Note: Descriptions are shown in the official language in which they were submitted.
CA 02560794 2011-10-31
54106-719
TANKAGE SYSTEM INCORPORATING ADSORPTION CLARIFICATION AND
PARALLEL PLATE SEPARATION
Field of the Invention
A water treatment process and equipment for implementation of the
process are provided. The equipment incorporates a high rate clarifier with
series
operated inclined parallel plate settlers, followed by adsorption
clarification with
buoyant media.
Summary of the Invention
While adsorption clarification and parallel plate separation are
commonly used in stand alone filtration systems, an integrated system
including both
an adsorption clarifier and an inclined parallel plate separator in
combination in a
single tankage system is desirable.
Accordingly, in a first aspect there is provided an apparatus for filtering
a liquid containing solids, the apparatus comprising: an inclined parallel
plate
separator; and an adsorption clarifier, wherein the inclined parallel plate
separator
and the adsorption clarifier are in a stacked configuration, wherein the
adsorption
clarifier is situated above the inclined parallel plate separator, and wherein
the
apparatus is configured to provide a liquid flow path such that the liquid
containing
solids first enters the inclined parallel plate separator, then the liquid,
from which a
portion of the solids has been removed, enters the adsorption clarifier, and
said
apparatus further comprises an air diffusion grid located in the liquid flow
path
between the inclined plate separator and the adsorption clarifier.
In a second aspect, there is provided an apparatus for filtering a liquid
containing solids, the apparatus comprising: an inclined parallel plate
separator; and
an adsorption clarifier, wherein the inclined parallel plate separator and the
adsorption clarifier are in a side-by-side configuration, and wherein the
apparatus is
configured to provide a liquid flow path such that the liquid containing
solids first
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enters the inclined parallel plate separator, then the liquid, from which a
portion of the
solids has been removed, enters the adsorption clarifier, and said apparatus
further
comprises an air diffusion grid located in the liquid flow path between the
inclined
plate separator and the adsorption clarifier.
In an embodiment of the second aspect, the apparatus further
comprises a contact tank, wherein the contact tank is upstream of an entry
into a
chamber containing the inclined parallel plate separator.
In an embodiment of the second aspect, the apparatus further
comprises a filter situated downstream of the adsorption clarifier.
In an embodiment of the second aspect, the apparatus further
comprises a filter situated downstream of the inclined parallel plate
separator.
In an embodiment of the second aspect, the apparatus further
comprises a porous hollow fiber membrane filter.
Brief Description of the Drawings
Figure 1 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator in a stacked
configuration.
Figure 2 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator, as well as a lower
air grid,
lower waste connection, and contact tank.
Figure 3 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator, as well as an
upper air grid,
lower waste connection, and contact tank.
Figure 4 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator, as well as a lower
air grid
and lower waste connection, but no contact tank.
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Figure 5 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator, as well as an
apparatus
employing a lower air grid, but no contact tank or lower waste connection.
Figure 6 depicts an apparatus of a preferred embodiment, employing an
adsorption clarifier and inclined parallel plate separator in a side-by-side
configuration
with each other and a membrane filter.
Figure 7 depicts a membrane filter wherein a jet is employed to inject air
into a membrane module.
Figure 8 depicts a membrane filter wherein a jet with an integrated air
line is employed to inject a mixture of air and sludge into a membrane module.
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Figure 9 depicts a membrane filter wherein a jet with an integrated air line
is employed to
inject a mixture of air and mixed liquor into a membrane module.
Figure 10 depicts a continuous microfiltration system.
Detailed Description of the Preferred Embodiment
The following description and examples illustrate a preferred embodiment of
the present
invention in detail. Those of skill in the art will recognize that there are
numerous variations and
modifications of this invention that are encompassed by its scope.
Accordingly, the description
of a preferred embodiment should not be deemed to limit the scope of the
present invention.
Water for Treatment
The liquid that is filtered can include water, such as raw water, chemically
dosed water,
or water that has been subjected to other pretreatments. Water having an
influent turbidity of 25
NTU or lower up to 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, or 300 NTU
or higher can
generally be treated according to the preferred embodiments. A variety of raw
water types can be
treated, including those containing turbidity, color, iron, manganese,
dissolved organic carbon,
microorganisms, arsenic, phosphate, silica, radionuclides, lead and other
heavy metals, copper,
selenium, and antimony, as well as water having taste and/or odor. While the
apparatus of
preferred embodiments is generally preferred for treatment of water, in
certain embodiments it
can also be employed to treat other liquids containing solids.
