Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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UNDERDRAIN FOR LIQUIO PURIFICATION SYSTEM
This invention relates generally to collecting and
distributing apparatus or underdrains which are part of liquid
purification systems.
One method of purifying liquid uses filtration
systems with filter beds having one or more layers of material.
The top layer consists of a granular media which is made up of
fine particulate matter such as anthracite, and, carbon, or
garnet. The next level below the granular filtration media
comprises support or packing gravel. Underdrain laterals are
placed below the layer of gravel. These are long narrow
channels which are laid laterally across the width or length of
the filter bed. A plurality of such underdrain laterals are
placed side by side, so that the entire lower portion of the
filter bed beneath the gravel layer as composed of the
laterals.
The liquid to be filtered is applied across the top
of the granular layer. As it seeps through the granular layer,
waste material removed from the liquid accumulates and adheres
to the particles of the granular layer. The liquid then flows
through the qranular layer through openings in the top of the
underdrain laterals and then through a flume be~eath the
underdrain, through which the filtered liquid is discharged.
To maintain the efficiency o~ the filtering system,
it is necessary to periodically clean the waste material from
the granular and gravel layers. This is accomplished by the
use of backwash water, which flows in the reverse direction
through the filtration system. The backwash water is
introduced at the flume beneath the underdrain. It flows
upward through the underdrain into and through the gravel layer
and the granular layer, from whence it is discharged.
In order to make the backwash process more
efficient, ~ gas such as air is often used. The purpose of the
gas is to sufficiently agitate the gravel and granular material
to loosen and fr,ee waste material which has adhered during the
filtering process. During the gas cycle, a water level
slightly above the top of the granular level is maintained.
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After and or during the gas cleansing cycle, the backwash water
is introduced ~o remove the waste material which has been
loosened and freed by the gas.
Two approaches are used with regard to the
cleansing of the fil~er media. In one approach, the gas cycle
is usPd first and immediately followed by a cycle during which
backwash water alone is used. Another approach is to use the
gas cycle fir~t and immediately follow with a cycle during
which both gas and backwash water are introduced and flow
through the filtration system simultaneously.
The use of the combined cycle of gas and backwash
water is more efficient since the ~mount of water required is
drastically reduced as compared to the backwash water required
with a second cycle of backwash water only. Fur~hermore, the
combination of gas and water for the second cycle provides a
~ore efficient cleaning operation during the use of water
alone. However, when the granular material is very fine, the
combined ~ycle cannot be used because some granular material is
carried away by the gas bubbles in the backwash water and lost.
A typical operation might be the use of gas only in
the order of 3-5 standard cubic feet per minutQ per square foot
of the filter bed 2-5 minutes. ~hen the gas at 2-5 standard
cubic feet per square foot per minute is mixed with water at 5-
7~ gallons per minute per square foot ~or 2-5 minutes. If the
second cycle is backwash water only, up to 30 gallons per
minute per square foot 3-5 minutes might be required depending
on the filtration media.
The filter bottom of M. L. Stuppy, United States
Letters Patent 3,110,667 specifies a block with two lower
chambers alongside each other and two upper cha~bers, each one
above a lower chamber. Ports be~ween the lower chamber and the
upper chamber provide compensation which assist in evening out
the pressure distribution of the backwash water and lowering
the amount of head pressure required. Stuppy however, does not
provide for insertion o~ gas such as air to assist in the
backwash process. The only way that gas can be applied in the
backwash process in Stuppy is to add a network of pipes to
supply gas above the granular material level, which would be
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prohibitively expensive, or to add a network of pipes above the
underdrain which would disturb the granular material and cause
it to mix with the gravel. The ~iner granules could then clog
the ports at the underdrain and seep into the underdrain.
Maldistribution of granular material across the filter bed
could also result.
Farrabough, United States Letters Patent No.
4,065,391, discloses an underdrain which provides for the use
of the gas for cleansing. Chambers are formed by diagonal
walls. ~his results in alternate chambers that mix gas and
water and chambers that carry water only, with compensating
orifices in the diagonal walls.
