The aim of the project was to provide a biological wastewater treatment plant to treat the glycol runoff from the airport runways prior to its discharge into the river Crane. An organic compound from the alcohol family, glycol is commonly found in antifreeze solutions and, as such, is used as a de-icer on aircrafts during the winter months.
The new glycol removal plant takes water from a runway collection lagoon, processes it and discharges it into a separate four-part clean water lagoon, prior to its release into the river Crane. The plant itself includes two 1,100 m3 AnoxKaldnes Moving Bed Biological Reactor (MBBR) biological treatment tanks, through which the effluent passes.
Next, the water 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 lagoon. In total, the plant processes 720,000 litres of runoff water per hour and 550kg of biochemical oxygen demand (BOD) per day.
An aerobic wastewater treatment method, MBBR systems use active biofilm carriers made from plastic with large surface areas on which bacteria can grow with optimal culture conditions. The carriers are kept constantly in motion within the tanks using aeration, allowing the bacteria to break down organic material in the wastewater – in this case BOD, of which glycol is rich, and ammonia.
After a competitive bid, VWT UK was selected to design, supply, install, commission and operate the plant. Having secured a further operations contract which began in December 2019, the provider of water treatment technologies and services will continue to operate the new plant for the next nine years.
The new plant is part of Heathrow’s environmental ambition to prevent the discharge of any contaminants into the river Crane in the future.
The plant also has space to increase the hydraulic capacity with the addition of a third MBBR system, should it be required by Heathrow in the future.