In certain embodiments, it can be preferred to subject the water to be treated
to a
pretreatment, such as chemical coagulation or precipitation to achieve some
degree of solids
removal. The water can be treated with alum, ferric sulfate, ferric chloride,
sodium aluminate,
and/or cationic polymers. In many situations wherein metal salts are used, it
is desirable to use a
non-ionic or anionic polymer, preferably in a small amount, for improving
solids capture in the
adsorption media. In some situations, for example, when a media filter is
employed downstream
of the adsorption clarifier, a cationic polymer can be employed to enhance
overall treatment.
Low molecular weight cationic polymers can also be used to augment or replace
metal salt
coagulants in the charge neutralization destabilization of colloidal particles
during pretreatment.
Phosphorous can also be removed according to methods of the preferred
embodiments.
Other elements, such as arsenic, uranium, or radium, can be removed by
appropriate chemical
pretreatment, such as coprecipitation with an aluminum or ferric salt.
Optionally, sorbent materials such as powdered activated carbon, ion exchange
resins,
hydrous manganese oxide, magnetic ion exchange resin (such as resins marketed
under the
MIEX trademark, available from Orica Advanced Water Technologies Pty. Ltd.,
of Ascot Vale,
Victoria, Australia) can be employed to remove certain contaminants.
Optionally, an inert, finely
divided material with a specific gravity greater than water, such as
bentonite, silica sand, or
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garnet sand, can be added to the raw water or to the coagulated water to
improve the settling
characteristics of the solids.
The raw water can also be treated with an oxidant to form insoluble metal
oxides, such as
ferric hydroxide or manganese oxide, to convert elements present as oxyanions,
such as arsenic,
to preferred valence states for removal by adsorption or co-precipitation, to
achieve partial
destruction of dissolved organic compounds such as those contributing to taste
and odor, or to
improve flocculation and overall particle removal across the system. Suitable
oxidant chemicals
include potassium permanganate and chlorine, which can be dosed as dissolved
chlorine gas, as
electrolytically generated chlorine produced on site, or as sodium or calcium
hypochlorite
solutions.
Various alkaline or acidic chemicals can also be added to adjust pH to a
preferred set
point.
Adsorption Clarifier
One of the components of the systems of preferred embodiments is an adsorption
clarifier. Adsorption clarifiers are generally constructed as tanks containing
buoyant media for
removal of turbidity and color from pre-coagulated water. Pre-engineered steel
tanks are
generally preferred; however, tanks of concrete or other material can also be
employed. Suitable
tanks, vessels, or other containment structures can be employed, as will be
appreciated by one
skilled in the art. The buoyant media is typically restrained in the tank with
a retention screen,
generally constructed of aluminum or stainless steel. A buoyant media is
preferably employed in
the clarifier. The specific gravity of such media can be less than 1.0, 0.9,
0.8, 0.7, 0.6, 0.5, 0.4,
0.3, 0.2, or 0.1. In a particularly preferred configuration, buoyant media
comprising a layer of
about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 inches in thickness is
restrained in the tank.
Preferably, the tank contains from about 15 or 20 inches to about 40 or 45
inches of buoyant
media, most preferably from about 24 to about 36 inches of buoyant media. In
certain
embodiments, however, the buoyant media can comprise a layer more than about
60, 65, 70, 80,
90, or 100 inches in thickness. Suitable buoyant media include those
consisting of flattened,
disk-shaped beads of polyethylene with a slightly roughened surface, or other
commercially
available buoyant media. Depending upon various factors, such as the nature of
the liquid to be
treated and the configuration of the apparatus, buoyant media having other
shapes can be
preferred, such as spherical, rod-shaped, irregularly shaped, or any suitable
shape. While
polyethylene . is preferred, other materials can also be employed, such as
other polymers,
ceramics, glass, metallic materials, minerals, or synthetic materials. The
media can be subjected
to surface treatment, for example, physical or chemical roughening, coating,
or other suitable
treatments.
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In certain embodiments, it can be preferred to employ a neutrally buoyant
media or a
media with a specific gravity greater than 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6,
1.7, 1.8, or 2 or more. In
these embodiments, the parallel plate separator can be placed above the
adsorption clarifier or
even placed beside the adsorption clarifier.
