Sustainable Treatment of Metronidazole-contaminated Wastewater via Integrated Adsorption and UV-assisted Degradation Using ZnO-modified Rice Husk Biochar and Silica–gelatin Composites
J. Environ. Nanotechnol., Volume 15, No 3 (September 2026) pp. 187-200
Abstract
This study developed ZnO-functionalized rice-husk biochar (RHB–ZnO) and a silica-reinforced gelatin composite (Gel–SiO₂) for the adsorption and UV-assisted removal of metronidazole (MET) from water. The composites were characterized using XRD, FTIR, and BET analyses and evaluated at MET concentrations of 0.1–10 mg L⁻¹ under 254-nm UV irradiation. Although biochar- and biopolymer-based materials have been investigated separately, their comparative adsorption, UV-assisted removal, mineralization, and long-term reusability toward pharmaceutical contaminants remain insufficiently understood. The novelty of this work lies in the direct evaluation of these two sustainable composite systems under identical treatment conditions over 15 reuse cycles. BET analysis showed that ZnO functionalization increased the specific surface area of rice-husk biochar from 546.32 to 564.22 m² g⁻¹, while XRD confirmed the formation of crystalline ZnO within the predominantly amorphous biochar matrix. Among the studied systems, the UV/Gel–SiO₂ composite exhibited approximately 94.5% MET removal, while the UV/RHB–ZnO material achieved approximately 96.8% removal at a contaminant concentration of 10 mg L⁻¹ after 120 min of irradiation. Mineralization studies further revealed that, the zinc oxide-modified biochar system promoted more extensive degradation of organic intermediates compared with the silica-reinforced gelatin matrix. Kinetic evaluation demonstrated rapid degradation behavior for both materials, indicating effective contaminant decomposition under UV irradiation. Adsorption experiments confirmed that the silica-containing biopolymeric network possessed greater contaminant uptake capability than the zinc oxide-functionalized biochar structure. After 15 consecutive treatment cycles, the Gel–SiO₂ and RHB–ZnO composites retained 87% and 91% removal efficiency, respectively, demonstrating good operational stability and potential for reuse in pharmaceutical wastewater treatment. However, further studies using real wastewater and continuous-flow reactors are required to evaluate their performance in the presence of competing contaminants and under practical operating conditions.
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