AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
Effects of Stack Surface to Volume Ratio and Air Exchange
Rate on Ammonia Emission of Laying Hen Manure Storage
Hong Li, Graduate Research Assistant
Hongwei Xin, Professor
Yi Liang, Post-doctoral Research Associate
Dept. of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011
Abstract: Frequent removal of manure out of the laying hen houses greatly improves indoor air
quality and reduces air emissions. Low ammonia emission is critical for meeting foreseeable
regulatory limits of emissions from animal feeding operations. While manure removal, via manure
belt system, is effective in achieving excellent indoor air quality, the challenge remains to control
emissions from manure storage. Many factors affect ammonia volatilization of poultry manure
storage, such as moisture content, pH, and temperature, all of which contribute to the microbial
activities inside the manure stack. The effects of two manure stack surface area to volume ratio (α)
(1.2 or 2.3) and two air exchange rates (10 or 20 ACH) on ammonia emission of laying hen manure
stacks were evaluated during a 40-day ventilated storage period. The ammonia emission was 2.2
g/kg of manure and 3.6 g/kg o manure, relatively, for α=1.2 and α=2.3 during the 40-day storage
period. The air change rates (10 and 20 ACH) showed no significant on the ammonia emission
during the 40-days of ventilated storage.
Keywords: laying hen, belt house, manure storage, ammonia emission
Introduction
Air quality associated with animal feeding operations (AFOs) remains a pressing issue for
both animal industry and academic communities. Research and regulatory agencies have
shown increased interest in ammonia as a potential air pollutant. A significant local source
of atmospheric ammonia is waste from large concentrations of domestic animals. Low
ammonia emission is critical for meeting foreseeable regulatory limits of emissions from
animal feeding operations. Commercial laying hen operation is one such enterprise, a prime
example of high density animal production. Frequent removal of laying hen manure out of
the houses, via manure belt, greatly improves indoor air quality (i.e., low ammonia and
dust levels) and reduces air emissions (Liang et al., 2004). Consequently using belt system
is expected to increase for future layer housing in the United States. While belt system is
effective in achieving excellent indoor air quality and thus meeting animal welfare
guidelines, the challenge remains to control emissions from manure storage. However, this
challenge is less complicated to tackle as chemically or physically treating or managing
manure without birds around may be more readily implemented. Although a number of
laboratory studies have examined ammonia losses from animal manures, losses may differ
greatly in practical situations where large volumes of manure are stored. Information on the
rate of loss of ammonia from stored laying hen manure is required to enable decision
making on the types of housing and manure storage systems that should be used in the
future commercial egg production systems. Many factors affect ammonia volatilization of
poultry manure storage, such as moisture content, pH, and temperature, all of which
contribute to the microbial activities inside the manure pile (Groot Koerkamp, 1994; Pratt
et al., 2002). Two management practices that may prove useful in controlling ammonia
emission are a) the available surface for emission of a manure pile; and b) pressure gradient
in ammonia between the manure pile and the boundary air. The objectives of this study
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
were: a) evaluate the effect of two manure stack surface area to volume ratios (α) on
ammonia emission; and b) evaluate the effect of two air exchange rates (β) on ammonia
emission of laying hen manure stacks.
