Study on denitrification effect of O/A two-stage biological sand filter

The biological sand filter process was used to treat the secondary effluent of WWTP, and the influences of water temperature, hydraulic loading and carbon nitrogen ratio on the performance of denitrification by biological sand filter were separately studied. The result showed that with the increasing of water temperature, the denitrification performance of biological sand filter was improved significantly. When the hydraulic loading increased from 3 m³/(m²·h) to 3 m³/(m²·h), and then increased to 4 m³/(m²·h), the average removal rate of TN dropped by 2.08% and 11.15%, respectively. With the increasing of the hydraulic loading, the downtrend of denitrification performance was obvious. The carbon nitrogen ratio was increased from 2.5∶1 to 3.5∶1, and to 4.0∶1, and then to 4.5∶1, the average removal rate of TN was gradually enhanced. But when the carbon nitrogen ratio was 4.5∶1, the average concentration of CODCr was 54.08mg/L in effluent, which was slightly beyond the level of A standard. Considering the influence of hydraulic loading and carbon nitrogen ratio on denitrification performance, concentration of organic matter in effluent and economic cost, in this experiment the optimal control parameters were determined that the hydraulic loading and carbon nitrogen ratio were 3 m³/m² and 3.5∶1, respectively.