U.S. patent application number 15/434698 was filed with the patent office on 2018-08-16 for device for wastewater purification.
The applicant listed for this patent is PROTERRGO INC.. Invention is credited to VALERIE LEVEILLE, NICOLE A. POIRIER, ROY RICHARD, PANAYOTIS G. TSANTRIZOS.
Application Number | 20180230025 15/434698 |
Document ID | / |
Family ID | 63106285 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180230025 |
Kind Code |
A1 |
TSANTRIZOS; PANAYOTIS G. ;
et al. |
August 16, 2018 |
DEVICE FOR WASTEWATER PURIFICATION
Abstract
An integrated device for wastewater purification, comprising a
coagulation zone; a flocculation zone connected to and in fluid
communication with the coagulation zone; a flotation zone connected
to and in fluid communication with the flocculation zone and
comprising a froth discharge port; and a separation zone below and
in fluid communication with the flotation zone and comprising a
contaminant separator and a purified wastewater discharge port; the
wastewater entering the device being mixed with
electrolytically-generated coagulants and gas bubbles in the
coagulation zone; the flocculation zone receiving and gently mixes
coagulated wastewater contaminants and gas bubbles formed in the
coagulation zone and aggregating them into flocs before flotation
of buoyant flocs in the flotation zone and the separation zone
being adapted for further floc formation, oil coalescence, settling
and discharge of non-buoyant contaminants.
Inventors: |
TSANTRIZOS; PANAYOTIS G.;
(MONTREAL, CA) ; LEVEILLE; VALERIE; (MONTREAL,
CA) ; POIRIER; NICOLE A.; (BEACONSFIELD, CA) ;
RICHARD; ROY; (NATICK, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PROTERRGO INC. |
Montreal |
|
CA |
|
|
Family ID: |
63106285 |
Appl. No.: |
15/434698 |
Filed: |
February 16, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F 2001/46119
20130101; C02F 2001/46152 20130101; C02F 2201/4611 20130101; C02F
2101/301 20130101; C02F 2101/325 20130101; C02F 1/465 20130101;
C02F 2103/005 20130101; C02F 1/463 20130101; C02F 2103/002
20130101; C02F 1/46109 20130101; C02F 2103/008 20130101 |
International
Class: |
C02F 1/463 20060101
C02F001/463; C02F 1/465 20060101 C02F001/465; C02F 1/461 20060101
C02F001/461 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made in part with Government support
contract #: ONR N00014-11-c-0166, ONR N00014-13-C-0218 and ONR
N00014-14-P-1223 awarded by the US Office of Naval Research; and
contract #: W56HZV-12-C-0438 awarded by the US Department of the
Army.
Claims
1. An integrated device for wastewater purification, comprising: a
coagulation zone, comprising a feed port for the wastewater to
enter the device; a flocculation zone connected to and in fluid
communication with said coagulation zone; a flotation zone
connected to and in fluid communication with said flocculation zone
and comprising a froth discharge port; and a separation zone below
and in fluid communication with said flotation zone and comprising
a contaminant separator and a purified wastewater discharge port;
wherein the wastewater entering the device through said feed port
is mixed with electrolytically-generated coagulants and gas bubbles
in said coagulation zone; said flocculation zone receives and
gently mixes coagulated wastewater contaminants and gas bubbles
formed in said coagulation zone and aggregates them into flocs
before flotation of buoyant flocs in said flotation zone; said
separation zone being adapted for further floc formation, oil
coalescence, settling and discharge of non-buoyant
contaminants.
2. The device of claim 1, wherein said coagulation zone comprises a
top electrode and a bottom electrode separated by a constant
inter-electrode gap, and an annular gap at a peripheral outer edge
of the electrodes; said annular flocculation zone being in
continuity with the annular gap at the peripheral outer edge of the
electrodes to receive and mix said coagulated wastewater
contaminants and gas bubbles formed in said inter-electrode
gap.
3. The device of claim 1, wherein said coagulation zone comprises a
top electrode and a bottom electrode separated by a constant
inter-electrode gap, and an annular gap at a peripheral outer edge
of the electrodes; said annular flocculation zone being a narrow
chamber extending up from said coagulation zone in continuity with
the annular gap at the peripheral outer edge of the electrodes to
receive and mix said coagulated wastewater contaminants and gas
bubbles formed in said inter-electrode gap.
4. The device of claim 1, wherein said separation zone comprises a
separator and a purified wastewater discharge port.
5. The device of claim 1, wherein said separation zone comprises a
separator, and wherein upon application of an electric potential to
the electrodes, the wastewater received through said feed port is
submitted to coagulation in said coagulation zone and then to
flocculation on its way up through said flocculation zone, part of
flocs exiting said flocculation zone floating up towards said froth
discharge port, while remaining part of the flocs and the
non-buoyant contaminants are entrained downwards to said separator,
said separator being adapted for contaminant aggregation, floc
formation and settlement of non-buoyant contaminants as a
sludge.
