Biochemical Basis for Environmental Management of Aircraft Deicing Fluid Waste Using Vegetation

Sigifredo Castro(1), Lawrence C. Davis(2), Larry E. Erickson(1)

(1)Department of Chemical Engineering and (2)Department of Biochemistry, Kansas State University, Manhattan, KS

Phytoremediation can be employed as a natural and feasible

strategy for treating the waste generated by aircraft deicing

operations. The environmental concern is due to the high oxygen

demand of ethylene glycol (EG) and propylene glycol (PG) and

the toxicity associated with corrosion inhibitors, such as

benzotriazole (BT) and methyl-benzotriazole (MBT). Land

application of this waste can take advantage of vegetation by two

mechanisms: enhancement of EG and PG biodegradation by the

rhizosphere effect and transformation of BTs by plant enzymatic

activities. This study focused on the uptake of BTs in hydroponic

culture of sunflowers (Helianthus annuus L.).

Introduction

• Find toxicity thresholds for plants to EG and BTs

• Estimate kinetic parameters for phytotransformation of different BTs

• Establish the rate-controlling mechanism by comparing rates of phytotransformation under different environmental conditions

• Determine whether phytotransformation is linked to photosynthesis and /or plant metabolism

• Evaluate effect of temperature and estimate activation energy

• Confirm observations on uptake and fate of BTs in plants by experimenting with 14C-MBT

Objectives

1.89 -1.36(Log KOW)

1.561.29Theoretical Oxygen demand, mgO2/mg

71.6SolubleSolubility in methanol, g / L (at 25°C)

5.5SolubleSolubility in water, g / L (at 25°C)

0.030.09Vapor pressure, mm Hg (at 20°C)

Methyl Benzotriazole

(MBT)

Ethylene Glycol (EG)

Property

N

4

53

7

61

2

N

N

H

Benzotriazole (BT) LogKOW = 1.4

N

4

53

7

61

2

N

N

H

CH3

5-Methyl-benzotriazole (MBT) LogKOW = 1.9

Chemical Properties

1-Hydroxy-benzotriazole (HBT) LogKOW = 0.1

N

4

53

7

61

2N

OH

N

1.89 -1.36(Log KOW)

1.561.29Theoretical Oxygen demand, mgO2/mg

71.6SolubleSolubility in methanol, g / L (at 25°C)

5.5SolubleSolubility in water, g / L (at 25°C)

0.030.09Vapor pressure, mm Hg (at 20°C)

Methyl Benzotriazole

(MBT)

Ethylene Glycol (EG)

Property

N

4

53

7

61

2

N

N

H

N

4

53

7

61

2

N

N

H

Benzotriazole (BT) LogKOW = 1.4

N

4

53

7

61

2

N

N

H

CH3

N

4

53

7

61

2

N

N

H

CH3

5-Methyl-benzotriazole (MBT) LogKOW = 1.9

Chemical Properties

1-Hydroxy-benzotriazole (HBT) LogKOW = 0.1

N

4

53

7

61

2N

OH

N

N

4

53

7

61

2N

OH

N

For benzotriazoles:Detector: UV ( 275 nm)Eluent: methanol/water Column: Polymeric Reverse Phase

EG: Indirect analysis by oxidation Detector: UV (260 nm) Eluent: Acidified sodium periodateReaction: 4 min, 65°C, on high- density polyethylene tubing

Aqueous solutions analyzed by HPLC:

Analytical Methods

Effect of lighting period

Experimental methodology

Plant: Sunflower Artificial lighting: 40-watt cool

white fluorescent lightMedia:- Sandy top soil mixed with

vermiculite- Hydroponics in Hoagland’s

solution

reduce water uptake during dark

12h 12h

Effect of temperature

T = 18°C

Cooling Circulator Heating

pump

T = 24°C T = 31°C

Effect of induced convection

Magnetic Stirrers

Reduce mass transfer resistance

Determination of activation energy for transformation

Toxicity Thresholds

Ethylene and propylene glycol:Healthy plant growth for aerobic conditions: EG concentration < 2 g/L in soil solution, drip irrigation, Hoagland’s 1X solution supplied. No accumulation of EG in soil and possible plant uptake leading to accumulation in leaves.Benzotriazoles:Healthy plant growth for concentrations < 100 mg/L in soil solutionHoagland’s 1X solution supplied

Concentration decreased with time. For continuous feeding, plants reached a “steady-state” condition, lower than dose concentration.

Loss of benzotriazole was greater than water uptake disappearance due to an active uptake process

Insignificant recovery of MBT from plant material by methanol extraction irreversibly binding and/or change in chemical structure

Triazole concentration

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6

Elapsed time (days)

Tri

azol

e co

ncen

trat

ion

(mg/

L)

BT HBT TT MBT MBT12

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Elapsed time (days)

Tri

azol

e co

ncen

trat

ion

(mg/

L)

BT HBT TT MBT

Linear

Michaelis-Menten

Experimental data

-20

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350 400 450 500 550

Average triazole concentration (μmol / L)

Infl

ux (

μmol

/ kg

.hr)

(a) MBT Phase 1Imax = 384 μmol / hr.kgKM = 503 μmol / L

R2 = 0.930

During dark period, evapo-transpiration was reduced but triazole uptake did not stop phytotransformation in/on the roots and not directly linked to photosynthesis.

Apparent kinetics fitted a Michaelis-Menten model. Large variation in parameters (KM, Imax) among treatments and stages of plant growth. Normalizing the rates by plant fresh weight was not successful.

Phytotransformation Kinetics and Photoperiod

01

234

567

89

0 1 2 3 4 5 6

Elapsed time (days)

Tot

al m

g tr

iazo

le lo

st /

mg

tria

zole

lost

by

wat

er u

ptak

e

BT TT MBT MBT12

Estimated activation energy ranged from 24 to 69 kJ/mol (18 to 30 °C) process is kinetically limited. Decrease in activation energy with plant age and plant size.

Stirring improved growth better aeration and nutrient uptake, higher temperature (23°C vs. 26°C). Phytotransformation rates normalized to plant fresh weight were similar.

Effect of Stirring and Temperature

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Elapsed time (days)

BT

con

cent

rati

on (

mg

/ L)

Unstirred Stirred

0

10

20

30

40

50

60

70

80

90

36 60 84 108 132 156 168

Elapsed time (hr)

Ea

(kJ

/ mol

)

Method 1 Method 2

Methanol soluble by-products, more polar than the MBT, corresponded to 77% of the recovered material. Remaining 23 % irreversibly bound to the plant structure, with the majority (85 %) located in the roots.

Phytotransformation confirmed with 14C-MBT. About 46% of estimated losses were recovered.

Preliminary Study with 14C-MBT

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12

Residence time in HPLC (min)

Nor

mal

ized

pea

k he

ight

HPLC spiked non-treated root extract Scintillation treated root

When enough nutrients are supplied and at concentrations less than 100 mg/L, BTs are phytotransformed into a soluble fraction and a bound fraction located mostly in the roots. Phytotransformation followed Michaelis-Menten kinetics, occurred on the roots, was not directly linked to the photosynthetic activity or plant transpiration, and was not diffusion-limited. Phytotransformation of BTs is the most promising biological treatment technology since microbial degradation in waste water treatment has not been demonstrated.

Main Findings

Castro, S., L. Davis, and L. Erickson, “Plant-enhanced remediation of glycol-based aircraft deicing fluids,” Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management, 5, 3, 141-152, 2001.Castro, S., L. Davis, and L. Erickson, “Phytotransformation of benzotriazoles,” International Journal of Phytoremediation, 5, 3, 245-265, 2003.

References