U.S. patent application number 13/120501 was filed with the patent office on 2011-07-21 for water treatment methods.
Invention is credited to Chad L. Felch, Michael Howdeshell, Bryan J. Kumfer, Eric a. Lorge, Stuart J. Munson, Matthew Patterson.
Application Number | 20110174746 13/120501 |
Document ID | / |
Family ID | 42060060 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174746 |
Kind Code |
A1 |
Felch; Chad L. ; et
al. |
July 21, 2011 |
Water Treatment Methods
Abstract
The present invention relates generally to a system and method
for treating wastewater in a filter media apparatus having a draft
tube system. The filter media may be walnut shell media.
Inventors: |
Felch; Chad L.; (Mosinee,
WI) ; Howdeshell; Michael; (Ringle, WI) ;
Lorge; Eric a.; (Mosinee, WI) ; Kumfer; Bryan J.;
(Ringle, WI) ; Munson; Stuart J.; (Minneapolis,
MN) ; Patterson; Matthew; (Hatley, WI) |
Family ID: |
42060060 |
Appl. No.: |
13/120501 |
Filed: |
September 23, 2009 |
PCT Filed: |
September 23, 2009 |
PCT NO: |
PCT/US09/57999 |
371 Date: |
March 23, 2011 |
Current U.S.
Class: |
210/795 ;
210/793; 210/794; 210/799 |
Current CPC
Class: |
C02F 2303/16 20130101;
B01D 24/4636 20130101; C02F 1/004 20130101; C02F 2209/005 20130101;
B01D 24/005 20130101; C02F 2101/32 20130101; C02F 2209/44 20130101;
C02F 2301/024 20130101; C02F 1/286 20130101; B01D 24/4884 20130101;
C02F 1/40 20130101 |
Class at
Publication: |
210/795 ;
210/799; 210/794; 210/793 |
International
Class: |
B01D 24/46 20060101
B01D024/46; B01D 24/00 20060101 B01D024/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 24, 2008 |
US |
61/099597 |
Sep 24, 2008 |
US |
61/099600 |
Sep 24, 2008 |
US |
61/099604 |
May 5, 2009 |
US |
61/175579 |
Claims
1. A method of filtering contaminants from a liquid comprising:
providing a liquid comprising an oil and suspended solids; passing
the liquid through a filter vessel, the filter vessel comprising
walnut shell media, a draft tube system, a peripheral zone between
a side wall of the draft tube system and a side wall of the vessel;
interrupting flow of the liquid through the vessel; passing a first
fluid through the filter media and the draft tube system in a
direction counter a flow of the liquid; passing a second fluid
through the filter media and the peripheral zone; interrupting flow
of the second fluid while continuing to pass the first fluid
through the filter media and the draft tube system; reestablishing
flow of the second fluid; removing at least a portion of the oil
and suspended solids from the filter vessel; interrupting flow of
the first fluid and the second fluid; and reestablishing flow of
the liquid through the filter vessel.
2. The method of claim 1, wherein passing the first fluid through
the filter media comprising passing a gas through the filter
media.
3. The method of claim 2, wherein passing the second fluid through
the filter media comprises passing a second liquid through the
filter media.
4. The method of claim 3, wherein passing the second fluid through
the filter media comprises passing the liquid comprising the at
least one contaminant.
5. The method of claim 1, wherein providing the liquid comprises
providing a liquid comprising oil and suspended solids.
6. The method of claim 1, wherein passing the first fluid through
the filter media and the draft tube system comprises passing the
first fluid for a first period of time, and wherein passing the
second fluid through the filter media and the peripheral zone
comprises passing the second fluid for a second period of time less
than the first period of time.
7. The method of claim 1, wherein passing the first fluid through
the filter media and the draft tube system comprises passing the
first fluid for a first period of time, and wherein passing the
second fluid through the filter media and the peripheral zone
comprises passing the second fluid for a second period of time
greater than the first period of time.
8. A method of backwashing a filter media comprising: passing a
feed liquid comprising a contaminant through a filter vessel
comprising a walnut shell filter media, a draft tube, a peripheral
zone between a side wall of the draft tube and a side wall of the
vessel to immobilize the contaminant on the media; interrupting
flow of the liquid through the vessel; passing a second liquid to
the filter vessel and into the walnut shell filter media for a
first period of time in a direction counter to the flow of the
liquid through the vessel; passing a gas through the walnut shell
filter media in the draft tube for a second period of time to
separate at least a portion of the contaminant from the filter
media; interrupting flow of the gas; removing the at least one
contaminant from the filter vessel; interrupting flow of the second
liquid; and reestablishing flow of the feed liquid through the
filter vessel.
9. The method of claim 8, wherein passing the second liquid to the
filter vessel comprises providing a pulsing flow of the second
liquid to the filter vessel.
10. The method of claim 9, wherein the liquid comprising a
contaminant is wastewater comprising oil and suspended solids.
11. The method of claim 9, wherein passing a gas through the walnut
shell filter media for the second period of time is less than the
first period of time.
12. A method of filtering contaminants from a feed liquid
comprising oil and suspended solids comprising: passing the feed
liquid through a walnut shell filter media positioned in a filter
vessel; and intermittently passing a backwash fluid into the walnut
shell filter media while passing the liquid through the walnut
shell filter media.
13. The method of claim 12, wherein the fluid is a gas.
14. The method of claim 13, wherein passing feed liquid through the
filter vessel comprises the feed liquid through a draft tube system
and a peripheral zone positioned within the filter vessel.
15. The method of claim 13, wherein intermittently passing the gas
through the walnut shell filter media comprises pulsing the air
through the walnut shell filter media for a predetermined period of
time.
16. A method of setting a filter bed comprising: passing a feed
liquid over a filter media bed positioned in a filter vessel
comprising the media, a draft tube system positioned in the filter
media, a peripheral zone between a side wall of the draft tube
system and a side wall of the vessel; interrupting flow of the feed
liquid; passing a gas through the draft tube system in a direction
counter to passing the feed liquid over the filter media;
interrupting flow of the gas; allowing the filter media to settle;
and alternating between the steps of passing the gas through the
draft tube system and allowing the filter media to settle for a
predetermined number of cycles to set the bed.
17. The method of claim 16, wherein passing the gas through the
draft tube comprises passing the gas for a first predetermined
period of time
18. The method of claim 17, further comprising passing a second
fluid through the filter media in the peripheral zone in a
direction counter to passing the feed liquid.
19. The method of claim 18, wherein passing the second fluid
comprises passing the second fluid for a second predetermined
period of time.
20. The method of claim 18, further comprising passing the second
fluid through the peripheral zone while passing the gas through the
draft tube system.
21. The method of claim 18, further comprising passing the second
fluid through the peripheral zone after interrupting flow of the
gas.
22. The method of claim 19, wherein the first predetermined period
of time is substantially the same as the second predetermined
period of time.
