A progressive passive filter is simply a series of screens with increasingly smaller openings that trap solids as the water flows through the unit (Figure 1). It is designed to be a gravity-fed process and is best suited for low volume flows. The screens are installed on an angle and the water level gradually climbs as the screen becomes clogged. If the screen becomes fully clogged, the washwater can overflow into the next area. The filter can be easily cleaned by removing the screens and washing off the solids. Depending on the settling capability of the solids begin filtered, the tank holding the screens may also need to be rinsed.
| This system is intended for low volume washing facilities with low solid loads. It will easily handle inconsistent flows as long as the flows don’t overwhelm the filters; it should be sized for the maximum flow or the flow be restricted to the filter’s capability. The number and sizes of the filters are chosen based on the type of solids to be removed. The final filter should be 100 microns as solids that pass through will not settle in pipes and block water flow. |  Figure 1: Diagram of a progressive passive filter |
The advantage of this type of system is that it is a compilation of parts that can be inexpensively sourced. It can be built to any size necessary and be fitted into an existing tank system. The disadvantage is that it is not useful in a large-scale production and it does require manual operation and maintenance.
Figure 2: Side view (far left), top view (center left), inside view (center right), and the outlet and 100 micron screen (far right) of the progressive passive filter constructed based on the diagram of Figure 1.
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