Fluidized bed flocculation-coagulation of seawater from the Algiers area

Abstract

Flocculation in a fluidized bed was tested as a new approach where the driving force for the aggregation of the constituents in solution is no longer generated by the regular motion of mechanical elements (conventional stirring). In this case, this force was generated by the random movement of fluidized bed particles. A hydrodynamic study allowed the definition of the minimum fluidization velocity. This, in turn, allowed the definition of the velocity gradient, the granular medium constituted of inert resin particles. It was on the order of 31.65 s −1, which is exactly in the flocculation interval of 30 to 100 s −1. Jar tests with aluminum sulfates led to the definition of optimal conditions of coagulation-flocculation for seawater from the region of Algiers doped with 10 mg/l of humic acids. Results suggest an isoefficiency area corresponding to an aluminum sulfate concentration interval of 40 to 130 mg/l for a pH interval of 5.5–8. The fluidized bed flocculator achieved performances comparable to jar test flocculation at flow velocities higher than the minimal fluidization velocity. Turbidity was reduced by 90%, and organic matter elimination was on the order of 70%. It is also important to report a slight decrease of conductivity of about 13%. This suggests that interactions between flocs and dissolved salts should not be ignored. On the other hand, expansion of the fluidized bed up to 32% did not affect performance, which corresponds to an increase of the flow velocity by threefold compared to the minimum fluidization velocity. Seawater flocculation-coagulation in a fluidized bed, therefore, is of great interest for the intensification of conventional processes. This type of flocculator offers a residence time of about 4.48 min, clearly less than a batch flocculator.