A novel method was conducted to modify activated sludge with cetyltrimethylammonium bromide (CB) to obtain an adsorbent to remove aqueous nitrobenzene. The adsorption characteristics of nitrobenzene onto modified activated sludge (MAS) were investigated, by contrast with those of unmodified activated sludge (UMAS). Nitrobenzene adsorption onto MAS is more favorable than that of UMAS at initial nitrobenzene concentrations below 150 mg/L, above which they have an equivalent adsorption capacity. pH value has a significant influence on the adsorption capacity, especially from 10.0 to 12.6 for MAS and from 9.0 to 11.0 for UMAS. The modification changes the steady even surface of activated sludge into uneven one, which is better for adsorption. The hydroxyl of activated sludge and hydrophobic group of CB adsorb nitrobenzene molecules, and CB increases the adsorption sites. The nitrobenzene adsorption onto MAS follows Langmuir isotherm, implying the adsorption occurrence tends to be on a homogeneous surface by monolayer adsorption other than multi-layer adsorption which accounts for the adsorption onto UMAS. The maximum adsorption capacity of MAS is 40.6, 25.0 and 25.6 mg/g at 6.0,25.0 and 40.0 degrees C, respectively. MAS presents to be a good adsorbent to remove nitrobenzene from water, and CB is a successful modifier. (C) 2010 Elsevier B.V. All rights reserved.