Page 376 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Rapid Filtration 331

12.1.1.3.3 Conventional Filtration sand (Baker, 1948, p. 179). The mechanical devices included
The ‘‘conventional’’ filtration mode is coagulation in a rapid jets of water applied on or just below the surface, a reverse
mix followed by flocculation, followed by settling, followed flow wash of the sand bed, and revolving sand agitators which
by filtration. Conventional filtration is the most common loosened the media from top to bottom.
mode and is essential when floc load must be reduced prior The impetus for the development the rapid filtration tech-
to filtration. nology for municipal drinking water seems to have been the
fact that the water in many American rivers was too turbid for
slow sand.
12.1.2 APPLICATIONS
12.2.1.1 Hyatt Filter
Rapid filtration may be applied for any water treatment task
According to Baker (1948, p. 183), the genesis of the modern
that involves removal of particles. Municipal wastewaters
rapid filter was the Hyatt mechanical filter. This filter was the
may be treated for such purposes as irrigation, boiler feed
result of an 1880 patent by Patrick Clark for a sand bed that
water, recharge of groundwater, etc. Industrial water supplies
could be cleaned by downward jets of water. In December,
and industrial wastewaters may be treated by rapid filtration,
1880, Clark, John W. Hyatt, and Albert Westervelt incorpor-
with variations that depend upon the purpose, unique to each
ated as the Newark Filtering Co. to build and market the filter.
industry.
John Hyatt used Clark’s patents and added his own innov-
ations that included a closed tank (a pressure filter) and a
12.1.3 VARIATIONS common header pipe to several filters for both raw water
and backwash water. He obtained a patent in 1881 for what
In addition to the three ‘‘modes’’ of rapid filtration, the tech-
would be the prototype for the rapid filtration concept. The
nology has many other variations. Some of the generic alter-
idea was to design a filter that could be cleaned by ‘‘mechan-
natives include (1) deep-bed mono media or dual media, (2)
ical’’ means.
constant flow or declining flow, (3) effluent control or rising
At the same time, Col. L.H. Gardner, Superintendent of the
headwater, (4) pressurized versus gravity, air scour versus
New Orleans Water Co., was experimenting with coagulation
surface wash or both, (5) gravel under-drain system or pro-
and was convinced that it was more effective than slow sand
prietary, etc. Proprietary ‘‘package’’ systems may include
filtration (called at that time, simply, ‘‘filtration’’) for dealing
combinations of the foregoing and, most likely, a unique
with muddy water. Isaiah Smith Hyatt, older brother of John,
feature.
was on the scene in New Orleans as sales agent for the
Newark Filtering Co., trying to clarify Mississippi River
12.2 DEVELOPMENT OF RAPID FILTRATION water for a New Orleans industrial plant. Col. Gardner sug-
gested using a coagulant, which was done in conjunction with
The rapid filtration technology evolved from proprietary the filtration and was successful. On February 19, 1884,
systems as proposed in the 1880s and took a generic form Isaiah Hyatt obtained a patent for simultaneous coagulation
during the period 1910–1920. Further innovations were in filtration, having had used ‘‘perchloride of iron’’ for the filtra-
the 1960s, for example, with media alternatives, (e.g., from tion of the Mississippi River waters. Also, Baker reported that
sand to dual media of anthracite and sand), and higher by 1889, John Hyatt had developed a filter that incorporated a
hydraulic loading rates, for example, from 0.082 to 0.204 backwash to expand the filter bed in what was essentially the
2
m=min (2.0–5.0 gpm=ft ). By the mid-1980s, theory, coupled genesis of the modern rapid rate filter.
with experiments with pilot plants, began to provide guid-
ance for design with deep beds of mono media (e.g., 2.0 m) 12.2.1.2 Warren Filter
2
and high filtration rates (e.g., 0.55 m=min or 13.5 gpm=ft ). Another proprietary filter was developed by John E. Warren,
By the early 1990s, pilot plants became established as essen- agent of the S.D. Warren & Co. paper mills, Cumberland,
tial for design and as permanent installations for operation. Maryland, who in 1884, planned and constructed a 45,000
Pilot plants were not new, however, having been used by m =day (12 mgd) filter plant for the mills, illustrated in
3
James Simpson in developing the slow sand technology for Figure 12.3. These filters were gravity type, contained
London and later at the Lawrence Experiment Station in in wooden tanks. An adjunct to the filter was an alum dosing
Massachusetts, c. 1890. apparatus, patented in 1890 by Professor Henry Carmichael of
Malden, Massachusetts (Baker, 1948, p. 199). As with the
Hyatt filters, several installations were completed for munici-
12.2.1 DEVELOPMENT OF RAPID FILTRATION
pal water supply systems. A coagulant was not used, however,
During the initial period of American water treatment prac- until the fourth plant was completed in 1892 at Macon,
tice, about 1870–1900, the so-called ‘‘English’’ filtration Georgia.
method, that is, slow sand, was emulated. At the same time,
during the early 1880s, experiments were underway with 12.2.1.3 Other Proprietary Filters
‘‘mechanical filters,’’ so named because the method of clean- After the mid-1880s, several more proprietary filters emerged
ing was mechanical rather than by manual labor as in slow on the scene. One prominent company was the National