Sustainable Valorization of Olive Pomace into Biochar–Pectin Composite for Enhanced Water Retention and Plant Growth in Arid Agriculture

Abstract

Agro-industrial residues from the olive oil industry present considerable environmental challenges due to their high organic load and phytotoxic phenolic content. This study explored the valorization of olive pomace by developing pectin, pectin gel, and a biochar–pectin gel composite (BPGC) for sustainable agricultural applications. The materials were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis, confirming successful composite formation and revealing the predominantly mesoporous characteristics of the olive pomace-derived biochar. Swelling analysis showed that pectin reached 121% within 10 min and 195% after 2 h, while BPGC exhibited superior moisture retention (60%) and water-holding capacity (97.9%). Germination studies demonstrated high seed viability (96% to 98%) across treatments, with BPGC producing the highest seedling-growth responses, including shoot length of 8.31 cm, root length of 4.03 cm, and a seedling vigor index of 1210. Enzymatic activity was also improved, with protease and lipase reaching 186 and 201 U/g FW, respectively, in BPGC-treated samples. No detectable phytotoxic effects were observed under the tested conditions. These findings indicate that BPGC is a promising bio-based water-retaining soil amendment for improving soil moisture management and early plant growth, particularly in arid and semi-arid agricultural systems.