23. The method of claim 19, wherein the first predetermined period
of time is less than the second predetermined period of time.
24. The method of claim 19, wherein the first predetermined period
of time is greater than the second predetermined period of time.
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Application Ser. No. 61/099,604,
titled "PULESD BACKWASH FOR WALNUT SHELL FILTER," filed on Sep. 24,
2008; and U.S. Provisional Application Ser. No. 61/099,608, titled
"PULSED AIR WALNUT SHELL FILTER," filed on Sep. 24, 2008; and U.S.
Provisional Application Ser. No. 61/099.597, titled "WALNUT SHELL
FILTER PROCESS," filed on Sep. 24, 2008; and U.S. Provisional
Application Ser. No. 61/165,579, titled "TUBE DESIGN AND PROCEDURE
FOR WALNUT SHELL FILTER," filed on May 5, 2009, each of which are
incorporated by reference in their entireties for all purposes.
BACKGROUND OF INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a system and method for
treating wastewater, and more particularly to a wastewater
treatment system and method utilizing a walnut shell filter
media.
[0004] 2. Discussion of Related Art
[0005] Walnut shell filter media is known for its affinity for both
water and oil, making it a desirable filter media and is typically
used for the removal of oil from water and wastewater. Conventional
walnut shell filters include pressurized deep bed applications in
which the water is forced through a bed depth. Periodic backwashes
are also routinely conducted to regenerate the bed. Typical
backwash methods include expanding or turning the bed by imparting
energy to the bed.
[0006] Conventional backwash systems include mechanical mixing and
mechanical scrubbing with impellors and recycle lines, as well as
the introduction of high velocity gas or high velocity water in a
countercurrent direction. Mechanical systems used to backwash beds
increase the initial costs of the system and may lead to increased
maintenance costs to service mechanical seals. Recirculation of the
bed also increases the initial and maintenance costs of the filter
unit and increases the footprint of the filter unit with additional
pumps for recirculation. The mechanical backwash methods also
utilize backwash fluid to remove any oil and suspended solids
released from the bed, which leads to the generation of significant
amounts of backwash fluid. Similarly, the use of high velocity
backwash liquid generates a large volume of backwash fluid.
Conventional backwash systems are also known to create dead spots
in which the filter media is not sufficiently turned and/or in
which the backwash fluid does not reach, effectively leaving oil
and suspended solids in the bed.
[0007] A need remains for a compact walnut shell filter media unit
having a footprint sufficiently small to be used in offshore
applications. Moreover, there is a need to reduce the amount of
backwash water generated during backwash of the walnut shell filter
unit and to reduce the number of dead spots which are not contacted
by the backwash fluid.
SUMMARY OF INVENTION
[0008] In accordance with one or more embodiments, the invention
relates to a system and method of treating wastewater.
[0009] One embodiment is directed to a method of filtering
contaminants including providing a liquid comprising an oil and
suspended solids, passing the liquid through a filter vessel
wherein the filter vessel comprising walnut shell media, a draft
tube system, a peripheral zone between a side wall of the draft
tube system and a side wall of the vessel. The method also includes
interrupting flow of the liquid through the vessel passing a first
fluid through the filter media and the draft tube system in a
direction counter a flow of the liquid, and passing a second fluid
through the filter media and the peripheral zone. The method
further includes interrupting flow of the second fluid while
continuing to pass the first fluid through the filter media and the
draft tube system, reestablishing flow of the second fluid,
removing at least a portion of the oil and suspended solids from
the filter vessel, interrupting flow of the first fluid and the
second fluid, and reestablishing flow of the liquid through the
filter vessel.
[0010] Another embodiment is directed to a method of backwashing a
filter media comprising passing a feed liquid comprising a
contaminant through a filter vessel comprising a walnut shell
filter media, a draft tube, a peripheral zone between a side wall
of the draft tube and a side wall of the vessel to immobilize the
contaminant on the media. The method also includes interrupting
flow of the liquid through the vessel, passing a second liquid to
the filter vessel and into the walnut shell filter media for a
first period of time in a direction counter to the flow of the
liquid through the vessel, and passing a gas through the walnut
shell filter media in the draft tube for a second period of time to
separate at least a portion of the contaminant from the filter
media. The method further includes interrupting flow of the gas,
removing the at least one contaminant from the filter vessel,
interrupting flow of the second liquid, and reestablishing flow of
the feed liquid through the filter vessel.
[0011] Another embodiment is directed to a method of filtering
contaminants from a feed liquid comprising oil and suspended solids
comprising passing the feed liquid through a walnut shell filter
media positioned in a filter vessel, and intermittently passing a
backwash fluid into the walnut shell filter media while passing the
liquid through the walnut shell filter media.
[0012] Yet another embodiment includes a method of setting a filter
bed comprising passing a feed liquid over a filter media bed
positioned in a filter vessel comprising the media, a draft tube
system positioned in the filter media, a peripheral zone between a
side wall of the draft tube system and a side wall of the vessel,
and interrupting flow of the feed liquid. The method also includes
passing a gas through the draft tube system in a direction counter
to passing the feed liquid over the filter media, interrupting flow
of the gas, allowing the filter media to settle, and alternating
between the steps of passing the gas through the draft tube system
and allowing the filter media to settle for a predetermined number
of cycles to set the bed.
[0013] Other advantages, novel features and objects of the
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings, which are schematic and are not intended
to be drawn to scale. In the figures, each identical or
substantially similar component is represented by a single numeral
or notation. For purposes of clarity, not every component is
labeled in every figure, nor is every component of each embodiment
of the invention shown where illustration is not necessary to allow
those of ordinary skill in the art to understand the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0014] The accompanying drawings are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component that is illustrated in various figures is represented by
a like numeral. For purposes of clarity, not every component may be
labeled in every drawing. In the drawings:
[0015] FIG. 1 is a schematic drawing of a filter apparatus
according to one or more aspects of the invention;
[0016] FIG. 2a is a schematic drawing showing one aspect of the
operation of a filter apparatus;
[0017] FIG. 2b is a schematic drawing showing an aspect of the
operation of the filter apparatus of 2a;
[0018] FIG. 2c is a schematic drawing showing an aspect of the
operation of the filter apparatus of 2b;
[0019] FIG. 3 is a cross-sectional schematic plan view of a filter
vessel according to one or more embodiments of the invention;
[0020] FIG. 4 is a schematic drawing showing a filter apparatus
according to one or more aspects of the invention;
[0021] FIG. 5 is an elevated schematic side view of a draft tube
base portion according to one or more aspects of the invention;
[0022] FIG. 6 is a block diagram showing a filter system according
to one or more aspects of the invention;
[0023] FIG. 7 is a graph showing the total outlet oil concentration
verses time according to one or more aspects of the invention;
and
[0024] FIG. 8 is a flow chart of one embodiment of the
invention.
