Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND SYSTEMS FOR TREATING TAILING POND WATER
FIELD OF THE DISCLOSURE
[0001] The present disclosure is related generally to treatment methods and
systems for tailing pond water produced during the mining and processing of
bitumen oil.
BACKGROUND INFORMATION
[0002] Bitumen mining, often referred to as the oil sands located in
northern
Alberta, Canada is an unconventional petroleum deposit. Oil sand is in the
form
of loose sand or partially consolidated sandstone. The sand is saturated with
a
viscous form of petroleum often referred to as bitumen. Natural bitumen
deposits are found in large quantities in Canada and are also found in smaller
deposits in other countries.
[0003] Bitumen mining utilizes and produces large amounts of fluids during
the mining operations and during the years of production. Mining bitumen may
require 1 to 3 barrels of water per barrel of bitumen produced. During the
past
40 years of mining the bitumen, large lakes or "tailing ponds" have been
created
to hold the water and fine tailings produced during the extraction process.
[0004] The tailing ponds in Alberta, Canada encompass over 135 sq.
kilometers. The tailing ponds are earthen dams that average 35 feet in height.
Dissolved constituents from the mining process include clay, bitumen, water
and chemicals used by the mining companies.
[0005] The majority of water used during the mining process is recycled
back
to the mining operations but up to 15% of the fluids are sent to the tailing
ponds.
These ponds are managed by the consortium of about 10 oil companies that
mine the bitumen.
[0006] It is a priority concern of local, provincial and federal government
agencies that tens of millions of gallons of fresh water is removed each month
from the Athabasca waterway and is permanently contaminated. The methods
of storing the effluent water in the earthen dams or 'tailing ponds' is an
environment risk in that over time the tailing ponds are leaching and leaking
into the groundwater and making its way back into the river system. These
temporary dams are not built to house the contaminated water year after year
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without consequences. The Alberta Government is now in the process of
establishing mandates and protocols to lower the environmental risk from the
tailing ponds. To date none of the oil companies have met goals set forth by
the
governmental entities in charg- of monitoring the ponds.
[0007] Due to the concerns over the shortage and cost of water available
for
oil sands mining as well as the environmental risk, the need to treat and
recycle
the contaminated water for re-use in the mining process or for discharge into
the waterways is a high priority to oil sands mining. However, finding a water
treatment process that is technically and economically viable for such
purposes
has proven challenging, partly because of the combination of suspended solids,
bitumen, and chemicals in the water.
[0008] Water treatment processes of the prior art, including a variety of
water
treatment technologies such as flotation, filtration, evaporation, reverse
osmosis, and combinations of these technologies have not proven to be
effective
to adequately treat the water to meet bioassay characteristics that will
enable
local fisheries to survive and flourish in treated water returned to the
Athabasca
River system.
SUMMARY OF THE DISCLOSURE
[0009] The present disclosure provides methods and systems for treating
tailing pond water in bitumen mining process. The treatment method and
system can comprise two steps, which each can include a plurality of sub-
steps,
or be combined with additional steps (before or after). The first step can
primarily
remove suspended solids, and the second step can primarily remove dissolved
toxic metals, organics, and other toxins and carcinogens from water. The
treatment methods and systems can allow for re-use of the treated water in the
mining process or for return of the treated water to the Athabasca River.
[0010] The first-step treatment process is carried out by using a system
that
uses flow momentum to induce a vortex. The flow-induced vortex is able to
produce a centrifugal acceleration up to thousands of gravitational constant
(g
= 9.8 m/s2) and separate the suspended solids from water by using the
centrifugal force. The separated solids include clay, sand, and other
particulate
suspended in water.
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[0011] The second-step treatment process can be carried out through an
electrocoagulation (or electropulse) technology. The equipment that carries
out
the electrocoagulation process can contain metal plates energized by a DC
electrical current.
