___________________________________________________________________________

36 IWA Specialist G roup on Use of Macrophytes in Water Pollution Control: Newsletter No. 37 DESIGN AND PERFORMANCE OF THE WETLAND WREATMENT SYSTEM AT

THE BUFFALO NIAGARA INTERNATIONAL AIRPORT

Scott Wallace and Mark Liner

Naturally Wallace Consulting, Vadnais Heights, Minnesota, USA ( scott.wallace@naturallywallace.com

, mark.liner@natu rallywallace.com )

Abstract The wetland treatment system at the Buffalo Niagara International Airport has been in operation for two years now, and represents one of the major applications of intensified wetlands for treatment of glycol

- based deicing fluid s. The full

- scale system is designed to remove 4,500 kg/d of biochemical oxygen demand (BOD 5 ). The wetland design was based on pilot testing conducted in 2007, which established degradation rate coefficients for both

aerated and non

- aerated modes of operat ion. Aeration was found to profoundly affect treatment performance. When aerated at 0.85 m 3
air per hour (per m 3 of wetland bed), the volumetric (2TIS) BOD 5 removal rate constant averaged 5.4 day − 1 with a temperature coefficient (θ) of 1.03, based on experiments

conducted at 22°C and 4°C. In contrast, the non

- aerated wetland had a rate coefficient of

0.55 day − 1

. Operation of the full

- scale system during the 2009/2010 deicing season revealed nutrie nt

limited conditions that resulted in polysaccharide slime for mation within the wetland bed. A system for nutrient addition was updated and expanded for the 2010/2011 deicing season, which resulted in successful operation at BOD 5 loadings of over 20,000 k g/d, which is almost five times gre ater than the original design. During the 2010/2011 deicing season,

BOD 5 removal averaged 98.3%.

Keywords aircraft deicing, airport, ethylene glycol, propylene glycol, intensified wetland, subsurface

flow wetland

INTROD UCTION In addition to other contaminants found in stormwater and snowmelt at airports (e.g., fuel & lubricant residuals, oil & greases, airport stormwater runoff contains large amounts of aircraft

de

- icing fluids during periods when de

- icing and anti

- icing operations are carried out. The ADFs may be ethylene glycol (EG), or propylene glycol (PG) based and are applied as water

solutions The volumes of de

- icing fluids used depend on weather conditions and the type of

aircraft involved ( Higgins and Maclean, 2002 )

.

Controlling and treating stormwater runoff from airport facilities is a matter of increasing

environmental concern and is now having a major effect on the design and operation of airports. Within the United States and Canada, new regulatory standards are being implemented for the management of de

- icing fluids used to remove ice from aircraft during winter operations. Pref

erred chemicals are EG and PG, which in the 50% concentrations commonly used for aircraft de

- icing and anti

- icing, has a BOD 5 of approximately
200,000 mg/L. Although this is diluted by ice

- melt, BOD 5 concentrations in excess of
20,000 mg/L are common. Thes e high influent concentrations, combined with the inherently variable nature of winter storms and the low temperature of de

- icing runoff, challenges the operation of conventional mechanical treatment p lants.____________________________________________________________________________________________________

IWA Specialist Group on Use of Macrophytes in Water Pollution Control: Newsletter No. 38 37 Constructed wetlands are an attractive option f or treatment of deicing runoff, because when operated in a subsurface mode, the risk to airfield operations is minimal and the systems require much less operation & maintenance than conventional systems.

PILOT TESTING Pilot testing was carried out at Camp us D‘Alfred of the University of Guelph in Ontario,

Canada. . The tests were carried out indoors in 1 m 3 vessels configured as mixing tanks (containing mixers and heaters), open aerated basins (AB cells, simulating aerated tanks and containing fine bubble aeration spargers), non

- aerated vertical subsurface flow (VSSF) constructed wetland cells and aerated VSSF intensified (IW) test cells. The wetland cells were vegetated with common reed ( Phragmites sp. ) taken from ditches near the test unit. Test

runs were preceded by month

- long calibration and acclimatization periods.

