Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Self-coagulant and zero / reduced liquid discharge
process for high hardness / high alkalinity
wastewater treatment
1 Description
1.1 Background of The Invention
The importance of the water as lifeline of many industrial applications is
well known. Therefore,
many inventions are developing to enhance water treatment systems.
Traditionally, different
water treatment methods such as chemical treatment, membrane separation
processes or a
combination of them can be used to treat high alkalinity wastewaters streams;
however, these
treatments usually require a significant dosage of coagulants to operate at
high efficiency.
Moreover, these processes are usually followed by producing other waste
streams to the system
whether it is produced sludge from the chemical treatment or the concentrated
retentate stream of
the membrane filtration processes. This presents economically and ecologically
undesirable
results since the mentioned disadvantages can significantly increase the
maintenance and capital
cost of the operation.
The present invention suggested a novel coagulant using high hardness
wastewater (e.g. IERW),
which is a waste stream produced in different applications such as ion
exchange (IX) processes.
IX units are commonly used in the purification processes for the removal of
magnesium and
calcium ions. In the regeneration of the IX process, a high saline brine
solution is produced
known as IERW. The disposal of the IERW is challenging since it contains a
relatively high
concentration of calcium and magnesium or other cations / anions. Thus, it is
highly beneficial to
reuse this waste stream for other applications.
The main objective of this invention is to propose a highly efficient hybrid
treatment, which is
capable of operating with a minimized/zero coagulant cost and producing high-
quality water for
different industrial and residential applications.
CA 3053050 2019-08-26
1.2 Description
This invention introduces two hybrid processes for the treatment of high
alkalinity wastewaters.
The chemical treatment using the IERW as the coagulant was configured in these
processes to
cut down the operational cost, which is spent on purchasing commercial
coagulants. The IERW
conditioning was proved to be capable of removing different contaminants such
as silica ions and
organic matters.
The first scenario involves pre-treating the high alkalinity wastewater by
IERW conditioning
followed by applying membrane filtration as the final treatment. A one-stage
treatment using
IERW conditioning might be enough depending on the target specification of the
treated water.
Moreover, another chemical pre-treatment can be applied before the membrane
filtration unit
based on the properties of the produced effluent from IERW conditioning unit
and requirement
of the membrane filtration module. The IERW conditioning is capable of
removing a significant
portion of organic matters and silica ions, which lowers the fouling
propensity and improves the
separation performance of the membrane. The type of membrane filtration unit
can be selected
based on the target specification of the treated water. For example, reverse
osmosis membranes
can be used in case of requiring a higher quality treated water.
In the second scenario, the high alkalinity water can be treated using a
direct membrane filtration
unit and this treatment can be followed by treating the concentrated retentate
with a hybrid of
IERW conditioning and a second membrane filtration unit. The filtration type
and water recovery
of the membrane separation can be adjusted according to the properties of the
wastewater and the
fouling characteristic of the filtration.
These integrated processes also are capable of operating with a zero liquid
discharge (ZLD)
configuration since all of the produced waste streams from these treatments
can be reused for
other purposes. The produced sludge from IERW conditioning can be utilized as
an industrial
by-product due to presence of calcium sulfate and silicate. Furthermore, the
concentrated
retentate of the membrane filtrations contained a high concentration of sodium
chloride making
it ideal to be reused as the regeneration solution for the IX module. The ZLD
system will be
further clarified in the examples.
The invention can be explained in more details by presenting an example of the
applicability of
this process in an industrial operation.
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1.3 Description of The Drawings
Figure A shows the schematic flow diagram of the hybrid process for the
treatment of high
alkaline wastewater using self-coagulant conditioning and a one-stage membrane
filtration. The
stream-1 and stream-2 are the produced high hardness and alkaline wastewaters,
respectively.
The stream-1 and stream-2 are directed to the self-coagulant reactor for
chemical treatment. The
stream-3 is the MgCl2 solution that can be used as an additional coagulant if
needed. After the
removal of contaminants by self-coagulant conditioning, the produced effluent
(stream-4) can be
further treated using a softening and membrane unit. These two post-treatments
are optional and
can be utilized based on the application and the targeted specification of the
treated water. The
stream-5 is the produced effluent from the softening unit and was used as the
feed of the
membrane filtration. The stream-6 is the purified water using this technique
and is directed to the
required section for reuse. The stream-7A and stream-7B are the side streams
or produced sludge
of the self-coagulant reactor and softening unit, respectively. The stream-7A
and stream-7B are
directed to the sludge dewatering units for maximum water recovery. The
produced effluent from
sludge dewatering unit 1 and 2 are the stream-8 and stream-9, respectively.
