Page 472 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Cake Filtration 427

particle size and distribution, pore size and distribution,
permeability, specific gravity, and dry bulk densities.
Manufacturers designate their respective products by
‘‘grade,’’ for example, Celite-560e. Table 14.1 lists selected
properties of different DE grades as designated by two
manufacturers, that is, Celitet (Celite=World Minerals Inc.,
Lompoc, California) and Celatomt (Eagle-Picher, Inc., Reno,
Nevada). The grades of diatomite are listed in an ascending
order of particle size, which corresponds to increasing pore
size and increasing permeability. As seen, the median particle
sizes are in the range of 7 d(diatoms) 50 100 mmand
median pore sizes are proportionately smaller, that is, in the
range of 1.5 d(pore) 50 22 mm. Figure 14.6 shows size
FIGURE 14.5 Ore ‘‘chunk’’ as obtained from mining operation
distributions for several grades of Celitet, which show that for
(ore from Ray McIndoe, c. 1984).
each grade a distribution exists, which results in the void volume
being filled to a large extent. The grades are differentiated
rotary kilns, followed by further milling and classifying; the by their d(50) sizes.
resulting powder is light pink in color. A ‘‘flux calcined’’
diatomite is manufactured by adding a ‘‘flux,’’ that is, soda
ash, before the calcining step, which gives still coarser 14.1.3 ATTRIBUTES
grades of DE, which are white in color (Kadey, 1975,
Some of the merits of DE filtration include compact size, low
p. 620).
operation and maintenance costs, simplicity of operation, and
With respect to Celitet, the finest grade is Filter-Celt,a
a system that can be shut down quickly and started quickly
‘‘natural’’ DE, which has been selectively quarried, dried,
(Spenser and Collins, 1995, p. 72). Examples are listed which
milled, and air classified. Three calcined grades of DE
illustrate the range of contextual situations.
include Celite 505t, Standard Super-Celt, and Celite 512t
(Johns Manville Brochure FA-304 6-80, p. 7). The flux-cal-
. Meeting summer peaking demand. Example: The DE
cined grades include Hyflo Super-Celt, Celite 501t, Celite
plant at Vacaville, California is operated 8 h per day
503t, Celite 535t, Celite 545t, Celite 540t, and Celite 560t
only during the summer.
(McIndoe, 1969a, p. 52). The flux-calcined products have a . Small footprint. Example: To treat the Croton water
more open pore structure within the bulk of the material
supply for New York, a diatomite plant was pro-
(i.e., not within the individual particles).
posed to be located in Jerome Park; Delaware
The finished product is packaged in 23 kg (50 lb) bags or
would utilize a smaller land area than rapid filtration.
shipped bulk in trucks or box cars; bulk loading is pneumatic. . Cost competitive. Example: For Georgetown, Color-
The average cost per ton was $55=metric ton ($50=U.S. ton),
ado a cost comparison between diatomite filtration
1960–1962; in 1972, the cost was $72=metric ton ($65=U.S.
and a rapid filtration pilot plant in 1986 indicated
ton). The total world production in 1972 was 2.2 million
lower annual costs using diatomite (Wirsig, 1986).
metric tons (2 million U.S. tons) (Kadey, 1975, p. 625). . Automated operation. Example: Hearst Castle in
California has a varying demand for drinking water
14.1.2.4 Characteristics of Media
over the annual cycle; two DE plants, rated at 113
The properties of diatomite are based in part on its method of
L=min (30 gpm) and 155 L=min (41 gpm), serve the
production, that is, whether it is a natural, calcined, or flux-
demand pattern. The plant is operated by PLC (pro-
calcined material. The properties of interest include color,
grammable logic controller), that is, pre-coat circu-
lates until turbidity is <0.5 NTU, then the unit
switches to produce treated water, the unit stops at
241 kPa (35 psi), and goes into the backwash mode
BOX 14.1 INTERNATIONAL DIATOMITE
(Rogers, 1997, p. 8).
PRODUCER’S ASSOCIATION
. Filtration is needed to follow another process.
The International Diatomite Producer’s Association Example: The water source for Lompoc, California
(IDPA) was formed in 1988 to provide a central office is a hard groundwater (782 mg=L as CaCO 3 ), which
to promote the use of diatomite. The IDPA represents is treated by lime soda. The effluent turbidity from
all diatomite producers who have elected to belong. The this process is about 2 NTU. The DE plant that
association provides information about diatomite and follows the softening treatment produces a finished
may act as a conduit from interested parties to the water with about 0.1 NTU (Rogers, 1997, p. 7).
diatomite producers regarding the availability of the . Cysts in ambient source waters are a particular issue.
product, its characteristics, and cost. Example: DE has demonstrated high removals, that
is, 4 < log R < 6 for cysts of Endameba histolytica,