عنوان مقاله [English]
Each year, more than 2000 million tons of wastewater is generated by oil refineries in the Middle East and European Union countries only. Oil refinery wastewater contains a wide range of toxic and non-biodegradable pollutants. Its discharge into the environment has created a major ecological problem throughout the world. An adsorption process for sewage refinery treatment would be an attractive method, if the adsorbent were inexpensive and available. In this study, activated carbon, prepared from almond shell and nut shells, are used as natural adsorbents for the treatment of petroleum refinery wastewater. The effect of pH, contact time and adsorbent concentration on TPH removal efficiency was studied. The results have shown that the effects of pH on the adsorption of petroleum hydrocarbons onto prepared activated carbon are small. It has also shown that about 90% of adsorption occurs in the first 30 minutes of the process and is completed in 60 minutes of contact time when the adsorption reaches equilibrium condition. The experiments demonstrated that an increase in adsorbent concentration leads to adsorbent particles attaching to each other. This reduces surface area and adsorption sites, therefore, decreasing adsorption efficiency per mass unit of adsorbent. The highest TPH removal efficiency obtained was 85% at pH=8, with a concentration of activated carbon=5 gr/L and contact time= 2 hours. Equilibrium sorption data were compared with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. The highest $R^2$ value was obtained for the Freundlich model, which indicated the heterogeneity of the adsorbent surface.Based on the Langmuir model, the maximum monolayer adsorption capacities of almond shell and nut shell activated carbon were estimated to be 83 mg/gr and 59 mg/gr, respectively. The heat of the sorption process for almond shell and nut shell activated carbon was estimated from the Temkin model to be 26.15 J/mol and 15.47 J/mole, respectively, which vividly proves that the adsorption experiment followed a physical process. Adsorption of petroleum hydrocarbons onto activated carbons was followed by pseudo-second-order reactions.