No abstract

Removal of Methylene Blue (MB) and Crystal Violet (CV) dyes from monocomponent and binary aqueous solutions by water hyacinth-E. Crassipes roots fixed on alginate (a low-cost adsorbent) has been investigated. The extent of adsorption was evaluated as a function of solution pH, initial dye concentration, and bead biomass loading. Kinetic sorption data were analysed by widely used models: pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The results showed that pseudo-second-order model better described the biosorption experimental data than the pseudo-first-order kinetic model for both dyes, whilst the Elovich model fitted the biosorption experimental data at lower dye concentrations. The intraparticle diffusion model indicated that sorption of CV and MB was characterized by rapid surface adsorption coupled with slow film diffusion process at higher initial dye concentration and at all initial bead biomass loading. The range of mean free energy values confirmed physical adsorption as the mechanism for dye removal from solution.

The effectiveness of continuous flow biosorption of methylene blue and crystal violet dyes from aqueous solution was investigated using water hyacinth immobilized in sodium alginate. Characterization of the biosorbent was carried out using Fourier Transform Infrared Spectrometer (FTIR) and scanning electron microscopy (SEM). The adsorption process was optimized for adsorbate flow rate, initial dye concentration, and bed depth at fixed pH 8 under room conditions. The SEM showed the presence of a macroporous structure, whilst FTIR confirmed the presence of amine and hydroxyl groups. Increasing linear flow rate and initial dye concentration reduced breakthrough time (t b ) and exhaustion time (t e ), whilst the adsorption capacity at breakthrough point (q b ) increased with initial dye concentration and column bed depth. The adsorption data fitted both the Bed Depth Service Time (BDST) and the Yoon-Nelson models, with a BDST model adsorption capacity per unit volume (N o ) value of 14.2 mg/L and a critical bed depth (X o ) of 2.23 cm obtained. Regeneration and reuse of adsorbent gave an adsorption efficiency above 80% for both dyes in the binary solution phase for 3-sorptiondesoprtion cycles. Water hyacinth showed great potential as a low-cost, efficient and effective biosorbent for the purification of dye-contaminated wastewater.