U.S. patent application number 13/381173 was filed with the patent office on 2012-06-28 for apparatus and method for electrochemical treatment of wastewater.
This patent application is currently assigned to PROTERRGO INC.. Invention is credited to Valerie Leveille, Nicole A. Poirier.
Application Number | 20120160706 13/381173 |
Document ID | / |
Family ID | 43410393 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120160706 |
Kind Code |
A1 |
Poirier; Nicole A. ; et
al. |
June 28, 2012 |
APPARATUS AND METHOD FOR ELECTROCHEMICAL TREATMENT OF
WASTEWATER
Abstract
The wastewater treatment apparatus of present invention has an
electro-coagulation unit for removing contaminants with at least
one anode and at least one cathode and an electro-oxidation unit
for oxidizing contaminants with at least one anode and at least one
cathode wherein oxidants are electrochemically generated. Based on
the type of wastewater, the apparatus can have an electro-flotation
unit between the electro-coagulation unit and the electro-oxidation
unit. The apparatus also has an oxidant removal unit which can have
a metal ion-liberating electrode for reacting with and removing
residual oxidants. In some cases, portions of effluent from the
oxidant removal unit can be recirculated to the electro-coagulation
unit for increased efficiency.
Inventors: |
Poirier; Nicole A.;
(Beaconsfield, CA) ; Leveille; Valerie; (Montreal,
CA) |
Assignee: |
PROTERRGO INC.
Montreal
QC
|
Family ID: |
43410393 |
Appl. No.: |
13/381173 |
Filed: |
June 23, 2010 |
PCT Filed: |
June 23, 2010 |
PCT NO: |
PCT/CA2010/000930 |
371 Date: |
March 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61221522 |
Jun 29, 2009 |
|
|
|
Current U.S.
Class: |
205/756 ;
204/229.4; 204/278 |
Current CPC
Class: |
C02F 1/32 20130101; C02F
2103/08 20130101; C02F 1/4674 20130101; C02F 1/463 20130101; C02F
2103/002 20130101; C02F 2103/008 20130101; C02F 1/76 20130101; C02F
2103/005 20130101; C02F 2201/46175 20130101; C02F 2209/11 20130101;
C02F 2209/40 20130101; C02F 1/465 20130101; C02F 2209/06 20130101;
C02F 2209/05 20130101; C02F 9/00 20130101; C02F 2209/02 20130101;
C02F 2201/4614 20130101; C02F 2209/04 20130101; C02F 2201/46135
20130101; C02F 2209/245 20130101; C02F 2209/29 20130101; C02F
2001/46138 20130101 |
Class at
Publication: |
205/756 ;
204/278; 204/229.4 |
International
Class: |
C02F 1/463 20060101
C02F001/463; C25B 9/00 20060101 C25B009/00 |
Claims
1. An apparatus for treating wastewater comprising: an
electro-coagulation unit to remove a first portion of contaminants
from said wastewater comprising at least one inlet to receive said
wastewater and at least one anode and at least one cathode, said
anode and said cathode being connected to an electric source; an
electro-oxidation unit to oxidize a second portion of contaminants
in said wastewater comprising at least one inlet to receive said
wastewater from said electro-coagulation unit, at least one anode
and, at least one cathode wherein oxidants are electrochemically
generated, at least one outlet to evacuate said wastewater; and an
oxidant removal unit to remove oxidants from said wastewater
comprising at least one inlet to receive said wastewater from said
electro-oxidation unit, a vessel to contain said wastewater during
an oxidant removal process and at least one outlet to discharge
treated wastewater from said apparatus.
2-3. (canceled)
4. The apparatus of claim 1, wherein the oxidant removal process
further comprises a metal ion-liberating electrode for reacting
residual oxidants with said metal ions.
5. The apparatus of claim 1, further comprising a loop between the
oxidant removal unit and any other upstream location such that
metal oxide from said oxidant removal unit can be delivered to said
upstream location.
6. (canceled)
7. The apparatus of claim 1, further comprising an
electro-flotation unit characterized in that at least one anode and
at least one cathode are connected to a source of electric current,
said electro-flotation unit being downstream from said
electro-coagulation unit and upstream from said electro-oxidation
unit to insure removal of residual suspended contaminants from the
wastewater of said electro-coagulation unit.
8. (canceled)
9. The apparatus of claim 1, further comprising a boron-doped
diamond coated electrode in the electro-oxidation unit.
10. The apparatus of claim 1, further comprising a controller
adapted to receive input from one or more sensors for carbon
dioxide, oxido-reduction potential, flowrate, pressure,
temperature, chlorine, turbidity, pH, conductivity, specific ions
and/or surface tension, current and voltage, said controller
programmed to control treatment parameters as a function of said
input in each unit.
11-12. (canceled)
13. The apparatus of claim 1, wherein said electro-coagulation unit
further comprises at least one dividing wall to separate said
electro-coagulation unit into at least two independent
electro-coagulation compartments that share some peripheral
equipment, each said compartment having an inlet and an outlet
adapted to deliver partially treated wastewater to any other said
unit.
14-17. (canceled)
18. The apparatus of claim 10, wherein said chlorine sensor is
configured to be actuated when said oxido-reduction potential
sensor reaches a predetermined threshold value.
19. (canceled)
20. The apparatus of claim 1, further comprising a device for
controlling an oxidation reaction as a function of CO2 measurements
comprising an oxidation chamber adapted to allow oxidation of
wastewater contaminants and a CO2 sensor in fluid communication
with said oxidation chamber configured to sends input relative to
an amount of CO2 to an oxidation chamber controller for controlling
treatment level and/or progression.
21-24. (canceled)
25. The apparatus of claim 20, further comprising an enzymatic or
chemical catalyst configured to remove gaseous carbon dioxide
evacuated from the oxidation chamber.
26. A process for treating wastewater comprising:
electro-coagulating contaminants of said wastewater in an
electro-coagulation unit; electro-oxidizing contaminants of said
wastewater in an electro-oxidation unit; and liberating metal ions
from an electrode to react with residual oxidants and produce metal
oxides that can be separated from the wastewater in an oxidant
removal unit.
27-29. (canceled)
30. The process of claim 26, further comprising passing the
wastewater through an electro-flotation unit after the
electro-coagulation unit or before the electro-oxidation unit.
31. The process of claim 26, further comprising passing the
wastewater through a dissolved flotation unit after the
electro-coagulation unit or before the electro-oxidation unit.
32. The process of claim 26, wherein an oily wastewater contains
more than 15 ppm of oil content and a treated wastewater complies
with the international maritime discharge standard for oil content
of less than 15 ppm.
