Effect of horizontal flow on oxygen transfer in clean water and in clean water with surfactants

The effect of horizontal flow on bubble size and on oxygen transfer was examined in a 400-L pilot of oxidation ditch. In clean water, the oxygen transfer was enhanced by 38% when applying a horizontal velocity of 0.44 m s−1, although bubble diameter was increased by 24%. The oxygen transfer increase is mainly due to the neutralisation of the liquid vertical circulation (spiral flows).The addition of surfactants to the clean water (1 mg L−1) did not allow to reproduce the reduction of the alpha factor observed on a real site when applying a horizontal flow. Anionic surfactants reduced the bubble size. In the presence of the anionic surfactant SLS, bubble diameter was identical with and without velocity, the alpha1 factor was thus slightly increased when applying a horizontal flow. The addition of a non-ionic surfactant had no effect on bubble size, the alpha1 factor was then identical with and without horizontal velocity.