DETAILED DESCRIPTION
[0025] The invention is directed to wastewater treatment systems
utilizing a filter media bed. "Wastewater," as used herein, defines
any wastewater to be treated such as surface water, ground water, a
stream of wastewater from industrial and municipal sources, having
contaminants such as oil and/or suspended solids, and includes
produced water from primary or secondary treatment systems.
[0026] One embodiment of the present invention includes a filter
apparatus comprising a vessel containing a filter media. The vessel
may be open to the atmosphere or closed to operate under pressure.
The vessel may be sized and shaped according to a desired
application and volume of wastewater to be treated to provide a
desired throughput and/or a desired period of operation before a
backwash is initiated. The vessel may have any bed depth desired
based upon the desired volume of wastewater to be treated and the
filter media selected for the particular application. Accordingly,
the vessel may have any bed depth of filter media, such as a
shallow bed of about 10 inches up to a deep bed of about 66 inches
or more. The filter vessel may be constructed of any material
suitable for a particular purpose. For example, an open filter
vessel may be an open tank formed of cement. In one embodiment, a
closed filter vessel may be formed of coated carbon steel,
stainless steel, or fiberglass reinforced polymer.
[0027] Any filter media suitable for removal of the target
contaminant or contaminants may be used so long as it is also
suitable for use in a filter bed. One filter media useful in
removing oil and suspended solids from wastewater is walnut shell
filter media, such as media made from English walnut shells and
black walnut shells.
[0028] One embodiment of the filter apparatus includes a vessel
having one or more sidewalls depending upon the desired shape of
the vessel. For example a cylindrical vessel may have one sidewall
while a square or rectangular vessel may have four side walls. In
one embodiment, the vessel has a cylindrical shape having one
continuous sidewall positioned between the first and second walls.
In one embodiment, the vessel is closed wherein the one or more
sidewalls extend between a first wall and a second wall.
[0029] The filter media may be positioned in the vessel at a
pre-selected depth and may fill the entire volume of the vessel or
be contained in a particular portion of the vessel. For example, a
portion of the volume of the vessel adjacent the first wall and/or
the second wall may be free of filter media. Filter media may be
contained within the vessel by one or more dividers, such as
screens or perforated plates, which retain the filter media in a
desired location within the vessel while allowing wastewater to
flow throughout the media in the vessel.
[0030] In some embodiments, the filter apparatus includes a draft
tube system. The draft tube system may be constructed and arranged
to intermittently backwash the filter media by providing a desired
volume and/or velocity of backwash fluid to roll the bed. As used
herein, "rolling the bed" is defined as the movement of the filter
media during backwash in which the filter media at or near the
second wall of the vessel is partially or completely moved through
the draft tube system toward the first wall of the vessel and back
toward the second wall of the vessel. The draft tube system may be
sized and shaped for a desired application and volume of filter
media to be backwashed and/or to operate within a preselected time
period for backwash operation. The draft tube system may comprise
one or more draft tubes positioned in the media. As used herein, a
"draft tube" is a structure having one or more sidewalls open at
both ends which when positioned in the filter media provides a
passageway for flow of filter media during backwash. In one
embodiment, the vessel may have a volume filter media of about 4 to
about 6 times the volume of a draft tube or the summation of the
volumes of the draft tubes in the draft tube system.
[0031] The draft tube may be constructed of any material suitable
for a particular purpose as long as it is abrasion and oil
resistant. For example, the draft tube may be formed of the same
material as the vessel or may be formed of other lighter and less
expensive materials, such as plastics, including fiberglass
reinforced plastics. The draft tube may be preformed for insertion
into the vessel or manufactured as part of the vessel. As such, the
draft tube may be designed to retrofit current filter media units.
The draft tube system may be supported on the second wall of the
vessel. Alternatively, the draft tube system may be supported on a
divider or media retention plate, such as a screen or perforated
plate, designed to retain the media within a region of the vessel
while allowing the flow of liquid and contaminants into and out of
the media.
[0032] An individual draft tube may be sized and shaped according
to a desired application and volume filter media to be backwashed
and/or to operate within a preselected time period for backwash
operation. The draft tube may also be sized and shaped to provide a
desired level of agitation within the draft tube to partially or
completely scrub the filter media thereby releasing at least a
portion of the oil and suspended solids from the filter media. The
desired draft tube system volume may be provided by a single draft
tube or by multiple draft tubes having a total volume substantially
equal to the desired volume. An individual draft tube may have a
cross sectional area of any shape, such as circular, elliptical,
square, rectangle, or any irregular shape. The individual draft
tube may have any overall shape, such as conical, rectangular and
cylindrical. In one embodiment, the draft tube is a cylinder. The
draft tube may be positioned in the filter media so as to be
entirely enveloped by the filter media as well as to be entirely
filled with the filter media. One or both ends of the draft tube
may be constructed and arranged to assist flow of filter media into
and/or out of the draft tube. For example, the side wall at a first
end of the draft tube may include one or more cut outs forming
passageways to allow some of the filter media at or near the first
end of the draft tube to enter through the sidewall of the draft
tube. The cutouts forming the passageways may have any shape to
allow a sufficient volume of filter media to enter the draft tube.
For example, cut outs may be triangular, square, semicircular or
have an irregular shape. Multiple passageways may be identical to
one another and uniformly positioned about the first end of the
draft tube to equally distribute flow of filter media in the draft
tube.
[0033] The draft tube or draft tubes may be positioned at any
suitable location within the filter media. For example, a single
draft tube may, but need not be positioned centrally in relation to
the vessel sidewalls. Similarly, multiple draft tubes in a single
vessel may be randomly positioned or positioned in a uniform
pattern in relation to the vessel sidewalls. In one embodiment, a
single draft tube is positioned in the filter media in relation to
the vessel so that an axis extending from each end of the draft
tube is co-axial with an axis parallel to the sidewall of the
vessel. Multiple draft tubes in a single vessel may, but need not
be identical in volume or cross sectional area. For example, a
single vessel may comprise cylindrical, conical and rectangular
draft tubes of varying height and cross sectional area. In one
embodiment, a vessel may have a first draft tube centrally
positioned having a first cross sectional area and a plurality of
second draft tubes positioned adjacent the side wall of vessel in
which each of the second draft tubes has a second cross sectional
area smaller than the first cross sectional area. In another
embodiment, a vessel has a plurality of identical draft tubes.
[0034] In another embodiment, the draft tube may include a baffle
to prevent or reduce backflow within the draft tube. The baffle may
have any size and shape suitable for a particular draft tube. For
example the baffle may be a plate suitably positioned on an inner
surface of the draft tube or a cylinder positioned in the draft
tube. In one embodiment, the baffle may be a solid or hollow
cylinder centrally positioned within the draft tube.
