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Allows sludge to accumulate during both scheduled and unscheduled outages
of dewatering equipment.
Depending on the type of sludge generated and subsequent treatment
required, it may be stored in process tanks, sludge treatment process systems, or in
separately designed tanks. Sludge may be stored in tanks from 24 hours up to several
days to provide a more stable and uniform feed for downstream conditioning and
dewatering processes. However, the storage time should be minimized, especially if the
sludge is mixed to maintain a sludge with homogenous characteristics. Following
conditioning, prolonged storage may result in an increase in the breakdown and
solubilization of solid particles, thus decreasing the overall filter performance. Storage
tanks for biological sludge are often provided with top-entry or submersible mechanical
mixers to prevent septicity and resultant odor. Odor generated during sludge storage is
typically controlled with chemicals such as chlorine, hydrogen peroxide, or iron salts.
Additional detailed information on sludge storage, mixing, and odor control is presented
in EPA (1979), EPA (1987), WPCF (1983), and WEF (1992).
Sludge Transport. Sludge is moved via sludge pumps before conditioning
into sludge feed systems. The major design consideration for the sludge feed system is
that it be capable of handling varying flows, such as 2 to 125 L/s (30 to 2,000 gpm) of a
viscous to abrasive slurry at pressures ranging from 170 to 1550 kPa (25 to 225 psi). In
addition to varying flows and pressures, time-dependent effects, such as thixotropic
effects, can also affect sludge feed systems and pumping. Detailed information on
sludge pumping and conditions that may affect sludge transport systems is presented in
Eckenfelder (1981), EPA (1979), and WEF (1992).
2-4.3.1 Sludge Feed Systems. The sludge feed system delivers conditioned sludge
to the filter press under varying flow and pressure conditions. The sludge feed system
should be capable of delivering sludge under the following conditions during the filtration
During the initial filter press fill period, the feed system should deliver the
sludge at a high flow rate under low pressure.
After the initial fill period, the feed system should continue to deliver sludge at
a constant high rate, while adjusting to increases in pressure caused by solids
buildup and cake formation, until the terminal pressure is obtained.
Once the terminal pressure is obtained, the feed system should be capable of
maintaining this constant pressure while allowing the sludge flow rate to
At the end of the filter cycle, the sludge flow rate from the feed system is
dropped to a minimum.