frankly, the easiest way would have been to meter it out to the sanitary system,” says Rick McQueen, assistant director at CAK. “But our local sanitary system couldn’t handle the load.”

“Once we determined that, we had to go back to the drawing board and find out what other technologies were available.”

So CAK hired Reynolds, Smith and Hills, a national consulting firm, for a deicing management study. Based on the most cost-effective options, CAK decided to stop allowing deicing at the gate and instead build three deicing pads to minimize the effluent collection area.

Deciding how to clean the collected effluent led to weighing more options.

“We looked at membrane bioreactors, we looked at the anaerobic fluidized bed reactors (AFBR) — which is the system we went with — and we also looked at ultra filtration reverse osmosis,” explains Brad Wente, PE and senior aviation engineer at Reynolds, Smith and Hills. “There are pros and cons to each.”

Ultimately, CAK went with AFBR, securing two Airport Improvement Program grants of $5 million each, for a total of $10 million, to cover the cost of the new deicing pads as well as the treatment center.

Tim Arendt, a principal at Gresham, Smith and Partners who worked on the Akron project, says there are two bioreactors to the system, each approximately 30 feet tall, that contain activated carbon — which looks similar to coffee grounds.

“The idea is to grow bacterial films on these particles,” Arendt says. “Then these bacteria, once they come in contact with the water containing the deicing chemicals, use the chemicals as food to grow and multiply and do all of the things that bacteria do.”

“In the process, they ultimately change the chemicals to carbon dioxide, water, methane, and more [bacteria]. So the water is then clean and can be discharged to the stream.”

The methane is captured and used to heat the effluent to a temperature most palatable to the bacteria. The bacteria, Arendt notes, are not the disease-causing variety. “Most sewage treatment plants also use bacteria,” Arendt says.

AFRB does require some maintenance. Arendt says CAK hired two operators for the system, both of whom worked in the airport’s maintenance and deicing operations and expressed interest.

Ongoing maintenance issues unique to the system, Arendt says, deal primarily with supplying adequate nutrients required for the bacteria to thrive.
A computer system helps measure the bioreactors and ensures the right balance for the bacterial environment. The concentration of glycol percentages versus stormwater are also measured and adjusted.

“The bacteria are happier if you can feed them the same amount of stuff all the time,” Arendt says. “If they get overfed and then starve it’s not really conducive to the operations. There are a lot of analogies to human beings here.”

A deciding factor on what treatment system to go with at CAK was seeing the treatment plant at Albany.

Comments McQueen at Akron, “They gave us a tour and a lot of information on their technology and how it works. We decided that that would be a very good alternative for us.”

Albany airport environmental planner Steve Iachetta says airport representatives from as far away as Tokyo and Copenhagen have come to tour the treatment plant since it opened nearly ten years ago. Located on a tributary to a drinking water supply, ALB has plenty of experience.

“Large-scale biological treatment is clearly the most cost-effective approach to address deicing stormwater issues,” says Iachetta. “We’ve tried every possible approach since 1989.”

The system saves ALB up to $750,000 a year in pumping, conveyance, and treatment fees that would be assessed for deicing stormwater sent to the local sewer system seven miles away. In round numbers, this represents a 75 percent annual operating cost reduction.

Unlike Akron, ALB still allows deicing at the gate, making use of an inherited containment collection system spanning 61 acres. Iachatta says the airport has about 11.5 million gallons of storage and the option to divert clean stormwater directly to a nearby stream. The system operates for more than 210 days per year and processes 35 million gallons of product.

Albany also uses the methane byproduct to heat stormwater, as well as to heat two airport buildings.

“It is a net energy producer,” says Iachetta. “It makes more energy than it uses.” Iachetta notes that ALB is in studies to find other uses for the methane, including aiding in the production of hydrogen fuel.

The system at Akron is similar, with two holding tanks capable of storing 750,000 gallons each.

“I think the range of flow rate is five to 50 gallons per minute,” Arendt says. It works out to processing approximately 2,000 pounds per day of propylene glycol.

Arendt says that in looking at the Albany system, there were a few additional issues they tried to keep in mind. “We were looking for a system that had the lowest operating costs,” he says.

“Another thing we were looking for is a system that doesn’t produce a high amount of sludge.”

The sludge is made up of dead bacteria — they do age and die, just not all at once. “This particular treatment process really produces a small amount of sludge compared to other biological processes,” he says.

With only two airports in the United States using the technology, AFBR is probably not going to take over the industry anytime soon.

“It’s really very airport-specific,” says Arendt. “This technology I think would be good for some airports and maybe not as good of a fit for other airports. It depends on how the rest of the airport is set up.”

Arendt says that Gresham, Smith and Partners is continuing to research the processes applicable to the industry. Particularly as the potential for more regulations, possibly at the federal level, continues to grow.

Comments Wente with Reynolds, Smith and Hills, “There’s going to be a need to come up with creative solutions like this for situations where you can’t discharge your effluent to local sanitary districts”