Protein recovery of wastewater and animal by-products from the rendering and tanning industries for application as biostimulant in agriculture

Free amino acids-based biostimulants have currently raised great interest at European level due to their potential application in regenerative agriculture, as they help stimulate plant growth, improve crop productivity and simplify the nitrogen life cycle in plants, while reducing dependence on synthetic fertilisers, which are highly reliant on imported and critical raw materials. In this context, the development of biostimulants by enzymatic hydrolysis has been identified as a more sustainable and versatile process, adding value by using processed animal proteins (PAPs) from by-products such as protein-rich greaves, wastewater and fleshing. First, an adequate conditioning stage was selected based on the animal by-product (ABP) and its suitability for an efficient enzymatic hydrolysis, with protein yields in the 78-97 (%) range, was determined. Subsequently, the protein hydrolysates obtained, which showed the best properties according to their amino acid composition for application as a free amino acids-based biostimulant, were validated to evaluate their potential to stimulate plant growth. Finally, the free amino acidsbased biostimulant reported satisfactory results, producing an improvement in growth of Chinese cabbage (Brassica rapa pekinensis) and lettuce (Lactuca Sativa) seeds between 17 and 39 (%). These results were obtained with the optimal dilution concentration of the biostimulant in the 0.05-0.3 (%) range, depending on the protein hydrolysate used.