First, when the carbon source is sufficient, the denitrification effect is poor because the internal reflux ratio is too small. In denitrification, internal reflux and carbon source are both important factors affecting denitrification effect;
Second, the anoxic environment of denitrification tank is destroyed, which may often lead to excessive ammonia nitrogen;
Thirdly, the denitrification reaction time is not enough, and the time should be controlled above 2 hours, and denitrification will not be complete below the minimum residence time;
Therefore, when the denitrification effect is not good, it is necessary to comprehensively consider and finally determine the reasons for the poor effect before taking remedial measures.