Valorization of poultry slaughterhouse waste for fertilizer purposes as an alternative for thermal utilization methods.

Abstract Slaughterhouse waste and dead animals are mainly disposed of by incineration, which generates greenhouse gases and NOx. These wastes are a source of nutrients that can be recovered by circular economy techniques if material recycling is given a priority over energy recovery. To valorize high-protein animal waste (containing bones, meat, feather) for fertilizer purposes, the waste was processed by acid solubilization and neutralized with potassium hydroxide solution, which yielded a liquid fertilizer with plant growth biostimulating properties (due to the amino acids presence). The composition analysis showed that new fertilizers met all quality requirements set by the law, contain ~0.5% m/m amino acids and are microbiologically pure. The fertilizer was enriched with microelements to the level of 0.2% m/m and tested for biological effectiveness in germination tests and field studies. Compared with the commercial formulation, the fertilizer increased stem length and chlorophyll content (by 8.2% and 27.0%, respectively), wheat crop yield and grain micronutrients density (Cu by 31.2%, Mn by 10.5%, Zn by 33.9%) and improved the wheat flour baking properties. The described solution propose a safe way to utilize hazardous waste via technological mobile installation, enabling no transportation of waste, which is an important aspect of sanitary-epidemiological risk minimization.