Abstract
Macroalgae have been increasingly valorized in many applications due to their diverse biochemical composition and sustainable resource utilization. However, their residues are still undervalued even though they remain unexhausted and retain a broad spectrum of nutrients and molecules likely to be used in crop production as plant biostimulants and as soil amendment. In this study, macroalgae residues were recovered after an industrial extraction of agar and valorized through two pathways: 1) extraction of the remaining bioactive compounds using thermal, mechanical, physical, and biological processes, and 2) production of biochar using pyrolysis. After that, both outputs; extracts and biochar were combined to produce a multifunctional product “extract-impregnated biochar”, where the two components with different functionalities were co-integrated in the same formulation. Then, their effects were tested on tomato growth and nutrients content in the soil. Results indicated that the extracts obtained through enzymatic pyrolysis contained the highest protein content on (10.6 g/L), whereas the acidic attack provided the highest phosphorus content (1.24 g/L). The shoot and root biomass of tomato increased by 54 % and 100 %, respectively, with untreated biochar whereas it rose by 123–146 % and 200–450 % with extract-impregnated biochar. In addition, a slight improvement in soil total N and P was observed with both untreated and treated biochar applications when compared to the control. In general, the acidic and enzymatic pretreatments of algae residues appear to yield favorable results.