In operation, pretreated water, having passed through the inclined plate
settler, enters the
bottom of the adsorption clarifier and flows upward through the media bed
where solids are
removed. Contact flocculation and clarification occur as the coagulated
particles move through
the bed of adsorption media and are retained. The process is enhanced by
repeated contact with
previously trapped solids. Hydraulic loading rates during operation are
generally from about 1, 2,
3, or 4 gpm/ft2 to about 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, or 50 or more
gpm/ft2, preferably
from about 5, 6, 7, 8, 9, or 10 gpm/ft2 to about 11, 12, 13, 14, or 15
gpm/ft2. However, in certain
embodiments higher or lower loading rates can be employed. The upper limit of
influent
turbidity for a stand-alone adsorption clarifier is typically about 75 NTU,
and the color limit is
typically about 25 color units. However, higher turbidity levels and color
limits can be tolerated,
particularly when they are of short duration. Turbidity as high as 100, 125,
150, 175, 200, 225,
250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 NTU or higher can
typically be tolerated
for periods up to several hours or more.
The adsorption clarifier is typically flushed with raw water or some other
liquid and
incorporates an air scour system to remove captured solids. The direction of
the water flow
during the flush cycle is preferably in the upward direction. However,
downward, sideward, or a
flush in other directions can also be employed. The air scour pxpands and
scrubs the media to
remove adhered solids. While manual control of the flush and/or air scour
systems can be
employed, it is generally preferred to employ automatic controls to monitor
the unit and provide
control during a flush cycle. Depending on flow rates and media type,
suspended solids
reductions of from about 40%, 45%, 50%, 55%, 60%, 65% or less to about 95% or
more are
achievable in an adsorption clarifier. Typically, the adsorption clarifier
removes from about 70%
or 75% to about 80%, 85%, or 90% of influent solids.
Parallel Plate Separator
One of the components of the systems of preferred embodiments is a parallel
plate
separator. Parallel plate separators provide a large settling area for
suspended solids in
considerably less space than conventional clarifiers do. Systems typically
range in capacity from
5, 10, or 15 gpm to several million gallons per day, using multiple units.
Hydraulic loading rates,
based on the superficial area of the settler, are typically from about 0.05,
0.1, 0.2, 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5,
3.75, 4, 4.25, 4.5, 4.75, or 5
gallons per minute per square foot (gpfh/ft2) or less to as high as about 6,
7, 8, 9, 10, 11,12, 13,
14, 15, 20, 25, 30, 35, 40, 45, 50 gpm/ft2 or more.
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Performance of parallel plate separators is generally equal to or better than
conventional
clarification apparatus, providing distinct advantages. Advantages of parallel
plate separators
include utilization of minimal floor space, and low maintenance, installation,
and capital costs.
Parallel plate separators can include lamella plate settlers incorporating
arrays of parallel flat
plates, generally all aligned in a single orientation, with a perpendicular
distance between plates
of from about 0.1, 0.2, 0.3, 0.4, 0.5 inches or less to about 1,2, 3,4, 5, 6,
7, 8, 9, 10 inches or
more. Other types of parallel plate separators include tube settlers, in which
thin sheets are
arranged in one or more orientations, providing flow paths which can include
one or more
direction changes. The thin sheets can be flat, corrugated, or incorporate
various other surface
configurations. Other clarification devices employ sheets of material that are
used to provide
additional surface area for solids to settle on, to modify the flow path of
the liquid to be clarified,
or both.
In a preferred embodiment, the parallel plate separator consists of an epoxy
coated
carbon steel vessel (or a vessel of another suitable material), fiber
reinforced plastics (FRP)
parallel plates, inlet, outlet, and sludge nozzles, sludge collection hopper,
influent feed and
distribution zone, effluent launder, and access manhole in the sludge hopper.
The plates are
typically inclined at an angle to enhance rapid settling. Generally, the angle
of inclination is from
about 15, 20, 25, 30, 35, 40, or 45 degrees or less to about 75, 80, or 85
degrees or more,
preferably from about 50 or 55 degrees to about 65 or 70 degrees, and most
preferably about 60
degrees. The plates can all be inclined to the same angle, or different plates
can be inclined at
different angles. Likewise, a plate can be curved, so as to provide varying
angles of inclination at
various points on its surface.
The plates are typically spaced from about 1/2 inch apart to about six inches
apart,
preferably about two inches apart. Typical hydraulic loading rates vary from a
0.05, 0.1, 0.15,
0.2, or 0.25 or less gpm/ft2 effective area for light hydroxide type
precipitates to a 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, or 0.9 or higher gpm/ft2 effective area for surface water
clarification. Higher or
lower loading rates can be preferred in certain embodiments. Effective area is
defined as the
surface area of the inclined plates available for settling.
The system can be configured such that settled solids are collected at the
bottom of the
tank, having settled out on the plates and having moved down the plates under
the influence of
gravity. Alternatively, the settler can be designed so that sludge is
collected towards the top of
the plates by allowing for a crossflow movement of sludge across the plates to
a sludge collector
system located at one side of the tank. With either type of sludge collector,
provision can be
made to collect a portion of the sludge and recycle it to a point close to the
introduction of
coagulant th the raw water, or some other point in the system. This
recirculation of pre-formed
floc generally improves the formation and growth of settlable floc.