[0012] In some embodimenis, the electrocoagulation system can contain
metal plates energized by a DC electrical current. As the contaminated water
passes through the plates, charged ions are introduced into water from the
plates, which neutralizes the charge on the surface of the oil and grease
droplets
and suspended solids. Oil and grease and suspended solids coagulate upon
neutralization of the charges on their surfaces.
[0013] In some embodiments, as water passes through the plates, heavy metal
ions dissolved in water may be reduced to an oxide and precipitate out of
water,
changing from a dissolved state to a suspended state.
[0014] In some embodiments, oxygen and hydrogen gas may form during
electrocoagulation, causing the coagulated contaminants to rise to the surface
of water.
[0015] In some embodiments, reactive oxygen species, broadly defined as
oxygen-containing reactive chemical species, including singlet oxygen,
superoxide anions, and hydroxyl radicals may be produced in the
electrocoagulation step. The reactive oxygen species may oxidize the organic
contaminates in water and convert them into less toxic or non-toxic species.
[0016] In some embodimen... of the present disclosure, an activated carbon
filter may be used in addition to the abovementioned first- and second-step
treatment processes to remove residual contaminants left from the previous two
processes before water is discharged.
[0017] In another example embodiment of the present disclosure, the water
treatment system is modularized. Both the vortex-induced suspended solids
removal process and the electrocoagulation processes can be carried out by
functional modules. The individual modules can be either (1) assembled and
installed on-site near the tailing ponds, or (2) skid mounted in containers
and
deployed for operations in remote oil sands area.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic illustration of two water treatment steps for
some
embodiments of the present disclosure;
[0019] FIG. 2 is a schematic illustration of the modified water treatment
process shown in FIG. 1 for some embodiments of the present disclosure, with
the sludge from the first-step treatment process and the second-step treatment
process being processed through a dewatering unit and the water separated
from the sludge being recycled to the influent.
[0020] FIG. 3 is a schematic illustration of the modified water treatment
process with an optional step to process the effluent from the second-step
treatment process with an activated carbon filter, for some embodiments of the
present disclosure.
[0021] FIG. 4 is a schematic illustration of the liquid-solid separation
system
used in the first-step treatment process.
[0022] FIG. 5 is a representative simulation result of the flow pattern
inside
the liquid-solid separation chamber by computer software.
[0023] FIG. 6 is a schematic illustration of a configuration for the liquid-
solid
separation system that can be deployed in the first-step treatment process,
where the effluent leaves the chamber from the top, for some embodiments of
the present disclosure.
[0024] FIG. 7 is a schematic illustration of a configuration for the liquid-
solid
separation system that can be deployed in the first-step treatment process,
where the separation system is placed horizontally.
[0025] FIG. 8 is an optical image of samples of untreated tailing pond
water
and treated water after the first-step treatment process.
[0026] FIG. 9 is an optical image of water sample treated by the first-step
process, the second-step process, and an activated carbon filter.
DETAILED DESCRIPTION
[0027] As used herein in the specification and claims, including as used in
the
examples and unless otherwise expressly specified, all numbers may be read as
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if prefaced by the word "about", even if the term does not expressly appear,
unless otherwise expressly stated. Also, any numerical range recited herein is
intended to include all sub-ranges subsumed therein.
[0028] In the present description, where used or otherwise designated to
apply
as described above, the terms "about" and "consisting essentially of" mean
20%
of the indicated range, value, or structure, unless otherwise indicated. It
should
be understood that the terms "a" and "an" as used herein refer to "one or
more"
of the enumerated components. The use of the alternative (e.g., "or") should
be
understood to mean either one, both, or any combination thereof of the
alternatives, unless otherwise expressly indicated. As used herein, the terms
"include" and "comprise" are used synonymously, and those terms, and variants
thereof, are intended to be construed as non-limiting unless otherwise
expressly
stated.
[0029] In the following description, certain specific details are set forth
in
order to provide a thorough understanding of various embodiments of the
disclosure. However, upon reviewing this disclosure one skilled in the art
will
understand that the disclosure may be practiced without many of these details.
