Using broiler litter and swine manure lagoon effluent in sawdust-based swine mortality composts: Effects on nutrients, bacteria, and gaseous emissions

Disposition of mortalities challenges confined animal feeding operations (CAFOs), especially sow (farrowing) farms, which experience mortalities daily. Regulations and transportation costs may preclude incineration, landfill burial, and rendering; therefore, swine CAFOs in Mississippi in the Mid-South U.S. often compost mortalities. In this study, a farm-standard composting mix of sawdust (S) and water (W) was compared with mixes where N was supplied by broiler litter (L) and water was replaced with swine lagoon effluent (E). The objective was to assess the effects of these manure byproducts: 1) on nutrients and bacteria in composts destined for land application; and 2) on emissions of ammonia and greenhouse gases. Three replications of four mixes (SW, SLW, SE, SLE) were compared in microcosms comprising modified plastic recycling bins. The experiment was repeated three times in different seasons in one year. Mixes were compared for differences in temperature, water content, nutrients (C, N, P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn), bacteria (Gram −, Gram +, Clostridium perfringens, Salmonella, Listeria, Escherichia coli), and emissions (NH₃, CO₂, CH₄, N₂O). Litter addition increased composting temperatures initially and after aerations; increased nutrient concentrations, except C, in start mixes and all except C and N, in finish mixes; increased Gram + bacteria, Salmonella, and E. coli in start mixes, but only Gram+s in finish mixes; and increased emissions. Effluent addition increased early composting temperatures; had no effect on nutrients or bacteria, except increased C. perfringens in start, but not finish mixes; and had no effect on emissions. Nutrients in finish composts did not differ among mixes for N (average 3.3%), but litter composts had more P and K, and lower N:P than composts without litter. Improving mortality composting is of global importance as increasing livestock populations and intensive animal production systems require practical, safe, environmentally sound disposal of carcasses. - Highlights: • All sawdust–manure mixes were effective in composting swine mortalities. • Litter mixes affected compost temperatures, nutrients, bacteria, and emissions. • Effluent mixes affected compost temperatures and C. perfringens levels. • Finish composts averaged 3.3% N, but N:P varied among mixes. • Composting reduced the incidence of Salmonella and eliminated Listeria