Nitrate contamination of surface and groundwater poses serious risks to human health and aquatic ecosystems, creating an urgent need for cost-effective, scalable, and sustainable treatment solutions. Conventional nitrate-removal technologies are often energy-intensive, generate secondary waste streams, or are poorly suited for decentralized systems. This project addresses these limitations by developing iron-functionalized biochar derived from forest-residue biomass as a high-performance, reusable adsorbent for nitrate remediation, with emphasis on process optimization, mechanistic understanding, and real-world applicability.
The project objectives are to: (1) synthesize iron-functionalized biochar (FBC700) from forest residues; (2) systematically optimize nitrate adsorption performance as a function of adsorbent dose, solution pH, and temperature using a full factorial design of experiments; (3) elucidate adsorption mechanisms through kinetic, isotherm, and thermodynamic analyses; and (4) evaluate regeneration, reusability, and comparative performance relative to raw and commercial biochars.
Forest-residue biochar was produced via pyrolysis at 700 °C under inert atmosphere and functionalized using FeCl₃ impregnation to introduce positively charged iron-based active sites. Nitrate adsorption was evaluated in batch systems using controlled aqueous solutions. A 3×3×3 full factorial design quantified the individual and interactive effects of adsorbent dose (1–5 g L⁻¹), pH (3–7), and temperature (25–45 °C) on nitrate removal efficiency and adsorption capacity. Material characterization (SEM–EDS, BET surface area, proximate and ultimate analyses) was used to link structural and chemical properties to adsorption performance, while kinetic, isotherm, and thermodynamic modeling established rate-controlling steps and adsorption energetics.
Key results demonstrate rapid and efficient nitrate removal, with equilibrium reached within approximately 2–2.5 h. Adsorbent dose was identified as the dominant operational parameter controlling removal efficiency, while adsorption capacity was maximized at lower doses. Adsorption exhibited strong pH dependence, with acidic conditions significantly enhancing nitrate uptake due to protonation of iron-based surface sites and electrostatic attraction. Elevated temperature moderately enhanced adsorption, indicating favorable thermodynamics and improved mass-transfer kinetics. Kinetic data were well described by a pseudo-second-order model, and equilibrium behavior followed the Freundlich isotherm, consistent with heterogeneous, multilayer adsorption. Thermodynamic analysis confirmed spontaneous adsorption across the studied temperature range. Regeneration studies demonstrated good reusability, with FBC700 retaining more than 85% of its initial adsorption efficiency after five adsorption–desorption cycles. Comparative studies showed clear performance advantages over raw forest-residue biochar and commercial biochar.
Conclusion: Results to date demonstrate that iron-functionalized forest-residue biochar is an effective, reusable, and sustainable adsorbent for nitrate removal, with strong potential for decentralized water-treatment and eutrophic-water remediation. Ongoing work will extend this approach to biochars produced at higher pyrolysis temperatures and to more complex water matrices to further enhance performance and scalability.