OXYGEN TRANSFER IN A BIOLOGICAL AERATED FILTER

The mass-transfer characteristics of a submerged-media biological aerated filter have been determined over a wide range of gas and liquid flow rates. The mass-transfer coefficients were measured using the nitrogen stripping method and were found to increase as both gas and liquid superficial velocities increase, with values ranging from approximately 80 to 500 h−1. Dynamic gas holdup was determined as the difference between total and stagnant gas holdup. The stagnant holdup was constant at about 4%, while the dynamic holdup increased from about 1% at the lowest gas flow rate to 3% at the highest gas flow rate. Further experiments will be conducted to determine the temperature dependence of the mass-transfer coefficient as well as the “dirty-water” correction factors. In the longer term, the biological uptake rate of oxygen from the water will also be measured. By evaluating the rates of oxygen supply and demand in the BAF, the rate-limiting process can be identified, and the knowledge used to optimize system performance.