Adsorption Mechanisms, Ecotoxicity, and Feasibility of Fixed-Bed Application for Benzalkonium Chloride Treatment in Aqueous Matrices

This study investigates the harmful effects of benzalkonium chloride (BZK) in aqueous environments and proposes adsorption as a tertiary treatment method. It assesses the viability and scalability of this approach, focusing on the sustainability achieved through the regeneration of solid adsorbents. The toxic effects of BZK were evaluated using in silico toxicity analysis (quantitative structure–activity relationship (QSAR) tools). In batch adsorption, optimal conditions were identified by varying the pH (2–10), contact time (0–180 min), and solid concentration (0.5–2.5 g/100 mL) and conducting kinetic, isotherm, and thermodynamic evaluations (last two at temperatures of 15, 25, 40, and 50 °C). For fixed-bed adsorption, a flow rate of 0.6 L/min and a bed height of 2 cm were used. The experimental results were analyzed using Bayesian statistics. Thermal regeneration of the adsorbent was conducted at 300 and 550 °C to assess the reuse potential. Using in silico toxicity analysis, it was revealed that BZK has moderate toxicity, being highly irritating to the eyes and potentially causing skin sensitization. In batch adsorption experiments, optimal conditions for BZK removal (83.7%) were identified at natural pH (∼8.1), with a contact time of 120 min and a solid concentration of 2 g/100 mL of granular activated carbon. Kinetic studies revealed a pseudo-first-order reaction, while equilibrium data fit the Sips amalgamated model, suggesting Langmuir characteristics. Thermodynamic analyses indicated that adsorption is more favorable at elevated temperatures, characterized as endothermic and spontaneous, with physisorption as the dominant mechanism. The regeneration efficiency reached 74.2% after 60 min at 300 °C, reaching 50% after 5 cycles of operation. Fixed-bed trials showcased consistent effectiveness over time, displaying superior conformity to the Log-Gompertz framework, at a contaminant concentration of 80 mg/L, signifying a saturation period of 259 min and an adsorption capability of 1.499 mg/g, rendering them apt for uninterrupted operation on an industrial magnitude. The application of Bayesian statistical methods further enhances the reliability of the empirical data, allowing for better predictions and understanding of the adsorption mechanisms. This research not only reinforces the efficacy of adsorption as a viable tertiary treatment method but also underscores the potential of combining QSAR and Bayesian analyses to advance water treatment strategie