The study aimed to investigate how adding external carbon sources can enhance denitrification potential in a pre-denitrification system. The researchers found that denitrification potential significantly increased with the addition of external carbon sources, such as ethanol, methanol, and acetate. Ethanol was identified as the most effective carbon source. By adding wasted ethanol, denitrification potential was enhanced, leading to improved nitrate removal efficiency. This research provides valuable information for optimizing carbon dosing in wastewater treatment plants.