Dispersed air flotation as a pretreatment process for seawater desalination

Pretreatment of seawater before reverse osmosis (RO) processes with dispersed air flotation involves a change in oxygen concentration in seawater. In order to understand this phenomenon, a series of experimental aeration studies was conducted. Aeration tests were performed under different operating conditions of seawater temperature, flow rate of the air and depth of the water in the aeration tank. The experimental results show that the overall mass transfer coefficient increases by increasing air flow rate. A measured increase in the overall mass transfer coefficient was observed with elevation of the temperature from 24 to 38 °C. The estimated value of activation energy of oxygen absorption in seawater is 42.5 kJ/mol. The value of the overall mass transfer coefficient is found to be affected by diffuser type and stirrer speed as these parameters influence the bubble size and the surface area available for mass transfer of oxygen from air bubbles to seawater.