Mooyoung Han

A theoretical consideration of algae removal with clays

Abstract Recently, periodic and widespread algal blooms have been reported in the estuaries and lakes of Korea, causing a variety of problems for aquatic life and human activity. Currently, the only remedial practice employed for removing algal blooms is to spread clay on the surface of the water. However, the mechanism of algae removal is not well identified. In addition, engineering details and specifications for the correct selection of particle size, concentration of clay, spreading method and effective conditions have not been identified. In this study, the clay spreading practice has been investigated theoretically. A set of trajectory analyses was performed to calculate the collision efficiency of clay particles and algal cells. The sensitivity of the removal efficiency to the physical characteristics of both clay and algae was investigated. It was found that both particle/cell size and zeta potential of clay and algae are the most important parameters that control removal efficiency. Conclusions that might prove helpful to understand and guide clay spreading practice have been made. Selection of the appropriate particle size of clay in relation to the size of algal cells was found to be most important. Clay particle size should be similar to the algal cell size to obtain the best removal efficiency. Although some removal is expected in sea water, no effect is expected in lake water because of the effects of ionic strength.

Collision efficiency factor in Brownian coagulation for unstable and stable suspension including hydrodynamics and interparticle forces

In order to realistically model the behavior of Brownian particles in water, collision efficiency factor in Brownian coagulation (αBr) should be included.αBr is calculated by solving the diffusion equation including the detailed mathematical description of hydrodynamics and interparticle forces.αBr is found to be a function of several parameters: particle size and ratio, Hamaker constant, ionic strength of liquid, surface potential of particle. Ionic strength and surface potential significantly affectαBr. The graphical plane of ionic strength and surface potential is divided into two regions by a curve: above this curve, no coagulation is expected, however, below this curve, coagulation is expected.αBr values in this region are the same as those predicted for no electric repulsion. The model qualitatively explains the change of coagulation efficiency at estuary or water treatment plant. Better prediction of suspensions at both stabilized and destabilized system can be made possible incorporating the collision efficiency factors of the other coagulation mechanisms such as differential sedimentation and fluid shear.