The study evaluated how different ways of injecting sulfur into a denitrification reactor affect its efficiency. By changing the direction of injection, researchers found that the up-flow method removed more nitrogen and organic matter compared to the down-flow method. The up-flow method had a nitrogen removal efficiency of 73.3-90.2%, which was over 10% higher than the down-flow method. The optimal operation condition for nitrogen removal was determined to be an Empty Bed Contact Time (EBCT) of 3 hours. To maintain legal nitrogen discharge levels, the nitrogen load in the reactor should be kept below 0.443 kgT-N/m^3/day.