[0035] The filter media vessel also includes a wastewater feed
inlet positioned above the filter media and a filtrate outlet
positioned below the filter media. The vessel also includes a first
inlet for a first fluid constructed and arranged to deliver the
first fluid to a first end of the draft tube to induce during
backwash a flow of the filter media within the draft tube from the
first end of the draft tube to the second end of the draft tube
while inducing flow of the filter media along an outside sidewall
of the draft tube from the second end of the draft tube to the
first end of the draft tube.
[0036] Operation of the draft tube system during backwashing
establishes countercurrent flows within the vessel and causes the
filter media to move as exemplarily shown in filter media apparatus
100 in FIG. 1. The filter media 16 moves from the first end 12 of
the vessel 20 along the outside of the draft tube 18 to the second
end 14 of the vessel 20 where it may then enter the first end 22 of
the draft tube 18 adjacent the second end 14 of the vessel 20 as
shown by the dashed flow lines (not labeled). The filter media 16
(shown only in part) then moves within the draft tube 18 in inner
region 50 from the first end 22 of the draft tube to the second end
24 of the draft tube where it exits the tube and enters a
peripheral zone 26 of the vessel 20 as shown by the dashed flow
lines (not labeled). As used herein, a "peripheral zone" is an
internal volume of the vessel not occupied by the draft tube
system. While flowing in the draft tube 18, the filter media 16 may
mix thereby releasing a portion of the oil and suspended solids
previously immobilized on the filter media. During backwash, upon
exiting the draft tube and entering the peripheral zone, the filter
media is in a turbulent zone above the draft tube in which the
filter media continues to mix releasing additional contaminants,
such as oil and suspended solids. Filter media 16 is represented in
the figures as uniform spherical particles, however, it is
understood that the filter media may be comprised of any particle
size and shape, including irregularly shaped particles.
[0037] The first fluid may be any fluid to induce movement of the
filter media through the draft tube. For example the first fluid
may be a gas, such as air or a produced gas; a liquid, such as the
filtrate or wastewater to be filtered; and combinations thereof In
one embodiment, the first fluid is a gas. Although the first fluid
inlet is shown below the filter media, in other embodiments, the
first fluid inlet may be positioned within the draft tube 18. The
first fluid inlet may comprise one or more inlets positioned within
the vessel to deliver the first fluid to the draft tube system to
impart flow of the filter media through the draft tube system. The
first fluid inlet may have any configuration suitable for
delivering the first fluid to the draft tube. For example, the
first fluid inlet may be an orifice, a nozzle, or a jet for
delivering a gas, liquid, or combination thereof to the draft tube.
In one embodiment the first inlet is a diffuser for delivering the
gas to the draft tube.
[0038] The filter vessel may also include one or more second inlets
to deliver a second fluid to a peripheral zone. The second inlets
may deliver the second fluid at or near the second wall of the
vessel to induce flow or assist in the flow of media towards the
first end of the draft tube. One or more second fluid inlets may be
positioned within the vessel to provide backwash flow to the vessel
and direct filter media toward the draft tube system. The second
fluid may be a gas, a liquid, such as the filtrate or wastewater to
be filtered, and combinations thereof In one embodiment, the second
fluid is the wastewater diverted from the wastewater feed inlet or
be diverted from the filtrate outlet. The second fluid inlet may
have any configuration suitable for delivering the second fluid to
the peripheral zone. For example the second fluid inlet may be an
orifice, a nozzle, or a jet for delivering a gas, liquid, or
combination thereof In one embodiment, the second inlet extends
into the peripheral zone. The second inlet may extend from any
suitable location to assist in water distribution. For example, the
second inlet may extend into the peripheral zone from the vessel
side wall and/or from the draft tube sidewall. In another
embodiment, the second inlet may extend into the peripheral zone at
an angle having a component tangential to the side wall of the
vessel.
[0039] In yet another embodiment, the peripheral zone may also
include one or more first fluid inlets to further agitate the
filter media bed. The first fluid inlets in the peripheral zone
may, but need not, be identical to the first fluid inlet
constructed and arranged to deliver the first fluid to the draft
tube.
[0040] The peripheral zone of the vessel may also include a scrub
zone located above the second end of the draft tube. The filter
media exiting the draft tube may be further mixed thereby releasing
additional oil and suspended solids from the filter media during
the backwash cycle.
[0041] In one embodiment, upon completion of a backwash cycle,
setting of the bed may be aided with the introduction of a gas,
such as air or produced gas, through the draft tube system to
disturb the media sufficiently to allow resettling. The gas may be
introduced intermittently during the bed setting stage. The bed may
be allowed to settle by gravity between pulses of gas.
[0042] Intermittent pulsing of the gas may also coincide with or
alternate with intermittent pulsing of liquid through the second
fluid inlet. Puling bursts of gas and liquid may disturb the bed
sufficiently to allow the bed to compact thereby reducing void
space and overall bed volume when compared to conventional bed
setting techniques. Typically after backwashing, filter media beds
are set by gravity and feed forward flow of wastewater, which may
result in insufficient set of the media and inefficiencies in which
the wastewater short circuits or channels in the filter media and
breakthrough of oil and suspended solids.
[0043] Another embodiment is directed to a wastewater treatment
system including a plurality of filter media units to provide
continuous filtration while one or more filter media units are off
line because of operating in a backwash cycle or bed setting stage.
In the wastewater treatment system, a source of wastewater
including at least one contaminant may be fed in parallel to a
plurality of media filter units. Wastewater feed flow to one of the
filter media units may be interrupted while wastewater feed flow to
the remaining filter media units continues. The filter media unit
taken offline may then be backwashed and have its bed set before
being brought back into service. Once the filter media unit is
brought back into service, another of the filter media units may be
taken out of service for the backwashing and bed setting
cycles.
[0044] In some embodiments, the system and/or individual filter
media apparatus may include a controller to interrupt and initiate
flows as desired. As used herein, the term "interrupt" is defined
as complete cessation of flow. A controller may direct the flow of
the wastewater feed, the first and second fluids and the gas
depending upon the desired operating conditions for the apparatus.
The controller may adjust or regulate valves associated with each
potential flow based upon signals generated by sensors positioned
within the apparatus. For example, a sensor may generate a first
signal indicating the pressure drop over the filter media bed has
reached a predetermined value thereby triggering the controller to
interrupt flow of the wastewater at the feed inlet and to initiate
flow of the wastewater through the second fluid inlet and gas
through the first fluid inlet. Similarly, the controller can
initiate backwash based upon a second signal generated by the
passage of a predetermined period of time. The controller may also
generate a control signal interrupting wastewater feed to one
filter media apparatus and initiating flow of wastewater feed to
another filter media apparatus based upon the first signal, the
second signal, and combinations thereof
[0045] Another embodiment is shown in FIG. 2a. Apparatus 200
comprises a cylindrical vessel 20 having a side wall 40, a first
wall 42, and a second wall 44. A filter media 16 is contained
within a portion of the vessel 20 with media retention plate 30
positioned adjacent the first end 12 of the vessel and screen 60
positioned adjacent the second end 14 of the vessel. Media
retention plate may have any structure suitable, such as a screen
or a perforated plate to retain the filter media within a portion
of the vessel while allowing the feed liquid and contaminants to
pass into and out of the media. Vessel 20 also comprises a first
end 12 adjacent the first wall 42, a second end 14 adjacent the
second wall 44, and a wastewater feed inlet 32 adjacent the first
end 12 of the vessel 20 and above the filter media 16. In FIG. 2a,
vessel 20 also includes a filtrate outlet 38 positioned below the
filter media 16 adjacent the second end 14 of the vessel 20.