Sassano et al., United States Letters Patent
4,214,992 specifies a block with an air and water chamber in
the center and water dispensing chambers on both sides. The
chambers are formed with diagonal and straight walls and are
rhombic in shape.
A major problem with the underdrains of Farrabough
and sassano is that when the gas and water mix in the chamber
during the gas cycle, turbulence is often set up which creates
standing waves which can become destructive. The turbulence
often result in the mixing of the granular particles with the
gravel, (six layers of gravel are required with Farrabaugh and
Sassano underdrains), and the seepage of yranular particles
into the chambers which clog the orifices on the top of the
underdrain and in the diagonal walls of the underdrain.
If the turbulence becomes severe enough,
catastrophic damage can occur and has occurred, causing poor
distribution of water and gas, damage to and breaking up of the
underdrain, and lifting of the underdrain blocks or laterals
off the filter bed floor.
Furthermore, it is not possible to connect the gas
chambers from one underdrain lateral to another with cutouts to
equalize the gas distribution. It is also not po~sible with
the underdrains of Farrabough and Sassano to interconnect with
cutouts the water chambers from one underdrain lateral to
another to equali.ze water distribution.
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Accordingly, it is the general ob~ect of the
instant invention to provide an underdrain for liquid
purification systems which overcomes the shortcomings of
present structures.
It is ~ further object of the instant invention to
provide an underdrain for liquid purification systems which
provides for a minimal amount of turbulence in the water during
the gas cleansing cycle and the combined gas and backwash water
cycle.
10It is still a further object of the instant
invention to provide an underdrain for liquid purification
systems which allows for cutout means for equalizing gas and
water pressures and distribution between the parallal units of
' the underdrain laterals.
! It is still yet a further object of the instant
! invention to provide an underdrain for liquid purification
systems which comprises a primary chamber, a compensatinq
chamber, and a separate gas chamber.
It is another object of the instant invention to
provide underdrain for liquid purification systems which allows
for easy manual adjustment of th2 level of the ports for the
entry of ~ackwash water tD flow out of the underdrain, in order
to equalize the water pressure at each port and to equalize the
distribution of the backwash water.
It is still another object of the instant invention
to provide an underdrain for liquid purification systems which
minimizes the required depth of the gravel layer.
It is still yet another object of the instant
invention to provide an underdrain for liquid purification
systems which prevents the clogging of the input ports to the
underdrain and the compensating orifices between the chambers
of the underdrain with granular material.
It is still an additional object of the instant
invention to provide an underdrain for liquid purification
systems which i6 inexpensive to manufacture and is easy to
install and maintain.
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These and other objects of the instant invention
are achieved by providing an underdrain comprised of laterals
which have three chambers; a lower chamber or primary chamber,
a middle chamber or compensating chamber, and a top gas
chamber. Compensating orifices are placed in the separator
wall between the compensating and primary chamber and in a
horizontal baffle which defines the top of the compensating
chamber and the bottom of the gas chamber. These compensating
orifices and the horizontal baffle ~end to equalize gas and
water pressures during cleansing operations and to prevent
turbulence or th~ creation of destructive standing waves during
bac~wash.
A series of nozzle assemblies are placed in the top
I wall of the underdrain lateral along its length. Filtered
¦ water flows through distribution orifices in the top of the
¦ nozzle assembly through a threaded stem into the compensating
chamber, to the primary chamber and through a flume from which
it is discharged.
Parallel runs of the laterals comprising the
chambers and nozzles assemblies are installed under the gravel
layer. There are various types of gas and water distribution
systems known to those familiar with the art. The instant
invention may be used with front flume designs, wall sleeve
designs and center flume designs, depending upon the size of
the filter bed and other factors in the design and
installation. Furthermore, the underdrain design of the
instant invention allows for cutouts in each lateral between
the parallel underdrain blocks which connect the primary
chambers together to e~ualize water pressure, distribution and
flow and which connect the gas chambers together to equalize
gas pressures and flow.
