ANALYSIS OF THE MAXIMUM POTENTIAL OF AMMONIA EMISSION, FROM LAYING HENS MANURE, THROUGH THE DYNAMICS OF SYSTEMS

FRANÇA, L.G.F.¹, GATES, R. S.², TINOCO, I. F. F.¹, SOUZA, C. F.¹

1 Federal University of Viçosa, Brazil;

2 University of Illinois at Urbana-Champaign, USA;

ABSTRACT: World egg production in 2015 was estimated at 71.5 million tons. The projections for 2030 correspond to a production of 86.8 million tons of eggs. Globally, this gain represents increased demand. In Brazil, this gain in production may be met using vertical cage systems for laying hens. These systems are composed of tiers of overlapping cages with manure belts beneath each tier. There can be tiers of cages, typically 6 to 12. In this housing model, a higher density of hens is obtained per unit barn floor area, which consequently leads to higher manure concentrations. The production and emission of ammonia (NH3) from laying hen manure depend on several factors, such as temperature, relative humidity of air, moisture content of manure, crude protein in the feed, efficiency of ration formulation, and others. This work aimed to create diagrams that interrelate physical, chemical and biological factors with the production and emission of NH3 from laying hens, as well as to use system dynamics to propose a maximum NH3 emission potential. A causal diagram was created relating the NH3 generation steps. These data were analyzed by the Vensim program, and it’s possible to determine a maximum emission potential for this gas, equal to 64.5% of the total nitrogen excreted by the hens.

Keywords: NH3, Manure, Vensim.

INTRODUCTION: Environmental factors, such as temperature and relative air humidity, and handling, such as crude protein levels and feed energy, may influence the rate of uric acid excretion of laying hens (Hsu et al., 1998). Mahmoud et al. (1996) reports that high temperature stress causes physiological changes in laying hens, damaging the acid-base balance and leading to reduced nutrient absorption.

It is observed the possibility of interacting through mathematical equations, the influence variables (temperature, moisture content and feed composition) and inferring the maximum amount of uric acid that can be excreted by laying hens. Based on these data, it would be possible to estimate the maximum potential of ammonia generation and emission into the atmosphere from the production of eggs.

In spite of all the efforts of the scientific community to establish protocols for measurement and quantification ammonia emissions from livestock farms, there aren’t still baseline parameters to compare the measured emissions, typically express in grams ammonia per unit time per bird. The proposition of an index of maximum ammonia emission potential, which varies according to the the environmental and handling characteristics is necessary to provide a benchmark for comparing emission levels. With this benchmark potential emission level, it is possible to evaluate the magnitude of what is being emitted by installation. The knowledge of how each process stage of animal production influences the maximum potential of ammonia generation and emission makes it possible to make changes in the

Modelling

management animals, and can suggest means of providing reductions in ammonia emissions into the atmosphere.

An appropriate tool for this sort of analysis is System Dynamics (DS), which can be defined as a language where it’s possible to more accurately express existing chains of events in nature (Villela, 2007). By using diagrams (causal or flow and inventory) it is possible to graphically describe and perform the equation of a productive system, thus allowing a clear analysis of its dynamic complexity (over time), and the interrelationships between each stage.

From the early 1980s onwards, numerous applications of DS have emerged in agroecological systems. Trenbath (1989) proposed a simple four-variable model where it was possible to verify the interaction between trees and soil and to accurately calculate the need for fallow.

When Van Noordwijk (2001) made changes to the original model, it was possible to determine maximum productivity values while keeping the system sustainable. Van Noordwijk et al. (2001) proposed a more specific simulation, in which forest felling was considered and the effect of burning of the forest remains on the minerals present in the soil. It was observed that for certain nutrients, such as nitrogen, there was loss, but for others there was an increase in its availability in the system, as was the case of phosphorus.

From the above, it can be seen that DS can be an important tool in the analysis and equation of the interrelations of the process of excretion of uric acid by laying hens. This analysis was performed when the environmental and management parameters were changed, to which the animals are submitted.

1. MATERIAL AND METHODS:System Dynamics (System Dynamics) is above all, a language allowing to express, more properly, existing chains of events in nature. Through the use of diagrams a graphical system system representation is constructed.

VenSim® is a computer program that was used to generate the desired diagrams. The database that will feed the Vensim consisted of a literature review of pre-existing studies, which are summarized below.

HSU et al. (1998) realized that there is a significant influence of nitrogen excretion rate (in the form of uric acid) in laying hens compared to the ambient temperature. According to Vogels and Drift (1976), the increase of the ambient temperature allows higher values for the decomposition rates of uric acid, causing greater potential of generation and emission of NH , with a strong increase between 20 and 30 °C, which can be observed in Figure 3.

Figure 3: Temperature effect on the

degradation of uric acid Figure 4: pH effect on the degradation of uric acid

Figure 5: Moisture content effect on the degradation of uric acid

The effect of variation of the moisture content of laying hens on uric acid degradation can be seen in the graph presented in Figure 3 presented by Groot Koerkamp (1994).

These were some of the main influence factors, on the degradation of the acid, used to feed the model generated by Vensim.

2. RESULTS AND DISCUSSION: The data gathered from literature reviews were entered in the causal diagram constructed in Vensim. Then we generate a new diagram, termed a ‘flow-stock’, as depicted in Figure 4.

Figure 6: Diagram generated by VenSim

Modelling

Maximum values were used to potentiate ammonia generation in the diagram generated by VenSim. These values were taken from the literature, as in previous studies (influence of temperature on uric acid degradation, moisture content of waste, pH, among others). The objective was to create the worst possible situation where the maximum amount of nitrogen Total, found in the manure, was converted to ammonia.

The simulation predicted that the maximum percentage of 64% of total nitrogen found in the manure has the potential to be converted to ammonia. Recalling that this condition is hypothetical and provides the maximum potential emission (according to the literature review and presented previously).

The percentage of 64% of the total nitrogen present in the conversion of laying hens in ammonia waste was obtained by the analysis conducted by Vensim to the parameters in the interrelations provided to the program.

3. CONCLUSION: The system dynamics is presented as a tool to combine the factors affecting the generation and emission of ammonia from the manure of laying hens and to predict the maximum quantity of ammonia that can be generated for a set of conditions.. Additional studies to adjust the displayed flow model and inventories are being conducted. By using this tool, we can predict how much will be the maximum emission of ammonia using the local environmental and management conditions, and to assess potential emissions reduction strategies.

Acknowledgements: To Federal University of Viçosa (UFV), Department of Agricultural Engineering (DEA), AmbiAgro, FAPEMIG, CAPES and CNPq.

REFERENCES:

Bellinger R.G.; Horton, P.M.; Gorsuch, C.S. Reduce pesticide drift. Clemson, SC: Clemson University. PIP-35, 1996.

Gay, S. W.; Knowlton, K. F. Ammonia emissions and animal agriculture. Virginia Cooperative Extension, p. 442-110, 2005.

Hsu, J.-C.; Lin, C.-Y.; Wen-Shyg Chiou, P. Effects of ambient temperature and methionine supplementation of a low protein diet on the performance of laying hens. Animal Feed Science and Technology, v. 74, n. 4, p. 289-299, 1998.

Groot Koerkamp, P.W. Review on emissions of ammonia from housing systems for laying hens in relation to sources, processes, building design and manure handling. Journal of Agricultural Engineering Research, v. 59, n. 2, p. 73-87, 1994.

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