Clarification by slotted surface microfilters

Metal microfilters, with a slotted pore geometry, have been used to filter colloidal suspensions using crossflow filtration to provide shear at the filter surface in order to reduce the deposition of solids on the filter. The slot widths tested varied from 10 to 2 μm and the slot length was about 400 μm. To assess the degree of pore blockage, challenge suspensions with particle diameters similar to the pore diameters were used. For comparison, a 10 μm pore width filter with circular pores was also tested. Under identical conditions, the slotted pore geometry did not foul as badly as the circular pore filter. Filtration fluxes of up to 9000 l m−2 h−1 were possible with minimum evidence of filter blockage or fouling. However, with a 2 μm slot width fouling was evident at filtration fluxes as low as 200 l m−2 h−1. An average filtration flux of 3000 l m−2 h−1 could be maintained with the 2 μm pore width filter by including a backflush, but it was important to exclude air from the filter; otherwise the capillary pressure to be overcome in order to remove the air from the filter became excessive. This new microfilter membrane design does not suffer from internal plugging of the filter matrix, because it does not have an internal structure, and can be made in to filters containing flat sheets or self-supporting tubes. The filter has many possibilities in fine particle processing and may be used to recycle clean liquid back to an industrial process.