Other objects of many of intended advantages of
this invention will be readily appreciated when the same
becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings wherein:
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Fig. 1 is a cross-sectional view of an underdrain
lateral installed at the bottom of the filtering system.
Fig. 2 is a plan view of the underdrain showing the
top of the underdrain laterals and the nozzle assemblies of the
underdrain.
Fig. 3 is a vertical cross-sectional view of the
filtering system which shows the granular media and gravel
packing levels and the underdrain laterals taken along the line
3-3 of Fig 2.
Fig. 4 is a partial, cross-sectional view taken
along the line 4-4 of Fig 3 which shows the gas inlet pipes for
a front flume distribution system.
Fig. 5 is a cross-sectional view of a filter bed
using a wall sleeve distribution system.
Fig. 6 is a cross-sectional view of a filter bed
using a center flume distribution system.
¦ Fig. 7 is a cross-sectional view of the underdrain
lateral of the alternative embodiment.
Fig. 8 is a cross-sectional view of a filter bed
using a wall sleeve distribution system with the alternative
embodiment.
Referring now in greater detail to the various
figures of the drawing, wherein like reference characters refer
to like parts, there is shown in Fig. 1 a vertical cross
; sectional view of an underdrain lateral 2 of the present
invention. As shown in Fig. 1, the underdrain lateral 2
comprises a lower, primary chamber 4, a middle, compensating
chamber 6 and an upper, gas chamber 8. Nozzle assembly 10 has a
threaded stem 12 with orifices 14 and 16 for gas input into the
filter bed during cleansing.
The nozzle assembly 10 is located on a spacer 18
which is positioned on top wall 20 of the underdrain lateral 2.
The inner surfaces of the ~pacer 18 and the top wall 20 ~ormed
by a hole for placement of the cylindrical stem 12, are
threaded to accept the threads at the top of the threaded stem
12. Distribution orifices 24 are placed in upper member 22 of
the nozzle assembly 10. ~he distribution orifices 24 are made
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small to prevent passage of any granular material which has
settled into the gravel packing level during filtering and
during cleansing.
Pormed in the separator wall 26, which defines the
top of ths primary chamber 4 and the bottom of the compensating
chamber 6 are compensating orifices 28 which equalize water
distribution and pre~sures during the filtering and the gas and
backwash cycles. A horizontal baffle 30 separates the
compensating chamber 6 from the gas chamber 8. The horizontal
baffle 30 contains orifices 32 which equalize gas and water
pressure during the filtering and t:he gas and backwash cycles.
As will be describad in detail la er, during
filtering of waste water, the water flows through the granular
media level and then through the gravel pac~ing level a~ shown
in figure 3, through distribution orifices 24 and into the
threaded stem 12. The waste water then flows through orifices
28 and then out through a liquid flume from which it is
discharged.
During backwash water is forced back into the
system first through the primary chamber 4 then into the
compensating chamber 6 and out through the threaded stem 12.
It then ~lows through the distribution orifices 24 into the
gravel layer and upward into and thro~gh granular layer from
whence it is conducted out of the filtering system and
discharged.
For greater cleansing efficiency a gas is
introduced into the gas chamber 8. The gas flows through
orifices 14 and 16 into threaded stem 12 and out of the
distribution orifices 24 through the gravel layer and then
through the granular layer. ~he gas bubbles ~ormed agitate the
granular material so as to loosen accumulated waste material
which was formed during the filtering cycle.
After the qas cycle, a backwash cycle is initiated
so that backwash water flows through the gravel and media
layers removing and carrying away the waste material which was
loosened during the gas cycle. As described previously, it i5
more efficient to follow the gas cycle with a combined gas and
backwash water cycle then to follow the gas cycle with a
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backwash cycle only. However, a combined cycle cannot be used
when the granular media is vary fine since the granular
material would be carried away in the gas bubbles by the
bacXwash water.
During the gas cycle, a water level above the
qranular level is maintained. The gas entering the qa~ chamber
8 forces the water in the underdrain downward until the level
of the water is slightly below the top of the compensating
chamber 6. Water enters at the opening at the bottom of the
cylindrical threaded stem 12 and yas enters the threaded stem
12 through the orifices 14 and 16. The gas and water then go
through the distribution orifices 24 and then rise through the
gravel and granular levels from whence they are discharged.
