Valorisation of food industry waste into high-performance biochar for environmental applications

Organic waste from the food industry can be thermochemically converted into valuable products, supporting the circular economy and reducing environmental and socio-economic impacts. This study explores the valorisation of food industry residues, such as rapeseed cake, maize cobs, and walnut shells, through slow pyrolysis at 600 °C under an inert atmosphere. The studied feedstocks were lignocellulosic materials with approximately 45% carbon content, but had different fibre contents, which subsequently affected the properties of the biochars. The highest char yield was observed for rapeseed cake (26%), followed by walnut shells (24%) and maize cobs (22%). Elemental analysis revealed that the carbon content in the biochars of maize cobs and walnut shells exceeded 80%, with a particularly significant surface area (356 m²/g) noted for the walnut shells, and very low for the rapeseed cake and maize cobs, respectively. Only after the chars underwent physical (steam activation at 850 °C) and chemical activation (using H₃PO₄ and ZnCl₂), resulting in a substantial increase in surface area, exceeding 300 m²/g for rapeseed cake and maize cobs and c.a. 550 m²/g for walnut shell biochar. These biochars effectively removed organic (phenol) and inorganic (Pb²⁺) pollutants from aqueous solutions (100% removal of Pb²⁺ and 82% removal of phenol for biochar of walnut shells) and additionally did not exhibit acute toxicity in Lemna minor tests, confirming their environmental safety. The work aligns with SDG 6 (Clean Water and Sanitation) by enabling low-cost pollutant removal, SDG 12 (Responsible Consumption and Production) by upcycling food waste, SDG 13 (Climate Action) through carbon sequestration and emissions mitigation, and SDG 15 (Life on Land) by offering materials that improve soil health and support circular economy principles. This research demonstrates how engineered biochar can serve as a multipurpose environmental tool, directly supporting global sustainability targets.