Biochemical Basis for Environmental Management of Aircraft
Deicing Fluid Waste Using Vegetation
Sigifredo
(2)
Davis ,
Lawrence C.
(1)
Erickson
Larry E.
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.).
Analytical Methods
Toxicity Thresholds
Aqueous solutions analyzed by HPLC:
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 solution
Hoagland’s 1X solution supplied
For benzotriazoles:
Detector: UV ( 275 nm)
Eluent: methanol/water
Column: Polymeric
Reverse Phase
Effect of Stirring and Temperature
35
30
25
20
15
10
5
0
0 1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16
Unstirred
Stirred
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.
EG: Indirect analysis by oxidation
Detector: UV (260 nm)
Eluent: Acidified sodium periodate
Reaction: 4 min, 65°C, on highdensity polyethylene tubing
Stirring improved growth 
better aeration and nutrient
uptake, higher temperature
(23°C vs. 26°C).
Phytotransformation rates
normalized to plant fresh
weight were similar.
Elapsed time (days)
Ea (kJ / mol)
Introduction
BT concentration (mg / L)
(1)Department
(1)
Castro ,
90
80
70
60
50
40
30
20
10
0
36
60
84
108
Triazole concentration
• 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
photosynthesis and /or plant metabolism
is
linked
30
25
20
15
10
5
0
0
1
2
3
4
5
Elapsed time (days)
BT
HBT
TT
MBT
MBT12
to
Insignificant recovery of MBT
from plant material by
methanol extraction 
irreversibly binding and/or
change in chemical structure
Effect of lighting period
• Evaluate effect of temperature and estimate activation energy
reduce water uptake during dark
• Confirm observations on uptake and fate of BTs in plants by
experimenting with 14C-MBT
12h
6
Triazole concentration (mg/L)
• Find toxicity thresholds for plants to EG and BTs
Triazole concentration (mg/L)
35
Plant: Sunflower
Artificial lighting: 40-watt cool
white fluorescent light
Media:
- Sandy top soil mixed with
vermiculite
- Hydroponics in Hoagland’s
solution
Vapor pressure, mm Hg (at 20°C)
0.09
0.03
Solubility in water, g / L (at 25°C)
Soluble
5.5
 Reduce mass transfer resistance
Magnetic Stirrers
40
20
0
0
100
Linear
1
Experimental data
(a) MBT Phase 1
Imax = 384 μmol / hr.kg
KM = 503 μmol / L
40
20
R2 = 0.930
0
Soluble
71.6
Theoretical Oxygen demand, mgO2/mg
(Log KOW)
1.29
-1.36
1.56
1.89
Benzotriazole (BT)
LogKOW = 1.4
5-Methyl-benzotriazole (MBT) 1-Hydroxy-benzotriazole (HBT)
LogKOW = 1.9
LogKOW = 0.1
H
H
7
N
7
1
6
5
4
3
N
1
6
2
OH
N
7
2
N
5
CH3
4
3
N
N
N
2
5
4
Cooling
Circulator
N
3
N
0
T = 18°C
T = 24°C
T = 31°C
50
100 150 200 250 300 350 400 450 500 550
Average triazole concentration (μmol / L)
Heating
pump
1
6
-20
Effect of temperature
 Determination of activation energy for transformation
During dark period, evapotranspiration was reduced but
triazole uptake did not stop 
phytotransformation in/on the
roots and not directly linked to
photosynthesis.
Total mg triazole lost /
mg triazole lost by water uptake
Solubility in methanol, g / L (at 25°C)
2
4
6
8
10
12
Scintillation treated root
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.
60
120
60
0.2
Residence time in HPLC (min)
80
Michaelis-Menten
80
0.4
100
140
Influx (μmol / kg.hr)
Property
0.6
0
2
3
4
5
6
7
8
HBT
TT
MBT
Phytotransformation Kinetics and Photoperiod
Methyl
Benzotriazole
(MBT)
0.8
HPLC spiked non-treated root extract
BT
Ethylene
Glycol
(EG)
Phytotransformation
confirmed with 14C-MBT.
About 46% of estimated
losses were recovered.
1
0
Elapsed time (days)
Effect of induced convection
Method 2
1.2
120
12h
Chemical Properties
168
Preliminary Study with 14C-MBT
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
Normalized peak height
Experimental methodology
156
Elapsed time (hr)
Method 1
Objectives
132
Main Findings
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.
9
8
7
6
5
4
3
2
1
0
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.
References
0
1
2
3
4
Elapsed time (days)
BT
TT
MBT
MBT12
5
6
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, 245265, 2003.