Scientific Abstract
The disposal of swine carcasses generated during disease outbreaks poses considerable biosecurity and ecological challenges. This research assessed leachate production and characteristics, disposal unit temperatures, and fate and transport of leachate contaminants for three carcass disposal techniques – whole carcass composting (WCC), ground carcass composting (GCC), and shallow burial with carbon (SBC) – with and without biochar addition. Six carcass disposal units measuring 4.3 x 6.7 m x 0.6 m were constructed, lined with 45 mil EPDM rubber pond liner, and equipped with perforated PVC pipe to convey leachate to vertical standpipes for collection. Wood chips were placed in each unit to a depth of 0.6 m. Twenty-five randomly assigned swine carcasses (2645 ±41.2 kg) were arranged in a single layer in the SBC and WCC units; carcasses assigned to GCC treatments were processed 1:1 with wood chips before being distributed in an even layer in GCC units. Four thermocouples were placed below and above carcasses along the centerline of each unit. One replicate of each treatment received 1.5 m3 of biochar distributed across carcass layers. Each of the WCC and GCC treatments were covered with approximately 30 m3 of wood chips while soil excavated to construct the SBC units was used to cover carcasses in those units. Temperature was logged every 15 min and leachate was collected from each unit every two weeks for the duration of the12-month study. Monthly leachate composites for each unit were analyzed for chemical characteristics, E. coli concentrations, and reactive oxygen and nitrogen species. Composites of leachate were created from units with (LB) and without biochar (L) addition. Soil columns (5 cm a 30 cm) were equipped with two common Nebraska soils – a silty clay and a sandy clay loam – to evaluate leachate contaminant fate and transport. Treatments (L, LB, or water (W)) were applied to columns in quadruplicate in a 2 x 3 factorial design for 33 d according to leachate production data from the field study. Regular additions of distilled water to columns modeled precipitation. The volume and characteristics of liquid discharged from soil columns were analyzed and soil samples from 0-5, 5-10, and 10-20 cm were obtained from each column for analysis upon study completion. Field study data revealed lower leachate production volumes for the two SBC units compared to the WCC and GCC units. SBC treatments reached and sustained internal temperatures of at least 40°C for five consecutive days and at least 55°C for at least four hours, achieving the EPA thresholds for routine pathogen destruction in compost. Nutrient fate and transport in soil columns varied by soil texture, as expected, but no significant nutrient fate and transport concerns were identified. Findings suggest that SBC is the most efficient on-farm carcass disposal technique compared to composting of either intact or ground carcasses. Biochar inclusion had no discernible impact on measured characteristics of disposal units. These insights can guide best practices for swine carcass disposal, particularly in ecologically sensitive regions.