The pilot facility was configured as a mixing tank; two open

- water AB cells; one non

- aerated VSSF CW cell containing gravel 0.3 m deep and; and two aerated gravel

- bed VSSF

intensified wetlan d cells (IW1 and IW2) containing gravel 0.8 m deep. There were two separate sets of cells which, after initial calibration and acclimation periods at room temperature, operated in parallel at the two design basis target temperatures. The set

- up for high te mperature operations consisted of a mixing tank and an AB cell followed by parallel CW and IW cells. (These were considered as two separate trains.) The set up for low temperature operations consisted of an AB Cell and one IW cell in series. These latter t wo vessels were located inside a walk

- in refrigerator at the Alfred Pilot Unit (Train 3). The initial configuration of the pilot facility is shown in Figure 1.

Figure 1. Pilot test facility schematic

Results from the four testing periods (Runs A, B, C, D) and the three process trains (Trains 1, 2, 3) are summarized in Table 1 ( Wallace et al. , 2007 )

. Train 2

Train 1 Mixing Tank

AB Cell

Hi Temp I W Cell

Lo Temp

CW Cell
Hi Temp AB Cell

Lo Temp

IW Cell
Hi Temp Walk

- in Refrigerator ADF SW from
Storage Tanks Train 3___________________________________________________________________________

38 IWA Specialist G roup on Use of Macrophytes in Water Pollution Control: Newsletter No. 37 Table 1. Average BOD 5 concentrations (mg/L); percent removal is listed in parenthesis

Train 1 Train 2 Train 3

Run Mixing

Tank

Influent AB Effluent

High Temp. IW Effluent

High Temp. AB Effluent

High Temp. CW Effluent

High Temp. AB Effluent

Low Temp. IW Effluent

Low Temp.

A 1,491 542 (64) 8 (99) 542 (64) 212 (61) 649 (56) 27 (96)

B 1,524 Not Used 56 (96) 257 (83) 119 (54) 679 (55) 21 (97)

C 773 Not Used 25 (7) 177 (77) 29 (84) 325 (58) 10 (7)

D 694 Not Used 4 (99) 130 (81) 34 (74) Not Used 24 (97)

Since the different tre atment trains were operated at different flow rates and temperatures, inspecting percent removals based on concentration (as summarized in Table 2) does not provide a complete understanding of treatment performance. The data were analyzed using a

tanks

- in

- series (TIS) flow model using a relaxed parameter, P ( Kadlec a nd Wallace, 2009 ) that accounts not only for the number of tanks but weathering of the BOD 5 as the PG degraded into daughter products.

Calculated rate coefficients for the aerated IW cells for the high temperature runs are

summarized in Table 2, based on a flow model with P = 2 (this is an approximate value based on previous tracer testing of aerated intensified wetland cells):

Table 2. Aerated intensified wetland rate coefficients for high temperature runs

Run Average BOD 5 (mg/L)

k 2TIS (d − 1 )

Influent Effluent

A 542.3 7.5 9.15

B 1,524.0 55.7 5.17

C 773.0 25.0 5.60

D 694.0 4.0 14.84 Average 8.69

The higher results from Run D where the aeration rate was increased from 0.85 m 3 air per hour (per m 3 of wetland bed) to 2 m 3 of air per hour indicate that even further improvement of treatment could be possible. A similar set of BOD 5 IW rate coefficient calculations were made for the low temperature operations and these are presented in Table 3:

Table 3. Aerated intensified wetland rate c oefficients for low temperature runs

Run Average BOD 5 (mg/L)

k 2TIS (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

For Runs B and C, the data can be used to determine the Arrhenius constant, θ, based on the following equation:

w here k

T is the rate constant at temperature T = T °C and k

20 is the rate constant at 20°C. Based on these results, the value of θ was calculated to be approximately 1.03.____________________________________________________________________________________________________