This process loosens and removes the waste material which has
accumulated on the granular particles.
After the gas cycle which was described above, a
cycle of backwash water or a combined cycle of backwash water
and gas may be used to clear away the waste material which has
been loosened during the gas cycle.
The underdrain prevents turbulence during the gas
and backwash water cycles as compared to underdrains in present
use. With the water level in the compensating chamber 6 just
below the hori20ntal baffle 3Q, the amplitude of ~tanding waves
! is reduced and water turbulence d~es not occur as in existing
devices. Furthermore, the threaded portion of the stem 12
enables, during installation and maintenance, the setting of
the entrances 33 of the various stems 12 to exact levels above
the underdrain floor to assure that the water pressure and flow
entering the various stems 12 are equalized throughout the
entire filtering system. Also by placing all stems at the same
level, the orifices 14 and 16 are positioned for even gas
pressure and flow in the filtering system.
The inside diameter of threaded stem 12 may be
reduced by inserts 35 placed near the orifice 14 to reduce
pressure during backwash allowing greater gas flow through the
orifice 14.
Fig. 2 shows a plan view of the underdrain laterals
2. Each underclrain lateral 2 sxtends laterally across the
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width or length of filter bed 34. The array of the nozzle
assemblies 10 are shown in the view. At the le~t are the gas
inlet pipes 54 which feed gas into each of the underdrain units
2. The fil~er bed 34 comprises side walls 36, 38, 40 and 42.
Shown dotted on the right hand ide of Fig. 2 are cutouts 56
which connect the primary chambers 4 of the underdrain laterals
2 together to equalize water flow and pressure in the
underdrain.
Fig. 3 shows a vertical cross section of the
`10 $iltering system along the line 3-3 of Fig. 2. As can be seen
in Fig. 3 a layer of granular material 46 is placed above a
layer of gravel 48. The underdrain laterals 2 cover the bsttom
44 of the filtering bed 34 beneath the gravel layer 48. Gas
inlet pipes 54 are placed in gas distribution chamber 49 for
feeding gas into each of the gas chambers 8 of the underdrain
laterals 2. Cutouts 51 at the end of each of the underdrain
laterals 2 connect the gas chambers 8 to equalize gas pressure
and allow an equal flow of gas throughout all the gas chambers
8.
Below the underdrain laterals 2 is a liquid flume
50 through which the filtered water exits and into which
bacXwash water flows during the backwash cycle.
The gas inlet pipes 54 are placed at the front of
ths filter bed ~4 are shown in Fig. 4, which is a partial cross
sectional view taXen along the line 4-4 of Fig 3. As can be
seen in Fig. 4 cut outs 56 in the bottom of the primary
chambers ~ at each end of each underdrain blocks 2 provide for
equalization of water pressure and water flow throughout the
underdrain.
As is well know to those skilled in the art,
various arrangements with regard to water and gas distribution
are in common use. The arrangement shown in Figs. 2, 3, and 4
is a front flume design. In addition to the front flume
design, water and gas distribution can be achieved through a
wall sleeve design as shown in Fig. 5 or through a center flume
design as 6hown in Fig. 6. The choice of distribution design
depends upon the size of the filtering system, the amount of
water to be filtered, and various other considerations with
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regard to any specific installation. However, the instant
invention is applicable to all such arrangements.
A wall sleeve water and gas clistribution system
with the present invention is 6hown in Fig. 5. Both gas inlet
pipes 58 and liquid flume 60 are in placed in side wall 42.
Cutout 62, at both ends of underdrain lateral 2 connect the
primary chambers 4 of each lateral 2 together to assure equal
distribu~ion of water pre6sure and flow throughout the
underdrain. Similarly, the gas chambers 8 of the underdrain
laterals 2 are connected together at one end of the laterals 2
by cutouts 64 which equalizes gas pressure and flow throughout
the underdrain.
