A chitosan-modified buckwheat hull biochar dynamic adsorption column as a sustainable and efficient technology for lead-acid battery wastewater treatment

Abstract

The treatment of lead-contaminated wastewater, particularly at low concentrations, remains a significant challenge. This study presents a novel dynamic adsorption process using a chitosan–buckwheat hull biochar composite (KQB) for efficient Pb²⁺ removal. Comprehensive characterization using SEM-EDS, FTIR, BET, XRD, and XPS was conducted to verify the successful modification and favorable physicochemical properties of the composite. By employing the response surface methodology based on the Box–Behnken design (RSM-BBD), critical parameters such as pH, adsorbent dosage, and adsorption time were optimized to achieve a removal efficiency of 95.31%, resulting in a residual Pb²⁺ concentration of ∼0.23 mg L⁻¹, which complies with the standard discharge limit. The adsorption kinetics and equilibrium data were best described by the pseudo-second-order (PSO) model and the Langmuir isotherm model, respectively, indicating a monolayer chemisorption process. Furthermore, XPS analysis confirmed that the primary removal mechanisms involve ion exchange and surface complexation with amino and hydroxyl groups. KQB outperforms conventional coagulation methods, demonstrating higher removal rates and a significantly reduced effluent pollution index (P_i = 0.56 vs. 1.72 for coagulation), coupled with lower operational costs. Furthermore, the composite exhibited excellent stability and reusability over 5 regeneration cycles. This dynamic adsorption process offers a sustainable and cost-effective alternative to traditional methods, with potential applications in wastewater treatment and broader environmental remediation.