33. The process of claim 26, further comprising providing and
influent containing more than 35 ppm Total Suspended Solids (TSS),
more than 125 ppm Chemical Oxygen Demand (COD), more than 25 ppm
Biological Oxygen Demands (BOD) and more than 100 CFU/100 ml Fecal
Coliform (F.C.), treating said influent and discharging an effluent
containing TSS lower than 35 ppm, COD lower than 125 ppm, BOD lower
than 25 ppm, pH between 6 and 8.5, Chlorine lower than 0.5 ppm and
F.C. lower than 100 CFU/100 ml.
34. (canceled)
35. The process of claim 26, further comprising re-circulating at
least part of said metal oxides from said oxidant removal unit to
said electro-coagulation unit or any location upstream of oxidant
removal unit.
36. (canceled)
37. The process of claim 26, further comprising generating mixed
wastewaters composed of any one or combination of blackwater,
graywater and oily water and treating said wastewaters as they are
generated on a watercraft.
38. (canceled)
39. The process of claim 26, further comprising the step of
measuring one or more of pH, chlorine content in the liquid and
amount of carbon dioxide in the gas evacuated from said oxidation
chamber and using the result as a level of decontamination of said
wastewater.
40-41. (canceled)
42. The process of claim 26, further comprising adjusting time
spent in each unit and allowing progression of wastewater to a
subsequent unit.
43-47. (canceled)
48. The process of claim 26, wherein said electro-oxidation further
comprises measuring a treatment progress indicator, wherein said
indicator is carbon dioxide; and adjusting said oxidation reaction
as a function of said indicator.
49-56. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of wastewater
treatment. More specifically, it relates to apparatuses and
processes for the electrochemical decontamination of
wastewaters.
BACKGROUND
[0002] There are many instances where small communities,
enterprises and groups of people do not have access to (or for
various reasons are unable to use) municipal wastewater treatment
systems. Examples include isolated habitats, ships and marine
platforms, small islands, research or military outposts, remote
agricultural or industrial operations and point sources of
wastewater.
[0003] These various communities generate a wide range of liquid
waste including graywater, blackwater, sewage, oily water, and any
other wastewater contaminated with pathogens, organic and inorganic
material, dissolved or suspended solids.
[0004] Amongst these small communities are watercrafts which
generate a multitude of wastewater streams. These streams comprise
bilge water from the engine room, blackwater from toilets and
urinals, and graywaters from showers, laundry, galleys and kitchen
rooms.
[0005] Local and international land-based effluent discharge
regulations as well as maritime effluent discharge standards are
becoming more stringent. The land-based regulations are becoming
more stringent especially for habitats located near body of water
where contaminants such as phosphates, nitrates, and fecal
coliforms are of major concern.
[0006] The international maritime regulations and other regulatory
bodies are also becoming more stringent for contaminants such as
oil, fecal coliforms, biological oxygen demand, chlorine as well as
nutrients such as phosphorus and ammonia in sensitive waters due to
their negative impact on the ecosystems. In fact, in many maritime
areas, watercraft-generated wastewater can no longer be discharged
without prior treatment.
[0007] There exist prior art references describing the need for
ship-based chemical-free water treatment systems such as that
taught by Leffler et al. in U.S. Pat. No. 6,923,901 and US Pub. No.
20040099607. Leffler et al. teach using air and electricity to
generate reactive gaseous oxygen and nitrogen ionic species that
will help decontaminate various water streams such as those
originating from ballast, toilet and laundry room. The systems of
Leffler et al. also teach using salt water to generate chlorine
from electrolysis of salt in water for disinfection purpose.
[0008] Several prior art references describe using various
combinations of electro-chemical devices which act in specific
sequences to produce decontaminated effluents. For example, Mehl
(U.S. Pat. No. 7,354,509) teaches a wastewater treatment system
that effectively considers space requirements and effluent quality
through the sequential steps of electro-coagulation, rotating
energized magnetic media filter system, UV-based sterilization and
a final sedimentation step.
[0009] Bradley (U.S. Pat. No. 6,960,301) teaches a system for
leachate and wastewater remediation comprising an initial
filtration screen to remove larger particles followed by ozone
pretreatment, an electro-coagulation unit for flocculating
particles, an oxidation unit and a polishing unit for removing
leftover ammonium contaminants using an ion-exchange unit.
[0010] There is, however, a need for a compact apparatus and method
capable of simultaneously treating complex and/or heterogeneous
streams without the use of chemical addition, biological treatment
or the generation of highly oxidising gases and with full
automation and on/off capability. Such an apparatus could be used
in applications where space is limited, in remote communities with
no access to centralized wastewater treatment systems, in
communities generating wastewater that cannot be discharged to
available wastewater treatment systems, and for wastewater streams
containing contaminants that are not removed or degraded by
conventional treatment approaches (e.g. pharmaceutical residues).
Thus, the apparatus and method would overcome the limitations and
drawbacks of the prior art.
SUMMARY
[0011] It has been discovered that a simple-to-use system called
Wastewater Electrochemical Treatment Technology (WETT) based on
electrochemical process units requiring only electricity to operate
and periodic low-cost electrode replacement can efficiently treat
individually or simultaneously heterogeneous wastewater streams.
Important characteristics of this system are that it is omnivorous
and does not require the addition of external chemicals, treatment
agents or biological treatment. Another important feature of WETT
is that it is fast compared to biological treatment and many other
treatment approaches.
[0012] Unlike most wastewater treatment technologies, Applicant's
system is an omnivorous system able to treat several and different
wastewaters rendering it safe for re-use or discharge to the
surrounding environment. Whereas many wastewater treatment
approaches are able to treat only one type of wastewater,
Applicant's technology was designed as a sequential process that
systematically removes most types of contaminants beginning with
the easiest (usually large-sized or easily recovered) all the way
to the most difficult (usually small-sized, dissolved or
recalcitrant).
[0013] Unlike most wastewater treatment technologies, Applicant's
system does not use chemicals, which are expensive and require safe
handling and storage (many remote communities cannot afford these
and/or do not have access to regular shipments) or biological
treatment (many remote communities do not have trained personnel,
the available space, or appropriate conditions to operate these
systems, which can be easily upset).
[0014] It is therefore an object of the present invention to
provide an apparatus for treating wastewater comprising an
electro-coagulation unit to remove contaminants from a wastewater
comprising at least one inlet to receive wastewater and at least
one anode and at least one cathode, the anode and the cathode being
connected to an electric source; and an electro-oxidation unit to
oxidize contaminants in the wastewater comprising at least one
inlet to receive the wastewater from the electro-coagulation unit,
at least one anode and, at least one cathode wherein oxidants are
electrochemically generated, at least one outlet to evacuate
wastewater; and an oxidant removal unit to remove oxidants from the
wastewater comprising at least one inlet to receive the wastewater
from the electro-oxidation unit, a vessel to contain the wastewater
during the oxidant removal process and at least one outlet adapted
to either discharge treated wastewater from the apparatus or return
treated wastewater to the electro-oxidation unit forming a closed
loop circuit for treated wastewater recirculation.
