AWMA 28 th Annual Conference & Exhibition 2005_ Li et al.
Hong Li , Graduate Research Assistant
Hongwei Xin , Professor,
Yi Liang , Postdoctoral Research Associate
Dept. of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011
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-days period. The ammonia emission was 2.2 g/kg and 3.6 g/kg, relatively, for α=1.2 and α=2.3 during the 40-day storage period. The data revealed no influence of air change rates of 10 and 20 ACH was shown on the ammonia emission rate.
Keywords: laying hen, belt house, manure storage, ammonia emission, effects
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 were: a) evaluate the effect of two manure stack
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al. surface area to volume ratios (α) on ammonia emission; and b) evaluate the effect of two air exchange rates on ammonia emission of laying hen manure stacks.
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 trunk, from the farm to our emission measurement laboratory. Manure was scraped and removed out of the house daily. Four environmentally controlled chambers were used to store the manure with the specified α and air change rate (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. An air handler unit (850 m
3
/hr)) was used to supply fresh air to each chamber. The air flow of each chamber was adjusted by an inlet baffle.
The plenum of each chamber had two electric heaters used to heat the incoming air to achieve the desired air temperature near 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 was 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 (NH
3
) concentration, b) carbon dioxide (CO
2
) concentration, c) methane (CH
4
) concentration, e) dew-point temperature and f) N
2
O. In addition, the following environmental variables were continuously measured: 1) dry-bulb air temperature in the center of each chamber and 30 cm above e foot above the manure surface, 2) manure stack temperature measured by type
T thermocouples (0.2 o
C 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 monitoring, including moisture content, total manure weight per chamber at start, total N, ammoniacal nitrogen (NH
3
plus NH
4
+
) 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 corners and the center) spots.
After mixing all the samples, one composite sample was analyzed by a certified analytical lab.
NH
3 emission rate (ER
NH3
, g/hr-ton manure) was calculated as:
ER
NH
3

