Water under low pressure enters the module and passes from the exterior to the interior of the membrane fibers. Cleansing is accomplished by high-pressure gas backwashing. Continuous microfiltration is especially effective after biological treatment systems such as activated sludge. Crossflow microfiltration removes metal precipitate particles down to 0.1 micron from waste streams in metal plating, metal finishing, printed circuit board fabrication and similar operations. After chemical treatment to precipitate dissolved metals, water is pumped through the system at a high velocity and pressure.
Clean water is forced through the membranes while particles remain suspended.
The filtrate is suitable for feed to reverse osmosis units. The PVDF membrane is extremely robust and can be cleaned with strong acids, caustics or bleach. However, it is subject to fouling by oily wastewater. In a typical configuration, ceramic membranes line feed stream channels within a porous structure of alumina. Filtration takes place at an operating pressure from 20 psi to 40 psi.