23 JULY 2003
Filtration using the plate and frame filter press is generally desirable for
sludge with poor dewatering characteristics or for sludge that requires a solids content
more than 30%, such as sludge that is disposed of by incineration. In general, if sludge
characteristics, such as concentration, are expected to change over a normal operating
period, or if minimal conditioning is required, the variable-volume press may be selected
over the fixed-volume press.
The paragraphs that follow compare general advantages and disadvantages
of the plate and frame filter press with other dewatering processes (Table 2-2). The
advantages and disadvantages of the variable-volume recessed filter press versus the
fixed-volume recessed filter press are also presented (Table 2-3).
Table 2-2. Advantages and disadvantages of filter press systems compared with
other dewatering processes.
Large quantities of inorganic conditioning chemicals are
High solids content cake.
Can dewater hard-to-dewater
Very high chemical conditioning dosages or thermal conditioning
may be required for hard-to-dewater sludges.
Very high solids capture.
High capital cost, especially for variable-volume filter presses.
Only mechanical device capable of
Labor cost may be high if sludge is poorly conditioned and if
producing a cake dry enough to
press is not automatic.
meet landfill requirements in some
Replacement of the media is both expensive and time
Noise levels caused by feed pumps can be very high.
Requires grinder or prescreening equipment on the feed.
Acid washing requirements to remove calcified deposits caused
by lime conditioning may be frequent and time consuming.
Batch discharge after each cycle requires detailed consideration
of ways of receiving and storing cake, or of converting it to a
continuous stream for delivery to an ultimate disposal method.
Source: EPA (1987)