Water Pollutants Adsorption through an Enhanced Activated Carbon Derived from Agriculture Waste

of the Study: A high nitrate and arsenic concentration in water resources represents a potential risk to the environment and public health. The present work improved a chemo-physically modified activated carbon derived from walnut shells as an adsorbent to improve nitrate and arsenic removal ability from water. To increase removal efficiency, activated carbon surface characteristics was improved by acidification. Chemical activation was achieved when the carbon was mixed with water and 5% (v/v) phosphoric acid. After adsorbent preparation, the contact time, pH, initial concentration were studied as variables. The effective pH for adsorption onto activated carbon was 6.5. The results indicate that 70 s and 3 mins was sufficient time to attain equilibrium for a maximum removal efficiency of 78.44% and 98% respectively for nitrate and arsenic. The adsorption capacity of the adsorbent was 10.60 mg nitrate/g carbon and 120 μg arsenic/g carbon. Removal obeyed the Langmuir isotherm and pseudo-second-order kinetic model. The results show a noticeable improvement in activated walnut-shell carbon absorbance (improvement in crystalline structure, chemical bonds, and morphology of micropores) by chemo-physical activation. Chemo-physical activation increased the surface area of the adsorbent from 1067 to 1437 m2g‒1 and decreased the mean pore size from 3.28 to 2.08 nm. The characterization results show the major reasons of adsorption could be structure, size and distributions of pores, high surface area and chemical bonds.