1. 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

2. Agenda
Over view of system
Case for change
Trial winter 2009/10
Aims and objective
Scope of quick wins
The Mayfield Farm process
Contingency
Forwards look
Questions

3. 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

4. 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

5. 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%, kg/ha-d
Richter et al. 2004

6. Overview of pollution control at Heathrow
Causeway Nature Reserve – part of Eastern Balancing Reservoirs
Spout Lane Lagoon
Clockhouse Lane Pit – Cable 1 part of Princes ski club
Mayfield Farm main reservoir
5 discharge consents covering Heathrow
3 are significant as they drain operational areas of the airfield
The other 2 drain roads and car parks (oil interceptors are all that’s needed on these sites)
All are regulated by the Environment agency
T5 (aka western) & Southern both have limits for de-icing chemical of 40mg/l biochemical oxygen demand (BOD). They both drain into Clockhouse Lane Pit and ultimately the River Thames at Hampton (upstream of drinking water abstraction point!).
Eastern is under discussion with the EA but is likely to have a limit of 40mg/l. It drains into the River Crane and then River Thames at Twickenham (downstream of drinking water abstractions).
System is designed to trap oil and treat de-icer but not other pollutants
High level process = TEST –STORE – TREAT - TEST
Photo’s
Spout Lane Lagoon – 60,000m3 of storage prior to discharge to foul runoff flows in at upto 430l/s but discharge is limited 50l/s. site of last years £1.2m tankering operation
Mayfield Farm Main Reservoir – 36,000m3 of storage prior to treatment in reed beds – focus of quick wins as overloading of the treatment process was the main cause of tankering operation
CLP – view from outfalls to ski club run off discharges directly into cable tow water ski lake
Causeway nature reserve – final polishing stage of treatment process prior to discharge. EBR combines treat and store in one place. Also provides firewater for majority of airport (except T5 and fuel farm)

7. The Case for Upgrading Mayfield Farm
2 Drivers – Increasing de-icer usage which results in increased regulatory pressure
System was designed based on 90’s data – not surprising it doesn’t cope
Exponential growth due to;
Changes in aircraft de-icer mix 50:50 to 75:25 - SAE
Worse winters
Precautionary applications?
Relatively mild winters post original construction (change in design basis)
More stringent consent limits

8. Buffalo Niagara International Airport
Heavy snow loads in winter
Airfield operations are heavily dependent on effective deicing operations

9. Treatability Testing
Measure glycol degradation in both warm and cold temperatures
With and without aeration

10. Aerated rate coefficients, low temperature runs
Average CBOD5 (mg/L)
k2TIS(d-1)
Influent
Effluent 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

11. 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

12. Comparing Treatment Effectiveness
Aerated rate coefficient: d-1
Non-aerated rate coefficient: d-1
An aerated wetland is 10X more effective in treating glycol!

14. 14

15. Buffalo – Completed Treatment System

18. 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)
Comparing the two systems provides insights for optimizing the Heathrow reed beds and how to increase treatment capacity

21. Full- ScaleTrial Winter 2009/10

22. It was demonstrated that adding FBA and nutrient requirements the FBA removed 14 times more BOD than the control.
It was found that temperature, whilst influencing the rate of treatment, is not a limiting factor.
It was demonstrated that re-engineering the flowpath improved treatment performance.
It was evident that a ramping-up regime needs to be implemented prior to the winter season.

23. Aims and objectives of quick wins
Improve environmental outcomes
Improve regulator perception
Reduce unplanned OPEX
Maintain biodiversity during construction and operation
Out of scope
Long term storage solution
Aeration to meet oxygen demands of influent loads
Online flow and organics monitoring to optimize performance
Nutrient dosing to promote bacterial growth
Optimized performance of existing Mayfield Farm works
No new tanks or lagoons
System optimization minimizes life cycle costs for BAA
Mayfield Farm is an existing hard asset
Upgrading the existing system improves performance by a factor of up to 14x
Upgrade cost is a fraction of original capital expenditure
Avoid loss of existing asset and capital expenditure on a new replacement asset

24. Scope of Heathrow Stormwater Quick Wins
Mayfield Farm
Treatment Upgrades to Floating Reedbeds, Balancing Lagoon, Horizontal Reedbeds, nutrient dosing facility, power and controls
Aeration to Main Reservoir
Eastern Balancing Reservoir
Aeration to upper pond & lower pond including power and controls
Clock House Lane Contingency
Aeration including power and controls
Spout Lane
The ability to increase pumping to foul from 50l/s to 100l/s, improve reliability and reduce cost (subject to TWU approval)
DECEMBER 2012 (LHRPSA1133K224P9)

25. Mayfield Farm Treatment Works
Original System
Re-engineered System
Horizontal subsurface flow wetlands
Balancing Reservoir
Floating treatment wetlands

26. Mayfield Farm Treatment Process
INFLUENT
PRIMARY
RESERVOIR
FLOATING
REED BEDS
BALANCING
LAGOON
HSSF
DISCHARGE
BOD
ANALYSIS
PLC
NUTRIENT
DOSING

27. Primary Treatment
Complete mix (CM) zone permits bacteria to grow relative to influent loads
Minimum detention time of 1.5 days provides increased flow through
Partial Mix (PM) zones designed for solids sedimentation, storage, and digestion

28. Secondary Treatment
During optimisation phase, the balancing lagoon will be refined as a dynamic system for hydraulic equalization, load equalization, solids management, or treatment
Inclusion of aeration provides flexibility with respect to managing variable flows and concentrations

29. Horizontal Flow Forced Bed Aeration™ Wetland
Here we have a basic section through a horizontal system. This comprises a lined excavation filled with media with large stone on the periphery providing support. The Inlet distribution manifold runs along the length of the bed with adjustable ‘Ts’ positioned at intervals to allow adjustment of the flow to ensure it is evenly distributed across the whole bed. The effluent move across the bed and is collected via a field drain on the bottom of the discharge side of the bed from where the effluent passes out through the level control system. This controls the level of the effluent in the bed.
It is common following commissioning to raise the level in the bed above the matrix to prevent weeds establishing on the exposed media before the reeds have established themselves. This also prevents rabbits etc from eating the young reeds.

30. Aerated Wetland Layout30

31. Aeration Tubing Plow

32. Tertiary Treatment

33. Contingency at Clock House Lane Pit

34. Thank You for Your Attention