Microalgae harvesting technology based on dynamic filtration with rotating disk

Abstract

A dynamic filtration method with a rotating disk was developed for effective microalgal cell harvesting. Firstly, its harvesting performance was investigated for different rotation speeds and disk configurations. Even at high biomass concentrations, increasing the rotation speed effectively helped improve the permeate flux mitigating mainly cell cake formation and to some degree adsorption fouling with the help of high shear stress created on the membrane surface. Cross-flow velocity and shear stress on the membrane surface were significantly higher with the perforated disk than those with the solid disk, which led to a more effective fouling alleviation and higher permeate flux. The performance of the dynamic filtration method developed in this study was compared with other methods of coagulation, electro-flotation, electro-coagulation-flotation, and centrifugation. It turned out to be best suited with desirable features of no biomass loss, high concentration of harvested biomass, and moderate energy consumption. A surface-modified membrane was tested for further reduction of adsorption fouling which could not be effectively removed even under high-shear conditions. The membrane coated by a hydrophilic polymer clearly exhibited an increased hydrophilicity, reduced mean pore size, and neutralized surface charge, which led to a decreased adsorption fouling and consequently an increased permeate flux. An integrated filtration system was newly developed in which the impeller of the circulating centrifugal pump acted as rotating disk also. Such pump-integrated module resulted in a simplified system and a much less energy consumption.