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

Background & Aims of the Study: A high nitrate and arsenic concentration in waterresources represent a potential risk to the environment and public health. The present workimproved a chemo-physically modified activated carbon derived from walnut shells as anadsorbent to improve nitrate and arsenic removal ability from water.Materials & Methods: To increase removal efficiency, activated carbon surfacecharacteristics were improved by acidification. Chemical activation was achieved when thecarbon was mixed with water and 5% (v/v) phosphoric acid. After adsorbent preparation,the contact time, pH and the initial concentration were studied as variables.Results: The effective pH for adsorption onto activated carbon was 6.5. The resultsindicated that 70 s and 3 mins was the sufficient time to attain equilibrium for a maximumremoval efficiency of 78.44% and 98% for nitrate and arsenic, respectively. The adsorptioncapacity 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.Conclusion: The results showed a noticeable improvement in activated walnut-shell carbonabsorbance (improvement in crystalline structure, chemical bonds, and morphology ofmicropores) by chemo-physical activation. Chemo-physical activation increased the surfacearea of the adsorbent from 1067 to 1437 m2g‒1 and decreased the mean pore size from 3.28to 2.08 nm. The characterization results showed the major reasons of adsorption could bestructure, size and distributions of pores, high surface area and chemical bonds.