Glycol Treatment at London’s Heathrow Airport

Scott Wallace and Mark Liner – Naturally Wallace Consulting

David Cooper and Clodagh Murphy – ARM, Ltd.

Russell Knight – British Airport Authority

Aircraft Deicing

• Deicing fluids include ethylene glycol (EG), propylene glycol (PG) and diethylene glycol (DEG).

• Commonly used as a 50% concentrate form (CBOD5 approximately 200,000 mg/L).

• Runoff can contain over 20,000 mg/L at 1 oC

• New environmental regulations are requiring treatment of deicing runoff.

• Major challenge for conventional treatment plants

Deicing Runoff Treatment Options

• Anaerobic Digestion (biogas)

–Shock loadings, limited net biogas

• Mechanical Treatment (activated sludge, MBRs)

–Shock loadings, energy intensive

• Discharge to Regional Sewer

–Long-term concerns over cost and capacity

• Passive (ponds and open-water wetlands)

–Land intensive, BASH

• Subsurface Flow Treatment Wetlands

– No water exposed, land intensive

Original Heathrow Constructed Wetlands

• Papers published in 2001 and 2004

• 12 reed beds, total area 2.08 ha

• Design flow rate 40 L/s; influent COD of 170 mg/L

• Removal efficiency of 30-68%, 24-77 kg/ha-d

Richter et al. 2004

Overview of pollution control at Heathrow

Spout Lane Lagoon

Mayfield Farm main reservoir

Causeway Nature Reserve – part of Eastern Balancing Reservoirs

Clockhouse Lane Pit – Cable 1 part of Princes ski club

The Case for Upgrading Mayfield Farm

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Aircraft Pavement• Relatively mild winters post original construction (change in design basis)

• More stringent consent limits

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Buffalo Niagara International Airport• Heavy snow loads in winter

• Airfield operations are heavily dependent on effective deicing operations

Treatability Testing

• Measure glycol degradation in both warm and cold temperatures

• With and without aeration

Aerated rate coefficients, low temperature runs

Run

Average CBOD5 (mg/L)

k2TIS(d-1)InfluentEffluent

A 648.8 26.5 4.81

B 679.3 21.0 5.72

C 325.0 10.3 5.63

D 694.0 23.5 5.41

Average 5.39

PG degradation without aeration…

Run

Average CBOD5 (mg/L)

k4TIS(d-1)Influent Effluent

A 542.3 212.3 0.68

B 257.0 119.0 0.27

C 177.0 29.0 0.73

D 129.5 33.5 0.51

Average 0.55

Comparing Treatment Effectiveness

• Aerated rate coefficient: 5.30 d-1

• Non-aerated rate coefficient: 0.55 d-1

• An aerated wetland is 10X more effective in treating glycol!

Buffalo – Completed Treatment System

Comparing Heathrow and Buffalo wetlands

Heathrow (prior to upgrade)

Buffalo

Design COD load 590 kg/d 4540 kg/d

Area 2.08 ha 1.67 ha

Bed Volume 12480 m3 28370 m3

COD Loading 47 g/m3-d 160 g/m3-d (clogging limited)

Aeration None 750 kW

Oxygen Transfer 2.4 – 7.7 g/m2-d 270 g/m2-d

COD Removal 4 – 13 g/m3-d Up to 160 g/m3-d

Flow Path Horizontal Vertical (due to high load)

Full- ScaleTrialWinter 2009/10

Effluent

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BED A BED B BED C

Effluent

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Effluent

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BED A BED B BED C

Mayfield Farm Treatment WorksOriginal System Re-engineered System

Horizontal subsurface

flow wetlands

Balancing Reservoir

Floating treatment wetlands

Primary Treatment

Secondary Treatment

Aerated Wetland Layout

Aeration Tubing Plow

Tertiary Treatment

Thank You for Your Attention