Removal of microcystin-LR cyanotoxin from water using magnesium oxide rice husk biochar composite

Abstract
The widespread occurrence of Microcystin-LR (MC-LR) in freshwater bodies has intensified concerns regarding its impact on drinking water quality and human health. This study developed a magnesium oxide (MgO)-modified rice husk biochar composite as an adsorbent for removing MC-LR from aqueous matrices. The composite was characterized using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) surface area analysis. A Central Composite Design (CCD) under Response Surface Methodology was employed in Design-Expert 13.0 to optimize operational parameters.
Characterization results confirmed that MgO modification enhanced the porous structure, yielding a hierarchical micro–mesoporous system with a specific surface area of 223.11 m²/g, indicating a substantial number of active adsorption sites. The highest removal efficiency (80.93%) was achieved at an initial MC-LR concentration of 25 ppb, an adsorbent dose of 20 mg, and a contact time of 60 min. The quadratic model demonstrated strong predictive capability (R² = 0.9559), explaining 95.59% of the variability in removal efficiency. Adsorption performance was influenced by the interaction among concentration, adsorbent dosage, and contact time. Increased dosage enhanced removal due to greater availability of binding sites, whereas higher toxin concentrations led to site saturation and a plateau in efficiency.
Overall, the MgO-modified biochar composite exhibited promising potential as an effective and sustainable adsorbent for MC-LR removal in water treatment applications.