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Proceedings available at: www.extension.org/67708 Ammonia emissions from cattle feedlots have been a topic for much debate regarding air quality and environmental impacts. With increasing concern about future regulation of the industry, understanding the fundamentals of ammonia emission and volatilization from feedlots has become crucial. Wu et al. 2003 described ammonia flux as demonstrating a strong environmental dependency on the ammonium concentration, pH, and the product of the acid dissociation and Henry constant. The objectives of this research are to address the production of ammonia via urea hydrolysis and quantify its release from the soil surface based on the Henry constant. This will be accomplished by studying the rate of urea hydrolysis in feedlots systems, as well as by looking at a new approach to measuring the Henry constant. Urea hydrolysis results will be discussed from a variety of feedlot soils at a fixed water content and urea concentration. Measuring the Henry constant includes measuring the gas phase ammonia above the solution and the ammonia present in the solution. The Henry constant values should provide insight as to how feedlot soil matrices deviate from less complex systems. The results of this work will allow for a better understanding of the fate of ammonia in feedlot systems from production to emission.
Citation preview
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
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
Back to the Basics
A. N. Hristov et al., Review: Ammonia emissions from dairy farms and beef feedlots. 2011. 3
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.
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.
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.
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.
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
8
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
9
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
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.
11
Approaching the Henry Constant
12
NH3 (g)
NH3 (aq)
NH4+ (aq)
Valve
Aqueous
Headspace
NH3 (g)
13
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)
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.
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
16
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
17
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)
Michaels-Menten
19
Areas of Concern: Ionic Strength
Montes 20
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