6. The device of claim 1, wherein said separation zone comprises a
separator, said separator comprising a series of concentric and
truncated upward pointing cones, below the flotation zone.
7. The device of claim 1, wherein said coagulation zone comprises a
top electrode and a bottom electrode separated by an
inter-electrode gap, and a wiper blade assembly within said
inter-electrode gap.
8. The device of claim 1, wherein said coagulation zone comprises a
top electrode and a spring-loaded bottom electrode, separated by an
inter-electrode gap, and a wiper blade assembly within said
inter-electrode gap.
9. The device of claim 1, further comprising a wastewater
recirculation loop within the inter-electrode gap.
10. The device of claim 1, wherein said coagulation zone comprises
a top electrode and a bottom electrode separated by an
inter-electrode gap, and a wiper blade assembly within said
inter-electrode gap, said wiper blade assembly comprising
fan-shaped wiper blades.
11. The device of claim 1, wherein said coagulation zone comprises
a top electrode and a bottom electrode separated by an
inter-electrode gap, and a wiper blade assembly within said
inter-electrode gap, said wiper blade assembly comprising
fan-shaped wiper blades, and a rotational speed of said wiper
blades is comprised in a range between 4 and 15 rpm.
12. The device of claim 1, wherein a residence time in said
coagulation zone is about 5 s and a residence time in said
flocculation zone is about 115 s.
13. A marinarized integrated device for onboard wastewater
purification, comprising: a coagulation zone, comprising a feed
port for the wastewater to enter the device; a flocculation zone
connected to and in fluid communication with said coagulation zone;
a flotation zone connected to and in fluid communication with said
flocculation zone; and a separation zone below and in fluid
communication with said flotation zone and comprising a contaminant
separator and a purified wastewater discharge port; wherein said
annular flocculation zone is a narrow chamber extending up from
said coagulation zone; said flotation zone comprises a floc
collection cone, the flocs being periodically discharged from said
collection cone; and said separation zone comprises a series of
concentric and truncated upward pointing cones, below the flotation
zone.
Description
FIELD OF THE INVENTION
[0002] The present invention relates to wastewater purification.
More specifically, the present invention is concerned with a device
for electrochemical wastewater purification.
BACKGROUND OF THE INVENTION
[0003] Electrochemical processes and more specifically the
electrocoagulation process are known since 1906, when A. E.
Dietrich patented the first electrocoagulation process for the
treatment of bilge oily water from ships. Treatment of wastewater
by electrocoagulation has been practiced for most of the 20th
century with increasing popularity. In the last decade,
electrocoagulation has been increasingly used in the United States,
South America and Europe for the treatment of industrial wastewater
containing metals. In North America, electrocoagulation has been
used primarily to treat wastewater from pulp and paper industries,
and mining and metal-processing industries. Recently,
electrocoagulation was applied to treat wastewater containing food
wastes, oily wastes, dyes and ink, chemical and mechanical
polishing wastes, organics in landfill leachates, and effluents
containing fluoride and synthetic detergent.
[0004] Current electrocoagulation devices are typically used in
combination with additional devices performing required steps of
the purification process such as contaminant coagulation,
flocculation, and separation from the treated effluent.
[0005] Limitations of electrocoagulation, as it is performed today
and that prevent it from wide commercial use for treating
contaminated wastewater such as sewage, bilge water, and industrial
wastewater include, for example, passivation of the electrode
surfaces; inability to treat concentrated wastewater without a
large number of electrodes or high electrode surface areas and long
hydraulic residence times, due to the need to use low current
densities to prevent passivation in the absence of continuous
electrode cleaning mechanisms; build-up of sludge inside the
treatment vessel leading to blockages and short circuits, which
requires stopping the process in order to clean the vessel;
inability to operate on marine vessels due to vessel motions such
as vibration, roll and pitch which can affect hydrodynamics and
alter the electrocoagulation process efficiency; inability to
maintain a constant and small inter-electrode gap in order to
operate at a constant and low voltage; inability to treat the
entire wastewater stream due to hydraulic short circuiting or
dosage of only a portion of the stream with the
electrolytically-generated coagulant, and necessity to add one or
more unit operations after the electrocoagulation process in order
to complete the desired wastewater treatment and separate purified
wastewater from contaminants.
[0006] There is still a need in the art for an optimized device for
electrochemical wastewater purification.
[0007] The present description refers to a number of documents, the
content of which is herein incorporated by reference in their
entirety.
SUMMARY OF THE INVENTION
[0008] More specifically, in accordance with the present invention,
there is provided an integrated device for wastewater purification,
comprising a coagulation zone, comprising a feed port for the
wastewater to enter the device; a flocculation zone connected to
and in fluid communication with the coagulation zone; a flotation
zone connected to and in fluid communication with the flocculation
zone and comprising a froth discharge port; and a separation zone
below and in fluid communication with the flotation zone and
comprising a contaminant separator and a purified wastewater
discharge port; wherein the wastewater entering the device through
the feed port is mixed with electrolytically-generated coagulants
and gas bubbles in the coagulation zone; the flocculation zone
receives and gently mixes coagulated wastewater contaminants and
gas bubbles formed in the coagulation zone and aggregates them into
flocs before flotation of buoyant flocs in the flotation zone; the
separation zone being adapted for further floc formation, oil
coalescence, settling and discharge of non-buoyant
contaminants.