In other instances, well-known structures, systems and methods in the relevant
fields have not been described in detail to avoid unnecessarily obscuring the
descriptions of the embodiments of the disclosure.
[0030] Whenever the terms, "for example," "such as," or variants thereof
are
used herein, the provided examples are assumed to be without limitation or
restriction, unless otherwise expressly indicated.
[0031] The present disclosui= relates to a water treatment process for
treating
contaminated water, including tailing pond water, generated from the oil sands
in Alberta, Canada. The water to be treated typically contains fluids and
solids
and dissolved constituents from the oil sands.
[0032] Water treatment methods and systems for treating tailing pond water
from the oil sands, according to the present disclosure, can reduce the levels
of
total suspended solids (also referred to herein as "TSS"), oil and grease
(also
referred to herein as "O&G"), chemical oxygen demand (also referred to herein
as "COD"), biological oxygen demand (also referred to herein as "BOD"), total
organic content (also referred to herein as "TOC"), dissolved toxic metals,
and
CA 02897950 2015-07-22
toxins and/or carcinogens from water. The treated water can be reclaimed for
use in the bitumen mining process and/or returned to the Athabasca River
system. In tests using the presently disclosed methods and systems as high as
99% suspended solids contained in tailing pond water were removed, and
adequate removal of toxins and carcinogens harmful to aquatic and other
wildlife species. It will be appreciated that in field use, the percentage of
suspended solids successfully removed may not be as high.
[0033] Some embodiments of the present disclosure comprise two treatment
steps, such as shown in Figure 1. The first step 100 primarily removes
suspended solid by using a system that uses flow momentum to induce a vortex.
The flow-induced vortex is able to produce a centrifugal acceleration up to
thousands of gravitational constant (g = 9.8 m/s2) and separate the suspended
solids from water by using the centrifugal force. The separated solids include
clay, sand, and other particulates suspended in water. The removed suspended
solids are discharged from this process 100 in the form of sludge.
[0034] The effluent from the first-step treatment process is directed to
the
second-step treatment process 110 which can remove 086G, dissolved toxic
metals, organics, and other toxins and carcinogens from water by an
electrocoagulation technology. The second-step treatment process 110
separates the 086G, dissolved toxic metals, organics, and other toxins and
carcinogens from water, which is discharged in the form of sludge.
[0035] In some embodiments, sludge from the first-step treatment process
100 and the second-step treatment process 110 will be processed through a
dewatering unit, and the water separated from the sludge is recycled to the
influent. The modified treatment process is illustrated in Figure 2.
[0036] In an example embodiment, the sludge from the first-step treatment
process 100 is directed to a dewatering unit 200 and is separated into a
liquid
stream and a waste solid typically in the form of a cake. The liquid stream is
recycled through a return line and mixed with the influent feed to the first-
step
treatment 100 unit. This dewatering unit can be chosen from various types of
dewatering units including filter press, centrifuge, and electro-dewatering
equipment.
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[0037] In another example embodiment, the concentrate from the second-step
treatment process 110 is directed to a dewatering unit 210 and separated into
a liquid stream and a waste solid typically in the form of a cake. The liquid
stream is recycled through a return line and mixed with the influent feed to
the
second-step treatment 110 unit. This dewatering unit can be chosen from
various types of dewatering units including filter press, centrifuge, and
electro-
dewatering equipment.
[0038] Preferably, by recycling the water separated from the sludge to the
influent of the treatment process in both treatment steps, the entire
treatment
system of the present disclosure is a zero liquid discharge system, meaning no
waste is discharged in a liquid form. In tests of the technology up to 99% of
water was able to be recycled and reused. The amount of water able to recycled
will, of course, vary depending upon a number of factors.
