Experimental and modeling evaluation of upward and downward velocities in the coaxial flotation column

This study was conducted to show the influence of upward velocity in the in ner column and downward velocity in the outer column of the coaxial cylinde r-type flotation column on the solids removal efficiency, solids concentrat ion in the treated water, and so on. The SIMPLE (Semi-Implicit Method for P ressure Linked Equation) solution was applied to the coaxial flotation colu mn to simulate the velocity vectors of the elements of water flowing in the column. The effects of solids loading and residence time in the agglomerat e separation zone on the solids removal efficiency were also tested. In the pilot scale coaxial DAF column experiments with solids concentration of 1,000-2,000 mg of SS per liter and solids loading less than 350 kg/m(2) /day, approximately 90% of the solids removal efficiencies were obtained us ing the upward velocity of up to 110 cm/min in the contact zone of the inne r column and the downward velocity of up to 30 cm/min in the outer column. In the simulation. similar results were observed as in the experiments. The solids loading in the excess of 350 kg/m(2)/day caused the instability of the sludge float layer and aggravated the quality of the treated water.