The diatomaceous earth filter is available both as a vacuum and as a pressure filter. Both are designed with either septums or leaves covered with screening or fine slots that have openings of 0.003 to 0.005 in. These septums are pre-coated with a matt of 0.10 to 0.15 lb per sq ft of di-atomaceous earth.
The head loss at the end of the run can be 35 to 100 psi with the pressure units. The solids removal capacity is rather low at about 1/8 lb per sq ft. For a feed with an SS concentration of 10 mg/l, the running time at 1 gpm per sq ft hydraulic loading is about 24 hr.
Diatomaceous earth filtration produces clear effluents with removal efficiencies of over 90%. However, the costs are also high. Colloidal substances are usually not removed (as with ordinary granular filters) unless coagulants are added. Coagulants are seldom added to diatomaceous earth filter influents because they shorten the runs.
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