[0009] There is further provided a marinarized integrated device
for onboard wastewater purification, comprising a coagulation zone
with a feed port for the wastewater to enter the device; a
flocculation zone connected to and in fluid communication with the
coagulation zone; a flotation zone connected to and in fluid
communication with the flocculation zone; and a separation zone
below and in fluid communication with the flotation zone and
comprising a contaminant separator and a purified wastewater
discharge port; wherein the annular flocculation zone is a narrow
chamber extending up from the coagulation zone; the flotation zone
comprises a floc collection cone, the flocs being periodically
discharged from the collection cone; and the separation zone
comprises a series of concentric and truncated upward pointing
cones, below the flotation zone.
[0010] Other objects, advantages and features of the present
invention will become more apparent upon reading of the following
non-restrictive description of specific embodiments thereof, given
by way of example only with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the appended drawings:
[0012] FIG. 1 is a cut-away view of a device according to an
embodiment of an aspect of the present invention;
[0013] FIG. 2 is a cut-way view of an electrode section of the
device of FIG. 1 according to an embodiment of an aspect of the
present invention;
[0014] FIG. 3 shows a wiper blade used in an electrode section
according to an embodiment of an aspect of the present
invention;
[0015] FIG. 4 shows the effect of the wiper blade rotational speed
(rpm) on the voltage drop across two disc electrodes arranged
horizontally in an electrode section and immersed in wastewater
according to an embodiment of an aspect of the present
invention;
[0016] FIG. 5 shows the effect of the wiper blade rotational speed
(rpm) on the voltage (V) across the two disc electrodes arranged
horizontally in the electrode section immersed in wastewater
according to an embodiment of an aspect of the present
invention;
[0017] FIG. 6 is a schematic view of a wastewater recirculation
loop in an electrode section of a device according to an embodiment
of an aspect of the present invention;
[0018] FIG. 7A shows a wiper blade without the wastewater
recirculation loop in the inter-electrode gap according to an
embodiment of an aspect of the present invention;
[0019] FIG. 7B shows a wiper blade with the wastewater
recirculation loop in the inter-electrode gap according to an
embodiment of an aspect of the present invention;
[0020] FIG. 8 shows the voltage across the electrodes with the
wastewater recirculation loop in the inter-electrode gap, circles
indicating when the recirculation is activated;
[0021] FIG. 9 shows characteristics of the wastewater before and
after treatment and the contaminant removal rate using a method
according to an embodiment of an aspect of the present invention;
and
[0022] FIG. 10 shows the emulsified oil and grease (EOG)
concentration in oily wastewater before and after treatment and the
EOG removal rate according to an embodiment of an aspect of the
present invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0023] The present invention is illustrated in further details by
the following non-limiting examples.
[0024] A device 10 according to an aspect of an embodiment of the
invention is illustrated in FIGS. 1 and 2. As illustrated, the
device 10 comprises a body of a generally cylindrical shape, formed
by an outer 20 cylinder capped at a top end thereof by a cone
28.
[0025] The device 10 generally comprises a coagulation zone 12, a
flocculation zone 24, a flotation zone 13 and a separation zone
15.
[0026] The coagulation zone, shown for example in FIG. 2, comprises
disc-shaped electrodes 14, 16, i.e. an anode and a cathode, facing
one another and separated by an inter-electrode gap d, and
positioned perpendicular to the walls of the body of the device 10,
at a bottom end thereof. The electrode acting as the anode is a
sacrificial electrode, in aluminium or iron for example. As
described hereinbelow, the wastewater received within the
coagulation zone 12 through an entry port 64 is rapidly mixed
therein with electrolytically-generated coagulants and gas
bubbles.
[0027] An inner cylinder 22, concentric with the outer cylinder 20,
defines, between parallel facing surfaces of the inner cylinder 22
and the outer cylinder 20, an annular narrow chamber extending up
from the coagulation zone 12.
[0028] This annular narrow chamber forms the flocculation zone 24,
connected to and in fluid communication with the coagulation zone
12, in continuity with annular gaps 26 provided at the outer edges
of the electrodes 14, 16. As described hereinbelow, the
flocculation zone 24 receives coagulated wastewater contaminants
and gas bubbles formed in the coagulation zone 12.
[0029] The flotation zone 13 is located at the top of the
flocculation chamber 24, in fluid communication with the
flocculation chamber 24, for flotation of buoyant coagulated and
flocculated wastewater contaminants, such as oil and particles for
example. As described hereinbelow, the flotation zone 13 comprises
a froth discharge port 30 at a top part thereof.
