Mechanisms for the Production and Amelioration of Ammonia (NH3) from Cattle Manure Using in vitro Methods

Abstract

<p>Ammonia (NH₃) is a nitrogenous environmental pollutant that is associated with eutrophication and contamination of terrestrial ecosystems and can have detrimental impacts on human and livestock health. Livestock production is a significant contributor to global NH₃ emissions largely as a result of nitrogen losses from the breakdown of manure. Intensively housed livestock situations, such as exporting live animals, lead to increased concentration of manure and development of the manure pad through accumulation of faeces and urine. This increase in higher concentrations of NH₃ may also lead to health and welfare concerns of both humans and animals. Due to the complex interactions of factors contributing to the volatilsation of NH₃ from manure, NH₃ production in livestock operations is difficult to accurately predict with the various methods and modelling approaches currently utilised. Live export is an example of an intensively housed livestock industry where NH₃ production has the potential to impact health and welfare of humans and animals on board. Quantification of NH₃ using current methods is difficult in this industry due to highly variable conditions and limited understanding of how voyage conditions may affect NH₃ production. Methods to quantify NH₃ emissions from manure have some limitations in adoption and understanding of manure pad variables introduced directly by animals, such as disturbance. Use of <i>in vitro</i> methods rather than large scale animal experiments allows understanding of ammonia and testing of dose rates of ameliorates and also aligns with the animal ethics replace, reduce and refine.</p> <p>The primary objectives of the current thesis were to develop an inexpensive, high throughput method of quantifying NH₃ in solution, and an <i>in vitro</i> method of quantifying NH₃ production from manure that would (1) evaluate the optimal microchamber design to quantify NH₃ production rates from manure; (2) quantify the effect of disturbance of manure on NH₃ production rates; (3) succeed as an alternative method of testing NH₃ production to reduce the need for, or better inform, large-scale animal experiments (4) successfully evaluate the effectiveness of mitigation techniques.</p> <p>This thesis includes a review of the available literature and three experimental chapters addressing the development and use of the <i>in vitro</i> method and assessment of an available NH₃ mitigation technique. Findings and implications of this thesis include: </p> <p>Development of a novel high-throughput plate-based analysis with a high degree of accuracy adapting the Berthelot method of quantifying NH₃-N in solution. Boric acid solution was shown to be an effective eluent for gas trap sampling of NH₃;</p> <p>Successful development of a novel microchamber system. The microchamber design was evaluated and a standard size chosen for the following experiments. It is hypothesised interactions with pad surface areas and depth were dependent on variables facilitating mass transfer such as air flow and headspace. Microchamber results did not meet hypotheses, as (i) increasing microchamber manure surface area did not result in constant rates of NH₃/m² production, and (ii) increasing manure depth resulted in lower rates of NH₃/m² as opposed to a consistent production relative to surface area. The standard size chosen for the experiment on clinoptilolite (zeolite) was a surface area of 90mm diameter (SA₉₀) and manure depth of 30mm (D₃₀), based on less variation in results and ease of use;</p> <p>Simulated animal movement through four repeated disturbances of cattle manure in micro-chambers every 90 minutes, resulted in increasing rates of NH₃ production (slope coefficients) with each disturbance over 480 min for all treatments. This suggests cattle movement may generate continual fluxes of NH₃ production from the manure over time;</p> <p>The application of zeolite was successful in reducing NH₃ production from cattle manure. All treatments achieved an immediate and sustained reduction in NH₃ production over 21 hours. The minimum (1%) and maximum (10%) in-pad application rates resulted in a 32% to 70% reduction in NH₃ emissions over 21 hours, respectively.</p> <p>Application of zeolite suspended in the microchamber headspace reduced the presence of gaseous NH₃ contamination in the air by 37% over 21 hours, similar to 1% zeolite applied in-pad over 21 hours.</p> <p>Overall, the high-throughput plate-based methodology and microchamber system provided valuable insight into increasing fluxes of NH₃ volatilsation with disturbance and optimal application rates of zeolite to reduce NH₃ production. The aim of the microchamber design was to standardise headspace and air exchange rates in order to quantify the effect of increasing manure surface area and depth. The results demonstrated air flow dynamics are important and challenging factors when comparing these variables, however a standardised microchamber was successfully deployed to compare and determine an optimal application rate of zeolite for NH₃ reduction.</p>