stormwater management edmonton’s ... -...

September 2011 | 59www.esemag.com

team with support from Naturally Wal-lace Consulting. Stuart Olson Dominionis responsible for construction manage-ment of the project. Subcontractor Nel-son Environmental is responsible for themajority of construction and equipment.

The project is currently under construc-tion, and will be commissioned this No-vember.

BackgroundAircraft are typically deiced with gly-

col-based solutions, such as propyleneglycol (PG). As over 758 litres of PG can

Airports and airlines are re-quired to protect nearbystreams and water bodiesfrom wintertime deicing ac-

tivity. Such is the case with Edmonton In-ternational Airport (EIA) and WhitemudCreek, which runs along its western side.

In 2000, the airport constructed a sub-surface flow wetland to provide treatmentof glycol, and other deicing chemicals,found in the stormwater during springmelt. Addressing a need to accommodateincreasing air traffic and associated deic-ing operations, EIA initiated an upgradeof the wetland system to increase treat-ment capacity and operational flexibility.

Through reconfiguration of the hy-draulics and the addition of aeration, thefull-scale system has the capacity to pro-vide up to 4,000 m3/d of treatment at aloading of 711 kg-BOD/day.

Associated Engineering led the design

be used for deicing a plane, BOD re-quirements for treatment become veryhigh. Each airport has different circum-stances that lead to varying strategies foraircraft deicing fluid (ADF) manage-ment. Those with centralized deicing

pads are able to capture and funnel themajority of deicing fluid as a concentrate,which makes it easier to dispose of it orrecycle. With at-gate deicing, airportsusually capture and hold glycol-richstormwater in larger storage basins, and

Addressing a need to accommodate increasingair traffic and associated deicing operations,

EIA initiated an upgrade of the wetland system to increase treatment capacity and

operational flexibility.

Edmonton’s airport upgrades its deicing fluid treatment system By Mark O. Liner

Stormwater Management

continued overleaf...

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Environmental Science & Engineering Magazine60 | September 2011

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treat or discharge it as time permits. EIA uses a combination of approaches

that include sewage plant discharge ofhigh strength concentrate, and storageand on-site treatment of low strength

stormwater. Previous design

At EIA, ADF-contaminated snow iscollected and stored to manage the releaseof glycol from the airfield. Glycol and

other plane and pavement deicing com-pounds are channeled to the 91,000 m3

Gun Club Pond, located northwest of theairport. BOD concentrations in the pondcan be as high as 600 mg/L during springmelt, so the water requires treatment priorto discharge to Whitemud Creek.

The existing wetland treatment systemconsists of 12 square gravel-filled bedsarranged in six trains of two cells each.Each bed is 43 m x 43 m, with a graveldepth of 0.6 m. Water from the Gun ClubPond is delivered, via a submersiblepump, with measured flows of betweeneight and 28 litres per second. Flow rateis governed by the hydraulic head differ-ence between the pond and the wetlandbeds.

System upgrade designThe system upgrade is designed to

provide over 711 kg-BOD/d of treatment,and to allow increased flow rates as theconcentration of the BOD drops duringspring melt. It includes reconfigurationof two existing treatment trains initiallyand a third train in the future. The firstcell of each of the upgraded trains hasbeen modified to a vertical flow config-

The upgrade of EIA’s glycol treatment system included a Forced Bed Aerationsystem.


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uration, and incorporates patented ForcedBed AerationTM.

The second cell in the train has beenreconfigured as a surface flow wetlandfor polishing of the effluent. Aggregatefrom the second cell was relocated to thefirst cell, to increase the aggregate andwater depth to 1 metre. The depth of ag-gregate in the second cell is 0.3 m, with atotal water depth of 0.6 m.

With the addition of aeration and nu-trients, the upgraded system can provideup to 10 times more treatment in half thefootprint of the existing wetland system.Aeration and nutrient systems are de-signed so that levels can be adjusted basedon influent concentrations. Converting tovertical flow removes the hydraulic con-straints previously experienced with theold horizontal flow wetlands. An up-graded lift station also provides substan-tially more flexibility, when meeting theaberrant flows of spring melt. Finally, in-corporation of a recycle system, withineach of the first cells, permits expeditedstart-up in the spring.

Adding aeration to enhance treatment

The aeration system uses speciallymanufactured tubing that is installed be-neath the gravel layer. Two positive dis-placement blowers, each sized to deliver1,500 SCFM, supply air.

Tubing is placed to provide a low levelof uniform aeration across the bed floor.Aeration holes, or emitters, are spacedsuch that there are 36 emitters for each

As over 758 litres of propylene glycol can be used for deicing a plane, BOD requirements become very high.

continued overleaf...

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Environmental Science & Engineering Magazine62 | September 2011


square metre. This provides efficient aer-ation of the gravel bed, and results in ro-bust growth of aerobic bacteria, that areresponsible for the degradation of pollu-tants in the stormwater.

Similar aeration systems have beenemployed for the glycol treatment sys-tems at London Heathrow and BuffaloNiagara International Airport. In eachcase, providing uniform aeration is cen-tral to increasing the capacity of treat-ment, and meeting the highly variableoxygen demands associated with deicingactivity.

Theory of operationAfter each winter, the concentration of

BOD will be measured in the Gun ClubPond to determine the amount of total or-ganic mass that needs to be treated. A cal-culation of supplemental nutrients will beundertaken to determine the amount ofnutrients that are required to achievehealthy bacterial growth. A nutrient solu-tion will be fed to the pond and mixed.

After this, an initial batch of glycol-contaminated stormwater will be intro-duced to the drained beds to begin the

initial “acclimatization” phase. Blowersand recirculation pumps will be startedand the contents of the bed will be aeratedand re-circulated, until there is evidenceof bacterial activity and BOD levels dropto acceptable discharge levels.

At this point, the first bed is accli-mated and the influent pumps will beturned on to provide automated dischargeinto the beds. Treated stormwater fromthe first bed will flow by gravity to thesecond bed, where it will be polished fur-ther and ultimately discharged to White-mud Creek.

As the Gun Club Pond is lowered, pe-riodic sampling will determine the levelof BOD in the system, and the influentpumping rate will be increased relative tothe decrease in BOD concentrations. Thiswill maintain a constant mass load to thebeds, within the capabilities of the treat-ment system.

Once the Gun Club Pond is empty,discharge into the treatment system willstop. However, aeration of the beds willcontinue. With no more influent or efflu-ent, aerobic bacteria generated during the

treatment period will be starved and un-dergo in situ aerobic digestion. Aerationand recirculation of the beds will con-tinue for two weeks and then be shut offto promote evaporation and plant uptakeof nutrients. Prior to the onset of winter,the beds will be drained to minimize iceformation.

Conclusion The upgrade of the EIA glycol treat-

ment system demonstrates how ForcedBed Aeration can be used to improve anexisting wetland system. Reconfigurationof the existing cells and the addition ofaeration greatly increase the capacity andoperational flexibility of the system. Inno-vative engineering allowed EIA to expandcapacity, by using existing infrastructure.In doing so, the airport can continue tomeet its environmental protection obliga-tions.

Mark O. Liner is with Naturally Wallace Consulting. E-mail:

[email protected]


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