[0039] In some embodiments of the present disclosure, an activated carbon
filter 300 may optionally be used after the second-step treatment process to
remove residual contaminants left from the previous two processes before water
is discharged, as schematically shown in Figure 3.
[0040] The first-step treatment process 100 primarily removes suspended
solids by using a liquid-solid separation system that uses flow momentum to
induce a vortex. Figure 4 presents the design of the system 400. It comprises
the following parts: an inlet 410, a stator 420, a separation chamber 430, a
tube 440 placed at the center of the storage tank that directs the liquid to
the
outlet 450, a solid storage tank 460 for temporary storage of the sludge and
the
solid, and an sludge outlet 470. The stator is a ring that has grooves and/or
textures on the inside surface designed to convert the axial momentum of the
flow into radial momentum arl generate a vortex when the fluid flows through
the stator. The flow-induced vortex is able to produce a centrifugal
acceleration
up to thousands of gravitational constant (g = 9.8 m/s2), depending on the
flow
velocity and the radius of the separation chamber. The centrifugal force
separates the suspended solid particles from the fluid based on the density
difference between the particles and the liquid. The liquid is pulled out of
the
separation chamber from the center by a tube 440, and the solid, once
separated
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from the liquid, is directed to the temporary solid storage tank 460 and
eventually removed from the sludge outlet 470.
[0041] Design of the liquid-solid separation system 400 typically involves
simulation of the flow pattern inside the separation chamber by computer
software based on the knowledge of the flow velocity of the fluid or the flow
rate,
the solid particle density, the liquid density, and the solid particle size
and size
distribution. The simulation can be conducted by those skilled in the relevant
art by using finite element analysis and/or computational fluid dynamic
simulations. Figure 5 shows the result of one such simulation where flow
patterns of the fluid can be visualized after the fluid passes through the
stator
420 that converts the axial flow momentum to radial momentum.
[0042] Compared to prior art of liquid-solid separators, including gravity-
based settling tank or baffled bank, membrane-based filtration, air flotation,
dissolved air flotation, and chemical-based flocculation and coagulation, the
liquid-solid separator described in the present disclosure has the following
advantages: it has no moving parts; it does not consume energy or chemicals or
filtration membrane or media; it takes small footprint and is easy to maintain
and operate.
[0043] It is worth noting that the liquid-solid separator described in the
present disclosure is different from prior art in making liquid-solid
separators
that also use flow-induced vortex to separate solid from liquid, such as a
hydro-
cyclone. The prior art introduces the fluid to the separation chamber in a
tangential direction, whereas the present disclosure introduces the fluid to
the
separation chamber in the axial direction. Compared to the prior art, the
present
disclosure is able to achieve higher separation efficiency with less pressure
drop
occurred inside the chamber.
[0044] The liquid-solid separator described in the present disclosure may
also
be constructed and deployed in different configurations. For example, in
Figure
6, the liquid effluent leaves the chamber from the top, and in Figure 7, the
separator is placed horizontally.
[0045] The effluent of the first-step treatment process 100 is directed to
the
second-step treatment process 110, where an electrocoagulation (or
electropulse) technology is used to remove 086G, dissolved toxic metals,
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organics, and other toxins and carcinogens from water. Depending on the pH of
the effluent of the first-step treatment process, the pH of the water may be
adjusted by an acid or a base. An example base for adjusting pH is sodium
hydroxide. An example acid for adjusting pH is hydrogen chloride. This pH
adjustment step is optional and when the pH of the feed water is satisfactory,
the water can be directed into the electrocoagulation system 110 without being
subjected to the pH adjustment process.
[0046] In some embodiments, the electrocoagulation system can contain
metal plates energized by a DC electrical current. As the contaminated water
passes through the plates, charged ions are introduced into water from the
plates, which neutralizes the charge on the surface of the oil and grease
droplets
and suspended solids. The charge neutralization causes these contaminants to
coagulate, as will be appreciated by those skilled in the art after reviewing
this
disclosure. Oil and grease and suspended solids coagulate upon neutralization
of the charges on their surfaces. Electrocoagulation systems such as these are
commercially available and will, therefore, not be further described.