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Flash mixing and flocculation basins can be employed in conjunction with the
parallel
plate separator, especially if the system employs coagulants and/or
flocculants. Variable speed
flocculator drives are typically employed on the flocculation basins. Chemical
pretreatment
systems, sludge pumping systems, tank covers, and special coatings are also
available. Separate
rapid mix and flocculation tanks can be provided if specific detention times
for specific
applications are desirable. Rapid mix conditions can also be provided by use
of static mixers.
Long detention times for the rapid mix and flocculation can result in
significant savings in
chemical consumption and sludge generation rates and disposal cost. The system
shown in
Figure 1 uses the hopper shaped volume immediately upstream of the plate
settler system as a
flocculation volume. If this volume is not sufficient for adequate
pretreatment, then separate
flocculation and rapid mix volumes can be provided upstream.
Integrated System
Figure 1 depicts a device of a preferred embodiment. The device combines two
technologies for clarification of water: Inclined parallel plate (inclined
parallel plate separator)
separation and adsorption clarification (adsorption clarifier). Both methods
are capable of
producing high quality treated water. When turbidity or solids content of the
water is increased,
however, both have drawbacks that negatively impact their water treatment
efficiency. Inclined
parallel plate separator separation generally requires additional projected
plate area per flow rate
provided for by more plates, a reduced angle of incline, or a greater plate
depth in order to
produce effluent with low suspended solids and/or turbidity. Adsorption
clarifier units generally
require more flushing and a possible reduction in flow rate when feed water
solids are increased.
By combining the two processes into a single series operated system, a feed
water with
high solids levels can be treated with enhanced efficiency. In devices of
preferred embodiments,
the portion of the device directed to inclined parallel plate separator
separation reduces the
influent solids level such that a low to normal concentration of solids is
directed to the adsorption
clarifier unit. Normal solids concentrations are typically defined as from
about 20, 21, 22, 23, 24,
25, 26, 27, 28, 29 or 30 NTU, however in certain embodiments higher or lower
solids
concentrations can be considered as normal, for example, 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, or 19 NTU, or 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,
90, 95, or 100 or
higher NTU. As discussed above, the adsorption clarifier is capable of
handling up to 300 NTU
or more for short periods of a few hours or less.
In certain embodiments, a sludge recycle system is incorporated into the
system to return
solids from the settling plate area to the influent water stream. There,
additional solids
contacting is provided, which promotes a more readily settled solid for the
inclined parallel plate
separator separation.
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The arrangement of the inclined parallel plate separator and adsorption
clarifier in a
stacked configuration is depicted in Figure 1. In the drawing, a contact tank
providing about 1,
1.5, or 2 minutes or less to 2.5, 3, 3.5, or 4 minutes or more of
coagulation/flocculation time is
situated before the entry to the chamber containing the inclined parallel
plate separator and
adsorption clarifier. The contact tank can be expanded or eliminated,
depending on site-specific
conditions. Figures 2 through 5 depict various configurations of apparatus of
preferred
embodiments, including a configuration including a lower air grid, lower waste
connection, and
contact tank (Figure 2), a configuration including an upper air grid, lower
waste connection, and
contact tank (Figure 3), a configuration including a lower air grid and lower
waste connection,
but no contact tank (Figure 4), and a configuration including a lower air
grid, but no contact tank
or lower waste connection (Figure 5).
Other configurations can also be employed, depending upon the particular
application
and other system requirements. For example, arrangement of the inclined
parallel plate separator
and adsorption clarifier in a side-by-side configuration is particularly
preferred. Such a side-by-
side configuration, including an incline plate separator, an interstage pump,
an adsorption
clarifier, a water collection manifold, and a membrane filter is illustrated
in Figure 6. In the
system depicted in Figure 6, water flows up through the incline plate settler,
up through the
adsorption clarifier, and down through the membrane filter.
A filter section can also follow the adsorption clarifier in a packaged
treatment unit. The
filter can include a media filter containing a bed of sand, anthracite,
granular activated carbon,
manganese greensand, any of the previously listed media coated with manganese
hydroxide, any
combination of these particular media, or any other suitable granular or other
filtration media.
The filter can function primarily as an adsorption or ion exchange contactor,
in which case the
media can include granular activated carbon, granular ferric hydroxide,
activated alumina, ion
exchange resin, or any other suitable sorption media.
