Continuous flow biosorptive removal of methylene blue and crystal violet dyes using alginate–water hyacinth beads

Abstract

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 (tb) and exhaustion time (te), whilst the adsorption capacity at breakthrough point (qb) 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 (No) value of 14.2 mg/L and a critical bed depth (Xo) 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-sorption-desoprtion cycles. Water hyacinth showed great potential as a low-cost, efficient and effective biosorbent for the purification of dye-contaminated wastewater.