Materials and Methods
Experimental Setup
Hen manure used in this study was acquired from a commercial layer farm that used
manure belt system with daily manure removal. The laying hens (100,000 per house) were
fed standard ration and watered though nipple drinkers. On the starting day of each trial,
manure removed from a layer house of similar bird age was transported using a manure
truck, from the farm to our emission measurement laboratory.. Four environmentally
controlled chambers were used to store the manure with the specified α and β (fig 1). Each
chamber had the dimension of 1.5 m wide × 1.8 m deep × 2.4 m high and operated as a
positive pressure system. A plastic film liner was used in each chamber to prevent the
moisture penetration loss from the manure stack to the floor pit. An air handler unit (850
m3/hr)) was used to supply fresh air to each chamber. The airflow of each chamber was
adjusted by an inlet baffle. The plenum of each chamber had two electric heaters to heat the
incoming air to achieve the desired air temperature near the manure level. Incoming and
exhaust air was sampled sequentially at 20 min intervals with the first 15 minutes for
stabilization and the remaining 5 minutes for measurement. Therefore, each measurement
cycle took 100 min. A multi-gas monitor (INNOVA 1312, Innova AirTech Instruments
A/S, Denmark) was used to measure the concentration of the following gases of the
sampling air: a) ammonia (NH3) concentration, b) carbon dioxide (CO2), c) methane (CH4)
c, e) N2O and f) dew-point temperature. In addition, the following environmental variables
were continuously measured: 1) dry-bulb air temperature in the center of each chamber and
30 cm above the manure surface, 2) manure stack temperature measured with type T
thermocouples (0.2 oC resolution), and 3) airflow rate through each chamber with
thermoelectric air mass flow meters placed in the supply air stream (fig.1). Moreover,
nutrient and physical properties of the manure were analyzed at the beginning and the end
of the trial, including moisture content, total manure weight per chamber at start, total N,
ammoniacal nitrogen (NH3 plus NH4+) and pH. Intermediate sampling of the manure
nutrients was not performed to avoid disturbing the manure stacks. Manure samples were
taken from each stack at five locations (four quadrants and the center) spots. After mixing
all the samples, one composite sample was delivered by a certified analytical lab.
NH3 emission rate (ERNH3, g/hr-ton manure) was calculated as:
Q
17 g / mol
min
ERNH 3  {[ NH 3 ]e  [ NH 3 ]i }  10 6  
 60
3
M 0.0224m / mol
hr
where
[NH3]e, [NH3]i = ammonia level at exhaust and inlet air, respectively, ppm
Q = ventilation rate, m3/min-chamber at STP
M = amount fresh manure placed in the chamber, metric ton
Experimental Regimens
Manure stacks were 43 cm high in two of the chambers and 81 cm high in the other two.
The 43 cm stacks had a manure volume of 1.20 m3 and a surface area to volume ratio (α)b
of 2.3, whereas the 81 cm stacks had a manure volume of 2.26 m3 and α of 1.23. One
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
chamber of each manure height was ventilated at 10 air changes per hour (ACH) (35 m3/hr),
whereas the other companion chamber of manure height was ventilated at 20 ACH (70
m3/hr) (table 1). The experimental regimens were designated as H43AC10, H43AC20,
H81AC10, and H81AC20. Each manure stack was randomly allocated to a chamber. All
chambers were maintained at the same air temperature of 25oC with a concomitant dewpoint temperature of 10-24oC. Emission from each chamber or regimen was measured
continuously for 40 days, and was replicated twice. The total weight of fresh manure for
replicate 1 and 2 was 6580 and 6490 kg, respectively. Four chambers were loaded
simultaneously to maximize homogeneity of manure among the chambers.
Results and Discussions
Properties of the Manure Stacks
Certain properties of the manure at the start of the trial period are shown in Table 2. The
dry matter (DM) contents of fresh manure in the two replicates were different probably due
to the difference in bird age and thus diet. In replicate 1, about 57% of the total nitrogen (N)
was present as ammoniacal N with a pH of 7.63, while 15% total N was present as
ammoniacal N with a pH of 8 in replicate 2.