The filter can also include a membrane filter. The membrane filter can include
a
submerged membrane, in which the membrane elements are immersed in a tank
during filtration
and the filtrate flow is driven by the pressure differential between the tank
liquid and the filtrate
side of the membrane. This pressure differential can arise solely due to
gravity, or can be
augmented by the suction provided by a filtrate pump, by a positive pressure
provided on the
tank, or by any combination of these. The membrane filter can also include a
pressurized
membrane system, wherein membrane modules are enclosed in housings, each
housing
containing one or more membrane modules. Pressurized membrane filters are
generally operated
with the pressure provided by a feed pump, but the driving force can also be
provided by gravity,
by pump suction, or by any combination of these methods.
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Any suitable membrane filter system can be employed with the parallel plate
separator
and adsorption clarifier systems of preferred embodiments, but particularly
preferred systems
utilize either a Continuous MicroFiltration System (CMF-S), or a Membrane
BioReactor (MBR)
filtration system.
Such membrane filtration systems are designed to draw filtrate from a
reservoir of liquid
substrate by the use of microporous hollow fibers immersed within the
substrate. The fibers can
be oriented in any suitable orientation; however, a vertical orientation is
particularly preferred for
ease and efficiency of manufacture, operation, and maintenance. Figures 7, 8,
and 9 illustrate
preferred designs for representative filtration systems. The figures show a
"cloverleaf" filtration
unit comprising four sub-modules. Typically, a plurality of such filtration
units, most commonly
in a linear "rack," is immersed in the substrate reservoir. The illustrated
filtration units include a
filtrate sub-manifold (not shown) and an air/liquid substrate sub-manifold,
which receive the
upper and lower ends, respectively, of the four sub-modules.
Each sub-manifold includes four circular fittings or receiving areas, each of
which
receives an end of one of the sub-modules. Each sub-module is structurally
defined by a top
cylindrical pot (not shown) and a bottom cylindrical pot. In preferred
embodiments, a cage (not
shown) connects the top and bottom pots and secures the fibers. Alternatively,
one or more rings,
ties, or other structures can also be employed to secure the fibers, or the
fibers are unsecured.
Instead of a cage configuration, rods can be employed to connect the top and
bottom pots, or
other arrangements can be employed. The pots secure the ends of the hollow
fibers in the MBR
module and can be formed of a resinous, polymeric, or other suitable material.
The ends of the
cage or other supporting member, if employed, are preferably fixed to the
outer surfaces of the
pots. Each pot and associated end of the cage is together received within one
of the circular
fittings of each sub-manifold. The sub-manifolds and pots of the sub-modules
are coupled
together with the aid of circular clips, 0-ring seals, or the like.
Each sub-module preferably includes fibers arranged vertically between its top
and
bottom pot. The fibers preferably have a length somewhat longer than the
distance between the
pots, such that the fibers can move laterally. Depending upon the application,
the length of the
fibers can be adjusted to provide various degrees of slack. When reduced
movement of the fibers
is desired, a cage can be employed to closely surround the fibers of the sub-
module so that, in
operation, the outer fibers touch the cage, and lateral movement of the fibers
is restricted by the
cage. The lumens of the lower ends of the fibers are typically sealed within
the bottom pot, while
the upper ends of the fibers are not sealed, permitting removal of filtrate
from the lumens of the
membranes upon application of a transmembrane pressure.
During filtration, a liquid substrate is introduced into the region of the
hollow fibers,
between the top and bottom pots. A pump (not shown) can be utilized to apply
suction to the
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filtrate manifold, creating a pressure differential across the walls of the
fibers, causing filtrate to
pass from the substrate into the lumens of the fibers. The filtrate flows
upward through the fiber
lumens into the filtrate sub-manifold, through the filtrate withdrawal tube,
and upward into the
filtrate manifold to be collected outside of a reservoir. For applications
wherein aeration of the
substrate is desired, the bottom pot can include a plurality of holes, slots,
or passages extending
from its lower face to its upper face, so that a mixture of air bubbles and
liquid substrate in the
air/liquid substrate sub-manifold can flow upward through the bottom pot to be
discharged
between the lower ends of the fibers. Alternatively, air can be injected into
the region
surrounding the membranes by means of tubes, perforated sheets, or the like
separate from the
bottom pot.
In one embodiment, the system includes an air manifold near the bases of the
filtration
units, as depicted in Figure 10. The air manifold can include a horizontal air
conduit just above
the air sub-manifolds. The horizontal air conduit can employ bottom
connections to central upper
surfaces of the air sub-manifolds, the bottom connections supplying air to the
air sub-manifolds.
