Short and Long-Term Responses to Changes in Hydraulic Loading in a Fixed Denitrifying Biofilm

The long- and short-term effects of hydraulic loading were investigated in a pilot packed tower bioreactor used for denitrifying a groundwater used for drinking water. Field experiments were conducted at hydraulic loading rates of 3.63 and 7.24 m³/hr/m². The long-term (21 day average) performance of the denitrification reactor and the short-term response (48 hour) to regular air scour are reported here. In summary, an increase in hydraulic loading resulted in a long-term increase in the half-order denitrification rate constant, so that, on average, nitrate removal was maintained in the 5.2 m tower. At the lower hydraulic loading rate (3.63 m³/hr/m²) denitrification performance in the first 48 hours after air scour was maintained; however at twice the hydraulic loading, several days were required to restore the biofilm performance to long-term average levels.