These two streams
were directed to the purification process for further treatment. The stream-10
and stream-11 are
the dry sludge of the sludge dewatering unit 1 and 2, respectively. These
streams can be used as
industrial by products through waste extraction. The stream-12 is the
concentrated retentate of
the membrane unit and is most likely a high salinity solution, which can be
reused for other
applications (e.g. the regeneration solution for IX process).
Figure B demonstrates the schematic flow diagram of the proposed integrated
system for the
treatment of high alkaline wastewater using a two-stage membrane filtration by
integrating the
self-coagulant conditioning as a chemical treatment for second membrane unit.
The stream-1 and
stream-2 are the produced high hardness. The stream-2 is proposed to be used
as the feed water
of the first membrane filtration unit. The stream- 3 is the permeate water
produced from the
membrane unit 1 and can be used as purified water. The stream-4 is the
concentrated retentate of
the membrane unit 1 and is expected to have a higher concentration of
contaminants compare to
the initial high alkaline wastewater. The stream-4 is directed to the self-
coagulant reactor for
purification using chemical treatment. The produced effluent from the self-
coagulant reactor is
labeled as strean-5 and is used as the feed water of the second membrane
filtration unit. The
stream-8 is the permeate water of the membrane unit-2 and can be used for
other industrial
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proposes. The stream-9 is the sludge stream of the self-coagulant reactor and
is directed to the
sludge dewatering unit. The stream- 10 is the produced effluent of the sludge
dewatering unit and
is moved to the treatment process for further purification. The stream-11 is
the dry sludge of the
sludge dewatering unit and can be used as industrial by-product. The stream-12
is the
concentrated retentate of the membrane unit and is most likely a high salinity
solution, which can
be reused for other applications (e.g. the regeneration solution for IX
process).
2 Detailed Description of Preferred Example Embodiments
The present invention can be further explained by presenting the details of a
process used for the
treatment of produced water from SAGD operation called BBD water. Two general
sections are
provided to clarify the details of this example. First, the potential of ion
exchange regeneration
wastewater (IERW) containing magnesium ions to act as a coagulant for steam-
assisted gravity
drainage (SAGD) boiler blowdown (BBD), was demonstrated with the aim of
reducing the water
consumption in a SAGD plant. After identifying the applicability of IERW
conditioning,
different membrane-based separation scenarios were examined to further purify
the IERW-
treating BBD water. In the second section, the feasibility of implementing
these hybrid
coagulation-membrane processes for the treatment of the boiler blow-down (BBD)
from an oil
sands SAGD operation was explored. The above-mentioned sections are written
below:
2.1 Efficient Treatment of Oil Sands Produced Water: Process
Integration Using Ion Exchange Regeneration Wastewater as a
Chemical Coagulant
Steam-assisted gravity drainage (SAGD) technology is considered a practical
process to recover
bitumen from oil sands reservoirs [1-4]. The SAGD process uses two parallel
horizontal wells,
which are drilled above each other deep underground into the oil sand
reservoir. To increase the
temperature and thus reduce the viscosity of the bitumen, steam is injected
through the upper
well and the low viscous drained bitumen collected into the lower well as a
mixture to be
pumped to the surface for bitumen extraction. This process requires a high
volume of fresh
4
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water, and currently about 80% - 90% of the boiler feed water (BFW) is coming
from the
recycled oil sands affected water.
Recently, significant attention has been given to water treatment methods of
SAGD plants since
a poor quality feed water for the steam generator will lower the efficiency of
the boiler, as such
BFW purity should be at an acceptable level. In SAGD industry, once through
steam generators
(OTSG) are widely used to generate steam. To provide feed water for OTSG,
water treatment
processes should reduce silica and hardness concentration to <50 mg/L and <1
mg/L,
respectively. Also, the BFW should have total dissolved solid (TDS) and oil
content, lower than
7000 mg/L and 0.5 mg/L [1,5,6]. Ion exchange regeneration treatment is a
commonly used
method to remove hardness from the BFW by replacing the calcium and magnesium
ions with
sodium ions [7]. In this process, a concentrated sodium chloride solution
regenerates the ion
exchanger. The purpose of the regeneration is to replace the calcium and
magnesium ions, which
were removed from the wastewater and retained in the ion exchanger, with
sodium ions and
return the resin to its original state. Therefore, this process results in
wastewater with a high
concentration of calcium, and magnesium, which is called the ion exchange
regeneration waste
(IERW) [8,9]. After removing hardness, the treated water is directed to the
boiler, and the IERW
is discharged to the disposal system. The OTSG steam generation process
typically produces
80% steam quality resulting in a concentrated solution, which is known as
boiler blowdown
(BBD). The BBD's impurity concentration is much higher than the BFW. In a
typical SAGD
plant, an amount of the BBD is recycled back to the water treatment section,
and the rest is
discharged to the disposal system. In conventional approaches, BBD can be
treated for reuse
with the help of membrane filtrations, evaporation, chemical and biological
treatment techniques.
