Project experience Surface water run-off treatment
System experience Horizontal flow reedbeds
Services Design
Project management
Year completed 2011
Client Heathrow Airport Holdings Ltd (formerly BAA)
Contractor ARM Ltd
 
 

Challenge

Mayfield Farm Treatment Works, commissioned in 2001, was designed to treat run-off from Heathrow Airport’s Southern Catchment. The run-off is contaminated with glycols resulting from the airport's de-icing operations.

Treating glycol-contaminated run-off is a challenge at every airport faced with varying cold-climate winter conditions. The run-off can contain over 20,000mg COD/L at 1°C.

The original treatment system consisted of balancing ponds, aeration lagoons, rafted reed beds and 12 horizontal subsurface flow reed beds covering 2.08 hectares. Designed to treat influent COD at 170mg/l with a design flow of 40l/s, the wetland cells consisted of open water zones and gravel zones and were planted with Phragmites australis. The original system operated passively with oxygen transfer rate of 2.4–7.7g/m3/d, removing 4–13g/m3/d of COD. This system was unable to treat current volumes of effluent and was failing to achieve compliance.

ARM conducted a full-scale trial comparing the existing reed bed design with a re-engineered reed bed and one fitted with Forced Bed Aeration™ (FBA™). The results indicated that there is enough wetland volume at Heathrow, but the limited oxygen transfer rate is limiting treatment performance.

Solution

ARM re-engineered the distribution and collection system and retrofitted FBA™ into the existing reedbeds. The open water zones were filled with gravel and the gravel depth increased by 500mm. The upgrade works at the Mayfield Farm included the addition / modification of:

  • Primary Reservoir Aeration + nutrient dosing point
  • Complete aerated mix zone + nutrient dosing
  • Partial aerated mix zone
  • Balancing pond aeration and nutrient dosing points
  • Horizontal subsurface flow reedbeds with FBA™
  • Variable speed transfers
  • Primary treatment by pass facility (motorised shut-off valve)

The upgraded reedbeds now transfer up to 165g/m3/d of oxygen and are capable of treating 3500kg/BOD/day at 40l/s average flow.


Challenge

Mayfield Farm Treatment Works, commissioned in 2001, was designed to treat run-off from Heathrow Airport’s Southern Catchment. The run-off is contaminated with glycols resulting from the airport's de-icing operations.

Treating glycol-contaminated run-off is a challenge at every airport faced with varying cold-climate winter conditions. The run-off can contain over 20,000mg COD/L at 1°C.

The original treatment system consisted of balancing ponds, aeration lagoons, rafted reed beds and 12 horizontal subsurface flow reed beds covering 2.08 hectares. Designed to treat influent COD at 170mg/l with a design flow of 40l/s, the wetland cells consisted of open water zones and gravel zones and were planted with Phragmites australis. The original system operated passively with oxygen transfer rate of 2.4–7.7g/m3/d, removing 4–13g/m3/d of COD. This system was unable to treat current volumes of effluent and was failing to achieve compliance.

ARM conducted a full-scale trial comparing the existing reed bed design with a re-engineered reed bed and one fitted with Forced Bed Aeration™ (FBA™). The results indicated that there is enough wetland volume at Heathrow, but the limited oxygen transfer rate is limiting treatment performance.

Solution

ARM re-engineered the distribution and collection system and retrofitted FBA™ into the existing reedbeds. The open water zones were filled with gravel and the gravel depth increased by 500mm. The upgrade works at the Mayfield Farm included the addition / modification of:

  • Primary Reservoir Aeration + nutrient dosing point
  • Complete aerated mix zone + nutrient dosing
  • Partial aerated mix zone
  • Balancing pond aeration and nutrient dosing points
  • Horizontal subsurface flow reedbeds with FBA™
  • Variable speed transfers
  • Primary treatment by pass facility (motorised shut-off valve)

The upgraded reedbeds now transfer up to 165g/m3/d of oxygen and are capable of treating 3500kg/BOD/day at 40l/s average flow.


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Call 01889 583811
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Downloads
  • Case Study: Mayfield Airport run-off treatment
    Case Study: Mayfield Airport run-off treatment
    1pp 342.03KB
    Download
  • Forced Bed Aeration™ technology
    Forced Bed Aeration™ technology
    2pp 347.3KB
    Download
  • Brochure - Horizontal flow reed beds
    Brochure - Horizontal flow reed beds
    2pp 224.37KB
    Download
 
 
 
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Airport run-off treatment, Mayfield Farm Treatment Works