Electrofiltration of Aqueous Suspensions

Capture of water-borne colloids in granular beds using external electric fields: improving removal of Cryptosporidium parvum

Suboptimal coagulation in water treatment plants often results in reduced removal efficiency of Cryptosporidium parvum oocysts by several orders of magnitude (J. AWWA 94(6) (2002) 97, J. AWWA 93(12) (2001) 64). The effect of external electric field on removal of C. parvum oocysts in packed granular beds was studied experimentally. A cylindrical configuration of electrodes, with granular media in the annular space was used. A negative DC potential was applied to the central electrode. No coagulants or flocculants were used and filtration was performed with and without application of an electric field to obtain improvement in removal efficiency. Results indicate that removal of C. parvum increased from 10% to 70% due to application of field in fine sand media and from 30% to 96% in MAGCHEM media. All other test particles (Kaolin and polystyrene latex microspheres) used in the study also exhibited increased removal in the presence of an electric field. Single collector efficiencies were also computed using approximate trajectory analysis, modified to account for the applied external electric field. The results of these calculations were used to qualitatively explain the trends in the experimental observations.

Effects of surface chemical and electrochemical factors on the dewatering characteristics of fine particle slurry

Coal suspension was employed in vacuum filtration process to observe the dewatering characteristics of fine particle slurry. Generally, as the size of coal particle decreased, the specific resistance was increased and dewatering efficiency was reduced. Slurries containing the particles with a broad size range had a higher compressibility and could not filter easily if modified process was not applied. This study also investigated the effects of an anionic and a cationic surfactants on filterability by examining the surface property of coal particles. Dewatering was observed to be more efficient when cationic surfactant was used. To improve dewatering rate and to reduce the final moisture content of slurry, electrodewatering combined with vacuum filtration was applied. The effects of some different variables were examined, such as the type of surfactants, electrode (arrangements and materials), and the electrical parameters (voltage and current). By application of electrodewatering, dewatering efficiency was found to be enhanced compared to conventional vacuum filtration. The specific resistance was represented to be 0.3815 at 0 V, whereas it was shown to be 0.2113 and 0.1631 at 20 V under direct current and alternative current, respectively.