However, these methods increase the capital cost and energy consumption of the
SAGD plant
and can result in significant waste [1]. What's more, the use of water
treatment applications for
the reuse of BBD demands specialized and expensive equipment. Therefore, it is
highly
beneficial to use inexpensive but efficient technology to treat the BBD.
In conventional water treatment plants, flocculation is an essential technique
to separate
impurities from contaminated water solutions [10,12,13]. At present, various
types of coagulants
(such as lime, soda ash, caustic) are used in wastewater treatment plants to
improve the
efficiency of the chemical process [14].
CA 3053050 2019-08-26
Although extensive research has been carried out using chemical coagulants to
treat the BBD,
the majority of those coagulants are not environmentally friendly and require
a high dosage.
Furthermore, usage of chemical additives may overload the water treatment
system and increase
the operating resources and costs. As such, if a waste stream in the SAGD
plant can be used as a
coagulant, this will lead to a more cost and energy effective process for BBD
treatment.
Therefore, the major objective of this study is to investigate the feasibility
of using the currently
unusable IERW as the coagulant to treat the BBD under different treatment
conditions. This
wastewater contains a high concentration of magnesium and calcium that can
potentially act as
an effective coagulant in reducing the silica and organic content of BBD
water.
This is the first report to our knowledge discussing the possibility of using
ion exchange
regeneration wastewater and boiler blowdown as a coagulant for the treatment
of SAGD process
water and exploring the resource recovery from coagulated sludge waste.
Another important
aspect of using IERW as the coagulant is that by applying this method of
treatment, the extra
cost and energy for the disposal of both IERW and BBD can be reduced. Finally,
the chemical
composition of the resulting sludge from this water treatment process was
analyzed to explore
the feasibility of resource recovery.
During experimental trails, two BBD water samples (BBD-1 and 13BD-2) with
varying dissolved
organic content were used. The IERW and BBD were used as a self-coagulant to
treat the
combined stream. The characteristics of BBD samples and IERW are presented in
Table I.
Additionally, another BBD wastewater sample was prepared by increasing the pH
and silica
concentration of the boiler feed water. The properties of the synthesized BBD
(BBD-2) are
written in Table 1.
Table 1: The properties of BBD-1, IERW and BBD-2 water at room temperature.
BBD reported
Parameter Unit IERW BBD-1 BBD-2 in
literature
[1,2]
TDS ppm 66625 375 6525 25 2212 35 4026-17200
pH 6.20 0.11 11.66 0.01 11.60 0.10 10.50-
12.33
Turbidity NTU 0.25 0.05 0.86 0.06 0.20-53
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UV absorbance at 254 -
- 0.07+0.01 0.72+0.04 0.55-0.87
nm
SUVA254 - 1.04+0.15 0.77+0.08 - 2.75-5.21
TOC ppm 6.71+0.07 92.12+0.11 274+2.40 695-2482
Silica ppm as SiO2 5.22+0.48 77.60+1.50 165+0.13 65-
238
Magnesium ppm 2201+351 0.24+0.03 57.3+1.10 0.68-0.08
_
Calcium ppm 9455+1059 2.97+2.59 310+2.20 4.25-4.80
Sodium ppm 22165+3244 1806+130 1830+59 819-5199
Chloride ppm 80650+4203 40 6 - 494-6715
Sulfate ppm 320+57 1230+310 - -
In order to analyze the coagulation process, a few measurable variables were
selected for the
chemical process. The control factors and the selected levels for this design
are provided in Table
2. These control factors were chosen based on the common industrial practices
to treat the
wastewaters using chemical coagulant. For all of the experiments, the mixing
(coagulation) and
precipitation time were 30 minutes. According to these variables, a total
number of sixteen runs
were conducted for this work. For all of the experiment, the response
variables considered were
turbidity, silica concentration and total organic carbon (TOC).
Table 2: Full factorial design factors and levels
Levels
Factors Unit
-1 1
IERW to BBD ratio Volumetric ratio (IERW:BBD) 1:12 2:12
Temperature C 40 80
The speed of the stirring rpm 0 60
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2.1.1 Removal efficiency analysis of treated water
Figure 1 presents the removal percentage of TOC and silica for different
experimental trials after
the chemical treatment. Based on this figure, the removal percentage for
silica varied from
97.77% to 99.44% and the removal percentage for TOC was from 78.64% to 83.22%.
The
removal percentages were obtained by comparing the initial value of the
parameters in the BBD-
1 to the treated supernatant samples. The mean removal percentage of all eight
runs for TOC and
silica concentration was 81.06% + 0.82% and 98.63% 0.61%, respectively.
Therefore, using
the IERW for the BBD-1 treatment resulted in a high removal percentage of
organic matter and
silica concentration for all of the experimental runs.