[0046] In FIG. 2a, a cylindrical draft tube 18 having a first end
22 and a second end 24 is centrally positioned within the filter
media 16 such that the first end 22 of the draft tube 18 is
adjacent the second end 14 of the vessel. Filter media 16 is also
positioned within draft tube 18, and is shown in part in FIG. 2a.
The second end 24 of the draft tube is positioned sufficiently
below an upper end of the filter media bed so that sufficient
filter media is present in the bed to refill the draft tube upon
completion of a backwash cycle. A peripheral zone 26 in vessel 20
is a region delineated by the volume of the filter media 16
excluding the space occupied by the filter media in the draft tube
18. A scrub zone 28 in the peripheral zone is positioned above a
top surface of the media, between the top surface of the media and
a screen 30. Screen 30 is positioned above the scrub zone 28
adjacent the first end 12 of the vessel 20 to prevent loss of media
during backwash. Also shown in FIG. 2a is scrub zone 28 in the
peripheral zone positioned between an upper surface of the filter
media bed 54 and a lower surface of the screen 30. FIG. 2A shows
screen 30 though it is understood that any device or structure that
maintains the media in the vessel may be used. For example, the
media may be retained by a perforated plate or cylinder as well as
a cylindrical screen. A first fluid inlet 34 is constructed and
arranged to provide a first fluid to the draft tube. In FIG. 2a, a
first fluid inlet 34 includes an air diffuser 46. Second fluid
inlet 36 is constructed and arranged to deliver the second fluid to
the peripheral zone adjacent the second end of vessel 20. The
vessel 20 in FIG. 2a includes contaminant outlet 50 for removing
contaminants such as oil and suspended solids from the vessel.
Optionally, the peripheral zone may comprise one or more first
fluid inlets to partially roll the bed during filtration and/or to
assist in expanding and rolling the bed during backwash.
[0047] During filtration, wastewater containing oil and suspended
solids is directed to feed inlet 32, passes through screen 30 and
enters the filter media 16 in the bed adjacent the first end 12 of
the vessel 20 towards the second end 14 as noted by dashed flow
arrows in FIG. 2a. Wastewater simultaneously passes through the
filter media 16 in the draft tube 18 from the second end 24 of the
draft tube to the first end 22 of the draft tube. Filtrate exits
the vessel 20 via filtrate exit 38 and may be directed to further
treatment or discharged.
[0048] To extend the period of time in which filtration occurs
between backwashes, the first fluid may be pulsed to the draft tube
via first fluid inlet 34 during the filtration cycle. Optionally,
the first fluid may be pulsed via one or more first fluid inlets
(not shown) positioned in the peripheral zone during filtration. As
used herein, a "pulsed flow" is defined as a flow of fluid which is
intermittently interrupted. A pulsed flow may occur at random
intervals or may be periodic, in that the flow regularly cycles
between off and on at preselected intervals. The period of time in
which the fluid flows may, but need not be the same as the period
of time in which the fluid flow is interrupted. For example, the
fluid may flow for a longer or shorter period of time than the
period of time in which fluid flow is interrupted. In one
embodiment, the period of time in which the fluid flows is
substantially identical to the period of time in which fluid flow
is interrupted. Pulsing the first fluid, such as a gas, may
partially turn the bed of filter media thereby reducing the
pressure drop and extending the run time between backwash cycles.
Extending the filtration run time between backwash cycles may
reduce the overall number of backwashes thereby reducing the volume
of backwash generated during the life of the filter apparatus.
[0049] Filtration continues through filter media 16 until it is
desirable to clean the filter media by backwashing the filter
media. In one embodiment, backwash may be initiated when the
pressure drop across the filter media reaches a predetermined value
or when the vessel has been in service for a predetermined
time.
[0050] As shown in FIG. 2b, upon initiating a backwash, wastewater
flow to feed inlet 32 and flow of the filtrate from the filtrate
outlet are interrupted. Flow of gas is initiated through first
fluid inlet 34 and diffuser 46 and flow of the wastewater is
initiated though second fluid inlet 36. In one embodiment, the flow
of the second fluid may occur via a filtrate outlet thereby
eliminating a separate inlet for the second fluid. Flow of the gas
through first fluid inlet 34 may, but need not, occur before the
flow of the second fluid is initialized. In one embodiment the flow
of the first and second fluids begins simultaneously, while in
another embodiment the flow of the second fluid begins before flow
of the first fluid is initialized. Upon introduction of the first
and second fluids, the bed of filter media expands and moves in
countercurrent flows within the vessel 20 as shown by the flow
arrows in FIG. 2a. In FIG. 2a, the filter media adjacent the first
end 22 of the draft tube moves toward the second end 24 in a
direction counter to the flow of wastewater during filtration. The
filter media 16 adjacent the second end 24 of the draft tube moves
along the outside of the draft tube towards the first end 22 of the
draft tube, thereby partially or completely rolling the bed.
[0051] Filter media moving through the draft tube mixes thereby
releasing a portion of the oil and suspended solids immobilized on
the filter media. Filter media exiting the draft tube may further
mix in a scrub zone thereby releasing additional oil and suspended
solids from the filter media. The oil and suspended solids are
drawn from the vessel 20 via contaminant outlet 50 in FIG. 2b. The
gas is also removed from the vessel 20 via contaminant outlet
50.
[0052] The first fluid and the second fluid may continuously flow
during backwash. Alternatively, the flow of one or both of the
first and second fluids may be intermittent. In one embodiment, air
continuously flows through the draft tube while water is pulsed
into the peripheral zone. The pulsed flow may be periodic, in that
the flow regularly cycles between off and on at preselected
intervals. The period of time in which the fluid flows may, but
need not be the same as the period of time in which the fluid flow
is interrupted. For example, the fluid may flow for a longer or
shorter period of time than the period of time in which fluid flow
is interrupted. In one embodiment, the period of time in which the
fluid flows is substantially identical to the period of time in
which fluid flow is interrupted.