[0015] In some embodiments of the present invention, the apparatus
further comprises a reverse osmosis unit or an
evaporation-condensation unit after the oxidant removal unit,
wherein the additional unit is able to generate potable water.
[0016] It is another object of the present invention to provide an
oxidant removal apparatus for removing oxidants from wastewater
comprising at least one inlet to receive the wastewater. In
addition, an oxidant removal vessel comprising at least one anode
and at least one cathode connected to an electric source, wherein
at least one anode is a metal anode adapted to release into the
wastewater metal ions that react with residual oxidants to form
metal oxides, and wherein the apparatus is adapted to separate
metal oxides from the wastewater; a controller that receives input
from at least one of an oxido-reduction potential sensor and a
chlorine sensor to determine the level of oxidant removal; and an
outlet to evacuate treated effluent.
[0017] It is yet another object of the present invention to provide
a device for controlling an oxidation reaction in a wastewater
treatment system as a function of one or more of CO.sub.2, pH,
chlorine and ORP measurements comprising an oxidation chamber
adapted to allow oxidation of wastewater contaminants and one or
more of a CO.sub.2, pH, chlorine and ORP sensor in fluid
communication with the oxidation chamber which sends input relative
to the amount of CO.sub.2, pH, chlorine and ORP to an oxidation
chamber controller for controlling treatment level and/or
progression.
[0018] It is yet another object of the present invention to provide
a process for treating wastewater comprising electro-coagulating
contaminants of the wastewaters in an electro-coagulation unit; and
electro-oxidizing contaminants of the wastewater in an
electro-oxidation unit; and liberating metal ions from an electrode
to react with residual oxidants and produce metal oxides that can
be separated from the wastewater in an oxidant removal unit; and
finally, discharging a treated effluent. In certain cases, such as
when a small quantity or known residual oxidants are discharged
from the electro-oxidation unit, the metal ion liberating electrode
of the oxidant removal unit can be replaced by a source of
ultraviolet radiation for oxidant decomposition.
[0019] In some aspects of the present invention, there is provided
a method for treating wastewater comprising submitting the
wastewater to an oxidation step; and submitting oxidized wastewater
to an oxidant removal step by passing the wastewater between
electrodes connected to an electric source, the electric source
causing an at least one sacrificial electrode to release metal ions
into the wastewater wherein the metal ions will react with oxidants
to generate metal oxides.
[0020] In some aspects of the present invention, there is provided
a method for treating a wastewater containing oxidants comprising
submitting the wastewater to an oxidant removal step by passing the
wastewater in a recirculation loop between electrodes connected to
an electric source, the electric source causing at least one
sacrificial electrode to release metal ions into the wastewater
wherein the metal ions will react with oxidants to generate metal
oxides; measuring the oxidant level in the wastewater with an ORP
and/or a chlorine sensor and finally discharging the wastewater as
a function of the amount of oxidants in the wastewater.
[0021] In yet other aspects of the present invention, there is
provided a method for controlling an oxidation reaction in an
oxidation chamber comprising oxidizing contaminants in an oxidation
chamber and measuring one or more treatment indicators that are
indicative of the treatment progress such as ORP, free chlorine, pH
and carbon dioxide; and then adjusting the oxidation reaction as a
function of the treatment indicators.
[0022] In some aspects of the present invention, there is provided
an apparatus comprising a loop between an oxidant removal unit and
any other upstream electrochemical unit such that metal
oxide-containing wastewater from the oxidant removal unit can be
delivered to the upstream location to enhance coagulation and
adsorption of natural organic or other matter, further increasing
energy efficiency of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be better understood by way of the
following detailed description of embodiments of the invention with
reference to the appended drawings, in which:
[0024] FIG. 1 is a schematic representation of the WETT process
including treatment units for electro-coagulation,
electro-flotation, electro-oxidation and oxidant reduction, the
principal online sensors used and the recycling of iron oxide.
[0025] FIG. 2 is a graph showing the free chlorine removal with
respect to treatment time with a lab-scale Oxidant Reduction (OR)
unit operating at 30 mA.
[0026] FIG. 3 is a graph showing the chloramine removal with
respect to treatment time with a lab-scale Oxidant Reduction (OR)
unit operation at 15 mA.
[0027] FIG. 4A is a schematic representation of a WETT unit for the
treatment of Blackwater/Greywater. FIG. 4B a schematic
representation of a WETT unit for the treatment of
Blackwater/Greywater with an oily water component.
[0028] FIG. 5 is a graph showing experimental results from COD,
CO.sub.2 and pH sensors to highlight their correlation with
oxidation treatment progression.
[0029] FIG. 6 shows the evolution of ORP and free chlorine in
solution during Oxidant Reduction (OR) treatment with the free
chlorine sensor activated when ORP value reaches 700 mV.
[0030] FIG. 7 shows experimental results for Total Suspended Solids
(TSS) and color measured in jar tests for blackwater (BW) and
graywater (GW) with various levels of metal oxide Fe(OH).sub.3
addition.
[0031] FIG. 8 is a schematic representation of the WETT apparatus
including effluent flow circuits and control circuits.
DETAILED DESCRIPTION
[0032] FIG. 1 is a schematic representation of the WETT process
including the various electrochemical treatment units, the
principal online sensors that may be used and the recycling of iron
oxide to previous electrochemical treatment units (shown as dashed
line). Not shown in FIG. 1 is a pre-treatment unit to remove bulk
solids or free oil that may be required depending on the
concentration of bulk solids and oil in the wastewater to be
treated. Well-known equipment such as bar screens, coarse filters,
and oil coalescers can be used to accomplish this task. The
pre-treatment unit can also be a mechanism to reduce bulk solid
size, such as a grinder.
[0033] The WETT units that may be involved in wastewater
decontamination processes are listed below as well as in FIG. 1. In
one preferred embodiment, the process consists of a series of four
electrochemical units: [0034] 1. Electro-coagulation (EC) [0035] 2.
Electro-flotation (EF) [0036] 3. Electrolytic Oxidation (EO) [0037]
4. Oxidant Removal (OR)
[0038] Some of the above units such as electro-coagulators are,
individually, known in the prior art, while others, such as oxidant
removal units are novel. Applicant's invention resides in the
arrangement, operation and control of each of these units for the
treatment of various wastewaters without the use of chemicals or
biological treatment and involves many innovative aspects which
make WETT a unique and previously unknown process and
apparatus.
[0039] It will be appreciated that wastewater is meant to include
all influent and effluent streams or liquids that can benefit from
an electro-chemical treatment according to the present invention.
