Innovative fertilizers and soil amendments based on hydrochar from brewery waste

Hydrothermal carbonization is one of the new ways to produce valuable products from waste materials. The aim of this study was to develop a novel method for the production of hydrochars from brewery residues for agricultural applications. Waste materials treated at 140 °C, 170 °C, and 200 °C were used as a source of renewable nitrogen and as delivery agents of fertilizer microelements (Cu, Mn, and Zn). HTC materials were enriched with nutrients using an innovative spray sorption method. The surface texture was characterized by the nitrogen adsorption technique, functional groups were identified (FT-IR), and thermogravimetric analysis of the materials was performed. Preliminary germination tests have shown phytotoxic effects at doses greater than 20% (relative to plant nitrogen requirements) for unenriched hydrochars. To minimize inhibition of plant growth, air aging tests were conducted for 30 days, followed by successive drying at 110 °C for 72 h. It was observed that the higher the temperature of the carbonization process, the faster the desorption of components in a solution simulating soil conditions (NaNO 3 ) occurs. The pot tests on cucumber ( Cornichon de Paris ) showed that the biometric parameters of the plant (stem length and root ball parameters) for the hydrochar obtained at 170 °C were higher than in the group fertilized with mineral fertilizer. Twice the fresh plant mass was noted for this group compared to the reference. In addition, the study recorded a particular increase in nitrogen content in plants fertilized with a 150% dose of enriched hydrochar, where the element content increased by about 100% compared to the group with mineral fertilizer applied (100% dose). The study shows that properly prepared hydrochars from brewery waste offer great potential as a nitrogen source and micronutrient delivery agents for the agrochemical sector. Graphical Abstract Innovative fertilizers and soil amendments based on hydrochar from brewery waste