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In this work, design variables and operating conditions in the adsorption of chlorinated volatile organic compounds (Cl-VOCs) using transition metal-modified natural zeolites (ZMt) are investigated. The levels of design variables are established: out-gassing temperature [350 °C, 550 °C], type of transition metal [Fe, Mn, Ag, Co, Cu, Ni], concentration of transition metal [0.05; 0.1 M], metal deposition method [impregnation, ion exchange], post-treatment of the deposited metal [calcination under O2 flow, reduction under H2 flow], whereas among operating parameters, the type of VOC-Cl [perchlorethylene, chlorobenzene], concentration of Cl-VOCs [1.5; 9.5 μmole dm-3], adsorption temperature [20; 100 °C], volumetric flow of Cl-VOCs [50; 100 cm³ min-1], mass of ZMt [0.15; 0.3 g] are chosen. D-Optimal design of experiment is used, and the number of experiments are reduced from 2.048 to 139. Adsorption experiments were carried out in a quartz U-shaped fixed bed adsorber, and the concentration of Cl-VOC was followed by gas chromatography. Experimental results are fitted to a second-order polynomial model. The analysis of variance (ANOVA) shows that the adjusted model is highly significant, with a satisfactory goodness of fit. ANOVA results also indicate that among the significant variables, modified zeolite samples by ion exchange using Fe or Cu increase the adsorption capacity toward Cl-VOC. The concentration of Cl-VOCs and the adsorption temperature show the biggest influence on the removal of Cl-VOCs, among all the studied operating variables. [ABSTRACT FROM AUTHOR]