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Activation Energy of Urea Hydrolysis and Ammonia Henry Constant Effects on
Ammonia Release from Confined Animal Feeding Operations (CAFOs)
Joshua StrattonDepartment of Chemistry
Colorado State University1
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What Controls Ammonia Emission?
2
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
Po
ten
tial
Am
mo
nia
Em
issi
on
s (g
/m
2/d
ay)
Date, Fall 2006 to Summer 2007
Simulated Potential Ammonia Emissions: Greeley, Colorado
WinterFall
Spring
Summer
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Back to the Basics
A. N. Hristov et al., Review: Ammonia emissions from dairy farms and beef feedlots. 2011. 3
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Modeling Ammonia Loss from Feedlots
4
• Underlying Factors– Temperature– Ionic Strength
hm = Mass transfer coefficientKa = Acid dissociation constantKh = Henry constantCNH4+(aq) = Ammonium concentration
CNH3(g) = Ammonia concentration
J. Wu, D. L. Nofziger, J. G. Warren, J. A. Hattey, Modeling Ammonia Volatilization from Surface-Applied Swine Effluent. 2003.
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Ammonium Production in Feedlots
Pseudo-first order Michaelis-Menten
5
How to accurately measure urea hydrolysis?
J. Wu, D. L. Nofziger, J. G. Warren, J. A. Hattey, Modeling Ammonia Volatilization from Surface-Applied Swine Effluent. 2003.
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Acid Dissociation Constant
6F. Montes, C. A. Rotz, H. Chaoui, Process Modeling of Ammonia Volatilization from Ammonium Solution
and Surfaces : a Review with Recommended Models 2009.
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Areas of Concern: Henry Constant
7F. Montes, C. A. Rotz, H. Chaoui, Process Modeling of Ammonia Volatilization from Ammonium Solution
and Surfaces : a Review with Recommended Models 2009.
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Research Objectives
• To determine Ea in Colorado CAFO soils– To better constrain available ammonium
• To create a system to measure the Henry constant in a complex mixture– To better quantify deviation from aqueous values
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Urease Kinetics Setup• Michaelis-Menten approach to determine
dependence on urea concentration– 1 mg N/ g soil
• Pseudo-first order approach to determined Ea in a dairy soil– 1 mg N/ g soil
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10
3.30
E-03
3.35
E-03
3.40
E-03
3.45
E-03
3.50
E-03
3.55
E-03
3.60
E-03
3.65
E-03
-1.20
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60Activation Energy
1/Temperature K
ln (
reac
tio
n r
ate)
Temperature(⁰C)
Half-life(min)
25 28.5
15 64.0
10 96.4
5 125.9
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Urease Hydrolysis Results
• Our Study– Ea = 51.92 kj/mol
• Soil (pseudo first order)– Ea = 24.18 kj/mol
• Fecal-Urine Mixture (Michaelis-Menten)– Ea = 51.88 kj/mol
Muck, Urease Activity in Bovine Feces 1982.Kumar and Wagner. Urease Activity and kinetics of Urea Transformations in Soils. 1984.
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Approaching the Henry Constant
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NH3 (g)
NH3 (aq)
NH4+ (aq)
Valve
Aqueous
Headspace
NH3 (g)
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13
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Approaching the Henry Constant
14
NH3 (g)
NH3 (aq)
NH4+ (aq)
Aqueous
Headspace
Valve
NH3 (g)
NH3 (g)
NH3 (aq)
NH4+ (aq)
Valve
NH3 (g)
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15
0.5 1 1.5 2 2.5 3 3.5 4-6
-5
-4
-3
-2
-1
0
0
10
20
30
40
50
60
70
80
90
100Preliminary Chamber Performance
log (NH3 Conc.)
-lo
g (
PN
H3)
Hen
ry C
on
stan
t (m
ol
L-1
atm
-1)
S. D. Hafner, J. J. Bisogni, W. J. Jewell, Measurement of Un-ionized Ammonia in Complex Mixtures. 2006.
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Summary• Estimating ammonia flux is sensitive to available
ammonium, the acid dissociation constant, and the Henry constant
• Ammonia production is fast with half lives as short as 28 min at 25 ⁰C
• This approach shows promise in measuring the Henry constant in complex mixtures
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Acknowledgments• Advisor: Dr. Thomas Borch• Dr. Jay Ham• Christina Williams• International Plant Nutrition Institute • Denver Metro Wastewater Reclamation District• Rocky Mountain Agri-Business Association• EPA • USDA
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Time Constant: 10.7 min18
13:1
2
13:2
6
13:4
0
13:5
5
14:0
9
14:2
4
14:3
8
14:5
2
15:0
70
50
100
150
200
250
300
350
400CO2 Seal Testing
Time of Day
Co
nce
ntr
atio
n C
O2
(pp
bv)
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Michaels-Menten
19
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Areas of Concern: Ionic Strength
Montes 20
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21
Evacuate headspace with multiple flushes to ensure >95% of ammonia(g) is trapped
Push known volume through PTFE membrane tubing to calculate ammonia(aq) activity