Central Composite Design Optimization of the Biological Decolorization of Cationic Dyes by Mix Algae Biomass in Bubble Column Reactor

A five factor, three-level Central composite design (CCD) combining with response surface (RSM) was employed for maximizing crystal violet adsorption capacity (qe) and removal dye from aqueous solution using a low-cost biosorbent prepared from a 50 : 50 mixture of two microalgae species: green (Chlorella vulgaris) and blue-green (Arthrospira platensis). The biosorbent was characterized by Fourier-transform infrared spectroscopy (FT-IR). Central composite design within response surface methodology (RSM) was employed to optimize five critical factors affecting crystal violet (CV) removal: pH 3‒11, biosorbent dose 250‒750 mg, temperature 20‒50°C, initial CV concentration 10‒30 ppm, and adsorption time 5‒15 min. MINITAB 18 software was used to maximize the adsorption capacity. The highest experimental crystal violet dye capacity of 140 mg/g was found in the lowest algae dose, consistent with calculated values based on numerical optimization. Kinetic modeling revealed the best fit with the pseudo-first-order model R2 (0.9829), while equilibrium isotherm data were best described by the Langmuir model R2 (0.9960). Thermodynamic parameters (ΔG0, ΔH0, and ΔS0) indicated the spontaneity and endothermic nature of the biosorption process. Finally, the study of mass transfer adsorption models was examined using the Weber and Morris model, the liquid film diffusion model, and Bangham and Burt’s model. When comparing these models, Bangham’s and Burt’s model has the highest R2 (0.9971). The rapid dye uptake suggests the potential of this algal biosorbent for efficient and simultaneous dye removal in real-world contaminated environments.