ENHANCED NITRIFICATION IN BIOFILMS BY OPTIMIZED OXYGEN ADDITION

Nitrification in a packed bed biofilm reactor (Biofor) for nitrification was strongly correlated to oxygen availability. Experiments controlling biofilm diffusion and external mass-transfer were performed.In one test the airflow was enriched with oxygen to variable levels without changing the total gasflow, thus eliminating hydraulic effects. The reactor was operated at an empty bed water velocity of 10 m/h. The nitrification rate increased instantaneously from 0.45 to 1.0 kg NH4− N/(m3.d) when the oxygen content increased from 20.9 to 50 % in the gasflow. The nitrification rate was correlated to follow a half order reaction rate with respect to oxygen, indicating that diffusion of oxygen into the biofilm was rate limiting.In another test the airflow at constant oxygen partial pressure changed from 0 to 2.5 – 3.5 Nm3/hr, during operation at three different empty bed water velocities, 6, 8 and 10 m/h, to investigate hydraulic effects on the nitrification rate. The reaction rate and bulk liquid oxygen concentration increased proportional with airflow. The reaction rate increased with increasing water velocity, indicating lower external mass transfer resistance. At 5 mg/l dissolved oxygen the nitrification rates in the reactor were 0.24, 0.39 and 0.53 kgNH4-N/(m3.d) at water velocity of 6, 8 and 10 m/h respectively.