Water purification using a packed bed reactor

In previous study, we have developed a novel water treatment technique to remove and inactivate bacteria such as Escherichia coli (E. coli) utilizing dielectrophoresis (DEP) induced by pulsed high voltage application. The result showed that E. coli was successfully trapped by DEP force and at the same time, inactivated by pulsed electric field (PEF). However, the effect of electrical properties of sample water on the collection and sterilization characteristics was not studied. In this study, influence of the conductivity of the samples on the collection and sterilization of E. coli was investigated. The conductivity of the samples was adjusted by NaCl and mannitol addition as well as bacteria concentration. As a result, removal and inactivation rate of E. coli decreased with conductivity of the sample. But around 50% inactivation rate was observed even for highly conductive sample, in which pulse width was less than 1μs and duty ratio was about 1/4000. Comparison between E. coli and PS beads having nearly the same size showed that E. coli was collected much more effectively than PS beads probably because of its agglomerative nature. High inactivation efficiency by PEF can be resulted from the agglomeration on the pellet surface, through which it is more likely for the cell membrane to be broken when the pulsed electrostatic field is induced.