The effect of the processes of carbonization and activation on adsorbents obtained from sewage sludge and evaluation of the sorption properties of such adsorbents towards NO₂ was studied. Carbonaceous adsorbents were obtained by carbonization of sludge at 600ºC for four different times (30, 60, 90 and 120 min.) followed by activation of the carbonisates by CO₂ at 800ºC for 60 min. Adsorption of NO₂ was carried out in dry air. It has been shown that by appropriate thermal and chemical treatment of sludge, mesoporous adsorbents can be obtained that are capable of NO₂ removal. The activation of the carbonisates with CO₂ was found to substantially improve their sorption properties. The best NO₂ sorption capacity from among the samples obtained by carbonization at 600ºC or by carbonization at 600ºC followed by activation by CO₂ at 800ºC was obtained for the samples carbonised for 90 minutes.