23 JULY 2003
Diaphragm: An elastomeric or polypropylene membrane attached to the surface of the
filter plate of a variable-volume filter press that is used to provide the "squeezing" force
during the "filtration" cycle by application of pressurized water or air.
Feed solids: The total amount of solids in the sludge feed. This term is usually
expressed as a percent weight of the dry solids feeding the press.
Filter cake: The volume of solids plus water that is retained within the filter press.
Filtrate: The liquid removed from the sludge during the dewatering process.
Filtration area: The total surface area through which the sludge is filtered. This area is
typically a major factor that governs the rate at which the filter press will handle the
sludge feed slurry.
Filtration volume: The volume of sludge feed slurry that can be passed through the filter
press before it is necessary to remove the sludge cake.
Filtration: The act of separating solid particles from a liquid by passing it through a po-
Filtration rate: The average rate that a particular sludge slurry will pass through a press,
usually expressed in terms of liters per hour per square meter of filter area (L/m2h)
(gallons per hour per square foot of filter area [gph/ft2]).
Flocculation: Agglomeration of colloidal particles to form a loose cluster of particles that
will settle at a faster rate.
Fixed-volume press: A plate and frame press that produces a sludge cake in chambers
formed by fixed-area filter plates.
Precoat: A material used to coat the filter media in the filter press before sludge feeding
begins. The primary function of this material is to ease sludge cake removal and prevent
the media from blinding, thus reducing the filtration rate of the sludge.
Recessed plate: The recessed cavity of a filter plate that forms half of the chamber
where the sludge cake develops in a plate and frame filter press.
Sludge: Solid and semisolid materials removed from the liquid wastewater stream by a
wastewater treatment process.
Stabilization: A sludge pretreatment process used to make treated sludge less odorous
and putrescible and to reduce the pathogenic organism content before final disposal.
Stabilization results in a reduction of gelatinous organic materials that tend to retard or
slow filtration of sludge.