Towards anaerobic digestate valorization to recover fertilizer nutrients: Elaboration of technology and profitability analysis

The study aimed to develop a technology for creating granular fertilizers, containing amino acids, based on food waste digestate. Pork hemoglobin (Ntot: 14.9 ± 1.5%, C: 47.2 ± 4.7%) served as an additional source of nitrogen and organic carbon. The proposed method comprises four unit processes: (1) chemical hydrolysis of raw materials with a mixture of sulfuric (VI) acid and phosphoric (V) acid, (2) neutralization with solid potassium hydroxide and correction of the composition with minerals (sulfate salts of copper, manganese, zinc and iron), (3) granulation with a mixture of biomass combustion, potato starch and peat, and (4) drying the granules. The prepared formulation meets the requirements of European Parliament Regulation 2019/1009 and is classified as PFC 1(B)(I): solid organo-mineral fertilizer (N: 4.49 ± 0.45%, C: 35.0 ± 3.50%, P2O5: 2.83 ± 0.57%, K2O: 4.78 ± 0.96%). The forms of nutrients were determined in accordance with current PN-EN standards. The effect of amino acid fertilizer on cucumber plants (Cucumis sativus, W. Legutko) was studied in 10-day germination tests under normal, salinity and drought conditions. It was noted that a low dose of the preparation under normal conditions had a stimulating effect on root development, while higher supplementation positively affected the aboveground parts of the plants. Under drought conditions, plants accumulated higher amounts of free amino acids, particularly glutamic acid, arginine, glycine, phenylalanine, serine and tryptophan. A significant portion of the study focused on the economic analysis, which included financial calculations for the production of the proposed fertilizer, an evaluation of profitability, and a sensitivity analysis.