Influence of agricultural wastes and a finished compost on the decomposition of slaughterhouse waste composts

• Rapid decomposition of organic matter was found in each compost.
• The finished composts were stable and had similar C:N ratios.
• Turning and mixing reactivates the bio-degradation process.
• Compost mass reduction and total carbon decomposition followed a first-order exponential decay relationship.
• Agricultural wastes and finished composts are viable feedstocks to compost SHW.

The objective of this study was to evaluate the efficacy of combining agricultural wastes or a finished compost (wheat straw, horse manure and bedding, sheep manure, and a wheat straw-SHW finished compost) as compost feedstocks with cattle slaughterhouse wastes (SHW) on a field-scale. The composts were managed in covered bins over 200 days and physico–chemical parameters related to organic matter bio-degradation were measured over time. Thermophilic temperatures were maintained above 55 °C for 12–46 days to meet the Canadian Council of Ministers of the Environment (CCME) guidelines for pathogen control. Final C:N ratios were highest in a horse manure and bedding:SHW compost at 23:1 but ranged from 18.5 to 20.5:1 for the remaining three treatments, representing a wheat straw:SHW compost and different combinations of horse manure and bedding, SHW, and/or sheep manure. Average reduction in mass of total carbon across all the composts in the current study was 54.2%. Maturity tests at the end of the study determined that the CO2–C evolution rate in all compost products was less than 1 mg g−1 organic matter day−1 suggesting highly stable final compost products. Compost mass reductions all responded as exponential decay functions with R2 values ranging from 0.84 to 0.99 regardless of compost feedstock composition. Agricultural by-products and composts are suitable feedstocks for use with SHW to generate a stable final product while meeting regulatory parameters to achieve conventional pathogen control.