Heathrow unveils new solution for safely treating glycol runoff

London Heathrow has become the latest airport to invest in an aerated reed bed and wetland technology to manage the glycol run off from its runways, writes Barry Hallam.

An organic compound from the alcohol family, glycol is commonly found in antifreeze solutions used on aircraft during the winter months and, without treatment, once used, the compound combines with other runway runoff water and eventually makes its way into local water courses.

The environmental effects of the chemical fluids are mostly related to the high oxygen demand it exerts when released into rivers and streams, as this can-do immeasurable damage to the surrounding wildlife.

For example, as algae decomposes, it consumes dissolved oxygen (DO), which is crucial to aquatic and human life – leading to aquatic hypoxia and fish kills. Unfortunately, even when diluted, glycol can still pose a toxic threat to the environment.

While the pre-existing management of glycol differs between airports, some have employed techniques using de-icing pads and vacuum trucks. Typically, the collected material is then taken to a municipal wastewater treatment plant. However, this option can be expensive, and many treatment plants will no longer accept such materials.

Another option is the use of aerated reed bed and wetland technology to manage the glycol run off. While a simple and robust solution, it requires a large land area and may not be cost effective.

As a final alternative, onsite wastewater treatment plants such as anaerobic digesters and filtration units can be used to manage the concentration of the chemical that eventually enters surrounding water courses.

Heathrow recently adopted the latter option to treat the glycol runoff from the airport runways prior to its discharge into the local River Crane.

It was necessary to create a solution that could be kept in a semi-ready state throughout the summer, for use during cold spells when the glycol is used most.

My company, Veolia Water Technologies UK (VWT UK), was selected to design, supply, install, commission and operate the plant which includes two 1,100m³ AnoxKaldne Moving Bed Biological Reactor (MBBR) biological treatment tanks.

Heathrow’s runoff water is collected in a collection lagoon before being passed into these two tanks.

Within the tanks the MBBR system utilises bacteria grown on plastic biofilm carriers. The carriers are kept in a continuous motion in the tanks using aeration, allowing the bacteria to break down the organic matter that exists within the wastewater.

Water then enters a coagulation tank, followed by a flocculation tank before the solid flocs are filtered through one of VWT UK’s Hydrotech Discfilters. The filtered solids, or sludge, are then thickened and disposed of while the treated water is discharged to the clean side of the collection lagoon.

In total, the plant processes 720,000 litres of runoff water per hour and 550kg of biochemical oxygen demand (BOD) per day.

Once this process is completed, the water is safe to be released into the nearby River Crane.

Any backwash wastewater from the Discfilter is dosed with more polymer and the solids are separated via a drum thickener. Finally, the solids are removed off site and disposed of.

Ultimately, airport managers and officials are responsible for the activities that take place on their sites. Keeping an aircraft safe from the effects of cold weather is a primary concern, but there is an ethical and environmental responsibility to safeguard the local environment.

It is recommended that airports work with a water treatment services provider to address their glycol concerns and find a solution that works within the constraints of their site.

You can find out more about VWT UK, what we do and our solutions by visiting www.veoliawatertechnologies.co.uk

• Barry Hallam is VWT UK’s project manager for the Heathrow initiative.