From batch to fixed-bed biosorption of Congo red using surfactant-modified wood chips: Mechanistic insights,...

This study examines the biosorption capacity of raw wood chip (WC) and cetyltrimethylammonium bromide-modified wood chips (WC-CTAB) in removal of Congo Red (CR) dye from aqueous solutions using integrated batch-column approach combined with artificial neural network (ANN) modelling. The lignocellulosic biosorbent was characterized using FTIR, SEM and pH_PZC analysis, confirming the successful introduction of cationic functional groups after CTAB treatment. Batch biosorption experiment showed that the maximum Langmuir biosorption capacity increased from 15.3 to 25.8 mg/g after modification, and the biosorption obeyed pseudo-first order kinetics and Langmuir-Hill isotherms, showing a mainly physisorption based monolayer type biosorption mechanism with a cooperative pattern. Thermodynamic parameters (ΔG° = -33.9 to -48.3 kJ/mol; ΔH° < 0) confirmed that biosorption was spontaneous and exothermic. In order to assess the scalability of the process, fixed-bed column experiments were carried out at different bed heights (5-10 cm), inlet concentrations (20-50 mg/L) and flow rates (5-10 mL/min). The dynamic biosorption capacity increased from 12 to 15 mg/g for WC to 19-26 mg/g for WC-CTAB and breakthrough time almost tripled with bed depth (46 vs. 138 min at 20 mg/L and 5 mL/min). Breakthrough data were well fitted by the Thomas and Yoon-Nelson models (R² > 0.97) while BDST revealed linear depth-service time behavior suitable for scale-up. Regeneration studies showed 70 % capacity retention in batch mode after three cycles and 85 % capacity retention in column mode after three cycles. ANN modelling accurately predicted biosorption performance and indicates potential usefulness as a support tool for process optimization. The findings show the possibility of transformation of low-value wood waste into an inexpensive, recyclable and scalable adsorbent for continuous industrial dye removal.