Functionalized Biochars Derived from Tomato Plant Residues (Solanum lycopersicum L.) and Shea Nut Shells (Vitellaria paradoxa) for Phosphorus Sorption: From Model Solutions to Real Wastewater Matrices

Waste biomass can serve as a feedstock to produce functionalized biochars (BCs) for phosphate removal. However, their sorption performance depends on feedstock properties, pyrolysis conditions, and modification strategy. This study compared BCs produced from tomato plant residues (Solanum lycopersicum L.; T) and shea nut shells (Vitellaria paradoxa; VP), pyrolyzed at 400 and 500 °C and modified with iron (Fe) or diatomite (DT). Their physicochemical and structural properties and phosphate sorption capacity were evaluated in a model solution and selected real wastewater matrices. Exploratory variance decomposition showed that modification type represented the largest proportion of variability in physicochemical and structural properties of 12 BC variants (59.75%), whereas feedstock type represented 84.84% of the observed variation in phosphate sorption across the 8 variants. The effect of modification was feedstock-dependent: DT was particularly beneficial for T-derived BCs, whereas Fe modification was more beneficial for VP-derived BCs. Selected magnetic BCs also removed phosphate from real wastewater matrices, although removal efficiency differed between matrices. Overall, phosphate sorption capacity could not be predicted from modification type or pyrolysis temperature alone, indicating that feedstock characteristics should be considered when selecting functionalization strategies.