Enhancing nitrogen removal performance of CAST for low ratio of C/N municipal wastewater treatment

Key words: 
• biological nitrogen removal /
• municipal wastewater /
• cyclic activated sludge technology

Abstract: The nitrogen removal performance of CAST treating low C/N wastewater under different operation conditions was investigated and the profiles of pH and ORP were analyzed. The results showed that TN removal rate couldn’t be improved by increasing the C/N ratio of wastewater when the system operated in traditional mold. Decreasing the filling ratio of wastewater was helpful for increasing TN removal rate, while sludge bulking and nitrate accumulation happened because of the operation under long-term condition of low carbon source and incomplete denitrification when the filling ratio was 16%. Nitrogen removal efficiency could be greatly enhanced by alternating anoxicaerobic process with step feeding without adding external carbon source, and it was increased by increasing feed frequency with the maximum value of 87.23%. When real-time control strategy was employed, the judgment on the ending of nitrification and denitrification could be based on the inflection point on the varied curve of ORP and pH during organic degradation, ammonia oxidation and nitrate reduction, and thus reducing aeration and mixing time for the purpose of energy saving.