[0030] Wastewater is made to enter the device 10 at a feed port 64
at a bottom thereof, using a feeding pump for example, and then to
flow radially in the inter-electrode gap d between the electrodes
14, 16 of the coagulation zone 12 toward the annular gaps 26, and
then up into the flocculation chamber 24.
[0031] Upon application of an electric potential to the electrodes,
multivalent metal ions are released from the anode, and hydrogen
micro-bubbles are released at the cathode with hydroxide ions. The
multivalent metal ions destabilize colloidal suspensions and
emulsions in the wastewater.
[0032] The inter-electrode gap d is selected to form a confined
space that generates an intense vigorous electrolytic bubbling,
resulting in rapid mixing, i. e. enough turbulence, to rapidly and
completely mix the metal ions released from the anode and the
wastewater flowing radially therethrough in a matter of seconds,
typically 5 s.+-.50% of residence time, thereby promoting
coagulation. This residence time is much shorter than the 30-180
seconds typically used in the rapid mixing stage of conventional
wastewater treatment systems and methods where chemical coagulants,
such as aluminum sulfate, aluminum chloride, ferric sulfate and
ferrous sulfate for example, are added to the wastewater and then
mixed. There are several factors which may explain this difference;
chemical coagulants must first be hydrolyzed before they can serve
to coagulate, while electrolytic coagulants are liberated in
ready-to-use ionic form; as well, the bubbling, radial flow and
shear forces that occur in the inter-electrode gap of the present
system result in unexpectedly effective and rapid mixing. An
inter-electrode gap d of 5 mm is found to result in this effective
mixing and minimises the system electrical resistance. A gap d of 4
mm or even 3 mm could be used. Gaps larger than 5 mm might not be
cost-effective since it would unnecessarily increase the electrical
consumption unless the electrical conductivity of the wastewater to
be treated is elevated, such as for instance at least 5 mS/cm.
[0033] The annular gaps 26 ensure a peripheral distribution and
continuous transfer of the coagulated contaminants and hydrogen
bubbles to the flocculation chamber 24 while minimizing hydrogen
bubble coalescence such as would occur if wastewater was
transferred using pipe or conduit from the coagulation zone 12 to a
flocculation or flotation zone.
[0034] The flocculation chamber 24 provides flow conditions that
allow gentle mixing and upward vertical flow of coagulated
particles and hydrogen bubbles, with, for example, 115
seconds.+-.50% of residence time for the bulk flow, although some
hydrogen bubbles may have significantly lower or higher residence
times than this depending on their size, leading to conditions
suitable for coagulated contaminants to form micro-flocs and then
flocs by the time they exit the flocculation chamber 24. This bulk
flow residence time is much shorter than the flocculation time of
15-60 minutes or more typically used in conventional wastewater
treatment systems and methods using baffled chambers or rotating
blades, frequently assisted by polymeric flocculants added to aid
with flocculation. There are several factors which may explain this
difference; orthokinetic flocculation is primarily dependent on
induced velocity gradients and time of flocculation, and it was
found that the narrow annulus of the flocculation chamber of the
present system coupled with the gentle mixing provided by the
rising gas bubbles provides an optimal arrangement for effective
flocculation.
[0035] The flocculation chamber 24 prevents the undesired
coalescence of electrolytically-generated hydrogen micro-bubbles,
so that they remain available and attach to the developing flocs
consisting of coagulant and contaminants, rendering them buoyant.
As a result, once exiting the flocculation chamber 24 into the
flotation zone 13, the flocs rapidly float to the surface of the
liquid and can then be separated from the wastewater being treated.
This flotation is far more rapid than gravity-based sedimentation
which is often used in conventional wastewater treatment systems
and methods to separate flocs from the treated effluent. Flotation
is dependent on the availability of a large number of micro-bubbles
as opposed to fewer bubbles of larger size, and the present system
makes use of a current density and has a configuration allowing
operating conditions that generate and maintain sufficient
micro-bubbles for extremely effective and rapid flotation of the
flocs created in the flocculation zone.
[0036] Once exiting the flocculation chamber 24 into the flotation
zone 13, the flocs float to the surface of the liquid and can then
be separated from the wastewater being treated. The relatively high
current density used in the present invention, for example between
30 and 70 A mA/cm.sup.2, results in a rapid and complete flotation
of the coagulated, flocculated contaminants. Some of the metallic
ions also react with hydroxyl ions to produce metal hydroxides and
complexes with many organic species. By means of attached
micro-bubbles, these can be floated upwards as well.
[0037] In the flotation zone 13, located above the flocculation
chamber 24, the flocs continue to form on their way up to the floc
collection cone 28 capping the device 10, while the treated
effluent flows downwards. The flocs are periodically discharged,
based on the depth of the floc floating layer in the collection
cone 28 for example, through the discharge port 30.
[0038] In fluid communication with and below the flotation zone 13,
the separation zone 15 comprises a separator 32 and a purified
wastewater discharge port 36.
