Soil Amendments and Biostimulants from the Hydrothermal Processing of Spent Coffee Grounds

Abstract Purpose Use of spent coffee grounds (SCG) in horticulture has deleterious effects on plant health and yields, suggesting that processing SCG is necessary prior to field application. To this end, two products an based biorefinery were investigated: primary chars from the hydrothermal carbonisation (HTC) enzymatic protein hydrolysates. Methods Primary produced under various HTC regimes raw SCG, alkaline pre-treated SCG. evaluated germination toxicity tests soil stress conditions using Arabidopsis thaliana ( ). Proteolytic enzymes screened production hydrolysates; biostimulant activity growth Saccharomyces Cerevisiae, normal cold auxin-like was assessed. Results Toxicity assays with land cress Barbarea verna L.) showed a maximum 35% increase root length, relative control. In trials, outstanding performances recorded at 100 t/ha for SCG: rosette diameter dry weight increased by 531 976%, respectively, hydrolysate Bacillus lichenformis proteolysis (glycine present 47% total) gave 140% seeds expanded cotyledons, Auxin-like also measured extracts. Conclusion Cascade process design used valorise major waste stream. Removal phytotoxic components hydrochars enhanced growth, while hydrolysates observed. Graphical