Composting as a cleaner strategy to broiler agro-industrial wastes: Selecting carbon source to optimize the process and improve the quality of the final compost

The growth of broiler meat production chain in Brazil has resulted in a strong increase in the wastes produced either at the pre-finishing stages (reproductive poultry litter and hatchery waste) or during finishing and meat processing (floatation sludge, sausage casings, and charcoal waste). These wastes are produced in high amount, mainly the floatation sludge which presents a low C:N ratio. Composting is the primary available stabilization process for broiler agro-industrial solid wastes in Brazil, but these high-nitrogen wastes must be combined with a compatible carbon source to accelerate the process and to produce high quality compost. In this study, five regional materials-cotton fiber waste, urban tree trimmings, sawdust, milled sugarcane bagasse and ground Napier grass-were assessed as potential carbon sources to improve composting of broiler agro-industrial solid wastes. Analyzed variables associated with composting area optimization included composting time and the reduction in dry matter weight and volume. Analyzed variables that reflected the quality of the final compost included electrical conductivity, germination index, concentrations of N, P and K, C:N and humic to fulvic acid ratios. Multivariate analysis, including cluster and principal component analyses, indicated that cotton fiber waste, as a carbon source, optimized composting area utilization and resulted in finished compost with high agronomic value. However, due to its high level of nutrients, cotton fiber waste showed the highest EC, which limits its use as seedling substrate.