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The leather tannery industry generates about 33 Mt/year of solid waste with different properties, turning its management into a challenge. One of the valorization methods of tannery wastes is the production of biochar by pyrolysis of leather scratches. Biochar's sorption properties and its high nitrogen content (10%) make it suitable for its application as a soil conditioner or carrier of microelements for fertilizers. The paper presents an innovative spray method to enrich biochar with cationic micronutrients: Cu, Mn, Zn. Enriched biochar contained 1095 mg/kg Cu(II), 1334 mg/kg Mn(II) and 1205 mg/kg Zn(II). The high bioavailability of nutrients and the effectiveness of the new fertilizer were demonstrated in extraction in vitro tests - the analysis of leachability of elements to water and bioavailability of micro-nutrients. The functional properties of enriched biochar were examined in vivo (germination, pot) tests. A high biomass increase (approximately 10%) was observed compared to the group fertilized with a commercial product. The proposed solution benefits the environment in that it is made from alternative resources from which innovative fertilizers are produced according to the circular economy concept.

The increase in livestock production creates a serious problem of managing animal waste and by-products. Among the wide range of waste valorization methods available, anaerobic digestion is very promising. It is a form of material recycling that also produces renewable energy in the form of biogas, which is reminiscent of energy recycling. The effluent and digestate from the anaerobic digestion process need to be processed further. These materials are widely used in agriculture due to their composition. Both the liquid and solid fractions of digestate are high in nitrogen, making them a valuable source for plants. Before soil or foliar application, conditioning (e.g., with inorganic acids) and neutralization (e.g., with potassium hydroxide) is required to eliminate odorous compounds and microorganisms. Various methods of conducting the process by anaerobic digestion (use of additives increasing activity of microorganisms, co-digestion, multiple techniques of substrate preparation) and the possibility of controlling process parameters such as optimal C/N ratio (15-30), optimal temperature (psychrophilic (20 °C), mesophilic (35-37 °C) and thermophilic (55 °C) for microorganism activity ensure high efficiency of the process. Literature data describing tests of various digestates on different plants prove high efficiency, determined by yield increase (even by 28%), nitrogen uptake (by 20%) or phosphorus recovery rate (by 43%) or increase of biometric parameters (e.g., leaf area).