It will also be appreciated that electro-coagulation should be
interpreted as encompassing electro-flotation in such cases where
electro-coagulation generates gas bubbles able to cause certain
contaminants to float to a surface of a liquid.
[0040] Additionally, a particular arrangement and mode of operation
will be described which is able to simultaneously treat the three
principal waste streams (blackwater, graywater and oily water)
generated onboard a ship; current state of the art provides systems
and methods which can only treat certain streams individually or
certain combinations of streams using separate equipment.
[0041] Each of the parts of the WETT process, illustrated
schematically in FIG. 1, will be discussed in more detail
below.
[0042] Electro-coagulation (EC)
[0043] Applicants use the electro-coagulation process to
destabilize the suspended solids, colloids, metal ions, oil and
emulsions contained in the wastewater and coagulate them. EC
consists of applying a voltage to one or more pairs of metal
electrodes (usually aluminum or iron) immersed in the wastewater to
be treated. The anode or anodes are sacrificial and release metal
ions which have a coagulating effect. Simultaneously, hydrogen gas
bubbles are created at the cathode or cathodes; depending on the
geometry and flow direction of the wastewater, these can be used to
float coagulated contaminants (including the liberated metal ions)
to the surface of the liquid being treated. Polarity reversal of
the electrodes, which is known to persons skilled in the art,
prevents deposit formation on the cathode (or cathodes) surface and
thus extends the lifetime of the electrodes and minimizes the
electrical loss in the electro-coagulation unit.
[0044] The preferred embodiment of an electro-coagulation unit uses
vertical aluminum parallel electrode plates but any other
arrangement of the EC unit electrodes that allow for the
coagulation of contaminants will do. Wastewater is pumped into the
unit from the bottom, and upwards between the electrode plates,
where coagulating metal ions are released and bubble generation
occurs. The electrode plates can be placed in the flocculation tank
or separate from it to facilitate their maintenance and
replacement. The turbulence caused by the release of the gas
bubbles at the cathode causes the coagulated particles to
flocculate, and the adhesion of the bubbles to the flocs combined
with the upward flow causes the flocculated contaminants to form a
froth at the surface of the liquid. This froth is removed
continuously by suction or any other froth removal mechanism such
as skimmer blades, and if dewatering is required, the concentrated
froth is sent to waste disposal and the liquid extracted from froth
dewatering is sent back to the head of the wastewater treatment
system or into any individual unit including EC, EF, EO or OR.
Current densities and specific surface areas used are typical for
the art, and the mode of operation is continuous, although this
process can easily be operated in batch mode. An arrangement
requiring the replacement of the electrodes assembly every few
months or so is preferred. All of the electro-chemical units can
utilize pulsed current in order to either reduce power consumption
or enhance treatment efficiency.
[0045] Electro-flotation (EF)
[0046] Applicants use this process as a polishing stage to float
the flocs which were not removed during EC treatment. Although FIG.
1 depicts EC and EF units as separate compartments, the EF unit can
be integrated into the EC unit. The purpose of the EF unit is to
provide micron bubbles of gas which serve to float the flocs
remaining in solution after EC treatment. The bubbles of hydrogen
and oxygen are generated electrochemically using non-sacrificial
electrodes, to which a current is applied. In this instance, a
titanium mesh is used for the cathode while the anode consists of a
titanium mesh coated with iridium oxide. Any other type of
electrode materials, such as platinum coated titanium for both
anode and cathode, can be used as long as it performs its EF
requirements and allows for reversing polarity. Furthermore, other
EF units are possible where the cathode releases micro-bubbles
while the sacrificial anode releases coagulating agents.
[0047] The mode of operation is continuous. After EC/EF treatment,
most of the suspended solids, metal ions, free and emulsified oils
have been removed along with a good portion of the dissolved
solids, as represented by the Chemical Oxygen Demand (COD) in the
solution. Polarity reversal of the electrodes can also be used in
this unit to prevent deposit formation on the cathode surface.
[0048] Electrolytic Oxidation (EO)
[0049] Applicants use this process to oxidize the remaining
dissolved materials comprising Chemical Oxygen Demand. Electrolytic
(or Electrochemical) Oxidation is an electrochemical process that
makes use of pairs of electrodes to which a current is applied.
This produces oxidizing species on the surface of the anodes and/or
in the bulk solution. The complete oxidation of organic molecules
results in the liberation of carbon dioxide (CO.sub.2) gas; the
process is thus sometimes referred to as electrochemical
combustion. Inorganic molecules can also be oxidized with this
process. In addition to the CO.sub.2 gas, hydrogen gas (created at
the cathode) and small quantities of other gases such as oxygen at
the anode are produced and vented continuously during the EO
treatment. The cathode can be made from a material that does not
allow for the generation of hydrogen gas in the EO unit as this
could facilitate the determination of CO.sub.2 levels and remove
the requirement for venting of the hydrogen gas in the
electro-oxidation unit.
[0050] The EO process makes use of electrodes consisting of a Boron
Doped Diamond (BDD) coating over a silicon, titanium or other
substrate. These can be enclosed in a stainless steel or plastic
reactor body. The EO electrodes can also be made of a pure BDD
plate by techniques such as thin-film chemical-vapour deposition.
Polarity reversal to prevent deposit formation on the cathode
surface is possible when both anodes and cathodes are BDD
electrodes. BDD electrodes have a high capacity for creating
hydroxyl radicals near the anode surface, although there are a few
other types of electrodes with similar capabilities that could also
be used. Hydroxyl radicals are more powerful than most of the
well-known oxidants such as chlorine and ozone.
[0051] As well, BDD electrodes create a significant level of
oxidative compounds in the bulk solution when salts (or seawater)
are present in the wastewater being treated. In particular, the
creation of sodium hypochlorite, which in equilibrium with
hypochlorous acid depending on the solution pH, acts in combination
with the hydroxyl radicals to oxidize dissolved contaminants,
inactivate pathogens such as bacteria, and augment the rate and
extent of oxidation that could be achieved using hydroxyl radicals
only.
[0052] This process is typically operated in a batch recirculation
mode since hydroxyl radicals are short-lived and remain close to
the anode surface rather than entering the bulk flow. At high
concentration of contaminants, the process is current-limited, but
as the concentration of contaminants decreases below a certain
level, the oxidation by hydroxyl radicals becomes mass transfer
limited; many passes through the EO reactor are required to reduce
the COD to low levels. However, when other oxidants are present in
solution, such as sodium hypochlorite generated from the
electrolysis of saltwater or seawater, enough oxidation might occur
in the bulk flow to enable the EO process to operate in continuous
mode. Therefore, depending on the operating conditions and desired
level of COD reduction, a continuous mode of operation for the EO
process is also possible. It is desirable to design the EO process
in such a way as to minimize the specific surface area and the
electrical consumption required for treatment.