100 , ____________________________________ 86
. 0 Slime Removal (%) - 85
TOG Removal (%) -
ci
0¨...
i 0
.-.9et. .
41
¨ 41µ 1 41 -83 ;52;
0
0 A 4
tX Ce
cz 98.6 - + -80
0
(.)
98 - ' _________________ ' 76
1 2 3 4 5 6 7 8
Experimental Run
Figure 1: Removal percentage of silica and TOC for all of the experimental
trials
The characterization of the supernatant samples from the chemical treatment
process indicated
that the treated water had a low concentration of magnesium, organic matter
and silica ions.
However, in the supernatant samples, the concentration of calcium and sodium
increased
significantly after the treatment. Since the calcium concentration varied
based on the IERW
dosage, the average concentration of calcium was presented based on the two
different dosages
of the IERW, 598 and 1102 ppm for the lower and higher dosages of IERW,
respectively.
8
CA 3053050 2019-08-26
The turbidity varied from 1.1 to 17.3 NTU for different runs. This result
indicates a noticeable
change in the results for different conditions indicating a significant effect
of the controllable
parameters on the turbidity of the treated water. The significance of the
different factors is more
evident when comparing run 1 and 8 since all of their factor levels are
different. This is because
after adding the coagulant, the silica and organic matters were removed from
dissolved phase,
but the formed flocs were not precipitated in the given time and remained
suspended in the
supernatant phase; the turbidity measurements confirm this explanation.
Based on the variation of the turbidity and the design factors, the optimized
level for each
parameter can be estimated. For temperature, removal efficiency was highest at
80 C, and the
removal was higher when the IERW and BBD-1 were mixed for 30 minutes at 60
rpm.
Furthermore, increasing the dose improved the flocculation and precipitation
so 2:12 volume
ratio is recommended coagulant dose to achieve better water quality.
2.1.2 Industrial by-products
The treatment of BBD-1 with IERW lead to coagulation followed by sludge
formation and water
recovery. The physicochemical characterization of the precipitated flocs was
further performed
to explore resources recovery from the sludge waste. The produced sludge after
IERW treatment
was analyzed using SEM, EDX, FTIR, XPS and XRD techniques. SEM and EDX
analyses show
the morphology and composition of the sludge residue (Figure 2 (a), (b) and
(c)). The SEM
micrographs show continuous amorphous phase with the semi-crystalline domain,
and an
average size of the particles, which was about 5 gm. The elemental composition
of the sludge
was obtained from the EDX analysis include Ca, Mg, Cl, Si, Na, 0 and C. It was
demonstrated
that the concentration of Mg and Ca was high in the precipitated solids. This
result shows that
particles were entrapped by magnesium due to flocculation mechanism, which
confirms the
silica and organic matter removal by using the IERW as the coagulant [46-49].
In order to identify the major chemical species and functional groups present
in the sludge, FTIR
analysis of the solid precipitates were performed which is demonstrated in
Figure 2 (d). The peak
at 1007 cm-1 can be attributed to the Si-0 band and the peaks from 1156-1200
cm-1 can be
assigned to silica bonding. The 1631 cm-1, 650 cm-1 and 3398 cm-1 bands can be
the
characteristics of bending vibration of 0-H. The 874 cm-1 peak observed at the
low-frequency
region can represent Mg-0 vibration. According to literature, peak at 1447 cm-
1 with high
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CA 3053050 2019-08-26
intensity can be due to the presence of C032- [18,50,51]. Therefore, FTIR data
are in agreement
with EDX results suggesting the existence of Mg, Ca and Si in the precipitated
sludge.
x103
re ' , = 1r 4 ,
it
µ. 4 - Mg 11=111C21
C 24,10
I
t 0 37,81
3 -
13.09
C CI 16.63
..,
21 '
1 2 - Ca 6.31
0 i
* , 17 a IIIL SI 2.03
0.4
, ' =µ,,,,,\ s C r
':11t:1'1.,7:111, Si
it) Ca
_
0 10 pm ¨ 0 1 2 3 4 5 6 7 8
x10-2 Energy (keV)
3398
8.
40.,.,.........-si 1447
Itii, 7 = 6 .
M i' 1631
4
.10- iit allip '`. ch 650
4. 874 11156 .1'.
.41001/4 w
. 1 43 i 1086
A = , 1007
2-
41
i 'A*
i
0- .
ci 500 1000 1500 2000 2500
3000 3500
b 2 pm ¨
Wavenumbers (crril)
Figure 2: SEM, EDX and FTIR analysis of the precipitated sludge obtained after
the treatment of BBD
water with IERW. Representative SEM images with a magnification of a) 100x, b)
330x, and c) EDX
results. (d) Representative FTIR spectra of precipitated sludge obtained after
the treatment of BBD water
with IERW.