[0053] In another embodiment, the first fluid may be intermittently
supplied to the draft tube while the second fluid is continuously
supplied during backwash. The second liquid is passed to the filter
vessel and into the walnut shell filter media for a first period of
time in a direction counter to the flow of the liquid through the
vessel and a first liquid is passed through the walnut shell filter
media in the draft tube for a second period of time to separate at
least a portion of the contaminant from the filter media. The
duration of the first period of time may be sufficient to perform a
partial roll or one or more complete bed rolls. The flow of the
first fluid may be interrupted while the flow of the second fluid
continues and contaminants are removed. Flow of filtrate through
the filtrate exit may be interrupted and flow of the first fluid
may be reestablished. The flow of the first fluid may then be
interrupted while the flow of the second fluid continues to once
again partially or completely roll the bed one or more times. Again
the flow of contaminants may be removed while the flow of the
second fluid continues. The flow of the first fluid may be
alternated continuously until the desired level of backwash is
achieved. To complete the backwash cycle, flow of the first fluid
may be interrupted while flow of the second fluid continues and
contaminants are removed from the vessel. Upon removal of the
contaminants, the flow of the second fluid may be interrupted and
feed forward flow of wastewater may be initiated. The combination
of pulsed backwashes may result in a partial or one or more
complete bed rolls during backwash. In one embodiment, the bed is
rolled about 3 times. In another embodiment, the bed is rolled
about 4 times.
[0054] The pulsed backwash system provides advantages over
conventional backwash methods in that it may reduce capital and
maintenance costs by eliminating mechanical equipment inside the
filter vessel or outside the vessel. The pulsed backwash method may
also be simpler to operate since it may eliminate conventional
recycle pumps which remove the filter media from the vessel for
regeneration and then return regenerated filter media back to the
vessel. Maintenance of the conventional recycle pumps is often
difficult since these pumps are often located 20 to 25 feet above
ground. Flushing of the recycle lines once the backwash cycle is
completed may also be difficult and may include manual removal of
the filter media. Furthermore, elimination of the mechanical mixers
and the recycle pumps reduces system weight and footprint. Also,
because backwash components are internal to the vessel, they may be
formed of less expensive materials, such as plastics, since they
are not operated in a pressure recycle system as are conventional
external backwash components. The use of lighter components may
also reduce the installation costs in some applications, such as
off shore platforms, where installation costs increase
significantly with increased system weight. Another advantage is
that the gas or air used in the pulsed backwash system may be
readily available in many facilities, such as production gas from
hydrocarbon production or refinery facilities, thereby eliminating
the need for a compressor to supply the gas to the pulsed backwash
system. More significantly, because the pulsed backwash system may
utilize a gas and a liquid, it reduces the volume of backwash
liquid generated. Furthermore, because the filter media is not
removed from the vessel during backwash, it's exposure to piping
and pumps is reduced so that filter media having a lower modulus of
elasticity than conventional filter media may be used. For example,
black and English walnut shells are known to provide superior
coalescing and filtration of wastewater containing oil, however
walnut shell filters are typically filled with the more expensive
black walnut shells because it has a higher modulus of elasticity
than English walnut shells and therefore has a more durable surface
for use in external backwash systems. Because backwashes are
performed internally according to one embodiment, it may be
possible to use the less expensive English walnut shell without
sacrificing efficiency.
[0055] Once it is determined that sufficient oil and suspended
solids have been removed from the filter media and/or the backwash
has been running for a predetermined period of time, flow of the
first and second fluids are then interrupted and wastewater flow to
the feed inlet is initiated as shown in FIG. 2c while the filter
media sets in the bed.
[0056] FIG. 3 is a cross sectional schematic plan view of filter
media apparatus 300 similar to filter media apparatus 200 other
than filter media apparatus comprises four draft tubes 18
positioned in filter media 16. Filter media apparatus 300 also
differs from filter media 200 in that apparatus 300 may also
comprise four first fluid inlets (not shown) to direct the first
fluid to each of the four draft tubes. Other structural features of
apparatus 300 may be similar or identical to those apparatus 200
and are therefore not shown. Filtration and backwash cycles in
apparatus 300 are performed in the same manner as with apparatus
200, other than flow to the four first fluid inlets may be either
initiated or interrupted simultaneously. As with apparatus 200,
filter media apparatus 300 may optionally include additional first
fluid inlets and/or second fluid inlets in the peripheral zone 26
to assist rolling the bed. The presence of multiple draft tubes
within the filter media may more uniformly distributes the gas
exiting the draft tubes and entering the scrub zone, thereby
increasing turbulence in the mixing scrub zone for more effective
removal of the oil and suspended solids from the filter media. The
elimination of a central draft tube as shown in FIG. 3, though not
necessary, may allow for easier and more versatile water
distribution.
[0057] FIG. 4 is a schematic drawing of filter media apparatus 400.
Filter media apparatus 400 is similar to filter media apparatus
with the exception that the draft tube 18 of apparatus 400 includes
a baffle 62. A baffle may be advantageous when a diameter of the
backwash tube is sufficiently large so as to have the potential for
back mixing to occur within the draft tube. Back mixing of the
wastewater and filter media within the draft tube may negatively
impact the flow and mixing of the filter media in the draft tube
resulting in poor suction at the first end of the draft tube and
reducing the filter media rolling efficiency. The baffle may be
sized and shaped for a particular purpose. FIG. 4 shows a
cylindrical baffle 62 centrally positioned within the draft tube
18. Although 4 draft tubes are show, it is understood that any
number and configuration of draft tubes may be used so long as the
draft tube system provides the desired volume of media rolling
through the vessel.
[0058] In apparatus 400, the first fluid inlet 34, such as a gas
inlet, may be constructed and arranged to direct air though the
entire draft tube including an outer portion 66 bounded by the
sidewall of the draft tube and the sidewall of the baffles, as well
as though a central portion 64 of the draft tube bounded by the
sidewall of baffle 62. The outer region 66 may be an annular region
surrounding bounded by a cylindrical draft tube and cylindrical
baffle. Filtration and backwash cycles in apparatus 400 are
performed in the same manner as with apparatus 200. As with
apparatus 200, filter media apparatus 400 may optionally include
additional first fluid inlets and/or second fluid inlets in the
peripheral zone 26 to assist rolling the bed. During backwash, the
filter media flows through the central portion 64 as well as the
outer region 66, while the filter media in the peripheral zone
flows in a counter current direction. During feed forward
filtration, the liquid containing contaminant flows through the
filter media positioned in the peripheral zone 26, the outer region
66 and the central portion 64.
[0059] FIG. 5 is an elevated schematic view of one embodiment of a
base portion 500 of a draft tube 518 suitable for use in any of
filter media units 200, 300, 400. In this embodiment draft tube 518
comprises a plurality of passageways 570 in the first end 522 of
the draft tube. The cut outs may assist the flow of filter media
from the peripheral zone (not shown) to the first end 522 and
through the draft tube 518. The passageways may be identical to one
another and regularly spaced about the second end of the draft tube
to provide consistent flow within the draft tube. The passageways
570 may have any size and shape to allow sufficient flow of the
filter media and backwash fluid within the draft tube to provide a
desired backwash cycle.