[0039] The separator 32, comprising a series of concentric and
truncated upward pointing cones, below the flotation zone 13, is
used to separate non-buoyant contaminants: it receives small
particles, which may include micro-flocs, particulates or
emulsified constituents that are entrained downwards between the
parallel surfaces of the upward pointing cones by the downward
flowing wastewater, allowing them to aggregate so that they may
either float upwards towards the floc collection cone 28, for
example in the case of emulsified oil droplets with a specific
density less than 1, or settle downwards towards a sludge collector
38.
[0040] A purified wastewater discharge cone 34 directs the purified
wastewater (effluent) to the discharge port 36, while the sludge
collector 38, which is shown as an inclined plate located below the
effluent discharge cone 34 and covering the entire cross-sectional
area of the inner cylinder of body of the device 10 in FIG. 1,
collects heavy sludge and particles and directs them to a sludge
discharge port 40.
[0041] The flotation zone 13 may include a spray nozzle 42, which
is periodically used in order to clean the inside of the device 10
from debris deposited onto the inner surface of the flotation zone
13 and floc collection cone 28.
[0042] The coagulation zone 12 illustrated for example in FIG. 2
comprises a bottom part and a top part, clamped together using a
clamp 74 or bolted together for example.
[0043] The bottom part supports the bottom electrode 16, a wiper
blade assembly 50, 52, 54, spring housings and springs 60, the feed
port 64, a recirculation port 66, and a bottom electrical
connection 56 to an electrode mounting plate 72.
[0044] The top part of the coagulation zone 12 comprises the top
electrode 14, a top plate 76, the annular gaps 26 discussed
hereinabove, a top electrical connection 80, and an electrode
mounting plate 82.
[0045] The top electrode 14 may be fixed while the bottom electrode
16 may be mounted on springs, located in the housings 60 or bare
springs, so as to maintain an upward pressure on the bottom
electrode 16, on the wiper blade 50 and on the upper electrode 14
in order to keep a constant inter-electrode gap d as both
electrodes 14, 16 wear down, i.e. as their thickness diminishes
upon the action of an imposed potential and the action of the
reversal of the polarity of the electrical voltage.
[0046] The wiper blade rotation within the inter-electrode gap
allows a continuous displacement of the electrolytic bubbles, i.e.
mainly hydrogen bubbles, in the inter-electrode gap, thereby
preventing their coalescence, which is not desirable since larger
bubbles might render the flotation process less effective.
[0047] A fan-shaped wiper blade arrangement consisting of three
blades 50 for example as illustrated in FIG. 3, activated within
the inter-electrode gap d by a rotating mechanism (shaft 52, motor
54), is used to wipe the facing surfaces of the electrodes 14, 16,
thereby preventing passivation of the electrodes. The blades may be
fan-shaped i. e. radially tapered as will be discussed hereinbelow
in relation to FIG. 3, in order to provide a uniform distribution
of the current density along the radius of the electrodes 14, 16,
thereby promoting a uniform electro-dissolution of the material of
the electrodes. The thickness of the blades can be varied in order
to vary the inter-electrode gap d. By using a reversible motor 54,
the rotational direction of the blades about their shaft 52 may be
reversed periodically so as to prevent accumulation of deposits on
the blade 50 edges not in contact with the surface of the
electrodes 14, 16.
[0048] As described hereinabove, wastewater enters by the entry
port 64 and first flows within the coagulation zone 12 between the
electrodes 14, 16 in the inter-electrode gap d where a uniform
mixing of the electro-chemically generated coagulants and
wastewater contaminants is caused by hydrogen bubble evolution and
other means. The coagulated contaminants and background fluid
outflow in the annular gaps 26, which gaps allow maintaining a
uniform flow distribution and minimize hydrogen bubble
coalescence.
[0049] A recirculation loop of wastewater is periodically or
permanently activated in order to flush the electrode gap d and
thus reduce electrode and wiper blade fouling and electrode
passivation (see FIG. 6).
[0050] The electrical connection to the top electrode 14 may be via
a connector through the side of the coagulation zone 12 then via a
cable 80 to the electrode mounting plate 82. The electrical
connection to the bottom electrode 16 may be through a connector 56
on the bottom of the coagulation zone 12, which is then fed through
a flexible cable such that the electrode 16 can translate up.
[0051] The polarity of the electrodes 14, 16 may be reversed
periodically with a 50% duty cycle and a period between 5 and 15
minutes for example depending on the contaminants concentration in
the wastewater to treat: for highly concentrated wastewater, a 5
minutes period may be used and for weakly concentrated wastewater a
15 minutes period may be used for example.
[0052] The device 10 may be used as a marinized device for
continuous electrochemical wastewater purification and continuous
ejection of coagulated contaminants and wastewater sludge on board
of a ship for example. Indeed, the provision of a narrow channeled
flocculation chamber 24 minimizes effects of ship motion such as
vibration, pitch and roll, and ensures efficient operation of the
device in a range of inclination, up to 45 degrees for example, and
in a range of motions relative to a centered vertical axis of
device 10. The floc collection cone 28 capping the device also
allows controllably discharging the flocs through the discharge
port 30 even when the device is in an inclined position, without
spillage of fluid regardless of ship motions. Moreover, the
separator 32 as described hereinabove contributes to minimizing
liquid movements within the device which may result from ship
motion.
