Stability Evaluation of Simulated Plant and Animal Composts Utilizing Respiration Rates and VOC Emissions

Composting livestock carcasses is an economically and biologically safe method to convert carcasses into odorless, humus like material useful as a soil amendment. One of the key factors to determine the quality of the end product is stability. In this study, mortality composting is simulated using a laboratory set-up operating under aerobic and anaerobic conditions. 85 µm Carboxen/PDMS SPME fiber coating and 10 minutes sampling time are used to sample headspace of decaying plant (corn silage) and animal (shredded whole pig body) tissues. Compounds are separated and identified on a multidimensional gas chromatography-mass spectrometry-olfactometry (MDGC-MS-O) system. Sulfur containing compounds (methyl mercaptan, carbondisulfide, dimethyl disulfide, dimethyl trisulfide, 1,4-dimethyl tetra sulfide) and 1-H-indole and 3-methyl-1H-indole are found as indicators of decaying animal tissue. Peak area counts of these compounds show a decrease after eight week composting time. This trend in VOC emissions can be explained by decrease in the microbial activity and stabilization of the composts. These results are also supported with respirometric measurements. The measured respiration rates of aerobically composted animal tissues during 60 days are half of the respiration rates of fresh animal tissues. Also, a significant difference is observed in VOC emissions from plant and animal materials composted under aerobic and anaerobic conditions. The number of detected compounds during anaerobic decomposition is twice as much as the ones detected under aerobic decomposition. It can be concluded that monitoring VOC emissions can be a useful tool to estimate aeration status and completion of real life mortality composts

Performance Evaluation of a Passively-Aerated Plastic-Wrapped Composting System Designed for Emergency Disposal of Swine Mortalities

Monitoring of a passively-aerated plastic-wrapped mortality composting system designed for emergency disposal of diseased swine highlighted the importance of the physical characteristics of materials used to envelop the carcasses. Inadequate moisture was a problem when using envelope materials such as ground cornstalks or straw having low density and high air-filled porosity. High O2 concentrations throughout these materials, and significantly higher moisture levels in the top layers than in the materials surrounding the carcasses, suggested significant air movement and transport of carcass moisture away from the carcasses, resulting in carcass desiccation and incomplete decay. Although internal temperatures and moisture levels in test units constructed with corn silage were much more favorable than in those constructed with cornstalks or straw, less carcass decomposition occurred. Settling and compaction, resulting in high bulk density and low air-filled porosity, caused low O2 concentrations that appeared to impair carcass decay in the silage test units

Performance of a Bio-secure Emergency Composting System for Disposal of Swine Carcasses

A plastic-wrapped passively-ventilated composting system used by the Canadian Food Inspection Agency for bio-secure emergency disposal of poultry mortalities during an avian influenza outbreak in 2004, was adapted and field tested to determine its feasibility for emergency disposal of infectious swine carcasses. System performance was evaluated during triple-replicated 8-week long trials, and 10-day long lab-scale studies were carried out to supplement the field results. Treatment variables included season (warm or cool), type of envelope material (cornstalks, oat straw, corn silage, wood shavings, alfalfa hay, and soybean straw), and initial moisture content of the envelope materials (low\u3c 20% w.b; moderate 40-65%). Performance variables included: final moisture content and leachate production; ability to sustain desirable internal O2 concentrations; % carcass (soft tissue) decomposition; and ability to attain and sustain pathogen-killing temperatures. Despite release of significant amounts of water from carcasses, and being wrapped in plastic sheeting, little leachate accumulation was observed and the moisture content of envelope materials was generally lower at the end of the trail than at the beginning. All materials, except corn silage, were able to maintain internal O2 concentrations of 10% or higher when air was supplied through flexible 10 cm diameter ducts spaced at 2m intervals. O2 concentrations in corn silage often dropped below 10% even though aeration ducts were spaced at 0.5m intervals. Corn silage demonstrated superior pathogen killing potential. Average daily temperatures in the carcass layer of silage test units during the first 30 days of composting (T30) exceeded 50 oC, and USEPA Class B criteria for pathogen reduction were achieved at 90% of monitored locations. T30 values for cornstalks, soybean straw, and alfalfa hay are about 40 oC, and Class B criteria were achieved in only 45-57% of monitored locations in the carcass layer. Wood shavings and oat straw had the worst temperature performance with T30 values of only about 30 oC, and a Class B success rate of about 35%. Mean soft tissue decomposition in the field was lowest in corn silage (72%), and highest in cornstalks and soybean straw (87% and 85% respectively)