There has been increasing interest in using biochar for nutrient removal from water, and its application for anionic nutrient removal such as in phosphate (PO₄³⁻) necessitates surface modifications of raw biochar. This study produced avocado seed biochar (AB), impregnated Fe- or Mg-(hydr)oxide onto biochar (post-pyrolysis), and tested their performance for aqueous phosphate removal. The Fe- or Mg-loaded biochar was prepared in either high (1:8 of biochar to metal salt in terms of mass ratio) or low (1:2) loading rates via the co-precipitation method. A total of 5 biochar materials (unmodified AB, AB + High Fe, AB + Low Fe, AB + High Mg, and AB + Low Mg) were characterized according to their selected physicochemical properties, and their phosphate adsorption performance was tested through pH effect and adsorption isotherm experiments. Fe-loaded AB contained Fe₃O₄, while Mg-loaded AB contained Mg(OH)₂. The metal (hydr)oxide inclusion was higher in Fe-loaded AB. Mg-loaded AB showed a unique free O–H functional group, while Fe-loaded AB showed an increase in its specific surface area more than 10-times compared to unmodified AB (1.8 m² g⁻¹). The effect of the initial pH on phosphate adsorption was not consistent between Fe-(anion adsorption envelope) vs. Mg-loaded AB. The phosphate adsorption capacity was higher with Fe-loaded AB in low concentration ranges (≤50 mg L⁻¹), while Mg-loaded AB outperformed Fe-loaded AB in high concentration ranges (75–500 mg L⁻¹). The phosphate adsorption isotherm by Fe-loaded AB fit well with the Langmuir model (R² = 0.91–0.96), indicating the adsorptive surfaces were relatively homogeneous. Mg-loaded biochar, however, fit much better with Freundlich model (R² = 0.94–0.96), indicating the presence of heterogenous adsorptive surfaces. No substantial benefit of high loading rates in metal impregnation was found for phosphate adsorption. The enhanced phosphate removal by Mg-loaded biochar in high concentration ranges highlights the important role of the chemical precipitation of phosphate associated with dissolved Mg²⁺.

Introduction: Recovering hemicellulose from woody biomass prior to acid hydrolysis/dehydration (AHDH) processing can improve the yield and economics of levulinic acid (LA) production, but the effects of chemical preconditioning on subsequent LA yields and process economics remain to be characterized for softwood feedstocks. Methods: A pilot-scale chemical preconditioning system (CPS), operated with and without dilute sulfuric acid (0.25 wt%) and steam, was used to recover hemicellulose from raw white pine wood chips (39.5% glucan, 16.6% total hemicellulose [3.8% xylan, 10.1% mannan, 1.9% galactan, 0.7% arabinan], and 44.6% acid-insoluble lignin, oven-dry basis) prior to processing in a bench-scale AHDH reactor. Preconditioning was evaluated across a range of temperatures, residence times, biomass species, moisture contents, and particle sizes (1 mm to ∼18 mm) to determine effects on LA yield. A techno-economic analysis was also performed to estimate the minimum selling price of the resulting mixed sugar stream. Results: CPS effectively removed hemicellulose from wood chips, achieving complete xylan removal at 200 °C. Preconditioning at 170 °C for 30 minutes with 0.25 wt% H ₂ SO ₄ increased LA yield from 0.21 mol/mol glucan (untreated) to 0.52–0.53 mol/mol glucan, a 2.5-fold improvement. CPS temperature, residence time, and biomass species influenced LA yields, whereas moisture content and particle size did not have a significant effect. The techno-economic analysis estimated a minimum selling price of $0.42/kg for a mixed sugar stream at ∼100 g/L concentration. Discussion: The LA yields achieved through mild chemical preconditioning (0.52–0.53 mol/mol glucan) were comparable to those obtained using more severe dilute acid (0.64 mol/mol) and SPORL (0.60 mol/mol) pretreatments, suggesting that CPS offers a less severe, potentially lower-cost alternative for enhancing LA production. The estimated minimum selling price of $0.42/kg falls within the $0.30–$0.60/kg range typical of commercial mixed C5/C6 fermentation feedstocks, indicating that CPS-based hemicellulose recovery is economically competitive and could be integrated into softwood-based AHDH processing without the need for more severe pretreatment conditions.