At the end of monitoring, a relatively rigid and dry top layer of 5-8 cm in depth was found
for the manure stacks. This layer was quite distinctive from the remaining much wetter
stack. Therefore, manure samples from the surface layer and subsurface were taken and
analyzed separately. Table 3 shows the compositions of the manure at the end of the 40-day
ventilated storage. The DM content of stacks increased (41.1% to 64.9%) in the top layer
but decreased (21.2% to 24.6%) in the remaining bottom layer. Manure pH in the top layer
were higher than that in the sub-surface. However, total ammoniacal N (as-is base) in the
surface was lower than that in the sub-surface. No significant differences on the properties
of manure (P>0.1) were found among the four treatments after 40 days of ventilated
storage. Although only the nutrient and physical properties of the manure stacks at the
onset and end of the storage period were available, some inferences could be made. First,
the surface layer of the manure stack seemed the main contributor to the ammonia loss due
to larger air gaps and with lower mass transfer resistance. Second, anaerobic condition
presumably existed under the surface due to the high moisture content. Finally, manure
nutrients would be more easily retained in the subsurface.
Ammonia Concentration
The profiles of ammonia concentration during the 40-day trial period are shown in figure 2.
The ammonia concentration in the chambers rapidly reached maximum after about 2 days:
approximately 400 ppm for the stacks with 10 ACH and approximately 200 ppm for the
stacks with 20 ACH. Then, the ammonia concentration began to decrease exponentially.
The stacks with 10 ACH took longer to reach stabilized ammonia emission. Ammonia
concentration of stacks with 10 ACH remained about twice that of stacks with 20 ACH.
Ammonia Emission
Figure 3 depicts the dynamic profiles of ammonia ER during the 40-day trial. The ER
profiles of the four regimens followed similar patterns to those of the concentrations. This
result expected as ventilation rate for each chamber was held essentially constant. The
exponential decrease in the loss of nitrogen from fresh poultry manure has been reported by
Kirchman and Witte (1989). The manure in the experiment had a low C:N ratio (7), and
thus limited source of available energy for microbial growth. Therefore, ammonia
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
emission was unlikely to sustain at a high rate. Ammonia ER on per chamber basis did not
show significant differences among the four regimens during the 40-day of ventilated
storage period. However, on per 1,000 kg manure basis, i.e. g NH3/hr-1,000kg, manure
ammonia ER of the shallow stacks (43 cm) was higher during the first 5 weeks, then the
difference in ammonia ERs tended to decrease. In addition, cumulative ammonia
emissions from each chamber ranged from 3.62 kg to 4.77 kg (SD=0.38 kg), without
significant difference (P=0.52). The cumulative ammonia emissions are shown in figure 4.
There were no significant effects of air change rate (P=0.94) or surface/volume ratio
(P=0.25) when evaluated on the basis of kg NH3/chamber. However, the effect of
surface/volume ratio was highly significant (P=0.008) when based on the unit of kg/1000
kg or g/kg manure. For the stacks with 43 cm depth, 40-day ammonia emission was 3.6
g/kg and the N loss as ammonia was about 16% of the total N in the fresh manure. For 81
cm stacks, 40-day ammonia emission was 2.2 g/kg and 9.9% of the total nitrogen was
emitted as ammonia (Table 4). From the stand point of mass transfer theory, increasing
partial ammonia pressure in the boundary air by reducing air exchange rate would reduce
ammonia emission. The reason of no significant ACH effect could be somewhat
complicated. If the manure stack surface had a constant ammonia concentration, the
ammonia emission rate would increase with the increase of ACH due to lower partial
ammonia pressure. Otherwise, ammonia emission rate would decrease when the ammonia
concentration in the manure stack surface decreased from lower diffusion rate of ammonia
in the top layer even if the ACH is increased. Figure 3 shows that the ammonia ER under
10 ACH was similar to or larger than ER under 20 ACH during the first 28-day period and
became afterwards. On the 40th day of storage, the ammonia ER under 20 ACH and 10
ACH were 1.72 mg/hr-kg and 1.41 mg/hr-kg for the 83 cm stacks, respectively; and 2.52
mg/hr-kg and 1.81 mg/hr-kg for the 43 cm manure stacks, respectively. That implied that
the air change rate did influence the ammonia emission after four weeks of storage and the
ammonia emission reduced with the decrease of ventilation rate. However, in the 40-day
period, the effect of ACH on ammonia emission during the last 12-day period could be
weakened or counteracted due to the large weight of data from the first four weeks in
which no significant effect showed. Finally, the effect of ACH on ammonia emission were
not significant in the conditions of this study during the 40-day of ventilated storage.