{[ NH
3
] e

[ NH
3
] i
}

10

6 
Q

N 0 .
17 g /
0224 m mol
3
/ mol

60 min hr where
[NH
3
] e
, [NH
3
] i
= ammonia level at exhaust and inlet air, respectively, ppm
Q = ventilation rate, m
3
/min-chamber at STP
N = amount fresh manure placed in the chamber, ton
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 m
3 and a surface area to volume ratio of 2.3,
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al. whereas the 81 cm stacks had a manure volume of 2.26 m
3 and a surface area to volume ratio of 1.23. One chamber of each manure height was ventilated at 10 air changes per hour
(ACH) (35 m 3 /hr), whereas the other companion chamber of manure height was ventilated at 20 ACH (70 m
3
/hr) (table 1). The experimental regimens were designed 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 25 o C with a concomitant dew-point temperature of 10-24 o
C. 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.
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 was present as ammoniacal nitrogen, and pH was 7.63, while 15% was present as ammoniacal nitrogen and pH was 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 stack. With distinct boundary, much wetter manure was under the cover. 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 the40-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 those in the subsurface. However, total ammoniacal nitrogen (as-is base) in the surface was found lower than that in the sub-surface. In each replicate, no significant differences on the properties of manure (P>0.05) 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 gap 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.
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 was about twice as high as that of stacks with 20
ACH.
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 was expected as ventilation rate for each chamber was held eventually constant. The
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al. exponential decrease in the loss of nitrogen from fresh poultry manure was found
(Kirchman and Witter, 1989). The manure in the experiment had a low C:N ratio, and thus limited source of available energy for microbial growth. Therefore, ammonia emission was unlikely to sustain at a high rate. Ammonia ER on per chamber basis did not show significant differences among the four regimens for the experiment period (P > 0.05).
However, on per 1,000 kg manure basis, i.e. g NH
3
/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 were 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) and surface/volume ratio (P=0.25) when using the unit of kg NH
3
/chamber. However, the effect of surface/volume ratio was significant (P=0.008) when the unit of kg/1000 kg or g/kg manure was used. For the stacks with 43 cm depth, 40-day ammonia emission was 3.6 g/kg while the N loss as ammonia was about 16% of the total N in 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 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 quite complicated. If the manure stack surface had a constant ammonia concentration, the ammonia emission rate would increase with the increase of
ACH associated with lower partial ammonia pressure. Otherwise, ammonia emission rate could decrease when the ammonia concentration in the manure stack surface was decreased with lower diffusion rate and ability of ammonia in the manure even if the ACH increased.
Therefore, the influence of ACH on the ammonia emission from the manure depended on the variation of surface ammonia concentration in the manure. In the long run, the influence of ACH could counteract itself. Figure 3 shows that the ammonia ER with 10
ACH was similar or larger during the first 28-day period and after then lower than that with
20 ACH. The effect of ACH could be negligible in the conditions of this study during the
40-day of ventilated storage.
The data produced from the study have quantified 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 while 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 and 9.9% of the total nitrogen was emitted as ammonia. The data revealed no influence of air change rates of 10 and 20 ACH was shown on the ammonia emission rate.
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.
2.
H. Kirchman and E. Witter, 1989. Ammonia volatilization during aerobic and aneaerobic manure decomposition. Plant and Soil. 115:35-41
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al.
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 28 th Annual Conference & Exhibition 2005_ Li et al.
Table 1. Experimental regimens to be examined and emission chamber assignment
Condition
Manure Stack Height, cm
Manure Volume, m 3
Surface to Volume Ratio
Air Changes per Hour
Air Temperature, o C
H43AC10 H81AC10 H81AC20 H43AC20
43
1.20
81
2.26
81
2.26
43
1.20
2.3
10
25
1.23
10
25
1.23
20
25
2.3
20
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)
Dry matter
Total Nitrogen
Ammoniacal Nitrogen pH
Rep. 1
26.7%
1.80%
1.03%
7.63
Rep. 2
31%
1.89%
0.28%
8.01
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al.
Table 3. Surface manure composition after the Experiment
Surface
Dry matter
Total N, g/kg (as-is)
Total N, g/kg (dry base)
Total Ammoniacal N, g/kg
(as-is)
Total Ammoniacal N, g/kg
(dry base) pH
Rep. 1 Rep. 2
H43AC10 H43AC20 H81AC10 H81AC20 H43AC10 H43AC20 H81AC10 H81AC20
47.7%
17.1
35.8
6.7
14.0
8.00
45.1%
17.1
37.9
7.3
16.2
7.96
45.0%
17.0
37.8
7.8
17.3
7.91
41.1%
17.8
43.3
7.9
19.2
7.93
53.0%
19.3
36.4
5.1
9.6
8.29
57.5%
17.6
30.6
4.8
8.3
8.10
50.4%
14.2
28.2
4.8
9.5
8.25
64.9%
16.1
24.8
5.4
8.3
8.11
Sub-surface
Dry matter
Total N, g/kg
Total N, g/kg (dry base)
Total Ammoniacal N, g/kg
(as-is)
Total Ammoniacal N, g/kg
(dry base) pH
24.0%
18.3
76.3
14.0
58.3
7.69
22.9%
19.0
83.0
14.1
61.6
7.76
21.8%
18.6
85.3
14
64.2
7.81
22.0%
18.7
85.0
14.4
65.5
7.72
23.6%
15.9
67.4
11.9
50.4
7.88
24.6%
16.8
68.3
13.3
54.1
7.63
23.2%
14.3
61.6
10.8
46.6
7.75
23.0%
13.5
58.7
12.4
53.9
7.83
Table 4. Nitrogen emitted as ammonia after 40 day of ventilated storage
Regimens
H43AC10
H43AC20
H81AC10
H81AC20
NH
3
Emission, g/kg
Rep 1 Rep 2 Average
N emitted as NH
Rep 1 Rep 2
3
, kg
Average Rep 1
% N loss as NH
3
Rep 2 Average
3.82
3.05
2.05
2.27
3.60
3.92
2.28
2.27
3.71
3.49
2.17
2.27
3.74
2.98
3.54
3.93
3.49
3.79
3.89
3.87
3.62
3.39
3.72
3.90
17.5%
13.9%
9.4%
10.4%
15.7%
17.1%
9.9%
9.9%
16.6%
15.5%
9.7%
10.2%
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al.
Figure 1. Schematic representation of emission measurement chambers and instrumentation
450
400
350
300
250
200
150
100
H81AC20
H81AC10
H43AC10
7
6
5
4
9
8
50
H43AC20
0
0 5 10 15 20 25 30 35 40
Time of Storage, day
Figure 2. Ammonia concentration profiles of layer manure stack during 40-day ventilated storage.
10 14
H43AC10
H43AC20
12
10
8
6
H43AC20
H81AC10
H81AC20
3
4
2
2
1 H43AC10
H81AC10 H81AC20
0 0
0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35
Time of Storage, day Time of Storage, day
Figure 3. Specific ammonia emission rates of laying hen manure stacks during 40-day ventilated
40 storage
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AWMA 28 th Annual Conference & Exhibition 2005_ Li et al.
5000
4000
3000
2000
1000
H43AC20
H43AC10
H81AC10
H81AC20
5000
4000
3000
2000
1000
H81AC10
H43AC20
H81AC20
H43AC10
0 0
0 5 10 15 20 25
Time of storage, day
30 35 40 0 5 10 15 20 25 30 35 40
Time of storage, day
Figure 4. Cumulative ammonia emission of laying hen manure stacks during 40-day ventilated storage
9