Apart from providing a total activated sludge (AS) inhibition, an efficient AS inhibition technique must preserve the biomass structure in order to maintain the real sorption phenomenon. Many inhibition techniques with different modes of action were used in previous studies for AS inhibition. But, the effectiveness of AS deactivation and the adverse effects on the biomass structure were rarely related. In this paper, five common AS inhibition techniques were evaluated: thermal, three chemical and gas purging techniques. The lowest chemical effective concentrations were determined in order to limit the negative impact on the AS structure. 100 mgHg(2)SO(4) g(TSS)(-1) and 30 mgHgCl(2) g(TSS)(-1) within 2 h of reaction were enough to provide a complete AS inhibition. However, after 20 h of reaction a full AS inhibition has never been achieved with sodium azide at 200 mgNaN(3) g(TSS)(-1), even by increasing NaN3 concentration. The analysis of the AS apparent viscosity, the median size D-50 of the flocs and the supernatant turbidity showed that the thermal technique destructured the AS completely. A significant AS deflocculation is induced by the three chemical reagents depending on the mode of action and the concentration used. Thermal and chemical inactivations are therefore not suitable to determine sorption properties. The only technique which kept the initial AS structure unchanged has several drawbacks since (i) a reaction might occur between the gas and the analyte of interest, and (ii) anaerobic activated sludge are not inhibited by this technique. Therefore, the establishment of anaerobic conditions without gas injection is recommended for implementing sorption experiments on aerobic AS. (C) 2013 Elsevier B.V. All rights reserved.