IWA Specialist Group on Use of Macrophytes in Water Pollution Control: Newsletter No. 38 39 The BOD 5 removal rate coefficients for the non

- aerated CW cell were also calculat ed based

on a flow model with P = 4. A higher value of P was assumed because there is less interna l mixing in non

- aerated cells. Results are summarized in Table 4:

Table 4. Non

- aerated constructed wet land rate coefficients for high

- temperature runs

Run Av erage BOD 5 (mg/L)

k 2TIS (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

NUTRIENT LIMITATIONS Operation of the full

- scale treatment wetland indicated that nutrient

- limited conditions occurred during the 2009 /2010 de

- icing season, since propylene glycol (C 3 H 8 O 2 ) and ethylene glycol (C 2 H 6 O 2 ) do not contain nitrogen, p hosphorus and other nutrients. The nutrient demands for bacterial growth can be estimated using the factors summarized in

Table 5.

Table 5. Appro ximate nutrient requirements for bacterial growth ( Grady et al. , 1999 )

Nutrient Approximate nutrient requirement

(g/kg of biomass produced) Nitrogen 85 Phosphorus 17

Potassium 10

Calcium 10 Magnesiu m 7

Sulfur 6

Sodium 3

Chloride 3

Iron 2

Zinc 0.2 Manganese 0.1 Copper 0.02 Molybdenum 0.004

Cobalt < 0.0004

One major unknown parameter in treatment wetlands is the yield ratio of microbial growth,

which can be defined as the fraction of the inf luent biochemical oxygen demand (BOD)

converted to microbial biomass. For suspended

- growth activated sludge systems, this parameter can be easily measured and is often quite high; in the range of 1.0 to 0.7.

Treatment wetlands are attached

- growth systems with a very long solids retention time where microbial predation would presumably substantially reduce the yield ratio. In one study of a pilot

- scale, fill

- and

- drain subsurface flow wetland, the yield ratio was estimated to be 0.068 ( Austin et al. , 2007 )

. With such a low yield rate, this would imply that treat ment wetlands would not require large amounts of nutrients to maintain a mature microbial community under steady

- state conditions.___________________________________________________________________________

40 IWA Specialist G roup on Use of Macrophytes in Water Pollution Control: Newsletter No. 37 Although the Buffalo design had anticipated the need for nutrient addition, establishment of effective treatment was slow, a nd the system began to experience foaming associated with the formation of polysaccharide slimes by the resident bacteria. Foaming and slime formation is known to occur at wastewater treatment plants subject to severe nutrient limitations ( Arias et
al. , 2008 ; Ayati and Ganjidoust, 2008 )

.

Owing to the observed slime formation at Buffalo, estimates on the yield rati o had to revised upwards, and was finally estimated by the authors to be at least 0.3. This had profound implications on the rate of nutrient addition, as the Buffalo wetland was designed to process 4,500 kg/d of BOD; a yield ratio of 0.3 implies 1,350 kg/ d per day of microbial biomass production. Based on the information in Table 5, this amount of biomass production would require 115 kg/d of nitrogen and 23 kg/d of phosphorus, in addition to micronutrients. After feeding the appropriate amount of nutrients , slime formation ceased and treatment performance improved dramatically.

FULL

- SCALE OPERATION Operation of the full

- scale treatment wetland was continued through the 2010/2011 de

- icing season (with improved nutrient addition). The full

- scale system consi sts of four subsurface flow wetland beds (saturated vertical downflow), each sized at 4,640 m 2 with a bed depth of

1.5 m. The distribution piping is buried under an insulating level of compost such that no water is exposed during the treatment process (Fig ure 2).

Figure 2. Full

- scale treatment wetland at Buffalo Niagara International Airport

.