[0053] As mentioned hereinabove, the shape of the wiper blades 50
may be selected so as to allow a uniform distribution of the
current density, i.e. electrical current divided by the electrode
active surface area, along the electrode radius. With rectangular
shaped blades, it was found that the surface of the electrodes
located near the shaft 52 was consumed less rapidly than the
surface of the electrodes located near the periphery of the
electrodes, which in turn resulted in the wiper blades 50
eventually failing to be in close contact with the surface of the
electrodes near the periphery of the electrodes while still being
in close contact therewith near the center of the electrodes. To
mitigate this situation, the wiper blades 50 may be designed to
have a smaller surface area covering the inner electrode surface
and a gradually larger surface area covering the peripheral
electrode surfaces as can be seen in FIG. 3. This configuration
allows gradually reducing the current density along the radius of
the electrode and from the inner to the outer surface of the
electrodes.
[0054] Moreover, in addition to distributing more uniformly the
current density on the surface of the electrodes from the center to
the outer edge thereof, such fan shape of the wiper blades 50
allows to constantly remove metal hydroxides from the electrode
surface to prevent metal hydroxides from attaching to the electrode
surface and eventually crystallizing and forming an oxide layer.
Other functions of the wiper blades 50 are to remove other debris
and foam formed by surfactants present in the wastewater as well as
electrolytic bubbles (mainly hydrogen) accumulating in the
inter-electrode gap d.
[0055] The wiper blades may be made by cutting from a plain sheet
of material a pattern of several, i.e. typically 3 or 4, fan-shaped
blades with a centered hole 51 in the middle for the shaft 52 to be
inserted to allow the blade assembly rotation. The shape of the
centered hole can be for instance hexagonal. The material of the
blades 50 is selected to be of a material of the same hardness or
harder than the material of the electrodes 14, 16. The blades
material may be fiber glass reinforced plastic, carbon fiber
reinforced plastic or any non-conductive material with a same
hardness or a higher hardness than aluminium or iron used for the
electrodes 14, 16 for instance. The centered hole 51 may be
reinforced with two disks 53 cut out from the same material as the
wiper blade 50 and attached to the blade 50 by use of an adhesive
for example.
[0056] The rotating speed of the wiper blades is adjusted to
maximize removal of metal hydroxide, debris, foam, and bubbles
while minimizing potential abrasion of the electrodes and depends
on the composition and concentration of the contaminants in the
wastewater being treated. A blade rotating speed in a range between
4 and 15 rpm, depending on the wastewater strength, was found
suitable, as shown for example in FIG. 4.
[0057] The effect of the fan-shape wiper blades rotational speed on
the cleanliness of the electrodes surface was studied using a
device according to an embodiment of the invention, comprising two
horizontal disk electrodes with a three fan-shaped wiper blades
assembly. As can be seen in FIG. 4, the voltage applied to the
electrodes to achieve a given current, when either the bottom or
the top electrode is the cathode, for the case of a concentrated
synthetic sewage recipe at a constant electrical conductivity of 2
mS/cm, is reduced to a same voltage value when the blades speed
reaches 15 rpm. In the present system, the rotational speed of said
wiper blades is comprised in a range between 4 and 15 rpm.
[0058] This indicates that the wiper blades provide sufficient
mixing to eliminate compositional differences and stratification in
the inter-electrode gap related to the position of the cathode.
When the cathode, which generates the hydrogen bubbles, is on the
top, the bubbles tend to float upwards and accumulate against the
underside surface of the cathode, whereas when the cathode is on
the bottom of the stack, such as occurs periodically when the
polarity is reversed, the bubbles are generated from the upper
surface of the cathode and bubble more easily through the
wastewater, which can lead to foaming, which is not conducive to
electrical flow if it builds up to any great extent.
[0059] Thus, when the wiper blade is at the optimal speed and the
voltage is the same whether the cathode is the top electrode or the
bottom electrode, it is clear that the mixture in the
inter-electrode gap is no longer influenced by the position of the
cathode.
[0060] This can be explained by the increase in resistance between
the electrodes caused by the presence of aluminum hydroxides,
non-conductive debris, foam, and bubbles, the behavior of the
latter two being affected by the position of the cathode as just
described hereinabove, or any insulation layer between the
electrodes and that are being displaced by the rotational movement
of the blades. Removing these substances in the inter-electrode gap
helps preventing passivation of the electrodes by removing any
passivation precursor and keeping the inter-electrode gap
resistivity low.
[0061] Another series of tests were conducted with another
concentrated synthetic wastewater recipe to determine an optimal
value for the wiper blades rotation speed. As can be seen in FIG.
5, by increasing the blades rotational speed from about 5 to about
15 rpm, the electrochemical voltage decreased by almost 30% with no
observed effect on treatment performance as measured by reductions
in total suspended solids and chemical oxygen demand.