[0053] Oxidant Removal (OR)
[0054] This is the final unit operation in the WETT process. Its
function is to decompose the residual oxidant remaining after the
EO treatment for those cases where this is required (most cases).
For example, International Maritime Organization (IMO) and
Convention for the Prevention of Pollution from Ships IMO/MARPOL
regulations prohibit marine vessels from discharging treated
wastewater containing residual chlorine oxidant >0.5 mg/L. If
seawater is present in one of the wastewaters or added to improve
conductivity of the wastewater, and an electrolytic process is used
for oxidation, chlorine-based oxidants will be created and there
will typically be a chlorine level above the IMO/MARPOL discharge
standards when levels of COD acceptable for discharge are attained.
The total chlorine value consists of the sum of free chlorine and
combined chlorine (generally chloramines), and unlike other
approaches the Applicant's approach is able to decompose both types
of chlorine-based oxidants, as well as other types of oxidants that
may be created by an electrolytic process (e.g. bromine-based) or
added as a chemical or gas. FIGS. 2 and 3 present typical results
for free chlorine and chloramine reduction using a lab-scale OR
unit.
[0055] In the prior art, dechlorination through the use of
well-known chemical reducing agents, granular activated carbon,
catalysts or other such consumables is described. There are many
drawbacks to these approaches, including their high cost and the
safety precautions required for the handling and disposal of
chemical products, and the fact that many isolated communities
cannot obtain these dechlorinating agents on a regular basis.
[0056] Instead, in keeping with the electrolytic approach forming
the core units of WETT, Applicants developed an electrolytic
approach for the removal of residual oxidant that is inexpensive
and rapid.
[0057] The OR unit operation makes use of parallel electrode plates
mainly made of iron (such as carbon steel) to which a current is
applied. The electrodes are encased in a stainless steel reactor,
and the fluid to be treated is circulated through the reactor until
the desired level of oxidant removal is attained. Alternatively,
the electrode stack could be placed inside a holding tank of
appropriate material of construction in which the wastewater is
held and stirred. The mode of operation is batch although depending
on the residual oxidant concentration and other particulars a
continuous operation could be envisaged.
[0058] The current applied to the electrodes has the effect of
liberating Fe.sup.2+ ions from the anodes, which react
instantaneously with residual oxidant to create Fe(OH).sub.3, an
insoluble precipitate at neutral pH also known as rust. As an
example, the oxidant sodium hypochlorite oxidizes the Fe.sup.2+
ions to Fe.sup.3+ ions while itself is reduced to harmless sodium
and chloride ions (dissolved NaCl or salt). The rate of oxidant
removal is principally determined by the concentration of oxidants
and Fe.sup.2+ liberated in the water, the later being a function of
current density, whereas the extent of oxidant removal is a
function of treatment time and rate.
[0059] Alternatively, oxidant removal can also be achieved by other
methods such as granular activated carbon, ion exchange, a filter,
chemical reducing agents, an aeration device, a heating device for
thermal decomposition of the oxidants and ultraviolet (UV)
radiation. For example, in an alternate embodiment of an Oxidant
Removal apparatus, a source of UV radiation decomposes chlorine and
other oxidants generated in the EO apparatus.
[0060] As with the EC anodes, it is preferred to size the
sacrificial OR electrodes so that their replacement is required
every few months or so with polarity reversal in operation.
Depending on the intended use of the treated effluent, a small
quantity of residual oxidant is sometimes desirable (for example as
is done in municipal wastewater treatment systems); in this case
the OR process is terminated before decomposing all of the residual
oxidant.
[0061] The extent of removal (if any) of the Fe(OH).sub.3 particles
from the treated effluent also depends on the final intended use of
the treated effluent. The removal of iron from drinking water is a
common practice because of aesthetic concerns (related to taste,
staining or accumulation) rather than danger to human health or the
environment. Iron is in fact essential for good human health, and
when iron is present in drinking water it can be found at
concentrations as high as 40 ppm (often in well water) although it
is usually less than 10 ppm. However, for aesthetic reasons, the
recommended limit is 0.3-1.0 ppm.
[0062] For the case of a naval vessel, the discharge of small
amounts of rust particulates into the ocean should be of little
concern; in fact, large amounts of glass and metal waste are
regularly crushed onboard ships to ensure that they will not float
prior to dumping them into the ocean. Furthermore, oceanographers
hypothesize that lack of iron causes barren areas in the ocean, and
many large-scale field experiments involving seeding the ocean with
iron have been performed.
[0063] For those cases where it is desirable to remove the
Fe(OH).sub.3 particles, several approaches can be used depending on
the Fe(OH).sub.3 concentration, TSS discharge standard, and various
other factors.
[0064] When the concentration of Fe(OH).sub.3 particles is large, a
clarifier can be used to separate Fe(OH).sub.3 particles from the
treated wastewater. The clarifier can operate in batch or
continuous mode depending on the application. It has been found
that for the typical levels of oxidant reduction required by the
WETT process, the concentration and particle size distribution of
Fe(OH).sub.3 is in some cases sufficient to allow for a reasonable
rate of settling of the particles which can be removed in a
concentrated slurry from the bottom of a clarifier operating in
batch mode by opening a valve located in the exit pipe attached to
the clarifier cone-shaped bottom. The flow during this period is
designed to be laminar so as to minimize swirling or turbulence in
the settled liquid.
[0065] For applications where the Fe(OH).sub.3 concentration is
high and solids need to be highly concentrated, equipment such as a
hydrocyclone, filter press or rotary drum filter can be employed.
Alternatively, when the Fe(OH).sub.3 concentration is low, a
backwash filter or other filtration means can be used to remove the
particles and produce a clear stream and a slurry containing a high
concentration of Fe(OH).sub.3 particles. The slurry containing the
Fe(OH).sub.3 particles can be either sent to disposal or routed
back to the untreated or partially-treated wastewater stream where
it provides significant advantages as described below.
[0066] WETT Process Description
[0067] In the case of combined blackwater (BW) and graywater (GW)
or oily water (OW) streams, the wastewater to be treated can simply
pass through each of the WETT units, as shown in FIG. 4A. Most
wastewater streams are sufficiently conductive to operate the
process, and the hydroxyl radicals generated during EO are
sufficient to reduce COD and biological agents in solution even
without the contribution of chlorine-based oxidants typically
generated in approaches based on the electrolysis of saline
solutions.
[0068] The addition of salt (or seawater or brine from a
reverse-osmosis desalination process) can be used as required to
increase electrical conductivity of the wastewater being treated by
the WETT process. This salt addition will have to be minimal to
prevent the generation of excessive amounts of chlorine-based
oxidants.
