Superheated Water Hydrolysis of Waste Wool in a Semi-Industrial Reactor to Obtain Nitrogen Fertilizers

A large amount of coarse wool, practically unserviceable for textile use, is generated in Europe from sheep shearing and butchery. Such a byproduct is either dumped, burned, or sent to landfill. Following the European Commission regulations on animal byproduct control, unserviceable raw wool is classified as a category 3 special waste materials. The collection, storage, transport, treatment, use, and disposal of such unserviceable raw wool are subject to European Union regulations because of a potential risk to human and animal health. This study aims at converting the waste wool into nitrogen fertilizers at a commercial scale for grassland management and cultivation purposes. The chemical transformation of waste wool in to fertilizer is based on a green economically sustainable hydrolysis treatment using superheated water. The experiments were carried out in a semi-industrial reactor feeding superheated water. The wool/superheated water system was maintained for different reaction times. The optimal conditions for this treatment were as follows: 170 degrees C for 60 min with a solid to liquor ratio (MLR) close to 1. The hydrolyzed product was analyzed using amino acid analysis and molecular weight distribution. Both the amino acid and molecular weight distribution analysis revealed that the wool was completely degraded and the hydrolyzed product contains a low molecular weight proteins and amino acids. Several hydrolyzed product obtained at different conditions were tested for germination which showed a germination index higher than 100% without collateral phytotoxicity. The presence of amino acids, primary nutrients, and micronutrients in wool hydrolyzates, along with a concentration of heavy metals below the standard limit, confirm the possibility of using wool hydrolyzates as a nitrogen based ecologically sound fertilizer.