Bya fixed volume press, the biosolids are pumped into the recesses over a of several hours to continually increase pressure and force the liquid through filter cloth. Low pressure units achieve a pressure of up to 100 pounds per square a pressure of up to is maintained until the filtrate essentially
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The most common vacuum filter consists of a large, horizontally mounted rotating drum, which is covered by a porous cloth or metal coils (see Figure 3-7). The bottom portion of the drum is submerged in a vat of biosolids. As the drum rotates, biosolids are picked up on the porous medium under a vacuum. The drum is divided into sections, and vacuum is applied by a rotary valve. The filter operates in three zones:

• Cake formation • Cake dewatering • Cake discharge

Vacuum filters can be successfully used with organic (polyelectrolyte) conditioning, inorganic (lime and ferric chloride) conditioning, and thermal conditioning.