[0069] The approach described in FIG. 4A is capable of producing
effluent meeting all of the IMO/MARPOL discharge standards for
treated sewage (GW, or BW+GW) with or without the addition of salt
(Table 1). As well, the approach described in FIG. 4A is capable of
producing effluent meeting all of the International Maritime
Discharge standards for treated OW (Table 2) even for sensitive
areas. Furthermore streams of BW+GW and OW can also be treated as
shown in FIG. 4B to produce a single final treated effluent,
although currently there is not yet a revised standard outlining
discharge standards for simultaneous treatment of these
streams.
TABLE-US-00001 TABLE 1 International Maritime Discharge standards
for sewage TSS <35 mg/L COD <125 mg/L pH 6.0-8.5 Fecal
Coliform <100 N/100 mL Free Cl.sub.2 residual <0.5 mg/L
TABLE-US-00002 TABLE 2 International Maritime Discharge standards
for oily water Oil & Grease <15 ppm in ocean <5 ppm in
sensitive area
[0070] For land-based applications, most developed countries have
discharge standards for discharge into a combined or domestic sewer
system, storm sewer system or into a waterway. These standards vary
according to country, state, province and municipality. Thus since
discharge standards are highly site and location specific they are
not presented in this application. Nevertheless, the stricter
land-based discharge standards are similar to the IMO/MARPOL
regulations and have in addition other regulated parameters such as
heavy metals, phosphates, nitrates, phenols, sulfides, sulfates,
THM, and temperature. The WETT approach described in FIG. 4A is
also able to meet the stricter land-based discharge standards for
wastewater.
[0071] The results obtained with lab-scale WETT treatment using EC,
EF and EO are presented in Table 3, for three types of model
wastewaters developed to closely mimic ship-generated blackwater
(BW), graywater (GW) and oily water (OW). The results for blends of
these streams are also shown. It can be seen that the lab-scale
WETT process was capable of high removal rates for total suspended
solids (TSS), COD, and Oil, and the final treated effluent values
meet the IMO/MARPOL discharge standards required for these
parameters. As well, the results obtained with the pilot-scale WETT
treatment of real ship-generated (OW, GW, BW+GW) and domestic
(BW+GW) wastewaters using EC, EF, EO and OR are presented in Table
4. WETT treatment meets all the IMO/MARPOL discharge standards for
OW and BW+GW.
TABLE-US-00003 TABLE 3 TSS, COD and Oil removal results for WETT
for model wastewaters simulating ship-generated wastewater Sample
BW + Measurement point GW OW BW + GW GW + OW TSS (ppm) Before EC
391 2942 807 1367 After EC 25 114 30 45 After EO 1 71 0 19 COD
(ppm) Before EC 1337 14685 1985 6670 After EC 470 300 351 402 After
EO 0 54 1 0 OIL (ppm) Before EC -- 6200 -- 6550 After EC -- 30 --
106 After EO -- 4 -- 12
TABLE-US-00004 TABLE 4 TSS, COD, BOD, Oil, free and Total Cl.sub.2
and Fecal Coliforms removal results for pilot-scale WETT for real
ship-generated and domestic wastewaters Measurement Sample point GW
OW BW + GW TSS (ppm) Before EC 460 810 750 After EF 28.5 5.5 17
After EO -- -- -- After OR 5 -- 20 COD (ppm) Before EC 2468 59100
1476 After EF 278 511 143 After EO 121 -- 7 After OR 116 -- 0 BOD
(ppm) Before EC 163 -- 556 After EF -- -- -- After EO -- -- --
After OR <25 -- 0 OIL (ppm) Before EC -- 23,600 -- After EF --
4.2 -- After EO -- -- -- After OR 1.21 FCl.sub.2 (TCl.sub.2) (ppm)
Before EC 0 0 (0) 0 After EF 50 0 (1) 0 After EO 100 -- 35 After OR
0.2 0 (0) 0.1 Fecal Coliforms Before EC -- -- 2E+4 (CFU/100 ml)
After EF -- -- -- After EO -- -- -- After OR 0 -- 0
[0072] The WETT process can treat an OW influent containing more
than 15 ppm of oil content and the treated effluent will comply
with the discharge standard for oil content of less than 15
ppm.
[0073] The WETT process can also treat a sewage or graywater
influent containing more than 35 ppm Total Suspended Solids (TSS),
more than 125 ppm Chemical Oxygen Demand (COD), more than 25 ppm
Biological Oxygen Demands (BOD) and more than 100 CFU/100 ml Fecal
Coliform (F.C.) and the treated effluent will comply with the
MARPOL discharge standards.
[0074] Although a dividing wall that allows treating wastewaters of
different composition (such as oily water and greywater) is
presented in FIG. 4B, it will be appreciated that EC units (as well
as EF, EO and OR units) can be placed in combination with a
plurality of other similar units either in series or in parallel
while sharing some peripheral equipment in order to minimize cost,
footprint/bulkiness of the apparatus.
[0075] WETT Process Control
[0076] Process control is an important aspect of the invention. As
mentioned above, the system must be able to adapt to wide
variations in contaminant loading caused by variations in influent
flowrate and/or quality.
[0077] There are many different approaches that could be envisaged,
some of which are very complex and expensive. In order to keep the
WETT process simple, minimize the cost of sensors and equipment,
and successfully meet the treatment requirements for a large number
of discharge parameters, the following approaches are selected for
each of the principal unit operations but other process control
strategies could be applied depending of the mode of operation of
each unit:
[0078] EC: operate preferably in a once-through mode at constant
flowrate; keep current at a constant value or modulate as required
based on inlet turbidity and/or oil content as measured by online
sensors.
[0079] EF: operate preferably in a once-through mode at constant
flowrate; keep current at a constant value or modulate as required
based on turbidity and/or oil content determined by online
sensors.
[0080] EO: operate preferably in a batch recirculation mode with
constant flowrate, constant current and terminate treatment based
on readings from one or a combination of online CO.sub.2 gas
concentration, ORP, Cl.sub.2 and pH sensors.
[0081] OR: operate in a batch recirculation or continuous mode with
constant flowrate, keep current constant or modulate as required
based on the reading from an online Oxidation Reduction Potential
(ORP) and/or Cl.sub.2 sensor, and terminate treatment based on
readings from an online ORP sensor and/or an online Cl.sub.2
sensor, or from an online ORP sensor only.
[0082] The selected semi-batch approach for operation and control
of the unit operations means that a number of holding tanks are
required in different parts of the process. The operation and
control approach is illustrated in FIG. 1 which shows the location
of the principal online sensors utilized for process control but
does not depict the holding tanks associated with each treatment
unit.
