Abstract: Dewatered alum sludge from drinking water treatment plants was exploited as carbon dioxide (CO2) adsorbent in a fixed-bed (CO2)lumn system. In this study, the effects of 6 parameters including particle size of adsorbent, heat treatment of adsorbent, adsorbents dosage, adsorption temperature, flow rate of adsorbate and (CO2) ncentration on the fixed-bed adsorption of (CO2) were investigated using Response Surface Methodology 2 2 (RSM). The experimental data was successfully fitted with the regression model to identify the significant parameters and predict the optimum value parameters for maximizing (CO2) adsorption capacity. Analysis of 2 Variance (ANOVA) revealed that (CO2) ncentration was the most significant factor influenced the (CO2) adsorption capacity. The experimental data of (CO2) adsorption capacity were in a good agreement with the 2 predicted data from the regression model. The highest fixed-bed (CO2) adsorption capacity of 10.028 mmol.g 2 1 (441.24 mg.g1) was achieved using 1 g of 450-500 μm of 800°C thermally treated alum sludge at (CO2) ncentration of 8000 mg.L1 with a flow rate of 90 mL.min1 at 25°C. The results suggested that thermally treated alum sludge is a promising solid adsorbent for (CO2) capture.