[0047] In some embodiments, as water passes through the plates, heavy metal
ions dissolved in water may be reduced to an oxide and precipitate out of
water,
changing from a dissolved state to a suspended state.
[0048] In some embodiments, oxygen and hydrogen gas may form during
electrocoagulation, causing the coagulated contaminants to rise to the surface
of water.
[0049] In some embodiments, as the DC electrical current passes through
water in the electrocoagulation system, reactive oxygen species (ROS) broadly
defined as oxygen-containing reactive chemical species, including singlet
oxygen, superoxide anions, and hydroxyl radicals may be produced. The reactive
oxygen species may oxidize the organic contaminates in water and convert them
into less toxic or non-toxic species.
[0050] In another example embodiment of the present disclosure, the water
treatment system is modularized. Both the vortex-induced suspended solids
removal process and the electrocoagulation processes can be carried out by
functional modules. The individual modules can be either (1) assembled and
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installed on-site near the tailing ponds, or (2) skid mounted in containers
and
deployed for operations in remote oil sands area.
WORKING EXAMPLE
[0051] The following example is intended to be illustrative and should not
be
construed as limiting the disclosure in any way.
[0052] This example uses a water treatment system constructed following the
schemes shown in Figure 3 to treat contaminated tailing pond water obtained
from Alberta, Canada.
[0053] The contaminated taiiing pond water was first treated by a liquid-
solid
separator constructed according to Figure 6. The liquid-solid separator was
operated at a flowrate of 50 gallon per minute and the pressure drop between
the inlet and the outlet of the operator was 60 psi. Optical images of the
untreated tailing pond water and the water after the first-step treatment were
shown in Figure 8.
[0054] The effluent from the first-step treatment process was fed into an
electrocoagulation system, followed by treatment with activated carbon. An
optical image of the treated water after the entire treatment process was
shown
in Figure 9.
[0055] Representative characteristics of tailing pond water before the
treatment are presented in Table 1. Representative characteristics of the
water
after the treatment process are presented in Table 2.
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Table 1. Characteristics of contaminated tailing pond water before
treatment.
Water Quality Parameters Unit Value
pH 7.10
Ammonia ppm <2500
Specific Conductance 1.1S/cm 2300
Oxygen Reduction Potential V +63.7
Dissolved Oxygen mg/I 10.0
Table 2. Characteristics of treated water.
Water Quality Parameters Unit Value
pH 8.18
Ammonia ppm 6.0
Specific Conductance i.IS/cnn 2300
Oxygen Reduction Potential V +85.0
Dissolved Oxygen mg/I 5.81
[0056] Two parallel tests were conducted to test the survival rate of trout
in
treated water. 10 rainbow trout less than 2" in length were raised in treated
and
untreated water simultaneously. Fish were fed once per day using crushed
Cichlid granules. In the untreated water, 10 fatalities were recorded within
initial
2 hour test period. In the treated water, initial test was conducted for 96
hours.
No loss was observed during the 96 hour process. Test was continued for an
additional 48 hours. All fish were still alive after 6 days (144 hours). Upon
completion of test, fish were released into a local trout lake.
[0057] Although specific embodiments and examples of the disclosure have
been described supra for illustrative purposes, various equivalent
modifications
can be made without departing from its spirit and scope, as will be recognized
by those skilled in the relevant art after reviewing the present disclosure.
The
various embodiments described can be combined to provide further
embodiments. The described systems, devices and methods can omit some
elements or acts, can add other elements or acts, or can combine the elements
or execute the acts in a different order than that illustrated, to achieve
various
advantages of the invention. These and other changes can be made to the
invention in light of the above detailed description.
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[0058] In
general, in the following claims, the terms used should not be
construed to limit the disclosure to the specific embodiments disclosed in the
specification.
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