To further investigate the elemental composition of the precipitated sludge
and their ionic state,
XPS analysis was performed. Figure 3 shows the XPS survey spectrum of the
precipitated sludge
and the high-resolution spectra of Ca 2p and Mg 2p. The peaks in the survey
spectrum were
assigned to Ca, Mg, Si, Na, Cl, 0, S, and C in the solid sample. The peak at
167.3 eV in the
survey indicate oxygenated sulfur species, possibly ¨SO4. These results are in
agreement with
CA 3053050 2019-08-26
EDX, FTIR and removal percentages. Furthermore, different atomic percent of
these elements,
given in Figure 3 (a), confirms the precipitation of corresponding compounds
after the chemical
treatment. Figure 3 (b) shows the high-resolution spectra for Mg 2p with a
peak binding energy
around 50.0 eV, which is close to those reported for magnesium hydroxides in
the literature.
These results shows that magnesium was mostly precipitated as magnesium
hydroxide [52]. The
Ca 2p high-resolution spectra clearly shows well-defined peaks at 351.0 eV and
347.5 eV
corresponding to 2p 1/2 and 2p 3/2 respectively with a peak area ratio of 1:2.
The Ca2+ chemical
shifts between various compounds (e.g., sulfates and carbonates) fall within a
small range (<
1 eV), so it is not possible to identify the nature of Ca2+ compounds from XPS
data alone.
Therefore, XRD analysis was performed on the sludge samples as the diffraction
data can be
used as fingerprints for sample identification.
The XRD pattern of the precipitated sludge collected after the treatment of
BBD water with
IERW is given in Figure 4. The presence of CaSO4, Mg(OH)2, CaCO3 and NaCI were
identified
after fingerprinting the standard spectra of these compounds with the XRD
pattern of the sludge.
The XRD results further confirm the EDX, FTIR and XPS results and show
successful
sedimentation of BBD-1 water in the presence of IERW coagulant. Moreover,
based on the
presence of calcium sulfate, which is considered as an industrial product, it
can be concluded that
this sludge has the potential to be used as a by-product through the
extraction of calcium sulfate.
11
CA 3053050 2019-08-26
55
_______________________________________________________________________________
_
x103
20 __________________________________________________________ Mg 2p a
ca as 50-
I Element Wt.% if
li
. ! i i
i i
Ma ls (6 45 .
Z i
i
1 C 34.16 z
! i
16 ..! 0 1
4
(,) 40 = 1 1 , 0 27.06 1.
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Na Nu CI V
12 16.68
0 -
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M 56 54 52 50 48 46
0 ' Ca 2p I
CI S2p i Mg 5'9
0 L) ,0010111 Binding
energy (eV)
8 Ca 2s 9 is i
Na 5.24 Ca 2p 3,2
, 'r 4 SI 1.71 450- Ca 2p
A
Mg 2p 400 -
4 = O. pi.
-.
:
. .
Si 21, 350 - !
=
8
300 -
1000 800 600 400 200 0 -200 ,..4
250 ===',
Binding energy (ev)
= 354 352 350 348 346
0 ID Binding energy
(eV)
Figure 3: XPS analysis of the precipitated sludge. (a) XPS- survey spectrum of
the precipitated sludge
showing component elemental peaks identified and their relative abundance. The
high-resolution XPS
spectra for Mg 2p and Ca 2p are shown in (b) and (c), respectively.
12
CA 3053050 2019-08-26
Evaporated sludge
129000 = Halite - NaCI
Brucite - Mg(OH)2
Anhydrite - CaSO4
C
886000 Calcite - CaCO3
43000 -
0
I
I Ii i
. .
. I . I . .1 .1 Al I . I L. E. I I .
0 10 20 30 40 50 60 70 80 90 100
Two-Theta (deg)
Figure 4: XRD Powder pattern of the dried sludge indicating the presence of
different crystal
patterns in the slurry phase
2.1.3 Softening of BBD after IERW coagulant treatment
Table 3 shows that the concentration of calcium after the coagulation process
by the IERW and
BBD-I mixing is high. If the supernatant would be recycled, this hardness can
reduce the
efficacy of the SAGD plant by causing scaling on the pipes, exchangers and the
boilers. Thus,
soda softening was applied to remove the abundant calcium ions from the
produced supernatant.
For this purpose, the supernatant of the most efficient run (run 8) was
extracted from the mixture
solution. Based on the IC analysis, the concentration of the chloride and
sulfate in this solution
was 10990 ppm and 1030 ppm, so presumably, most of the remaining calcium in
the solution is
in the form of non-carbonate hardness (permanent hardness) such as CaSO4 and
CaCl2. This
13
CA 3053050 2019-08-26
observation also demonstrates that the coagulation process significantly
increased the chloride
concentration of the BBD-1 however, the concentration of sulfate decreased
presumably due to
the formation of calcium sulfate. Soda ash (sodium bicarbonate) was chosen to
remove calcium
ions from the solution because this coagulant has high efficiency in the
removal of permanent
hardness from water. For this purpose, 5 g of soda ash was added to 1 liter of
supernatant with
the same experimental method as the run 8. This dosage was selected based on
some primary
experiments, which analyzed the hardness removal at a different dosage of soda
ash.
