Estimate Ammonia (NH3) Emissions from Manure-Belt Layer Houses: An Effective Modeling Tool

AEX-723.5
Agriculture and Natural Resources
Date: 
08/11/2014
Lingying Zhao, Associate Professor and State Extension Specialist
Shunli Wang, Former Graduate Research Associate
Harold Keener, Professor Emeritus, Department of Food, Agricultural and Biological Engineering, Ohio State University Extension

Animal feeding operations inevitably have issues with ammonia (NH3) emissions due to inefficient conversion of nitrogen in feed. Agricultural animal production has been traditionally exempt from federal and state air quality regulations. However, increased public concerns on impacts of air emissions from animal feeding operations on health and environmental quality are leading the USEPA to establish air emission monitoring and estimation methods for farms. Currently in the U.S., animal producers are required to report ammonia emissions from a farm exceeding 100 pounds of ammonia in any 24-hour period under the Emergency Planning and Community Right-to-Know Act (EPCRA) of the Clean Air Act (CAA).

Most animal producers do not know how much ammonia is emitted from their farms and do not have effective tools to estimate ammonia for better nitrogen nutrient management and meeting the EPCRA reporting requirement. The USEPA requires animal feeding operations to comply with air quality laws, but has also found it was difficult to determine if an animal feeding operation is in violation and the extent of the violation. Currently, the most accurate measurement method for ammonia emissions from animal facilities is considered to be continuous monitoring of ventilation airflow rates and ammonia concentrations of the animal facilities using ammonia gas analyzers and fan operation sensors (Ni and Heber, 2001). However, this research method is difficult for farmers to use for evaluation and management of ammonia emissions from their facilities because it is costly, very complicated and time-consuming. An accurate, cost effective and simple method is needed to help farmers evaluate and manage ammonia emissions from their specific operations. This fact sheet introduces an effective tool developed by the Ohio Agricultural Research and Development Center (OARDC) researchers for layer producers or their consultants to estimate ammonia emissions from poultry layer houses.

An Alternative Nitrogen Mass-Balance Analysis of Animal Production

Previous researchers used nitrogen-balance method to estimate nitrogen loss from commercial layer houses. However, traditional nitrogen-balance analysis requires accurate measurement of feed consumption, animal production and manure generation rates. Commercial egg farm operations do not closely track manure production due to its relative low values in comparison with feed and eggs. An alternative mass-balance method has been developed by researchers of The Ohio State University (Keener et al., 2002; Keener and Zhao, 2008; and Wang et al., 2014) to effectively estimate NH3 emissions from poultry layer facilities without the need to closely track manure production.

For a nutrient-mass balance, the input nutrient flow of an animal production system should be equal to the output nutrient flow. In a poultry egg production system, the inputs include air, water, feed and hens entering the production system. The outputs include air, eggs, manure, mortalities, possible leachate and gas emissions leaving the facility (Figure 1) (Keener and Zhao, 2008). Some of the nitrogen does not need to be measured. Nitrogen in the air entering and leaving the system does not participate in the nitrogen conversion process, and nitrogen in drinking water is negligible. Change of laying hen body weight over a short production period is negligible. Mortality is very low as well in a short period (about 20 mortalities per day in a layer house with 0.15–0.2 million chickens). Leachate is not a problem at manure-belt (MB) layer houses with a concrete floor.

Nitrogen gas emissions from a poultry house are primarily in the form of ammonia emissions. According to the above assumptions, the relevant nutrient input, storage and output factors of an egg production system for the alternative mass-balance analysis is shown in Figure 1.


Figure 1. An egg production system with nutrient inputs, storage and outputs.


To estimate ammonia emissions, you need to know:

  • Nitrogen content of the feed (from feed formula)
  • Nitrogen content of the egg
  • Nitrogen content of the manure
  • Ash content of the feed (from feed formula)
  • Ash content of the manure
  • Ash content of the egg
  • Feed consumption rate
  • Egg production rate
Equation 1:
N emission=Feed N–Egg N–Manure N/ash ratio*[Feed ash–Egg ash]
Feed N=Nitrogen content of feed (%)*feed consumption rate/100 
(grams/hen/day)
Egg N=Nitrogen content of egg (%)*egg production rate/100 
(grams/hen/day)
N/Ash ratio of manure=Nitrogen content of manure (%)/Ash content of manure (%)
Feed ash=Ash content of feed (%)*feed consumption rate/100
(grams/hen/day)
Egg ash in egg=Ash content of egg (%)*egg production rate/100
(grams/hen/day)

The alternative mass-balance method avoids direct monitoring of manure flow rates by introducing the use of the system's ash balance for estimating ammonia emission with parameters that are easier to measure or obtain. This method determines the total nitrogen loss in the whole production process. Since nitrogen loss from nitrogenous gases other than ammonia is very limited, the ammonia emissions can be estimated as the total nitrogen (N) emissions (Coufal et al., 2005).