[0062] As mentioned hereinabove, a wastewater recirculation loop
83, co-current to the main wastewater flow direction, may be used
in the inter-electrode gap d as shown for example in FIG. 6, to
further clean the edges of the blades not in contact with the
surface of the electrodes 14, 16, so as to prevent hard debris from
building up and accumulating thereon over time. A wastewater
recirculation loop 83 according to an embodiment of an aspect of
the invention is diagrammatically shown in FIG. 6. The wastewater
is recirculated using a pump 84. The typical bulk wastewater
velocity created by the wastewater recirculation in the
inter-electrode gap d should be larger than the bulk velocity of
the influent wastewater flowing in the inter-electrode gap and for
instance it is 0.2 m/s in an embodiment with a wastewater feed rate
of 1 liter per minute. The periodic cleaning of the blade edges
using the wastewater recirculation loop keeps the active surface
area of the electrodes 14, 16 maximized.
[0063] FIG. 7 show pictures of a blade part of a wiper blade
assembly in a coagulation zone comprising two disc-shaped parallel
horizontal electrodes, and which was opened after several hours of
wastewater treatment, without (FIG. 7A) and with (FIG. 7B) a
wastewater recirculation loop as described above. It can be seen
that the wastewater recirculation in the inter-electrode gap
removed debris from the blade edges. This was observed with 3 blade
or 4 blade assemblies between the electrodes.
[0064] The effect of the wastewater recirculation loop 83 on the
overall inter-electrode gap d electrical resistance was also
studied. The inter-electrode gap d electrical resistance which
affects the voltage required for a given electrical current may be
used as an indicator of the presence of non-conductive materials,
such as debris, foam, accumulating coagulant or coagulated
contaminants, and bubbles, between the electrodes. An example of
the positive effect of the wastewater recirculation loop 83 in the
inter-electrode gap d is presented in FIG. 8, showing results of a
test done while a synthetic wastewater recipe simulating sewage
generated onboard a navy ship with a conductivity of 1 mS/cm was
treated at a rate of 1 liter per minute and constant electrical
current of 30 A applied to an coagulation zone comprising 2 disc
parallel horizontal electrodes and a 3-wiper blade assembly, with a
reversing polarity with a period of 15 minutes. The circles
indicate the moment when the wastewater recirculation loop was
activated. It can be seen that the voltage was significantly
decreased during recirculation and came back to a voltage which was
slightly lower than the initial voltage prior to the recirculation.
This temporary effect of the wastewater recirculation loop in the
inter-electrode gap indicates that the material accumulating in the
inter-electrode gap is easy to remove and forms rapidly.
[0065] In another test, a wastewater was treated at a rate of 0.8
liter per minute, using a coagulation zone with a constant
electrical current of 24 A and a polarity reversal duty cycle of
50% and a period of 5 minutes. When the cathode was at the top of
the cartridge, the voltage measured across the electrodes was 30 V
and when the cathode was at the bottom of the coagulation zone, the
measured voltage across the electrodes was 55 V. With the cathode
at the bottom and with the wastewater recirculation loop 83 valve
half opened, the measured voltage dropped to 45 V from 55 V; with
the wastewater recirculation loop 83 valve opened to 3/4, the
measured voltage dropped further down to 30 V and when the
recirculation loop 83 valve was fully open, yielding a flow rate of
about 30 liters per minute, the measured voltage dropped even lower
to 21 V. When the wastewater recirculation was stopped for 10
seconds, the measured voltage increased back to 55 V when the
cathode was at the bottom of the cartridge. With the cathode being
the top electrode in the coagulation zone, the voltage reduced from
30 V to 19 V with the velocity wastewater recirculation loop 83
valve fully open.
[0066] The present device may be used for the treatment of
wastewater generated by ships, such as bilge oily water, which
contains free and emulsified oil, grease, surfactants, heavy
metals, and other industrial contaminants generated from the ship
and that can reach the ship bilge.
[0067] The present device may also be used to treat a
ship-generated gray water (laundry, showers, sinks and kitchen,
which contain elevated concentration of detergents, grease, oil,
bacteria, organic matter, micro-organisms) and black water (mainly
composed of feces, urine and toilet paper, which have very high
concentration of organics, salts, nutrients such as phosphorus and
nitrogen and micro-organisms), or a combination of gray water and
black water.
[0068] The present device may also be used to treat wastewater
streams generated from commercial or industrial operations.
[0069] In one exemplary application, the device according to the
present invention was used to treat five batches of synthetic
concentrated wastewater simulating real wastewater generated by a
military operating base activities related to hygiene (shower,
laundry), food services (kitchen) and latrine. Prior to treatment,
the raw wastewater was partially treated in a lamella plate
separator to remove large debris. Then, the wastewater was sent to
the present device and its effluent characteristics were measured
and the results are presented in FIG. 9, which indicates the water
parameters of the influent wastewater entering the device and the
treated wastewater effluent exiting the device.
