Removal of a basic organic dye Methylene blue from aqueous solution by adsorption onto a low-cost Biosorbent made from water hyacinth (Eichhornia crassipes)

The aim of this study was to evaluate the ability of water hyacinth (Eichhornia crassipes) used as biosorbent (ECB) to remove methylene blue dye (MB) from water. Adsorption was carried out in batch tests by varying several parameters including mass of the biosorbent, contact time, initial concentration and pH of the MB solution. After adsorption the supernatant was analysed by UV-Visspectrophotometry to determine the residual concentration of the MB solution. Adsorption modeling was done with the surface reaction kinetic model and Langmuir and Freundlich equilibrium models. The obtained results showed that the biosorbent from water hyacinth ECB has apHZPC of 5.51, a specific surface area of 292.52 m2 g-1 and a maximum observed capacity (Qmo) of 89.99 mg g-1. The maximum adsorption percentage increases with biosorbent mass, contact time, and initial MB concentration due to the availability of the number of active sites that gradually saturate to reach the maximum apparent adsorption percentage (%mAds) and the maximum apparent adsorption capacity (Qm).The maximum adsorption capacity and maximum adsorption percentage increase with the pH of the solution due to stronger electrostatic interactions appearing at pH above the pHZPC between ECB surface and cationic ions from MB.The optimal adsorption weight was evaluated to be 800 mg, with a %mAds of 88.63% at pH 8.06, after 270 min. The modeling results show that adsorption of MB on ECB is best described by the pseudo-second-order kinetic model and the Langmuir model. The values of RL and 1/n lower than 1 indicate that the adsorption of BM on ECB biosorbent is favorable. Thus, water hyacinth biosorbent is promising for the biosorption of methylene blue dye from wastewater.