Each air sub-manifold ducts the air to the lower faces of the four bottom pots
of the filtration
unit, the air then flowing upward through holes or passages in the bottom
pots. One or more
vertical air droppers can be employed between the filtration units to deploy
air from above the
tank down to the horizontal air manifold.
The filtrate sub-manifold can be connected to a vertically oriented filtrate
withdrawal
tube that in turn connects to a filtrate manifold (not shown) that receives
filtrate from all of the
filtration units (such as the illustrated cloverleaf unit) of a rack. The
filtrate withdrawal tube is in
fluid communication with the upper faces of the top pots of the sub-modules,
so that filtrate can
be removed through the withdrawal tube. In addition, the system can include an
air line that
injects air into the open skirt under the air/liquid substrate sub-manifold.
The air line can inject
air through the top of the air/liquid substrate sub-manifold and into the open
skirt, or alternatively
the air line can be integrated with the line providing liquid substrate for
jet mixing. While such
embodiments are particularly preferred, other arrangements can also be
employed, as will be
appreciated by one skilled in the art.
It is desirable to provide for additional chemical feeds to the system between
each
separation stage. This allows a different chemical environment to be created
in each separation
stage, thereby improving or optimizing the performance of each stage.
Furthermore, removal
conditions for different contaminants can be optimized at each stage. For
example, if iron,
manganese, and aluminum are to be removed in the system, the raw water can be
aerated to form
ferric hydroxide floc. The pH in the clarifier can be adjusted to about pH 6.5
to minimize
aluminum solubility and thereby achieve maximum aluminum removal through the
plate settler
and adsorption clarified stages. An oxidant chemical can be added to oxidize
manganese oxide,
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and the pH in the filter system can be adjusted to above pH 8Ø A polymer can
be added to the
adsorption clarifier effluent to maximize manganese capture in the filter
section, which
preferably employs a manganese oxide coated media. Other pH can be preferred
if different
contaminants are present.
Chemicals can also be added to improve the separation performance of each
stage, or to
optimize the overall performance of the system. For example, unreacted polymer
carryover from
adsorption clarifiers or other types of clarifiers is known to produce rapid
head loss development
in media filter systems and rapid fouling of membrane filter systems. A
chemical can be added to
the adsorption clarifier effluent to react with or destroy some or all of this
polymer carryover.
The chemical can be either a charged species with charge opposite to the
polymer, an oxidant, a
finely divided solid or colloid, or other suitable chemical.
Backwash
In certain preferred embodiments, a backwash is conducted to clean the
filtration media.
It is generally preferred to combine air and water simultaneously for the
duration of the
backwash. The combined air and water wash provide a vigorous scouring action
to clean the
media, during which all of the filter media is lifted to the bed surface by an
air/lift pumping
action. The highly agitated backwash water promotes intense collusions of the
media grains to
effectively detach and dislodge adhered solids from the bottom of the bed to
the top, where they
are removed. The combined cleaning action of air and water is effective at sub-
fluidization rates,
reducing the volume of backwash water required and the volume of backwash
waste produced.
Specially designed wash trough baffles can optionally be employed to eliminate
media loss. The
superior cleaning performance of the backwash methods of preferred embodiments
minimizes
chemical and biological fouling of the filter media, eliminating the necessity
of expensive
chemical cleaning or media replacement.
Advantages of the backwash method can include increased scouring energy,
superior
cleaning performance, longer filter runs, significantly lower backwash water
usage rates, lower
operating costs, flexibility in media selection such as the ability to use
larger media, elimination
of a need for additional chemical cleaning systems, and reduced pumping and
piping costs.
In a preferred backwash process, a drain down step is followed by an air scour
step.
After the air scour step, a step is conducted wherein air scour is provided in
combination with
low-rate water. Air scour is then terminated, and low-rate water is provided
for a period of time,
after which the rate increases to the high-rate water rate. The preferred
duration for the drain
down step is typically from about 0.25, 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 minutes
or less to about 4.5,5,
5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 minutes or more, preferably about 4
minutes. The preferred
duration of the air scour only is from about 0.1,02, 0.3, 0.4, 0.5, 0.6, 0.7,
0.8, 0.9, 1.25, 1.5, 1.75,
2, 2.25, 2.5, or 2.75 minutes or less to about 3.25, 2.5, 3.75, 4, 4.25, 4.5,
4.75, 5, 5.5, 6, 6.5, 7, 8,
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9, or 10 minutes, preferably about 3 minutes. The preferred duration of the
air scour and low-rate
water step is about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.25, 1.5, or
1.75 minutes or less to
about 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75 4, 4.5, 5, 5.5, 6, 7, 8, 9, or 10
minutes or more, preferably
about 2 minutes or less. The water rate is preferably ramped up over from
about 0.25, 0.5, 0.75,
1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or 6.5 minutes or less to about
7.5, 8, 8.5, 9, 9.5, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, or 20 minutes or more, preferably over about 7
minutes, to the high-
rate water rate. Total backwash time is preferably from about 5 or 10 minutes
or less to about 25,
30, 35, 40, 45, 50, 55, or 60 minutes or more, preferably about 11, 12, 13,
14, 15, 16, or 17
minutes to about 19, 20, 21, 22, 23, or 24 minutes, and most preferably about
18 minutes.
