Characterisation and Performance Evaluation of a Fishbone Biochar-Rice Husk Silica Nanoparticle Hybrid for the Removal of Micropollutants from Wastewater

Abstract

Wastewater contamination by toxic heavy metals, synthetic dyes, and pathogenic microorganisms poses significant environmental and public health risks. The conversion of agricultural and food-processing wastes into functional adsorbent materials offers a sustainable approach to wastewater treatment. This study investigated the physicochemical characteristics and pollutant removal performance of fishbone biochar (FBB), rice husk-derived silica nanoparticles (SiNPs), and an FBB-SiNPs hybrid prepared at a mass ratio of 2:1. Fishbone biochar was produced through pyrolysis, while silica nanoparticles were synthesised from rice husk ash and incorporated into FBB to produce the hybrid material. The prepared adsorbents were characterised using X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Their treatment efficiencies were evaluated against five heavy metals (Pb, Cd, Cu, Zn, and Ni), methylene blue (MB) dye, and two bacterial species, Escherichia coli and Staphylococcus aureus. The results revealed that the hybrid exhibited the highest removal efficiencies for Cd²⁺ (98.3 ± 0.5%) and Cu²⁺ (97.7 ± 0.6%), whereas FBB reduced the residual concentrations of Pb²⁺, Zn²⁺, and Ni²⁺ to below the reported analytical detection limit of 0.001 mg/L. The hybrid also demonstrated the greatest reduction in MB absorbance at 662 nm, corresponding to an apparent removal efficiency of 95.45%. In the microbial assessments, SiNPs produced the highest reduction in the reported E. coli response (96.6%), whereas the hybrid achieved the highest reduction in the S. aureus response (94.4%). Overall, the findings demonstrated that pollutant removal performance depended on contaminant type, with hybridisation enhancing some treatment outcomes but not consistently outperforming the individual materials. Although the results highlight the potential of these waste-derived materials for multifunctional wastewater treatment, further investigations involving validated microbial enumeration, adsorption mechanisms, and real wastewater systems are required to establish their practical applicability.