After the sedimentation, the solution was analyzed for calcium removal. The
properties of this
solution are provided in Table 3. From this table, it can be observed that the
concentration of
calcium decreased from 1084 ppm to zero ppm, but the sodium concentration
increased from
4397 ppm to 6973 ppm. This result shows that after the two treatments, almost
all of the
hardness was removed. It is worth noting that in a SAGD plant, the volume of
BBD is only a
portion of the BFW; the volumetric ratio of BBD used in this study was about
10% of the BFW.
It can be said that in the industrial practices, the treated BBD will be mixed
with the BFW before
entering the boilers. Therefore, the treated BBD-1 in this study can be
diluted almost ten times
and then be reused as the BFW. Thus, after dilution, the treated water will
have an acceptable
concentration range of TDS and sodium too. This provide an opportunity to use
a lower volume
of fresh water for the boilers.
Table 3: Comparison of the properties of the supernatant after soda softening.
Supernatant before soda Supernatant after soda
Parameter Unit
softening softening
Calcium ppm 1084 0
Magnesium ppm 1.29 0.01
Sodium ppm 4311 6973
pH 10.75 10.96
TDS ppm 11350 16665
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2.1.4 Applicability of IERW as a coagulant in the treatment of wastewaters
In order to assess the treatment efficiency of IERW with other types of
wastewater, a BBD-2
sample with a higher concentration of organic matter was treated with the IERW
coagulant (see
Table 1). IERW water was added to the BBD-2 sample with the same experimental
conditions as
run 8. In this experiment, three different dosages of IERW was used for the
treatment of BBD-2,
and the precipitation of the mixture solution was observed for 1 hour. Figure
5 shows the effect
of using different dosages of IERW for the treatment of the Athabasca BBD-2.
It can be seen that
high silica and organic matter removal were achieved and the color of BBD-2
became lighter
after the treatment with IERW due to the removal of organic matter. An
increase in the IERW
dosage shows higher removal of TOC and silica, possibly due to the presence of
more
magnesium ions. These results confirm that the precipitation of the magnesium
hydroxide was
effective in removing the silica particles and organic matters in the BBD-2 by
the coagulation-
flocculation process.
100 __________________________
Silica removal IP
90 __ TOC removal
IP 1111,
, P442,
r 7 ,
-
o>
E 50 =
cc
40 -
= ,
2 12 4 12 6.12 (a) (b) (c) (d)
IERW/BBD water volume ratio
Figure 5: Demonstrate the treatment of BBD-2 water using IERW as coagulant.
The silica and TOC
removal percentages using IERW for the treatment of BBD-2 are depicted in the
graph. The solution
labelled (a) is BBD-2 and the (b), (c) and (d) represent the mixture solution
after sedimentation with 2:12,
4:12, 6:12 IERW/BBD volumetric ratio, respectively.
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2.1.5 Highlights of IERW conditioning
In the present work, a systematic study has been conducted to investigate the
feasibility of using
IERW as a coagulant for the treatment of BBD and vice versa. It was observed
that the IERW is
capable of reducing some major impurities. These contaminants can be
responsible for reducing
the plant water recycling and efficiency of the OSTG, from the BBD and this
takes into account
not only the silica removal but also the organic matter presented in the BBD.
The efficiency of
silica and TOC removal is 98.72% and 81.34%, respectively, which can be
considered effective
in a chemical treatment process. The turbidity measurements indicate that when
the temperature
decreased from 80 C to 40 C, the number of settled particles was reduced.
Moreover, it was
observed that using mixing and increasing the temperature and dosage of the
IERW improved
the flocculation process significantly and larger flocs were formed and
precipitated. However,
the concentration of calcium increased after this treatment; this problem was
solved by using
soda ash softening process to remove the calcium from the solution. The sludge
characterization
supported the hypothesis of silica and organic matter removal by coagulation-
flocculation of
magnesium hydroxide. The usage of IERW was found to be effective for the
treatment of
Athabasca BBD. Therefore, even by considering the usage of a softening
treatment, this process
can be practiced reducing the extensive use of fresh water for BFW and
eliminate the operation
cost of disposal well plugging.