[0060] FIG. 6 is a block diagram of wastewater treatment system 600
comprising a first filter media apparatus 610 and a second filter
media apparatus 620 operating in parallel. Filter media units 610
and 620 may comprise a vessel, a filter media, and a draft tube
positioned within the media. A source of wastewater 630 containing
oil and suspended solids is fluidly connected to a wastewater feed
inlet of filter media apparatus 610 via valve 632. Similarly the
source of wastewater 630 is fluidly connected to a wastewater feed
inlet of filter media apparatus 620 vial valve 634. The source of
wastewater is fluidly connected to a second fluid inlet of
apparatus 610 via valve 636, and is also fluidly connected to a
second fluid inlet of apparatus 620 via valve 638.
[0061] A source of gas 640, such as an air blower, is fluidly
connected to a gas inlet to apparatus 610 vial valve 646. The
source of the gas 640 is also fluidly connected to a gas inlet of
apparatus 620 via valve 648.
[0062] While apparatus 610 is running in a filtration cycle, valve
632 is open to supply wastewater to the apparatus. Accordingly,
valves 636, 646 are closed to prevent backwash of the bed with the
wastewater and the gas, respectively. Similarly, valve 642 remains
closed to prevent the gas from displacing the wastewater during
filtration.
[0063] Apparatus 620 may be operating in a backwash cycle for all
or a portion of the time that apparatus 610 is operating in the
filtration cycle. While apparatus 620 is operating in the backwash
cycle, valve 634 is closed to prevent wastewater from entering the
feed inlet of the apparatus. Valves 638, 648 are open to provide
wastewater and gas to the backwash cycle. In the system of FIG. 6,
controller 650 may respond to a signal generated by a timer
indicating a predetermined backwash period has elapsed and generate
one or more control signals to cause valves 638, 648 to close and
valve 634 to open so that apparatus 620 may operate under
filtration conditions.
[0064] Optionally, a source of filtrate may be fluidly connected to
the second fluid inlet of the first apparatus and to the second
fluid inlet of the second apparatus. In another embodiment, the
second fluid may be connected to the first and second filtrate
outlets to provide the second fluid to the first apparatus and the
second apparatus, thereby eliminating separate second fluid
inlets.
[0065] In the system of FIG. 6, controller 650 may also respond to
signals from sensors (not shown) positioned at any particular
location within the system. For example, a sensor in filter media
apparatus 610 operating in the filtration cycle may generate a
signal indicating that the pressure drop across the filter media
bed has reached a predetermined value at which it may be desirable
to perform a backwash of the media in apparatus 610. The controller
650 may respond by generating one or more control signals to close
valve 632 and open valves 636, 646 to start the backwash cycle. The
controller 650 may then receive and respond to signals by
alternatively place one or both units 610, 620 in service or take
one or the other out of service to run a backwash cycle.
[0066] During the backwash cycles of either apparatus 610, 620,
controller 650 may signal valves 636, 638, 646, 648 to remain
continuously open or to open and close intermittently to pulse the
backwash. During the switch over of each bed from the backwash
cycle, controller 650 may also intermittently open and close valve
646, 648 to provide pulses of gas to the draft tube to aid in
setting the bed. A pulse of gas through the draft tube may disturb
the bed after which the bed gravity settles. A pulse of gas may
then again be directed through the draft tube to again disturb the
bed after which the bed gravity settles. The pulsed bed setting may
continue for a predetermined period of time or pulses, or until the
bed has settled to a desired height, at which time the valves 646,
648 may remain closed as forward feed of the source of wastewater
630 is initiated. During pulsed bed settling with gas, a liquid
may, but need not, be pulsed into the vessel via valves 636, 638 to
assist settling. Pulsing the liquid may occur between or at the
same time as the gas pulses to settle the bed.
[0067] FIG. 8 is a flow chart illustrating an embodiment of the
invention. In FIG. 8, step 801 includes passing a feed liquid to a
filter apparatus. Filtrate is removed during feed forward
filtration of step 801. While passing the feed liquid, a sensor
monitors pressure in first filter apparatus to determine if the
pressure drop across the filter media has reached a predetermined
value shown in step 802. If the value of the pressure drop has not
reached the predetermined value, liquid feed continues to pass
through the first filer apparatus as in step 801. If the pressure
reading is determined to have reached or exceeded a predetermined
value, the flow of feed liquid to the filter apparatus is
interrupted in step 803.
[0068] In FIG. 8, after the flow of the feed liquid is interrupted,
a flow of a first fluid is introduced into a draft tube in the
vessel per step 804 in a direction counter to the flow of feed
liquid. A flow of a second fluid is also introduced into a
peripheral zone per step 805. In step 806, a determination is made
as to whether or not the filter media has been sufficiently rolled.
This determination may be made upon the overall time period passing
in steps 804 and 805. Per step 806, if the filter media has been
sufficiently rolled, the flow of the first fluid is interrupted in
step 807. If the filter media has not been sufficiently rolled, the
flow of the second fluid is interrupted in step 809. After
interrupting the flow of the second fluid, the flow of the second
fluid is again initiated in step 810. Once again, a determination
is made in step 811 as to whether or not the filter media has been
sufficiently rolled. If the bed has been sufficiently rolled, the
flow of the first fluid is interrupted in step 807. If the filter
media has not been sufficiently rolled, the flow of the second
fluid is interrupted in step 809. Steps 809-811 are repeated until
it is determined in step 811 that the filter media has been
sufficiently rolled.
[0069] Once the flow of the first fluid has been interrupted in
step 807 after a determination that the filter media has been
sufficiently rolled, contaminants are removed from the filter
apparatus in step 812. After removal of contaminants, the flow of
the second fluid is interrupted in step 813 and the flow of the
feed liquid to the filter apparatus is reestablished in step 814.
Filtrate is again removed during feed forward filtration of step
814.
[0070] The function and advantages of these and other embodiments
of the present invention will be more fully understood from the
following examples. These examples are intended to be illustrative
in nature and are not considered to be limiting the scope of the
invention.
EXAMPLE I
[0071] An experiment was conducted to determine the effectiveness
of a pulsed water backwash. A test apparatus was configured with a
clear plastic column having a diameter of about 12 inches and a
height of about 12 feet. A draft tube having a diameter of about 3
inches and a height of about 5 feet was placed at the center of the
column. An air diffuser was attached to an air inlet at the base of
the draft tube. Three nozzles for delivering water were equally
spaced about the periphery of the column. Each nozzle included an
elbow to direct water tangentially in the column. The column was
filled with 66 inches of black walnut shells so that the shell bed
extended approximately 6 feet above the height of the draft
tube.