[0083] For control purposes, Applicants use a CO.sub.2 gas sensor
in conjunction with the ED process. Contrary to other control
approaches where expensive and sophisticated online COD sensors are
used during EO treatment to control the process, the use of a
CO.sub.2 gas sensor is simple and much less costly. Alternatively,
a free chlorine sensor or a pH sensor can be used to indirectly
detect the extent of treatment progression in an EO unit.
[0084] It has been discovered in lab-scale and pilot-scale
experiments that, for certain wastewater types, the shape of the
CO.sub.2 emission curve, in conjunction with pH measurement, gives
a clear indication of the time at which most of the reactions
occurring during batch EO treatment are completed. This is shown in
FIG. 5.
[0085] Another control approach is the use of an online
Oxidation-Reduction Potential (ORP) probe for monitoring high
concentrations of residual oxidant during the OR process. Once the
ORP signal is below a certain value, a conventional chlorine sensor
(which cannot be used at high residual oxidant concentrations) is
brought online to precisely monitor the progress of the OR process
and indicate when it should be terminated. It is also possible to
use the ORP probe only to control the OR process once an accurate
correlation is made between the ORP level and the Cl.sub.2
concentration for a particular solution. The FIG. 6 shows typical
measurement of the ORP and free chlorine sensor during OR
process.
[0086] Treatment for Combined Ship-generated Wastewaters
[0087] For the particular case of wastewaters generated by ships or
platforms operating in the ocean (or any combination of wastewaters
which resemble BW, GW and OW), an original approach which allows
simultaneous treatment of various streams will now be described. It
should be noted that simultaneous treatment of various streams is
not the norm; typically each wastewater stream requires treatment
with a specific type of equipment and process. However an
integrated omnivorous system capable of handling all wastewater
streams is highly desirable, as evidenced by progress being made in
the development of marine discharge standards anticipating the
development of such an approach.
[0088] FIG. 4B shows the approach for treating the three principal
ship-generated wastewater streams, namely BW, GW and OW. It should
be noted that not all of the wastewater is treated by all of the
WETT unit operations. As well, salt or seawater is only added to
the BW+GW blend as required to attain the minimal required solution
conductivity for WETT operations. If the BW is gravity-collected
using saltwater (as opposed to vacuum-collected with freshwater) a
high-saline content stream will be generated and no salt addition
is required. The OW stream (for an ocean-going vessel) contains a
high proportion of seawater and does not require the addition of
salt.
[0089] The BW+GW stream and the OW stream are treated in parallel
EC/EF units which are joined but do not allow contact between the
two streams. These parallel EC/EF units may share some of the
system components (for example froth removal system, power supply,
etc.) to eliminate duplication of equipment.
[0090] EC/EF treatment is normally sufficient to remove most of the
oil contained in the OW, which does not go on to EO treatment. This
minimizes the EO treatment time and/or equipment size, keeping in
mind that this is the most expensive and energy consuming part of
the WETT process. Furthermore, diverting the OW stream from the EO
is advantageous since the elevated salt content results in
excessively high concentrations of bulk oxidant which will require
significant effort to decompose in the OR unit. However, the BW+GW
stream, with generally much lower salt content, proceeds onwards to
EO treatment which is required to reduce its COD.
[0091] After the EO unit, the BW+GW stream is blended with the
EC/EF-treated OW stream. The residual oxidant contained in the
BW+GW stream oxidizes some of the residual COD contained in the OW
stream, and reduces the extent of treatment required by the OR
unit. Finally, the BW+GW stream and EC/EF-treated OW stream are
treated in OR unit to reduce the residual oxidants. Table 5
presents the treatment results for BW+GW and OW streams using the
process depicted in FIG. 4B.
TABLE-US-00005 TABLE 5 Lab-scale results for WETT treatment of
combined OW and BW + GW streams Effluent Effluent Effluent
Treatment Influent number COD (ppm) FCl.sub.2 (ppm) EC + EF OW 1
629 0 EC + EF + EO BW + GW 2 44 770 Mixing Effluent 1 + 3 256 114
Effluent 2 OR Effluent 3 4 217 0
[0092] Finally, the WETT process can treat an influent combining OW
and sewage and containing more than 15 ppm oil content, more than
35 ppm TSS, more than 125 ppm COD, more than 25 ppm BOD and more
than 100 CFU/100 ml F.C., and the treated effluent will contain oil
content lower than 15 ppm, TSS lower than 35 ppm, COD lower than
125 ppm, BOD lower than 25 ppm, pH between 6 and 8.5, Chlorine
lower than 0.5 ppm and F.C. lower than 100 CFU/100 ml.
[0093] Recycling Hydrated Iron Oxide Fe(OH).sub.3 Particles
[0094] It is another aspect of the WETT process to recycle the iron
oxide created in the OR unit to enhance the efficiency of the
preceding WETT unit operations. In addition to being a well-known
adsorbent, iron oxide (for example as created by the addition of
ferric chloride (FeCl.sub.2)) is a well-known coagulant widely used
in wastewater treatment in the same way as alum is used.
[0095] Coagulation of Suspended Solids and Contaminants
[0096] The recycling/recirculation of iron oxide prior to the EC
unit (FIG. 1) assists in the coagulation and flocculation of
contaminants and decreases the contribution required from the EC
unit. This is of great benefit since the electrical consumption and
the frequency of aluminum plate change for the EC unit can be
reduced.
[0097] Adsorption of Disinfection By-Product Precursors
[0098] The creation of disinfection by-products (DBP) during
wastewater treatment for potable use (rather than discharge to the
environment or the sewer) has become a great concern over the last
decades. However, the elimination of oxidants and resulting lack of
water sanitation is far more dangerous for human health.
[0099] Because of the predominant use of chlorine-based compounds
for sanitation of municipal water systems, regulations exist for
allowable levels of trihalomethanes (THMs) and haloacetic acids
(HAAs) in potable water and are also being considered for many
non-potable applications since they are considered to be
potentially carcinogenic to humans. These compounds are known to be
created by the interaction of the chlorine-based disinfectants with
natural organic matter (NOM) contained in the wastewater, which may
be of fulvic or humic origin. Similar regulations exist for DBP
created with the use of other oxidants based on ozone, chlorine
dioxide, bromine etc.
[0100] No satisfactory approach has been found to completely
eliminate the formation of DBP. Many of the approaches for
mitigating the formation of DBP involve the removal of NOM prior to
sanitation. Granular activated carbon and other approaches are
known to be capable of removing NOM for potable water systems. In
particular, the adsorption of NOM on various types of iron oxides
has been widely discussed in the literature.
