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Abstract: Water pollution due to toxic heavy metals has been a main cause of concern for the environmental engineers. Heavy metals are individual metals that negatively affect people's health. In very small amounts, many of these metals are necessary to support life. However, in larger amounts, they become toxic. Lead is one the important heavy metals that is applied in different industries such as manufacture of batteries, metal products and ammunition. Its standard limits in drinking water are 0.05 mg/L, because it affects all organs and functions of the body to varying degrees. The frequency and severity of symptoms among exposed individuals depends upon the amount of exposure. Lead entering the respiratory and digestive systems is released to the blood and distributed throughout the body. It is stored and may be released into the blood, re-exposing organ systems long after the original exposure. This is why the wastewater includes lead should be treated before discharging to the environment. Different kinds of physical, chemical and biological methods are used to remove lead. The main techniques are including precipitation, ion exchange, adsorption, membrane processing and electrolyte methods. Adsorption with many advantages is a proper method that is applied to treat heavy metal removal. In recent years, use of low cost materials as adsorbent for metal ion removal has been highlighted. Since natural absorbents are inexpensive and may be achieved without any cost and they are usually in abundance in nature, absorption of solute ions by these materials are a proper method to eliminate heavy metals from polluted waters and industrial wastewaters. In this study, following continuous column method, sawdust and ash, as two absorbents were used for removing lead. The experiments were carried out with the initial pH of 5 and different densities (50 and 100 ppm). In order to optimize the process of adsorption, three combined absorbents were also used which made from the above two absorbents with the ratios of 1:3, 1:4 and 1:6. Batch experiments were carried out in order to determine the parameters of adsorption. The results of sorption with sawdust have shown that Langmuir adsorption isotherm were suitable. Based on the results of the column experiments study, lead removal efficiency was more than 98 percent when combined absorbents were used. In batch experiments, the percent efficiency was 76 and 98 percent with sawdust and ash, respectively.

Keywords: sawdust, sorbent, ash, continuous

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