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Increasing attention is being paid to health and environmental risk as a result of the presence of trace steroid estrogens in the effluent discharged from municipal sewage treatment plants. This paper focuses on assessment of removal of these trace compounds using H-3-labeled estrone as the model compound. Jar tests over a range of ferric chloride dosages and pH conditions showed that coagulation was ineffective in removal of estrone from secondary effluent. The experiments showed that the combination of powdered activated carbon (PAC) and microfiltration could be effective for removal of trace estrone from water. The rate and extent of estrone removal by PAC are functions of PAC dosage and retention time of PAC in the system. Mathematical analysis of the results using a homogeneous surface diffusion model indicates that the adsorption of estrone on PAC can be limited by film diffusion and internal surface diffusion. The surface and film mass transfer coefficients were determined to be 1.59 x 10(-9) cm(2)/ min and 0.6 cm/min, respectively, under the conditions used.