Elimination of arsenic contamination from water using chemically modified wheat straw

Presence of arsenic in natural water resource as a common contaminant has always been a great concern for the scientists. The objective of this study was to explore the possibility of wheat straw modified with sodium bicarbonate (NaHCO3) for removing arsenate from aqueous solution. Adsorption process was accomplished in a laboratory-scale batch with emphasis on the effect of various parameters such as pH, contact time, arsenic concentration, and adsorbent dosage on the adsorption efficiency. In order to understand the adsorption process, sorption kinetics and equilibrium isotherms were also determined. It was found that adsorption of the arsenic is influenced by several parameters such as arsenic initial concentration, adsorbent dosage, and solution pH. Maximum adsorption efficiency was achieved at a pH of 7. The equilibrium adsorbed amount also increased with the initial concentration of the metal ions, as expected. NaHCO3 was used to modify wheat straw and scanning electron microscopy images showed that all of the adsorbents have been affected and modified by NaHCO3 solution. Among the models tested, both the Langmuir and Freundlich models represented the experimental data well. According to the Dubinin-Radushkevich isotherm model, mean free energy of adsorption (15.2 kJ mol(-1)) indicates that adsorption of arsenic by wheat straw might follow a chemisorption mechanism. It was also found that adsorption of arsenic by wheat straw followed pseudo-second-order kinetics. It is concluded that adsorption using modified wheat straw is an efficient and reliable method for arsenate removal from liquid solutions.