Biogeochemical Implications of Animal Mortality Burial

Abstract

Large scale livestock production facilities produce a variety of waste streams. Of those, animal mortality carcass disposal poses a significant threat to the environment depending on the chosen disposal route. Carcass burial is a common approach for both routine mortalities as well as large-scale catastrophic mortality events and has been studied in very limited detail. This study provided further assessment of carcass burial leachate and its inorganic chemical constituents and transport processes in the subsurface. The objectives of this thesis were to: (1) determine the likely geochemical impacts of the ionic strength of carcass burial leachate; (2) provide an assessment utilizing common numerical models to predict contaminant transport based on burial guidelines; (3) investigate existing burial sites for model validation; and (4) evaluate the effects at an existing site that the leachate had on indigenous microbiology and evaluate transport of microbes. These objectives were accomplished by laboratory testing, numerical modelling, and field investigations with the findings contained in four manuscripts that make up the bulk of this thesis. Major findings determined that the high ionic strength of the leachate at maximal concentrations (1.4 to 1.5 molar), lie in a grey area with respect to ion activity calculations for geochemical modelling and that ion activity calculations utilizing the Truesdell-Jones technique provided the best estimate of ion activity. Geochemically, speciation assessment indicated specific species of concern that can transport unattenuated and include ammonium sulfate compounds (up to 300 mg/L), phosphate and phosphoric acid compounds. Two-dimensional conservative and non-conservative (sorption) models and one-dimensional reactive transport models demonstrated plume evolution over a range of hydraulic conductivities, and predicted changes in ammonium retardation with subsequent developments of hard water plumes due to ion exchange reactions. Model validation was achieved by the investigation of two existing carcass burial sites in Saskatchewan and provided the first assessment of plume development and biogeochemical interactions by soil coring and pore water analysis. The site investigations concluded that ammonium and potassium in the leachate was adsorbed and exchanged for calcium and magnesium (as predicted by models). Biogeochemically, anaerobic microorganisms dominated the subsurface and were zoned based on geochemistry. The tools created and used for the microbiological aspects of this work can be useful in fingerprinting existing burial sites.