Page 315 - Biosystems Engineering

292 Cha pte r Ni ne

practiced (flocculation). Several flocculating agents, among them
inorganic (aluminum, iron, and silicon derivatives), organic (such as
polymers), and natural products (such as starch and tannin) are used
in industry (e.g., clarification of municipal water, processing of ura-
nium ore, and black liquor treatment in paper industry).

9.3.5 Filtration
Filtration is the removal of solid particles from fluid by passing
the fluid through a filtering medium, or septum, on which the sol-
ids are deposited. Advantages and disadvantages of filter press
systems are compared with other dewatering processes in table 9.2.

Advantages Disadvantages
High solids content cake Large quantities of inorganic conditioning
chemicals are commonly used
Can dewater hard-to-dewater Very high chemical conditioning dosages
sludges or thermal conditioning may be required
for hard-to-dewater sludge
Very high solids capture High capital cost, especially for variable-
volume filter presses
Only mechanical device capable Labor cost may be high if sludge is poorly
of producing a cake dry enough conditioned and if press is not automatic
to meet landfill requirements in
some locations
Replacement of the media is both
expensive and time consuming
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: EPA (1987, pp. 114 through 117). Summarizes performance results
and operating and maintenance problems from a survey of 50 filter press wastewater
applications.
TABLE 9.2 Advantages and Disadvantages of Filter Press Systems Compared with
Other Dewatering Processes