[0101] The recycling/recirculation of iron oxide prior to the EO
unit (FIG. 1) may be more effective in targeting the dissolved NOM
which have not been removed by EC/EF, but may also require the use
of a clarification or filtration stage prior to or during the EO
process. The reduction in DBP formation potential and the reduced
treatment required by ED would constitute the major benefits of
this option. FIG. 7 shows jar tests (method familiar to those
skilled in the art of wastewater treatment) where different amounts
of Fe(OH).sub.3 particles are added to ship-generated BW+GW. It can
be seen that the Fe(OH).sub.3 is an effective coagulant, as
evidenced by the large decrease in total suspended solids (TSS) of
the solution. As well, the Fe(OH).sub.3 particles are effective in
adsorbing contaminants, as evidenced by the large decrease in
solution color, which is often related to the dissolved
contaminants and which are not generally removed by coagulation. It
can be seen that beyond a certain level (in this case about 2,000
mg/L Fe(OH).sub.3), there is no benefit to further addition of
Fe(OH).sub.3 for this particular type of BW+GW wastewater.
[0102] Table 6 shows the jar test results obtained for BW+GW when
the contribution of an aluminum-based coagulant (as would be
generated in EC with aluminum plates) as well as Fe(OH).sub.3
addition is considered. When both coagulants are mixed with the
BW+GW, with a concentration of 21 ppm Al.sup.3+ and 1,000 ppm
Fe(OH).sub.3, a TSS value of 17 ppm is obtained. This represents a
50% lower consumption of aluminum-based coagulant (with a
corresponding reduction in EC energy consumption) than would be
required if only aluminum-based coagulant was used. Furthermore, it
can be seen that the use of Fe(OH).sub.3 alone does not reach the
low TSS levels that can be obtained with much smaller amounts of
aluminum-based coagulant.
TABLE-US-00006 TABLE 6 Experimental results for TSS and Color in a
BW + GW solution with different Al3+ and Fe(OH)3 concentrations
Fe(OH).sub.3 (ppm) 0 333 1000 Color TSS Color TSS Color Al (ppm)
TSS (ppm) (a.u.) (ppm) (a.u.) (ppm) (a.u.) 0 213 1564 100 1015 44
512 21 51 515 35 457 17 235 42 20 267 17 241 8 140 63 9 148 9 149 5
102 84 7 124 6 119 3 92 105 9 132 7 121 N/A N/A
[0103] FIG. 8 is a detailed schematic representation of the
preferred embodiment of the WETT apparatus including effluent flow
circuits (solid lines) and control circuits (dashed lines). In
typical cycle of operation, wastewater flows into the apparatus and
passes through a selector 12 which allows an operator to select the
type of wastewater if it is known. Knowing the composition or
origin of the wastewater(s) can allow to implement a predefined
treatment protocol. This can also be done automatically through the
controller 24 or a plurality of controllers. The wastewater then
proceeds though a solid/liquid separation unit 1 which prevents
particulate matter of predetermined size from entering into the
system, as this could have detrimental effects. The solid/liquid
separation unit 1 can be a screen. Wastewater comes in contact with
one or more sensors 2 which can sense turbidity or oil to help
characterize the wastewater composition and/or type of treatment
required. The wastewater then enters the EC unit 4 through the EC
unit inlet 3 and encounters an anode 5 and a cathode 6. These
electrodes serve as electro-coagulation electrodes and are known in
the art. Wastewater (hereinafter referred to as effluent which will
be understood as including influent as well as any wastewater
flowing through the system) then exits the EC unit and enters the
EF unit 9 through the EF unit inlet 8. In the EF unit 9, effluent
encounters anode 105 and cathode 106. After exiting the EF unit 9,
the effluent encounters a valve 10 which allows for directing the
effluent to an outlet as treated effluent or to continue in the
system of the present invention, through a pump 11 and to an EO
unit 14 through an EO unit inlet 13. The EO unit 14 comprises an
oxidation chamber 17 that can form a closed loop circuit using
valve 110 and an electrode chamber 207 containing anode 205 and
cathode 206. This closed loop further comprises a pH sensor 20 in
communication with the controller 24 in order to evaluate the
oxidation level of the effluent. The oxidation chamber has a gas
outlet 21 for preventing build-up of pressure inside the EO unit
14. Upon exiting the EO unit 14 through the gas outlet 21, the gas
comes in contact with a CO.sub.2 sensor 22 for quantifying the
level of CO.sub.2 as this is an indication of treatment completion.
Optionally, a CO.sub.2 catalyst 23 for quenching CO.sub.2 by
chemical or enzymatic means can be provided. Once oxidation in the
closed circuit is complete as indicated by CO.sub.2 evacuated
through the gas outlet 21, valve 110 allows effluent to exit
through the EO unit outlet 18 and into the OR unit 30. The OR unit
30 consists of an OR vessel 29 which receives effluent from the OR
unit inlet 31. The OR unit 30 can form a closed loop system due to
the actuation of valve 210. Effluent in the "closed loop" system
comes in contact with an ORP sensor 25 and a Cl.sub.2 sensor 26
before entering the OR electrode chamber 307. Once OR treatment is
complete (i.e. a predetermined level of oxidants has been reached),
the valve 210 can direct effluent to a solid/liquid separation unit
28 designed to separate metal oxides from treated effluent, which
exits the system through the OR outlet 32. Metal oxides recovered
in the solid/liquid separation unit 28 can be recycled to the head
of the system, either to a wastewater holding tank upstream of the
soli/liquid separation unit 1 as shown or upstream of EC unit 4
(not shown). The metal oxides can also be recycled upstream of the
EO unit 14 either before or after the pump 11. It will be
appreciated that all units, sensors, electrodes, valves and pumps
are in communication with controller 24 (see dashed lines) such
that controller 24 receives input from sensors and sends
instructions to actuators. All unit operations are powered by a
power source 7 which can be one single power source or many
individual power sources as shown in FIG. 8.
[0104] In an alternate embodiment, the OR unit can function
exclusively by providing a UV source rather than using sacrificial
electrodes. In such an apparatus, the ultraviolet source can
replaced the electrode chamber 307. It will be appreciated that if
the oxidant removal capability is provided by a source of UV
radiation rather than electrodes, the OR unit 30 could not require
an OR vessel 29 as the UV source can be provided directly inside
the effluent conduits. It will be also appreciated that if UV
radiation is used instead of sacrificial electrodes, the
solid/liquid separation unit 28 is not required and no recycling of
metal oxide is necessary.
[0105] In another embodiment, the OR unit 30 can be provided in a
closed loop system in combination with the EO unit 14. In such an
embodiment, contaminants are oxidized upon passing through the
electrode chamber 207 but all unused or unreacted oxidants can be
removed directly in the closed-loop system. It will be appreciated
that the OR unit of this closed-loop system can be the standard
sacrificial electrode type or the ultra-violet based oxidant
removal technique.
[0106] It will be appreciated by those skilled in the art that a
high number of permutations are possible for this system and that
such permutations would not depart from the essence of the
invention.
* * * * *