Abstract. This study focuses on the valorization of extraction residues of medicinal plants which represent approximately 80% of the gross weight of the plant. In this context we proceeded to the transformation of "marc oregano" to a material adsorbent type activated carbon. The oregano marc, obtained after extraction of essential oils and organic compounds, has undergone a chemical activation using the phosphoric acid 85% (H 3 PO 4 ). It is well known as precursors of lignocellulosic activating agent, allows the development of a large porosity in the activated material. The activated product has subsequently underwent heat treatment in the temperature range from 200 to 350 • C. The optimum temperature for development was set at 300 • C. The results obtained showed that the adsorbent material O 300 has developed the interesting textural properties. It is an adsorbent material like activated carbon, which presents, according to the BET method, a specific surface of 1200 m 2 · g −1 (specific surface area of commercial activated carbon is of about 905 m 2 · g −1 ). The application of adsorbent material developed O 300 in microbial decontamination of urban waste water, has revealed its effectiveness and its important adsorptive properties against pathogens pollutants from wastewater.