In another preferred backwash method, air scour and low rate water are
provided for from
about 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4.5, 5, 5.5, 6, 6.5, 7, or 7.5
minutes or less to about 8.5, 9,
9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 minutes or more, preferably
about 8 minutes.
Then, air scouring is terminated and the water rate is ramped up to the high-
rate water rate over
from about 0.25, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 4.5 minutes or less
to about 5.5, 6, or 6.5
7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 minutes or
more, preferably over
about 5 minutes, to the high-rate water rate. The total backwash time for this
method is
preferably from about seven minutes to about twenty minutes, most preferably
about thirteen
minutes.
While it is generally preferred to employ simultaneous air scour and water for
at least a
portion of the backwash cycle, other backwash methods may also be employed
which utilize
various combinations of air scour and/or water steps, conducted simultaneously
or separately, at
different rates, and for different durations, as suitable for the particular
filtration media and
system configuration employed.
Cleaning the Clarifier
Cleaning of the clarifier system is preferably accomplished according to
either of the
following two methods.
Method 1
Method 1 utilizes an air scouring step and a liquid flush to clean the
clarifier system,
followed removal of dislodged solids. When the headloss through the clarifier
reaches a preset
point, or time duration has been exceeded, the clarifier is taken off line to
remove accumulated
solids. Influent flow is stopped and an air scour is initiated. The air scour
can be conducted
intermittently or continuously. If conducted intermittently, it is generally
preferred that air scour
be conducted in cycles of from about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,
0.9, 1, 1.1, 1.2, 1.3, 1.4,
1.5, 1.6, 1.7, 1.8, 1.9, or 2 minutes to about 2.25, 2.5, 2.75, 3, 3.25, 3.5,
3.75, 4, 4.25, 4.5, 4.75, 5,
5.5, 6, 6:5, 7, 7.5, 8, 8.5, 9,9.5, 10, 11, 12, 13,14, or 15 minutes of air on
followed by from about
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6,
1.7, 1.8, 1.9, or 2 minutes to
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about 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.5, 6, 6.5,
7, 7.5, 8, 8.5, 9, 9.5, 10,
11, 12, 13, 14, or 15 minutes of air off (or air at a lower flow rate, for
example, 90%, 85%, 80%,
75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5% or
less of
the higher, or air on, flow rate). Aeration can be provided wherein the air is
in the form of
bubbles of uniform sizes, or a combination of different bubble sizes can be
employed, for
example, coarse bubbles and/or fine bubbles. Regular or irregular cycles (in
which the air on and
air off times vary) can be employed, as can sinusoidal, triangular, or other
types of cycles,
wherein the rate of air is not varied in a discontinuous fashion, but rather
in a gradual fashion, at
a preferred rate or varying rate. Different cycle parameters can be combined
and varied, as
suitable.
The flow rate of air provided to the clarifier during air scour can vary
depending upon
system design, but generally from about 0.01 or less to about 30, 40, 50, 60,
70, 80, 90, 100 or
more standard cubic feet per minute per square foot (scfm/ft2) is employed,
preferably from about
0.05, 0.1, 0.5, 1, 2, 3, 4, or 5 scfm/ft2 to about 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, or
20 scfm/ft2. While air is generally preferred for use in the air scour
process, any suitable gas or
mixture of gases can be employed. Generally, air scour is initiated after a
headloss of from about
two feet to about four feet, or after operation of the device for from about
4, 5, 6, 7, 8, or 9 hours
to about 10, 11, 12, 13, or 14 hours. However, in certain embodiments, it can
be preferred to
initiate air scour at a headloss higher than four feet or lower than two feet,
or after a longer or
shorter duration of operation. The amount of solids in the water to be treated
can impact the
desired air scour frequency. Generally, the more solids present, the greater
the air scour
frequency preferred for optimal filtration efficiency.