Practical Application Procedures of the Method: A Case Study

A typical manure-belt layer house was selected to test the method and demonstrate its specific procedures. The layer house has dimensions of 161.6 m in length, 15.9 m in width, and 7 m in height. It housed 154,500 Lohmann white hens in six rows and seven tiers of cages with hen ages ranged between 20 to 75 weeks and an average weight of 1.25 kg during the sampling period. Drinking nipples supplied water and feed chains, and troughs provided feed to the hens. Eggs produced in the cages rolled onto the egg collection belts from bottoms of the cages. The mechanical cross ventilation system with fifty 1.22-m (48-inch) fans on two side walls of the buildings were automatically controlled according to the temperature settings of the layer house. Manure was removed by manure belts under the cages to a manure storage/semi-composting building near the layer house. In this layer house, the manure belt was operated for nine minutes each day, and one-fifth of total manure on the belt was removed daily.

Sampling Methods, Procedures and Sample Size

Sampling should occur on the days that manure is removed. Samples were taken from each belt as the manure fell onto the main conveyor belt moving out of the house. For each row, six subsamples were collected with a 250 mL polyethylene sampler at a 1.5-minute interval. The sampling time interval was determined by the total moving manure belt length and the belt moving speed to make sure that six manure subsamples were collected evenly on the belt. Subsamples of each row were mixed to form one sample. Three manure samples, three eggs samples in which each egg sample contained four eggs, were picked randomly in the house on each sampling day, and three feed samples were taken from the feed bin supplying this house directly.

Lab Analysis of Feed, Eggs and Manure Samples

Composite feed, egg and manures samples can be shipped in ice coolers to a nutrient and composition analysis lab for analysis, such as the OARDC Service Testing and Research (STAR) Lab (oardc.osu.edu/starlab/t08_pageview3/Home.htm). Ash, total nitrogen and total solid values of the samples need to be analyzed for the calculations.

Estimation of NH3-N Emission Using the Alternative Mass-Balance Model

To make the calculations easier, a table, like Table 1, can be used to estimate the ammonia emissions. The estimated NH3-N emissions were calculated based on Equation 1 using the nitrogen and ash content values for each sampling event.

Sampling feed in a layer house can be a challenge due to possible nonuniformity of the feed mixture and layer hen selection of feed. The sample feed compositions resulted in an average of ammonia emission rate of 0.505 g NH3-N hen-1d-1, which was significantly higher than 0.284 g NH3-N hen-1d-1 calculated from producer feed formula. The estimated NH3-N emissions using the producer feed formula is very close to a measured average NH3-N emission of 0.237 g NH3-N hen-1d-1 from the same house through a previous study (Sun et al., 2005). This suggests that using producer formula as feed nitrogen and ash contents inputs for the alternative mass-balance analysis is not only simpler and economical, but also relatively accurate.

Estimation of an Ammonia Emission Factor for This MB Layer House

The above method can be used to directly estimate average NH3-N emission over any specific manure removal interval of a layer farm operation. Since the NH3-N emission rates did not demonstrate a significant seasonal difference, replication of the sampling and modeling events can result in a reliable estimate of the NH3-N emission factors (mean NH3-N emission with a unit of g hen-1d-1) for a poultry house. The minimum replication number of the sampling and modeling events was estimated to be 21–24 for estimation of a NH3-N emission factor of this manure-belt layer house using the alternative-mass balance model. A spread of sampling events over four seasons of a year is recommended to cover any possible variations in NH3 emission over a long time period.

Summary

An effective and practical tool for estimating ammonia (NH3) nitrogen emission from animal feeding operations is needed to enable the animal producers to report ammonia emission required by the Emergency Planning and Community Right-to-Know Act (EPCRA) of the Clean Air Act (CAA). The tool is also needed by producers to evaluate and adopt various nitrogen conservation management practices or technologies. This fact sheet introduces an innovative mass-balance modeling tool for estimation of ammonia emission from manure-belt poultry houses.

The alternative mass-balance method can be used to estimate ammonia emission factors from manure-belt poultry layer houses. Three composite manure samples from three manure belts can be sampled during a manure removal event. Nitrogen and ash contents of feed can be obtained directly from producer formula or feed samples from feed bins. The nitrogen and ash content of eggs can be sampled as little as once or twice due to the low variance in N and ash values. Then with the egg production and feed consumption rate data, an average ammonia emission rate over the manure storage period of a manure-belt layer house can be estimated using the alternative mass-balance model.