Conclusions
The effects of two surface area to volume ratios α, (1.2 or 2.3), on the rate of ammonia emission
from large scales of stored laying hen manure from belt house. For the stacks with 43 cm depth
(α=1.2), the ammonia emission was 3.6 g/kg manure and the nitrogen loss as ammonia was
about 16% of the total nitrogen in fresh manure. For 81 cm stacks (α=2.3), the ammonia
emission was 2.2 g/kg manure and 9.9% of the total nitrogen was emitted as ammonia. Air
change rate (10 or 20 ACH) positively affected the ammonia emission rate after the first four
weeks of storage. However, air change rates of 10 or 20 ACH showed no effect on the cumulative
ammonia emission during the 40-day ventilated storage.
References
1. L.E. Carr, F.W. Wheaton and L.W. Douglass, 1990. Empirical models to determine ammonia
concentrations from broiler chicken litter, Transaction of the ASAE. 33(4): 1337-1342.
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
2. H. Kirchman and E. Witter, 1989. Ammonia volatilization during aerobic and aneaerobic
manure decomposition. Plant and Soil. 115:35-41
3. Groot Koerkamp, 1994; Review on emission of ammonia from housing systems for
laying hens in relation to sources, processes, building designs and manure handling, J.
agric. Engng Res. 59: 73-87.
4. Y. Liang, H. Xin, E.F. Wheeler, R.S. Gates, H. Li, J.S. Zajaczkowski, P. Topper, K.D. Casey,
B.R. Behrends, D.J. Burnham and F.J. Zajaczkowski , 2004. Ammonia Emissions from U.S.
Poultry Houses: Laying Hens, Transaction of the ASAE. in review.
5. E.V. Pratt, S.P. Rose and A.A Keeling, 2002. Effect of ambient temperature on losses
of volatile nitrogen compounds from stored laying hen manure, Bioresource
Technology, 84: 203-205.
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
Table 1. Experimental regimens examined and emission chamber assignment
Condition
H43AC10 H81AC10 H81AC20 H43AC20
Manure Stack Height, cm
43
81
81
43
Manure Volume, m3
1.20
2.26
2.26
1.20
Surface to Volume Ratio
2.3
1.23
1.23
2.3
Air Changes per Hour
10
10
20
20
Air Temperature, oC
25
25
25
25
* H43AC10: 43 cm height stack with 10 ACH
H43AC20: 43 cm height stack with 20 ACH
H81AC10: 81 cm height stack with 10 ACH
H81AC20: 81cm height stack with 20 ACH
Table 2. Fresh manure composition (as-is base)
Rep. 1
Rep. 2
Dry matter
26.7%
31%
Total Nitrogen
1.80%
1.89%
Ammoniacal Nitrogen
1.03%
0.28%
pH
7.63
8.01
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
Table 3. Manure composition at the end of the 40-day ventilated storage
H43AC10
Rep 1
Rep 2
Avg
Dry matter
47.7%
53.0%
50.4%
Total N, g/kg (as-is)
17.1
19.3
18.2
Total N, g/kg (dry base)
35.8
36.4
36.1
Total
Ammoniacal
N,
g/kg
Surface
6.7
5.1
5.9
(as-is)
Total Ammoniacal N, g/kg
14
9.6
11.8