2.2 Integrated Coagulation-Membrane Processes with Zero Liquid
Discharge (ZLD) Configuration for the Treatment of Oil Sands
Produced Water
In this section, different membrane-based separation scenarios were examined
to reduce the TDS
concentration of the IERW-treated BBD water. The primary goal was to convert
SAGD BBD
water, composing high concentration of TOC, TDS, and silica into high-quality
feed water for
reuse in boilers. The efficiency of the proposed separation scenarios was
assessed based on
permeation performance and fouling properties. Accordingly, different membrane
processes
were compared to nominate an economically feasible module for the treatment of
the BBD
water.
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According to table I, the sample BBD water (BBD-1) had a high concentration of
silica and
organic matter. The IERW contained a high concentration of calcium, magnesium,
chloride, and
sodium.
2.2.1 Coagulation-Membrane Hybrid Processes
Five coagulation-membrane hybrid processes were evaluated to treat BBD water.
The chemical
coagulants were either IERW or soda ash solutions or a combination of both.
Figure 6 illustrates
the treatment processes in a schematic flow diagram. The details of each
process are as follows:
Process-1: In the first process, the BBD water (Feed-1) was treated by NF in
order to evaluate
the capability of a single filtration step with a 50% water recovery. The
permeate solution was
named BFW-1.
Process-2: In the second process, the concentrate solution (Retentate-1) of
process-1 was treated
by IERW (IERW conditioning). The details about this pre-treatment are provided
in the previous
work [38]. In summary, the chemical pre-treatment was conducted by adding IERW
as a
coagulant to BBD water at a 2:12 (IERW:BBD) ratio. The mixture solution was
stirred for 30
min at 60 rpm followed by 30 min of sedimentation. Afterward, the supernatant
was decanted
and sent to NF unit as Feed-2. The permeate solution after NE was labeled as
BFW-2.
Process-3: In the third process, the BBD water was first pre-treated by IERW.
The supernatant
(Feed-3) was sent to the NF unit. The resulting permeate solution was called
BFW-3.
Process-4: After IERW-conditioning, most of the organic matter and silica
particles were
removed from the BBD water, but the concentration of the dissolved calcium
ions increased
significantly. In order to remove the calcium ions, the IERW-treated 13I3D
water was further pre-
treated using soda ash in the fourth process [39,40]. 5000 ppm of soda ash was
added to IERW-
treated BBD water. After 30 min mixing at stirring speed of 60 rpm, the
supernatant was sent to
the NF unit as Feed-4. The permeate solution after NF was labeled as BFW-4.
Process-5: In the final process, IERW was used as a draw solution to recover
water from BBD
solution in an FO process. The IERW contained a high concentration of sodium
chloride (see
Table 4) that can potentially provide high osmotic pressure for the FO
application [15].
Afterward, the diluted IERW was sent to NF unit as Feed-5. The resulting
permeate solution was
called BFW-5.
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Table 4 presents the properties of the Retentate-1 and Feed-1 to Feed-5
solutions, which were
labeled based on the schematic flow diagram in Figure 6.
- ' - BBD Water
=
41 ' Retentate-1
, I Feed
N t pk,..
_________________ OP 1ERW
conditioning !UM
con ,... ditioning riw,
_....._õ,,,,,... - ,
I
F0
Permeate V I Draw
1 = 1t
, Feed-1 ' Feed-2
Feed , ,..,
Feed Soda Ash
i Softening
"
, -
Permeate Permeate
1
f li Feed-ii% ,- - - -
-- - -- ------,
t Feed-4
Feed . Feed'I
.._ =
bill'N I NF
, -
Permeate Permeate
BFW-1 BF W-2 , BFW-3 BFW-4 BFW-5
i
, , . ,,,, ., $ . ,., .. ..
.,
, ,
Process-1 Process-2 Process-3 Process-4 Process-
5
Figure 6: Schematic flow diagram of coagulation-membrane processes for the
treatment of steam assisted
gravity drainage (SAGD) BBD water.
Table 4: Properties of different feed solutions in coagulation-membrane hybrid
processes.
Parameter Unit Retentate-1 Feed-1 Feed-2 Feed-3 Feed-4 Feed-5
TDS ppm 8500 6525 16,750 11,350 16,665 34,535
pH - 10.90 11.66 11.60 10.75 10.96
6.20
Turbidity_ NTU 0.90 0.86 1.20 1.40 1.80 0.80
TOC ppm __ 443.30 229.80 107.70 17.00 16.60
3.00
Silica as dissolved ppm 111 77.60 3.17 1.43 0.93
3.00
mg2-, ppm 0.16 0.24 0.07 1.29 __ 0.01 1131
Ca2+ ppm 2.78 2.97 3.82 1084 0.00
5325
Na + ppm 3975 1806 8069 4311 6973 11,436
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The nanofiltration (NF) was performed using NF90 (DuPont Water Solutions
(FILMTECTm))
membrane. The forward osmosis (FO) experiments were conducted by a commercial
thin film
composite (TFC) polyamide membrane, which was purchased from Hydration
Technology
Innovation (HTI, Albany, NY, USA).
