en Environmental Health Environmental Health پژوهشي Original Article <table align="left" cellpadding="0" cellspacing="0" hspace="0" vspace="0"> <tbody> <tr> <td align="left"> <table align="left" cellpadding="0" cellspacing="0" hspace="0" vspace="0"> <tbody> <tr> <td align="left"> <p><strong>Background & Aims of the Study</strong><strong>:</strong> A high nitrate and arsenic concentration in water resources represent 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.</p> <p><strong>Materials & Methods:</strong> To increase removal efficiency, activated carbon surface characteristics were 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 and the initial concentration were studied as variables.</p> <p><strong>Results:</strong> &nbsp;The effective pH for adsorption onto activated carbon was 6.5. The results indicated that 70 s and 3 mins was the sufficient time to attain equilibrium for a maximum removal efficiency of 78.44% and 98% for nitrate and arsenic, respectively. The adsorption capacity of the adsorbent was 10.60 mg nitrate/g carbon and 120 &mu;g arsenic/g carbon. Removal obeyed the Langmuir isotherm and pseudo-second-order kinetic model.</p> </td> </tr> </tbody> </table> <div style="clear: both;"></div> </td> </tr> </tbody> </table> <p dir="ltr"><strong>Conclusion:</strong> The results showed 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 showed the major reasons of adsorption could be structure, size and distributions of pores, high surface area and chemical bonds.</p> Nitrate, Arsenic, Walnut shells, Adsorption, Activated Carbon, Agriculture Waste, Iran 286 294 http://jhygiene.muq.ac.ir/browse.php?a_code=A-10-58-1&slc_lang=en&sid=1 Mojtaba Fazeli مجتبی فاضلی m_fazeli@sbu.ac.ir No Department of water and wastewater engineering, School of Water and Environmental Engineering, University of Shahid Beheshti, Tehran, Iran استادیار دانشگاه شهید بهشتی، دانشکده آب و محیط زیست Mohammadjavad Kazemibalgehshiri محمدجواد کاظمی بلگه شیری mj_kazemi@ace.sbu.ac.ir No Department of water and wastewater engineering, School of Water and Environmental Engineering, University of Shahid Beheshti, Tehran, Iran کارشناسی ارشد دانشگاه شهید بهشتی، دانشکده آب و محیط زیست Abolghasem Alighardashi ابوالقاسم علی قارداشی a_ghardashi@sbu.ac.ir Yes Department of water and wastewater engineering, School of Water and Environmental Engineering, University of Shahid Beheshti, Tehran, Iran استادیار دانشگاه شهید بهشتی، دانشکده آب و محیط زیست