SEPARATION OF THE 2 FUNCTIONS AERATION AND MIXING IN OXIDATION DITCHES - APPLICATION TO THE DENITRIFICATION BY ACTIVATED-SLUDGE

To increase the efficiency of removal of nitrogen removal by activated sludge, oxidation ditches were used with a new configuration based on the separation of the two functions aeration and mixing. Experiments were carried out on full scale plants, completed by one pilot plant. T he liquid circulation was created by horizontal mixer and the oxygen w as supplied by flat flexible membranes. Several theoretical approaches have been used in order to predict the mean velocity in the ditches. Due to this circulation, the oxygen supply was increased by about 50%. Removal of nitrogen was also found to be 20 % higher with conventiona l system (surface aeration).