The support system for the inclined parallel plate separator typically
incorporates an air
diffusion grid. Air, or another suitable gas, passes through the inclined
parallel plate separator
and upward through the adsorption clarifier media. The air dislodges solids
accumulated on the
inclined parallel plate separator and expands the adsorption clarifier media
to allow removal of
captured solids. The adsorption clarifier media can expand into the inclined
parallel plate
separator section to provide additional scouring of the plates.
Air only agitation occurs for a period of time (typically from about 5, 6, 7,
8, 9, 10, 11,
12, 13, 14, 15, 20, 25, 30, 45, 50, or 55 seconds to about 5.5, 6, 6.5, 7,
8.5, 9, 9.5, or 10 or more
minutes, preferably from about one minute to about 1.25, 1.5, 1.75, 2, 2.25,
3, 3.25, 3.5, 3.75, 4,
4.25, 4.5, 4.75, or 5 minutes) prior to a raw water flush or flush of other
suitable liquid upward
through the unit. The waste gate is then opened to allow the solids to be
flushed to waste through
the waste trough and piping. Air scouring and water flushing typically
continue for about less
than about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 45, 50, or 55
seconds to about 11,12,
13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 or more minutes, preferably
from about 1 minute
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to about 1.25, 1.5, 1.75, 2, 2.25, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5,
5.5, 6, 6.5, 7, 8.5, 9, 9.5,
or 10 minutes. Air is then discontinued and a water only flush continues for
about less than about
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 45, 50, or 55 seconds to
about 5.5, 6, 6.5, 7, 8.5, 9,
9.5,10, 11, 12, 13, 14, 15, 20, 25, or 30 or more minutes, preferably from
about 1 minute to about
1.25, 1.5, 1.75, 2, 2.25, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, or 5
minutes. At the end of the cycle,
the waste gate is closed and the treated flow is sent to effluent. In addition
to the air scouring and
water flushing methods discussed above, chemical cleaning can also be
employed.
Method 2
Method 2 utilizes an air scouring step to clean the clarifier system, followed
removal of
dislodged solids. When the headloss through the clarifier reaches a preset
point, or time duration
has been exceeded, the clarifier is taken off line to remove accumulated
solids. Influent flow is
stopped and an air scour is initiated. The air scour can be conducted
intermittently or
continuously, as described above in regard to Method 1. The support system can
be configured
as described above in regard to Method 1.
Air only agitation occurs for a period of time (typically from about 5, 6, 7,
8, 9, 10, 11,
12, 13, 14, 15, 20, 25, 30, 45, 50, or 55 seconds to about 5.5, 6, 6.5, 7,
8.5, 9, 9.5, or 10 or more
minutes, preferably from about one minute to about 1.25, 1.5, 1.75, 2, 2.25,
3, 3.25, 3.5, 3.75, 4,
4.25, 4.5, 4.75, or 5 minutes), after which the waste pipe at the bottom of
the clarifier is opened
and the solids in the clarifier are flushed to waste from the bottom of the
tank. Air scour is then
discontinued prior to media being lost to waste. Once the draining down is
complete, the tank is
refilled.
In certain preferred embodiments, a disinfection module can be incorporated in
the
system downstream of the filter and this can incorporate ultraviolet radiation
or a chemical
disinfectant such as chlorine. Both ultraviolet and chemical disinfection can
be used in some
cases. Incorporation of a disinfection module is particularly useful in
municipal drinking water
treatment applications because it allows the system to be credited with very
high efficiency in
inactivation of pathogens.
Systems and methods relating to the preferred embodiments are disclosed
in copending U.S. Provisional Application No. 60/556,141, filed March 24,
2004.
The term "comprising" as used herein is synonymous with "including",
"containing", or "characterized by", and is inclusive or open-ended and does
not exclude additional, unrecited elements or method steps.
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All numbers expressing quantities of ingredients, reaction conditions, and so
forth used
in the specification and claims are to be understood as being modified in all
instances by the term
"about." Accordingly, unless indicated to the contrary, the numerical
parameters set forth in the
specification and attached claims are approximations that may vary depending
upon the desired
properties sought to be obtained by the present invention. At the very least,
and not as an attempt
to limit the application of the doctrine of equivalents to the scope of the
claims, each numerical
parameter should be construed in light of the number of significant digits and
ordinary rounding
approaches.
The above description discloses several methods and materials of the present
invention.
This invention is susceptible to modifications in the methods and materials,
as well as alterations
in the fabrication methods and equipment. Such modifications will become
apparent to those
skilled in the art from a consideration of this disclosure or practice of the
invention disclosed
herein. Consequently, it is not intended that this invention be limited to the
specific
embodiments disclosed herein, but that it cover all modifications and
alternatives coming within
the true scope and spirit of the invention as embodied in the attached claims.
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