Biochar and Iron oxide nanoparticle-impregnated alginate beads as adsorbents for enhanced ex situ bioremediation of petroleum-contaminated freshwater

Nutrient washout remains a key drawback of nutrient supplementation during bioremediation interventions in aquatic systems. This study assessed the adsorption and controlled release properties of biochar‑iron oxide nanoparticle (IONPs) beads laden with bacteria and nutrients for treatment of petroleum spills in freshwater ecosystems in a bid to counter the challenge of nutrient washout. The IONPs synthesised from phytoextracts were decorated on biochar made from cow bones at 500 °C. The composite produced was embedded in an alginate matrix with degradative bacteria and inorganic nutrients via physical crosslinking. Swelling indices revealed better release properties for the monoammonium phosphate nutrients with the beads that had the biochar‑iron oxide nanocomposite incorporated (BCNP). The 15-min swelling indices (SI₁₅) for the beads ranged from 0.13 to 2.00. Batch adsorption experiments revealed that adsorption was physical in nature and higher at lower adsorbate concentrations with significant differences (p ≤ 0.05) between the three groups of adsorbents. The BCNP bead showed the greatest sorption levels (71.69%) compared to the plain biochar beads (57.83%) and the biochar powder (46.12%). Based on the adsorption parameters obtained, it was concluded that the adsorption data were more suited to the Freundlich isotherm model and the pseudo-second order kinetic model. The study developed a slow-release nanocomposite that could counter the challenge of nutrient washout associated with bioremediation in aquatic ecosystems.