Biological nitrogen removal in a bubble column with a draught tube

A bubble column with a draught tube was applied as a small scale treatment unit of anaerobic-aerobic activated sludge processes in which nitrogen and phosphorus compounds were removed together with BOD sources. The inside of a draught tube was used as an aerobic zone and the annulus as an anaerobic zone. The circulation flow rate of the mixed liquor between these two zones was varied by changing the air flow rate into the draught tube. There existed the optimum values for volume ratio of aerobic/anaerobic zones, air flow rate and liquid circulation flow rate between two zones depending on the activities of nitrification and denitrification . The performance of the treatment unit was simulated by using the model of the liquid flow in the reactor and the kinetics of simultaneous nitrification and denitrification in the activated sludge floc. It became clear that the consumption of BOD source inside the floc should be considered to explain the drop of nitrogen removal at high aeration rate and long residence time.