[0070] As can be seen in FIG. 9, using the device according to the
present invention to treat synthetic concentrated military forward
operating base sewage, the average BOD.sub.5 (indicated as BOD in
FIG. 9) removal was on average 67%, the average COD removal was on
average 69% and the TSS removal was on average of 87%. Clearly, the
single compact electrochemical purification device is efficient in
treating wastewater by separating and rejecting the majority of
contaminants leading to BOD, COD and TSS at least comparable to
those obtained with standard systems using residence times that are
much shorter than those for typical physico-chemical treatment in
conventional wastewater treatment systems and methods.
[0071] In another example, a device according to the present
invention was used to treat real bilge oily water generated from
ships as well as concentrated synthetic oily water. The total oil
and grease (TOG) in oily water includes several forms, such as free
oil and emulsified oil, based primarily on the size of oil droplets
and the miscibility of the oil in water. Dispersed, i. e. very
small droplets in water that take a long time to float and
therefore stay in water and are difficult to treat, and emulsified
form, i.e. oil droplets smaller than 20 .mu.m, are the hardest to
treat because their neutral buoyancy makes it difficult to separate
by gravity alone. In the experiment, the bilge oily water was first
treated in a free oil media separator in order to remove the free
oil and grease. The partially treated effluent with only emulsified
oil and grease (EOG) was then treated using a device according to
the present invention. As can be seen in the FIG. 10, 99.8% of the
emulsified oil and grease (EOG) was removed from raw oily water
containing between 1190 and 2660 ppm EOG. It can be seen that the
device of the present invention is able to very effectively remove
EOG.
[0072] The present device allows the efficient treatment of
wastewater by electrocoagulation, flocculation, flotation, and
separation and ejection of buoyant as well as non-buoyant
contaminants in a single closed reactor. The present device is a
highly effective, electrochemical reactor that continuously
purifies wastewater and collects, separates and ejects coagulated
contaminants as a froth and non-buoyant contaminants as a sludge,
in a continuous process. The device can be fully-automated and
marinized. The purification and contaminant removal are achieved
using only electrochemical processes without any added chemicals.
No additional equipment external to the device is required to
separate contaminants in order to achieve the high removal rates
presented herein.
[0073] Fan-shape wiper blades may be used for the continuous
cleaning of the surface of the electrodes of the device. A constant
inter-electrode gap is maintained, and a wastewater recirculation
loop may be further provided for cleaning of the blades edges.
Electrodes may be monitored for passivation, allowing operation
under relatively high current density which minimizes the electrode
surface area required to treat highly contaminated wastewaters. The
mechanical configuration allows operation on marine platforms as
the device is closed with a cone-shaped top, and a narrow and
elongated enclosed flocculation chamber prevents marine motion from
affecting hydrodynamic processes within the device.
[0074] There is thus provided a device for the electrochemical
treatment of wastewaters including gray water, black water, oily
water and a combination thereof, i.e. sewage, as well as industrial
and commercial wastewaters for instance wash water generated by the
cosmetic industry or garages.
[0075] The present combination of electrode cleaning mechanisms,
including polarity reversal, a wiper blade acting in constant
contact with the anode and cathode, and a periodic wastewater
recirculation are effective at removing debris, deposits, foams,
gas bubble and ions from the electrode surfaces and the wiper blade
edges without human intervention. These cleaning mechanisms have
been found to greatly prevent or delay passivation of the
electrodes.
[0076] There is thus provided a compact device, generally
integrating and combining four zones, i.e. a coagulation zone, a
flocculation chamber, a flotation zone and a separation zone, the
flocculation chamber being in fluid communication with the
coagulation zone, and receiving coagulants formed in the
coagulation zone, the flotation zone above said flocculation
chamber comprising a discharge port for collection of light solid
particles, a separation zone being in fluid communication with the
flotation zone and comprising a separator allowing non-buoyant
contaminants separation and a sludge collector allowing collection
of sludge and heavy solid particles. The present combination
provides the conditions to carry out effective mixing of coagulant
in the coagulation zone, optimal gentle mixing to promote
flocculation in the flocculation zone using a greatly reduced
flocculation time, as well as effective and rapid flotation of the
flocs created in the flocculation zone.
[0077] The present device was shown to provide efficient wastewater
purification and contaminant removal in a single unit that is not
affected by ship motion and which also includes fully-automated and
integrated cleaning mechanisms for the electrode surfaces.
[0078] There is thus provided a highly effective, fully-automated
marinized electrochemical reactor that continuously purifies
wastewater and collects, separates and ejects coagulated
contaminants and sludge.
[0079] The applications of the present device are numerous and
include the treatment of shipboard-generated wastewaters, the
treatment of gray water and black water or a combination of these,
as generated by households, communities, hotels, resorts, military
bases and work camps.
[0080] The scope of the claims should not be limited by the
embodiments set forth in the examples, but should be given the
broadest interpretation consistent with the description as a
whole.
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