The annual average NH3-N emission factor for the MB poultry layer house was estimated using this method as 0.284+/-0.129 g NH3-N hen-1d-1 and measured as 0.237+/-0.211 g NH3-N hen-1d-1. The model overestimated the NH3 emission factor because it estimates total nitrogen emission, an upper limit of NH3-N emission. The relative difference between the estimated and measured ammonia emission factor is about 18%. A minimum of 21–24 sampling and analysis events are suggested to obtain a statistically reliable ammonia (NH3) emission factor for the MB layer houses with a maximum of 15% error.

This alternative ammonia (NH3) estimation method is relatively simple, inexpensive and accurate. It can be used to effectively estimate ammonia (NH3) emission factors of manure belt layer houses. 

 

Table 1. List of nitrogen and ash contents and the estimated NH3-N emissions from the manure belt layer house (Wang et al., 2014).

Month

Hen age

Feed sampled

Feed formula

Eggs

Manure N/Ash

Mass flow
(g hen-1d-1)

NH3-N emissions
(g hen-1d-1)

(week)

N (%)

Ash (%)

N (%)

Ash (%)

N (%)

Ash (%)

 

Feed

Eggs

Estimate (feed sample)

Estimate (feed formula)

Apr.

24

2.94

10.25

3.47

15.77

5.87

33.10

0.19

77.18

8.22

0.819

0.431

24

3.76

16.56

3.47

15.77

5.76

33.96

0.20

77.91

9.40

0.453

0.354

24

3.77

15.14

3.47

15.77

6.14

33.12

0.18

79.05

8.60

0.816

0.490

Aug.

40

3.45

16.33

2.87

14.57

5.77

33.24

0.19

90.49

15.17

0.432

0.209

40

3.24

16.22

2.87

14.57

5.74

33.73

0.17

90.84

15.14

0.423

0.347

42

3.09

14.77

2.83

14.58

5.61

32.26

0.18

91.11

15.29

0.438

0.237

Sep.

47

3.31

16.25

2.76

14.74

5.60

33.63

0.17

90.95

13.52

0.491

0.229

Oct.

51

2.99

15.93

2.73

14.81

5.78

33.29

0.18

91.21

15.17

0.174

0.116

Dec.

59

3.16

15.61

2.67

15.07

5.78

33.29

0.16

91.41

15.17

0.505

0.138

Avg.

 

3.30

15.23

3.02

15.07

5.79

33.29

0.18

86.68

12.85

0.505

0.284

Acknowledgments

The fact sheet has been reviewed by Karen Mancl, Professor, and Larry Brown, Professor, Food, Agricultural and Biological Engineering, The Ohio State University. This method was developed with financial support by the Research Enhancement Competitive Grants Program of the Ohio Agricultural Research and Development Center.

References

  • Coufal, C.D., C. Chavez, P.R. Niemeyer, and J.B. Carey. 2005. "Nitrogen Emissions From Broilers Measured by Mass Balance Over Eighteen Consecutive Flocks." Poultry Science 85: 384–391.
  • Keener, H.M., D.L. Elwell, and D. Grande. 2002. "NH3 Emissions and N-Balances for a 1.6 Million Caged Layer Facility: Manure Belt/Composting vs. Deep Pit Operation." Transactions of ASABE 45(6): 1977–1984.
  • Keener, H.M. and L. Zhao. 2008. "A Modified Mass Balance Method for Predicting NH3 Emissions From Manure N for Livestock and Storage Facilities." Biosystems Engineering 99: 81–87.
  • Ni, J. and A.J. Heber. 2001. "Sampling and Measurement of Ammonia Concentration at Animal Facilities: A Review." ASABE meeting paper No. 014090. St. Joseph, MI: ASABE.
  • Sun, H., L.Y. Zhao, T.T. Lim, J.Q. Ni, P.C. Tao, A.J. Heber, C.A. Diehl, and S. Hanni. 2005. "Ammonia Emissions From a Belt-Battery Layer House." ASABE meeting paper No. 054166. St. Joseph, MI: ASABE.
  • Wang, S., L.Y. Zhao, X. Wang, R. Manuzon, M. Darr, H. Li, and H.M. Keener. 2014. "Estimation of Ammonia Emission From Manure Belt Poultry Layer Houses Using an Alternative Mass-Balance Method." Transactions of the ASABE 57(3): 937–947.
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