2.2.2 Comparison of Different Hybrid Processes
Figure 7 presents the total flux decline, flux recovery ratio, and TDS
rejection of different
processes after the nanofiltration unit. These parameters were considered to
select the most
efficient process for the treatment of the BBD water. The total flux decline
ratio demonstrates the
efficiency for achieving a higher volume of the treated water under similar
transmembrane
pressure, and the flux recovery ratio is a measure of the fouling resistance
of the membrane. The
process-1 and process-2 showed a TOC removal rate of 90% and 92%,
respectively. Among all
the processes, process-3 showed the lowest performance with high DRt (93.4%)
and low FRR
(69.7%). Process-5 can also be eliminated from the candidate pool as the
transmembrane
pressure for this process was elevated to 350 psi, and the permeate flux
declined about 96.2%.
The three remaining processes (1, 2, and 4) showed an almost identical flux
recovery ratio above
97%. Among these three processes, process-2 showed lower performance with
higher flux
decline and lower TDS rejection. Process-4 showed a lower flux decline (about
3.5%) than
process-1, suggesting that this process can be chosen if a higher permeation
rate is the selection
criterion. However, if higher TDS removal is required, process-1 was more
efficient than
process-4 with 10% higher TDS rejection percentage.
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100 - [7 / DRt N\,.. ERR Li TDS Removal
. 7 7
,f
90 - __
...---, \ \:\
...,0
.......-
C13 ,
.4¨.
= . ;
(1) ',.;,;';;0 77
C.) õ
1 . .,,,i,'4; 0 \s\s: 1.'
" 70 -
a) ,.
,
t ,:,.'''''';
\':, ,
7 ,'
a. :,..i \ ,,
, I
> ',i:, .
,,,, , \ N
60 - \ l';',,
.1..:-. :;..,
:: :
,, i
,v< .
/) \, '..,.\\ I
50 /iv
Process-1 Process-2 Process-3 Process-4 Process-5
Figure 7: Comparison of total flux decline (DRt), flux recovery ration (FRR),
and total dissolved solids
(TDS) removal of different processes.
2.2.3 Optimized hybrid process
The present study evaluated different chemical-membrane hybrid processes for
the treatment of
BBD water in order to be reused as BFW. It was found that a direct treatment
of BBD water
using single-stage nanofiltration could result in the highest TDS removal from
the feed solution.
Although a flux recovery of 97% was obtained after simple hydraulic washing,
the high flux
decline (-90%) was the notable adverse side of the direct NF treatment of BBD
water. This
observation emphasizes the necessity of chemical treatment prior to the
membrane filtration unit
for such industrial waters. Application of dual chemical pre-treatment using
IERW and soda ash
solutions resulted in the highest permeation rate with lowest flux decline and
highest flux
recovery, demonstrating a potential solution to the fouling issue, which was
also observed in
other works that treated SAGD produced water with one-stage membrane
separation processes
[6,7,15]. Additionally, the IERW conditioning only uses a waste stream as the
coagulant
CA 3053050 2019-08-26
minimizing the operating expanse of chemical coagulant. However, lower TDS
rejection
compared to direct NF treatment (70% compared to 80%) can be mentioned as the
main
drawback of this process. In overall, a combination of these two processes
could be used as a
zero-liquid discharge (ZLD) scheme by reusing the waste products in different
applications. For
instance, the produced sludge from the IERW conditioning unit can be used for
extraction of
calcium sulfate, which is used as a direct additive in many applications such
as cement, water
treatment, and food industries. Moreover, the concentrate solution from the NF
of soda ash
treated water can be potentially used as a regeneration solution for the ion
exchanger as it
contains a high concentration of sodium ions. For future work, different types
of membrane
filtration such as RO or UF can be studied to achieve a higher efficiency or
to provide a higher
quality BFW for the boilers. Moreover, different levels for the operating
conditions and other
types of solutions for hydraulic backwashing can be selected in order to
recommend an
optimized condition for the hybrid process.
3 References
[1] G. Hurwitz, D.J. Pemitsky, S. Bhattacharjee, E.M.V. Hoek, Targeted
removal of dissolved
organic matter in boiler-blowdown wastewater: Integrated membrane filtration
for
produced water reuse, Ind. Eng. Chem. Res. 54 (2015) 9431-9439.
doi:10.1021/acs.iecr.5b02035.
[2] R.G. Pillai, N. Yang, S. Thi, J. Fatema, M. Sadrzadeh, D. Pemitsky,
Characterization and
comparison of dissolved organic matter signatures in steam-assisted gravity
drainage
process water samples from athabasca oil sands, Energy and Fuels. 31(2017)
8363-8373.
doi:10.1021/acs.energyfuels.7b00483.
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