The subsurface vertical flow wetlands have an internal array of aeration tubes to enhance oxygen transfer as a means of intensification. The enhanced oxygen transf er rate allows for the aerobic degradation of glycol compounds. Each wetland can be supplied with air up to

140 m 3 /min, which allows an oxygen transfer rate approximately 60 times greater than what would be supplied through passive atmospheric diffusion.____________________________________________________________________________________________________

IWA Specialist Group on Use of Macrophytes in Water Pollution Control: Newsletter No. 38 41 During the 2010/2011 de

- icing season, influent BOD 5 concentrations were in excess of 15,000 mg/L. Generally, the system had very low effluent values, which averaged 77 mg/L (based on a correlation between online total organic carbon measurements and labora tory
BOD 5 values), as shown in Figure 3.

Figure 3. Influent and e ffluent BOD 5 values for the intensified wetland at Buffalo Niagara International Airport

.

The wetland system also experienced BOD 5 loadings well in excess of the original design

parameter s. While the design was based on a BOD 5 loading rate of 4,500 kg/d, actual loadings exceeded 20,000 kg/d. BOD 5 removals remained in the range of 90 to 100% (with an average removal rate of 98.3%), and reductions in treatment efficiency were only observed

a t the heaviest organic loadings (Figure 4).

Figure 4. BOD 5 loadings and treatment efficiency for the intensified wetland at Buffalo Niagara International Airport___________________________________________________________________________

42 IWA Specialist G roup on Use of Macrophytes in Water Pollution Control: Newsletter No. 37 CONCLUSIONS The Buffalo Niagara system has demonstrated that aerated, intensified subsurfa ce flow wetlands are a viable technology for treatment of deicing runoff at airport facilities. The Buffalo system was successfully scaled up from pilot testing results, and has demonstrated high levels of treatment effectiveness even when subjected to org anic loadings well in excess of the original design parameters.

The Buffalo Niagara wetland has served as a template for the upgrade and refurbishment of existing treatment wetlands at London‘s Heathrow airport and the airport facility in
Edmonton, Albert a. However, the Buffalo facility has also demonstrated that nutrient limitations in deicing runoff can be a significant impediment to treatment of deicing runoff, and that nutrient addition is necessary to reach the full potential of wetland treatment

syst ems.

REFERENCES Arias, C.A., Vollersten, J., Lange, K.H., Pedersen, J., Hallager, P., Bruus, A., Laustsen, A., Bundensen, V.W., Nielsen, A.H., Nielsen, N.H., Wium

- Andersen, T., Hvitved

- Jacobsen, T., Brix, H. ( 2008 ) . Integrating constru cted wetland filters and wet detention ponds for the treatment of urban stormwater runoff. In: Proceedings of the 11th International Conference on Wetland Systems for Water Pollution Control, 1

- 7 November 2008. Billore S.K., Dass P., Vymazal J. eds. Vikram University and IWA: Indore, India. pp. 781. Austin, D.C., Maciolek, D .J., Davis, B.M., Wallace, S.D. ( 2007 ) . Damköhler number design method to avoid clogging of subsurface flow constructed wetlands by heterotrophic

biofilms. Water Science and Technology 5 6 (3)

, 7

– 14. Ayati, B., Ganjidoust, H. ( 2008 ) . Investigation of pollution sources in Anzali reserved wetland. In: Proceedings of the 11th International Conference on Wetland Systems for Water Pollution Control, 1

– 7 November 2008. Billore S.K., Dass P., Vyma zal J. eds. Vikram University and IWA: Indore, India. pp. 116

- 122. Higgins, J.P., Maclean, J. ( 2002 ) . The use of a very large constructed sub

- surface flow wetland to treat glycol

- contaminated stormwater from aircraft de

- icing operations. Water Quality Re se arch Journal of Canada 37 (4), 785

– 792. Kadlec, R.H., Wallace, S.D. ( 2009 )

. Treatment Wetlands

, second ed ition. Boca Raton,

Florida: CRC Press. Wallace, S.D., Higgin s, J., Liner, M.O., Diebold, J. ( 2007 ) . Degradation of aircraft deicing

runoff in aerated en gineered wetlands. In: Multi Functions of Wetland Systems: An International Conference, 26

- 29 June 2007. University of Padova and International Water Association: Padova, Italy.