23 JULY 2003
in a U-shaped trough or enclosed in a tubular housing. A drive mechanism turns the
center shaft, which is supported by end bearings and intermediate bearings as
necessary to reduce shaft deflection.
Standard augers are most useful for moving dewatered sludge horizontally
over relatively short distances. The length of auger systems in most wastewater
treatment facilities is limited to 9 to 12 m (30 to 40 feet), although longer augers are
possible. Inclined augers require different design criteria than horizontal augers and are
less efficient. The capacity of an inclined auger is reduced approximately 2% for each
degree of incline over 10 degrees.
Design considerations for auger systems are similar to those for belt convey-
ors. Characteristics, volume, and variability of the sludge are important design consid-
erations. A major advantage of an auger system over a belt conveyor is that the auger
can be completely enclosed to control odors and reduce housekeeping requirements.
2-4.9.3 Pumping Systems. Only two types of pumps, progressive cavity and
hydraulically driven reciprocating piston pumps, have been used with limited success to
transport sludge cake in lieu of belt conveyors and augers. Advantages of pumps
include control of odors, spills, and noise. However, pumps usually require more energy
than conveyor systems. Head losses for most sludge cake pumping systems are high
and often range from 1.4 to 6.9 MPa (200 to 1000 psig), depending upon the length,
diameter, and configuration of the discharge piping.
Progressive cavity pumps have been used with limited success to pump
sludge cake, and these pumps should be limited to pumping wet sludge cakes with
solids concentrations of approximately 15% or less. Hydraulically driven reciprocating
piston pumps were developed from concrete pumping technology and have also been
successfully used to pump sludge cake. The principal advantage of these pumps over
other pumps is that they can move sludge cakes with a wider range of plasticities.
Additional descriptions of these two types of pumps is also presented in Paragraph 4.3.
Filtrate and Cake Waste Management.
2-4.10.1 Filtrate Management. The filtrate management system is an important part
of monitoring the effectiveness of the filtration cycle. The minimum filtrate flow rate is
typically used in combination with a terminal pressure to determine the end of the
filtration cycle. The filtrate flow rate is normally slightly less than the feed rate of sludge
to the press. The filtrate typically has a low solids content because of the removal of
solids in the press, and it has biological oxygen demand (BOD) and chemical oxygen
demand (COD) concentrations. For HTRW sites, the filtrate may contain contaminant
concentrations that are similar to or lower than that of the sludge feed The quality and
rate of filtrate flow should also be monitored throughout the filtration cycle for changes
that indicate required conditioning adjustments or suggest filter media blinding.
Filtrate is typically discharged to an overflow tank to prevent solids from
escaping in the event of media failure. The filtrate tank is typically equipped with an