Investigation on the effect of flocculants on the filtration behavior in microfiltration of fine particles

Flocculated particles can form a highly porous filtration cake and prevent the deposition of particles on the membrane in combination with crosflow micro filtration, which would enable a higher permeate flux [8]. Using this concept, a study was carried out to investigate the possibility of using flocculants to enhance the permeate flux in micro filtration of fine particles. The study consists of several experimental series involving the various flocculants, changes in the suspensions pH value and different stirring rates. Promising results, indicating that interactions between membrane–particle–flocculant, which can cause complicated effects on the permeate flux, were obtained. The option of using flocculants to increase permeate flux is also indicated.

The following conclusions can be drawn: 1. The possibility to enhance the permeate flux in micro filtration of suspensions of fine particles is confirmed. 2. The effect of flocculants on permeate flux is complex. It can be positive or negative. There is a critical dosage at which an enhancement of permeate flux can be obtained. 3. Small amount of flocculant can already have a significant effect on the permeate flux. 4. Once the flocculant is introduced into the filtration systems, it can not only create flocs with particles but also adsorb on the walls of the membrane pores and form a gel layer on the membrane surface. These duplicated activities can lead to an increase in hydraulic resistance.