Fig. 6 shows a center flume gas and water
i distribution system. Liquid flume 66 is shown centered in
bottom wall 44. Gas distribution also takes place centrally.
The gas enters into the gas chambers 8 via J tube 68. Cutouts
i (not shown) may also be used to equalize water and gas
pressures and flow.
An alternative embodiment of the invention is shown
in Figs. 7 and 8. In this embodiment, the distribution
orifices 24 in the upper member 22 of the nozzle assembly 10
are made larger. The dimensions of the distribution orifices
24 of the alternative embodiment are 1/4 inch wide by 1 inch
long as compared to 1/32 inch wide by 1 inch long in the first
embodiment. Also as can be seen in Figs. 7 and 8, the
threaded stem 12 is made longer so that entrance 33 is in the
lower chamber 4. In addition, the middle chamber 6 is made
longer and the lower chamber 4 is shortened.
Also in ~his alternative embodiment, the functions
of the chambers 4 and 6 are reversed. Chamber 6 is the primary
chamber into which the backwash water is inserted. The lower
chamber 4 is now the compensating chamber.
Fig. 8 is a cross-sectional view of a filter bed
with a wall sleeve distribution system using the alternative
emoodiment. As can be seen in Fig. 8, backwash water enters
through liquid ~lume 60 into the middle primary chamber. The
upper chamber 8 remains ths gas chamber as in the first
embodiment and gas enters through gas inlet pipes 58.
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The alternative embodiment is intended to guard
against the p~ssibility that after about five years of service,
waste material might clog the openings of the distribution
orifices 24. The orifices 24 are therefore made wider. This
necessitates three to four layers of the gravel 48 beneath the
granular material 46. The larger s.L~e gravel is placed in the
lower layer with each higher layer being successively of
smaller size with the smallest ~iZI' gravel in the top layer,
beneath ths granular layer. In the first embodiment, on the
other hand, only one gravel layer iis required because smaller
size gravel can be used abutting the noz~le assembly 10,
because the openings of the distribution orifices 24 are much
narrower.
With this system it is possible that large gulps of
air entering with the backwash water could lift the finer
I gravel which could be washed out when the backwash water is
¦ discharged. Therefore, the threaded stem 12 made longer so
that the entrance 33 was considerably below the backwash intake
into the middle chamber 6 to prevent air from entering into the
threaded stem 12 and thence through the distribution orifices
1 24 rising up through the gravel layers.
An underdrain system which provides for
several clear and i~portant advantages over the previous and
current art has been described. These include the use of a gas
cleansing cycle and a backwash liquid cycle or a combined gas
and backwash liquid cycle wherein turbulence in the liquid is
minimized. Existing systems often create sufficient turbulence
to result in the mixing o~ the granular media with the gravel,
causing clogging of orifices which jams the system.
Furthermore, the disturbances are sometimes severe enough to
cause catastrophic results such as the lifting or breaking up
of the laterals of the underdrain.
The reduction in turbulence during the cleansing
cycles allows for the reduction of the amount of granular media
required as less mixing between tbe granular and gravel layers
occurs as well as less shifting of granular materials causing
unequal amounts of material at various locations in the filter
bed. While the systems in common use today require six layers
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of gravel, the first embodimen~ of this invention requires only
one layer of gravel, whilç the 6econd embodiment requires only
three or four layers of gravel.
The underdrain laterals 2 may be composed of
ceramic, fiber glass, plast$c, metal or any other suitable
material.
The instant invention also provides an easy means
for leveling the back~ash liguid intakes to provide for even
liquid distribution by rotating the threaded stems of the
nozzles. Also, through the use of cut outs in the underdrain
laterals 2, gas and liquid pressures and flow are equalized
within each of the underdrain laterals and throughout the
filter bed 34.
Although the embodiments described herein use
filtration to purify waste water it should be noted that the
instant invention is equally applicable to other methods of
purification and to purify liquids other than waste water.
Without further elaboration, the foregoing will so
fully illustrate my invention that others may, by applying
current or future knowledge, readily adapt the same for use
under the various conditions of service.