(dry base)
pH
8
8.29
8.15
Dry matter
24.0%
23.6%
23.8%
Total N, g/kg
18.3
15.9
17.1
Total N, g/kg (dry base)
76.3
67.4
71.85
SubTotal Ammoniacal N, g/kg
14
11.9
12.95
surface
(as-is)
Total Ammoniacal N, g/kg
58.3
50.4
54.35
(dry base)
pH
7.69
7.88
7.79
Rep 1
45.1%
17.1
37.9
H43AC20
Rep 2
Avg
57.5%
51.3%
17.6
17.35
30.6
34.25
Rep 1
45.0%
17
37.8
H81AC10
Rep 2
Avg
50.4%
47.7%
14.2
15.6
28.2
33
Rep 1
41.1%
17.8
43.3
H81AC20
Rep 2
Avg
64.9% 53.0%
16.1
16.95
24.8
34.05
7.3
4.8
6.05
7.8
4.8
6.3
7.9
5.4
6.65
16.2
8.3
12.25
17.3
9.5
13.4
19.2
8.3
13.75
7.96
22.9%
19
83
8.1
24.6%
16.8
68.3
8.03
23.8%
17.9
75.65
7.91
21.8%
18.6
85.3
8.25
23.2%
14.3
61.6
8.08
22.5%
16.45
73.45
7.93
22.0%
18.7
85
8.11
23.0%
13.5
58.7
8.02
22.5%
16.1
71.85
14.1
13.3
13.7
14
10.8
12.4
14.4
12.4
13.4
61.6
54.1
57.85
64.2
46.6
55.4
65.5
53.9
59.7
7.76
7.63
7.70
7.81
7.75
7.78
7.72
7.83
7.78
Avg
2.17
3.72
0.097
Rep 1
2.27
3.93
0.104
H81AC20
Rep 2
2.27
3.87
0.099
Table 4. Nitrogen emitted as ammonia after 40 day of ventilated storage
H43AC10
H43AC20
Rep 1
Rep 2
Avg
Rep 1
Rep 2
NH3 Emission, g/kg
3.82
3.6
3.71
3.05
3.92
N emitted as NH3, kg
3.74
3.49
3.62
2.98
3.79
% N loss as NH3
0.175
0.157
0.166
0.139
0.171
Avg
3.49
3.39
0.155
Rep 1
2.05
3.54
0.094
H81AC10
Rep 2
2.28
3.89
0.099
Avg
2.27
3.9
0.102
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
Figure 1. Schematic representation of emission measurement chambers and instrumentation
450
NH3 Concentration, ppm
400
350
300
H81AC10
250
200
H81AC20
150
H43AC10
100
50
H43AC20
0
0
5
10
15
20
25
Time of Storage, day
30
35
40
Figure 2. Ammonia concentration profiles of layer manure stacks during 40-day ventilated storage
with different stack height (41 or 83 cm) and air exchange rate (10 or 2 ACH)
10
14
12
8
NH3 Emission rate, g/hr
NH3 Emission rate, g/hr-1000kg
9
10
7
6
H43AC10
5
H43AC20
4
3
H43AC20
8
H81AC10
H81AC20
6
4
2
2
1
H81AC10
H43AC10
H81AC20
0
0
0
5
10
15
20
25
Time of Storage, day
30
35
40
0
5
10
15
20
25
Time of Storage, day
30
35
40
Figure 3. Specific ammonia emission rates of laying hen manure stacks during 40-day ventilated
storage with different stack height (41 or 83 cm) and air exchange rate (10 or 2 ACH)
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AWMA 28th Annual Conference & Exhibition 2005_ Li et al.
Cumulative NH3 Emission, g/chamber
Cumulative NH3 Emission,g/1000kg
5000
4000
H43AC20
3000
H43AC10
2000
H81AC10
H81AC20
1000
5000
4000
H81AC10
H43AC20
H43AC10
3000
2000
H81AC20
1000
0
0
0
5
10
15
20
25
Time of storage, day
30
35
40
0
5
10
15
20
25
Time of storage, day
30
35
40
Figure 4. Cumulative ammonia emission of laying hen manure stacks during 40-day ventilated storage
with different stack height (41 or 83 cm) and air exchange rate (10 or 2 ACH)
9