The Study of Nitrate Removal from Raw Sewage of Tehran City by Walnut Tree Sawdust using the Surface Absorption Method

In this paper, the removal of nitrates from urban raw sewage (Tehran) by walnut tree sawdust using the surface absorption method was introduced as an efficient green method, and the effect of various parameters was studied. The results obtained from Langmuir isotherms R2=0.9951 and Freundlich R2 = 0.9936 indicated better absorption in low concentrations, which follows the Langmuir model. To complete the present studies, the adsorption diagram, the effect of pH, thermodynamic and kinetic studies were investigated. Kinetic studies showed that the surface adsorption process of nitrate by walnut tree sawdust follows the pseudo-first order kinetic. The absorption capacity obtained from this equation was 34.2 mg/g (its experimental value of 32 mg/g). The results showed that this process is controlled by reversible physical adsorption. According to the FT-IR spectrum of the absorbent, the phenomenon of nitrate absorption takes place with the help of the cellulose structure of the absorbent. The use of walnut tree sawdust (micro size) without chemical modification as a natural, green, environmentally friendly, efficient, and effective adsorbent in removing nitrates from the raw sewage of Tehran city was one of the important features of this research.