Black liquor (BL) as lignocellulosic-based industrial wastewater is largely attained from a chemical pretreatment process. When treated with the commonly used coagulant polyaluminum chloride (PACl), BL was decolourized but its pH decreased drastically from 13 to 4-5. Chitosan as a natural flocculant was added to the BL treatment process to support the PACl. The combination of coagulant-flocculant (PACl-Chitosan) effectively generated sludge, rejuvenated the treated BL pH level to neutral, and decolourized and reduced several parameters required for the treated BL disposal. To establish a sustainable recycling process and enhance the BL treatment, the generated sludge as a potential source was recovered and converted to a carbonaceous adsorbent (CA) by applying a two-stage carbonization process, heat and steam carbonization, during which the temperature and time in the first stage of the heat-carbonization process differ. The first BL sludge-based CA (BLS-CA 1) is produced by employing the first stage heating at 575 degrees C for 180min while the second black liquor sludge-based CA (BLS-CA 2) is produced by employing the first stage heating at 450 degrees C for 60min. Both CAs were able to adsorb about 99% methylene blue (MB) at MB concentration 100mg/L for 16h though they have smaller surface areas than commercially activated carbon, which is only able to adsorb about 70% MB at the same concentration and adsorption time. This study demonstrates a potential way to reduce the emerging problem from the generated sludge through a sustainable recycling process as well as BL treatment.