Bioremoval of toxic dye by using different marine macroalgae

The removal of malachite green dye from aqueous solution by Ulva lactuca, Sargassum crassifolium, and Gracilaria corticata has been demonstrated in order to examine their potential use as low-cost adsorbents. The optimum pH (8.0), temperature (25 °C), contact time (150 min), and biomass (2.0 g) for removal of dye by algae are reported. The maximum removal percentage of the dye ranged between 95.6% and 98.3% by using Sargassum crassifolium at the optimal conditions. Minimum removal of dye by algae (69%-77.1%) was observed with the high dye concentration of 35 mg L-1 at the optimal conditions. Adsorption of the dye by using the biomass was found to fit well with Langmuir and Freundlich isotherms. The adsorption reaction was spontaneous, exothermic, and highly favorable by the tested algae. The FT-IR analyses confirmed that hydroxyl, carboxyl, amino, and carbonyl groups were responsible for the dye binding process. Scanning electron microscopy showed great porosity on the algal surface, which allows the free passage of dye molecules. The biomass of brown algae was the most effective in the removal of malachite green, followed by green and red algae. The highest affinity of the brown biomass for dye removal may be due to its high binding site affinity, the negative free energy of adsorption, and the great pores on its surface.