Activated carbon prepared from industrial wastewater treatment plant dry sludge was proven to be efficient for the removal of refractory dye red scarlet nylosan (F3GL). Mixed treatment (chemical followed by thermal) considerably improved the adsorption capacity of the sludge. Batch tests at 40 °C gave maximal adsorption capacity. Application of Langmuir model gave 434.78 mg/g for treated material (SNHC) and 169.49 mg/g for the unmodified material (S). Thermodynamic parameters indicated that the adsorption is favored by an increase of temperature. The values of the enthalpy revealed physic-sorption. The results clearly showed that the mixed treatment of the adsorbent is the most adequate for the removal of toxic substances such as dyes present in industrial wastewaters