[0072] A series of tests were performed to measure the effect of
air and water flow rates during backwash. Backwash efficiency was
measured in the velocity of the walnut shells traveling down the
outside of the draft tub in the peripheral zone. A portion of the
walnut shells were painted for visual confirmation of motion during
backwash. Initial results indicated that that by pulsing the water
the generation of backwash volume from the walnut shell filter was
significantly reduced without sacrificing backwash efficiency.
[0073] Further tests were conducted with the above apparatus to
compare continuously flowing backwash water to pulsing the water
while maintaining a constant flow rate of air through the draft
tube. In a first test, the water continuously flowed into the
peripheral zone at a rate of about 3 GPM while in a comparative
test water flow was pulsed into the peripheral zone at with a water
pulse of about 6 GPM for about 1 second followed by no flow for
about 1 second to achieve an overall flow of 3 GPM. In a second
test, the water continuously flowed into the peripheral zone at a
rate of about 4 GPM while in a comparative test water flow was
pulsed into the peripheral zone at with a water pulse of about 8
GPM for about 1 second followed by no flow for about 1 second to
achieve an overall flow of about 4 GPM. The results are shown in
Table I.
TABLE-US-00001 TABLE I Water Flow Rate (GPM) Velocity (in/min) Time
to Roll Bed (min.) 3 Continuous 23.5 2.8 3 Pulsed 26.4 2.5 4
Continuous 28.1 2.3 4 Pulsed 34.2 1.9
[0074] As can be seen, pulsing the water increased the velocity of
the walnut shells by about 12 percent and reduces the time to roll
the bed by about 11 percent when compared to the continuous flow
rates of 3 GPM while producing the same volume of backwash.
Similarly, pulsing the water increased the velocity of the walnut
shells by about 21 percent and reduces the time to roll the bed by
about 17 percent when compared to the continuous flow rates of 4
GPM while producing the same volume of backwash.
[0075] These results indicate that pulsing the water during
backwash is more efficient so that the backwash cycle may be
performed in a shorter period of time, generate less backwash, or a
combination of both. Based upon this data, it was estimated that
the pulsed backwash would generate 20-30 gallons of water per
square foot of filtering area compared to generating about 160
gallons of water per square foot of filtering area with
continuously flowing water.
EXAMPLE II
[0076] A test was conducted to determine the effectiveness of
backwashing a black walnut shell filter having multiple draft tubes
in comparison to a single draft tube. In a first test, a vessel
having a diameter of 4 feet had one centrally located draft tube
having a diameter of 12 inches was fabricated. A portion of the
walnut shells were painted for identification and windows were
positioned at various locations in the vessel to observe the
movement of the walnut shells. In a second test, a vessel having a
diameter of 4 feet included 4 draft tubes each having a diameter of
6 inches was fabricated. The 4 draft tubes were equally spaced
throughout the vessel. Backwash water volume and gas volume were
identical for both tests.
[0077] Visual results indicated that the multiple draft tube design
was at least as effective at rolling the bed as the single draft
tube design, and in some instances was even more effective. Without
being bound by any particular theory, the presence of multiple
draft tubes more uniformly distributes the air exiting the draft
tubes and entering the scrub zone, thereby increasing turbulence in
the mixing scrub zone for more effective removal of the oil and
suspended solids from the filter media.
EXAMPLE III
[0078] A pilot test was conducted to determine the effectiveness of
backwashing a black walnut shell filter having a baffle positioned
in a draft tube. A filter media vessel having a diameter of 4 feet
was fitted with a draft tube made from a 12 inch diameter pipe. A
baffle formed from a 6 inch diameter pipe and centrally located in
the draft tube. Clear windows were installed in the filter medial
vessel in order to observe backwash efficiency. Visual results of
the pilot test confirmed that the draft tube with a baffle provided
adequate backwash for the 4 ft large diameter vessel.
EXAMPLE IV
[0079] A test was conducted to determine the effectiveness of
delivering alternating pulses of wastewater and air to a bed of
black walnut shell media to set the bed after a backwash cycle.
Walnut shell media was conventionally set in a vessel having a
diameter of 12 inches by feeding wastewater in a forward flow to a
bed depth of 60 inches. The walnut shell media was then expanded
during the backwash cycle to a height of 66 inches. For comparison,
the bed was conventionally set back to 60 inches with continuously
flowing forward feed for about 5 minutes. Forward flow feed was
then performed to measure the efficiency of the bed
[0080] The walnut shell media was then again expanded to a height
of 66 inches after which alternating pulses or short burst of
wastewater and air were added to the walnut shell media in a
reverse feed direction for about 2 minutes and allowed to settle.
Water was pulsed through the bed at a flow rate of about 1.5
gal/min for one second after which air was pulsed through the bed
in a short burst for one second. The bed set to a depth of 53
inches, which is 7 inches less than the original depth resulting in
a condensed bed having a reduced void volume in the filter media.
Forward flow feed was then performed on the condensed bed to
determine the efficiency of the condensed bed compared to the
conventionally set bed. The results of the total outlet oil
concentration verses time in feed forward filtration are shown in
FIG. 7. Linear regression equations were calculated from the data
for the conventionally set bed, labeled as a loose bed, and the
pulsed set bed, labeled a set bed. Data
TABLE-US-00002 TABLE II Total Oil in Total Oil in Effluent (ppm)
Effluent (ppm) % Change in Time (min) Conventional Set Pulsed Set
Oil in Effluent 100 19.364 21.292 +10.0 200 26.984 25.512 -4.3 300
34.604 29.732 -14.1 400 42.224 33.952 -19.6 500 49.844 28.172 -23.4
600 57.464 42.392 -26.2 700 65.084 46.612 -28.4 800 72.704 50.832
-30.1
[0081] At seen in the tables above, as filter time increased, the
pulsed set bed was significantly more effective in removing total
and free oil from the wastewater, by as much as 30 percent at 800
minutes. Similarly the graph also shows that as time increased the
pulsed set bed removed more oil than the conventionally set
bed.
[0082] The pulsed set bed may therefore allow the walnut filter
media to be run for a longer period of time than conventionally set
beds before it is desirable to run a backwash. Extending the period
of time between backwash cycles may also reduce the total amount of
generated backwash over the life of the media. Compacting the bed
may also result in bed designs with a smaller bed depth reducing
vessel size and weight.
[0083] Having thus described several aspects of at least one
embodiment of this invention, it is to be appreciated various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are
intended to be within the spirit and scope of the invention.
Accordingly, the foregoing description and drawings are by way of
example only.
[0084] This invention is not limited in its application to the
details of construction and the arrangement of components set forth
in the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced or
of being carried out in various ways. Also, the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having," "containing," "involving," and
variations thereof herein, is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items.
Only the transitional phrases "consisting of" and "consisting
essentially of" are closed or semi-closed transitional phrases,
respectively, with respect to the claims. As used herein, the term
"plurality" refers to two or more items or components.
* * * * *