Advanced Denitrification of Secondary Effluent of a Wastewater Treatment Plant in Deep Bed Filter

The secondary effluent from a wastewater treatment plant was treated by a deep bed filter, so as to improve TN in the effluent to the surface water class Ⅳ criteria. When the average TN and NH4^+-N concentrations in the influent of the pilot-scale system were 13.88 mg/L and 0.68 mg/L, dosage of the carbon source (99% acetic acid) was 60 mg/L and empty bed hydraulic retention time was 15 min and 30 min, the average TN concentrations in the effluent were 0.81 mg/L and 0.74 mg/L, the corresponding average removal efficiencies were 94.16% and 94.67%, respectively , and the average volumetric loading rate was 0.64-1.28 kgNO3^--N/(m³·d). When the average TN and NH4^+-N concentrations in the influent increased to 18.05 mg/L and 1.40 mg/L, and the dosage of carbon source was 40 mg/L, the average TN concentrations in the effluent and the removal efficiencies were 5.04 mg/L and 2.36 mg/L and 72.08% and 86.93% under the same operational conditions. When TN and NH4⁺-N in the secondary effluent were controlled to be less than 15 mg/L and 0.5 mg/L, empty bed hydraulic retention time was 30 min and dosage of the carbon source (C/N=4.5) was sufficient in the pilot-scale system, TN in the effluent of the deep bed filter denitrification system could always meet the surface water class IV criteria.