Technologies to reduce the environmental impacts and nitrogen losses of livestock manure

Summary

Increased attention is today paid to the environmental impact of livestock production due changes in agricultural practice and livestock manure handling. Livestock manure is an excellent source of plant nutrients, but recycling of its nutrients is greatly dependent on manure management practices. As well, several environmental effects are related to the storage and handling of livestock manure, including emissions of ammonia, odour, and greenhouse gases. The present research deals with technologies for reducing the environmental impacts and nitrogen losses of livestock manure.
Livestock manure is an important source of ammonia (NH3), being responsible for more than 80% of national emissions. The volatilisation of ammonia reduces the nitrogen content of the manure and has various environmental impacts. Livestock manure is also an important source of the greenhouse gases methane (CH4) and nitrous oxide (N2O), which have a major impact on the global warming. As well, livestock manure is an important source of odour. The main hypothesis of this thesis is that the nitrogen losses from and environmental impacts of livestock manure can be reduced using currently available technologies. The main objective of the research has been to study how different technologies effect emissions of polluting gases during storage and land application of livestock manure.
The major finding of the research has been that choice of technology for manure management has a significant impact on the environmental impacts and nitrogen losses from livestock manure. Shallow injection of slurry was found to reduce NH3 emissions following slurry application; however, type and design of the injectors have a major impact on the NH3 reduction potential. Reduction in NH3 emissions was correlated with injection depth, volume of the slot created, and demand for draught force. Reduction of ammonia emissions by means of shallow slurry injection consequently increases the emission of the greenhouse gas carbon dioxide due to the additional energy requirement.
Anaerobic digestion and separation of slurry change the composition of slurry, which influences the emission of odorous components following storage and land application. Slurry concentrations of malodorous volatile fatty acids were found to be reduced by between 79 and 97% by anaerobic digestion, while emissions of malodorous phenolic and indolic odour components were found to be reduced by both anaerobic digestion and subsequent separation. Odour concentration above undisturbed slurry storage tanks was reduced by anaerobic digestion. However, following mixing of slurry stores prior to land application, odour concentration was observed to be higher above stores of anaerobically digested slurry types. Odour concentration in air sampled above land applied slurry was reduced by 17% when the slurry was anaerobically digested and by 50% when the slurry was treated by combined anaerobic digestion and separation.
Considerable amounts of greenhouse gases were found to be emitted during storage of the solids separated from pig slurry. The production and emission of greenhouse gases were found to be influenced by the oxygenation level inside the manure storage heap. Covering the heap with an airtight material delayed aeration of the bulk of the stored manure, which reduced internal heat production, degradation of organic matter, and emissions of NH3, N2O, and CH4 by 12, 99, and 88%, respectively.
Storage of solid manure prior to land application was found to have a major impact on the emission of ammonia and on spreading evenness during subsequent land application. The content of ammonium in solid manure was reduced by storage, which reduces the potential for ammonia volatilisation following land application. Ammonia volatilisation following land application was thus 44% lower from stored than from unstored manure. Storage additionally increased the spreading evenness in terms of both the mass and nutrient content of solid manure, which decreases the potential for nitrate leaching.