Mahboobin 10:00
L07
GRAPHENE DESALINATION AND ITS IMPACT ON HUMANS, THE
ENVIRONMENT, AND THE EARTH
Sam Cooke ([email protected])
INTRODUCTION
Over the past several decades, we have seen a tremendous
growth in the size of the human population. There is no sign
of this population growth slowing down, and due to this fact
there is an ever-increasing demand for basic resources, one of
which being water. It is reported by the Center for Disease
Control that 780 million people lack access to improved water
sources, which include protected wells, piped household
connections, and rainwater collection [1]. Many more do not
have access to sanitary facilities due to the poor infrastructure
in developing nations.
One way to solve this problem is by taking advantage of
the abundance of salt water found around the world by using
desalination so that it can be converted to fresh water and used
safely for everyday uses. Desalination is the process of
filtering salt out of seawater so that fresh water is produced.
The traditional method of desalination involves applying a
high pressure to a membrane designed to separate water and
the unwanted pollutants such as salt. This is called reverse
osmosis, and the problem with implementing this technology
in third world nations is that they commonly do not have
access to the power, resources, or infrastructure required to
operate a water desalination plant. However, with new ideas
for water desalination on the horizon, it may be possible to
use this technique to help meet the demand for water
worldwide. Reverse osmosis filters are slow and the
membrane can become contaminated after filtering large
amounts of water. However, by using graphene, an incredibly
strong material, water can be filtered through extremely small
pores. This could be thought of as the same method that
everyday coffee filters use, only at the nano scale. Due to
graphene’s toughness, the membrane for water to pass
through can be extremely thin and water can be desalinated
easily and quickly compared to reverse osmosis methods of
purification, which would require much more pressure to
force water through the membrane. We must make it a priority
to solve the problem of water shortages and make this
technology more accessible, because an estimated 801,000
children under 5 years old die from diarrheal disease every
year, and innovations to provide sanitary water sources could
lessen the amount of these deaths [2]. Using this technology,
we could considerably decrease this number to ensure that
every one of us has access to clean water and does not have
to risk their health every time they drink.
GRAPHENE NANOPORE DESALINATION
University of Pittsburgh, Swanson School of Engineering
2014-10-28
Instead of using an inefficient method such as reverse
osmosis for water filtration, we could use a new method that
involves pores narrower than a nanometer. By using nanopore
filtration methods, water molecules can pass through the
graphene membrane while the membrane stops the salts that
try to make it through. To do this, we would utilize graphene.
Graphene is a material consisting of carbon atoms arranged in
a hexagonal lattice, and has a variety of applications in many
fields of engineering and science due to its unique properties.
It is incredibly strong and is only one atom thick, while having
a crystal lattice structure that can be modified using other
chemicals. This makes it ideal for water desalination because
the thickness and versatility allows it to be fine-tuned to allow
only
water
molecules
pass
through.
FIGURE 1 [3]
This graphene nanopore seperates water molecules and salt
molecules
Due to water molecules’ small size compared to salt
molecules, we can change the membrane so that it has pores
that are a specific size that is large enough for water molecules
Sam Cooke
of the nation’s potable water is obtained through desalination
plants [7]. If other nations that cannot harvest clean
groundwater effectively begin using desalination as an
alternative, they will need a way to dispose of brine so that it
does not seep into the groundwater and harm agriculture and
ecosystems that rely on nutrient-rich soil and clean water.
to pass through but small enough so that the salt molecules
cannot, as shown in Figure 1. With such a thin membrane with
so many pores, permeability of the membrane increases,
indicating that water is able to flow through it more easily and
quickly than a polymeric membrane. According to
researchers at MIT, this technology allows for membranes
with a permeability 50 times greater than traditional
membranes, speeding up the desalination process
considerably [4]. Because of this, a graphene membrane
would not require as much pressure and therefore not as much
power to operate. The energy savings could be reduced by
46% compared to a reverse osmosis method for treating
brackish water [5]. This could make it more feasible with a
community without access to large amounts of power to
implement. The benefits of this technology would be
tremendous; David Cohen-Tanugni and Jeffrey Grossman at
MIT indicate that nanopore desalination can yield 66 L per
cm2 * day * MPa, compared to only about 0.01-0.05 L per
cm2 * day * MPa which is the typical output of reverse
osmosis desalination. Graphene desalination is something
that would be a big step in the field of water treatment and
purification, and could have a major impact on the global
demand for water.
BRINE WASTE DISPOSAL
In the future, I find myself working at a company on a
project that will patent a product based on this graphene
desalination method to be used around the world. One major
problem that faces the project and its production is the
disposal of the waste product produced. Our biggest investors
are well aware of the potential harm caused by the use of our
product, if actions are not taken to dispose of brine waste
properly. At the last meeting we held to show our investors
our product’s progress, they were very adamant that they
would not continue to support this technology financially if
we did not have a plan for effectively disposing of the brine
in an environmentally-friendly manner. In order to address
this issue, we decided to ship storage tanks to the consumers
which would attach to the filter and would hold the brine
produced during desalination. We also set up a plan for
periodically shipping the brine-filled tanks back to our
facility. We would be able to dispose of it in a manner that
does not endanger marine life and does not pollute the
groundwater of other communities.
The project manager, John, already unhappy with the fact
that we’ve had to delay the release of the product because of
this, wants to build a facility on the coast where the brine
could be pumped into the ocean. The way it would work is by
utilizing a pipe underwater that brings the brine away from
the shoreline to be pumped so that it would not stay at the
coast and cause harm to the coast’s water quality, and would
not make its way into the soil and the groundwater. Although
this solution is better than simply dumping it into the ocean
from the shore, it still causes harm. The rationale John uses is
that with there being so much sea water and so little brine, the
brine will be diluted enough so that it has negligible impact
on the overall salinity. The problem with this line of thinking
is that the brine does not instantaneously dissolve evenly into
a large volume of water; the location you release the brine will
have a much higher salinity than the surrounding water. As
stated previously, an alternative method would involve
mixing the brine with concrete to be used in roads. Another
option could be to dilute the brine with sea water before it is
pumped into the ocean, so that the brine has less of a
difference in salinity than the surroundings and the salt would
be pumped into the ocean at a decreased rate, which would
give it more time to mix with the sea water. John doesn’t want
to take either of these approaches, because according to our
projections for the amount of waste product produced, neither
of those methods will be able to keep up with the amount of
brine being produced.
PRODUCTION OF BRINE
There is one problem with using desalination on a large
scale: it produces brine, an extremely salty and polluted form
of water. Typical seawater contains 35 to 37 grams of NaCl
per liter of water, but brine can contain more than 60 grams
of NaCl per liter of water, which is well above the ‘comfort
zone’ which would be safe for many forms of underwater life
[6]. The average desalination plant can turns 55% of the
collected seawater into brine, which could potentially wreak
havoc on marine life if dumped into the ocean, and could
cause severe damage to any ecosystem near a site where it is
dumped [6]. This leads to another question we have to ask
ourselves as engineers: what precautions must be taken to
ensure that the emergence of this technology minimizes harm
to the environment? One method of accomplishing this task is
to use the brine water in the production of saltcrete. Saltcrete
is made when concrete or asphalt is mixed with brine in order
to stop the brine from leaking into groundwater or streams.
This material can then be used to make roads, and would be
an effective way to both stop the waste from contaminating
ecosystems and recycle it for a useful cause. Another way of
reducing the harm caused by the desalination process is to
perform reverse osmosis on the brine, which would result in
clean water and super concentrated brine. This would then
allow us to dry the brine and sell the salt that results from this.
Not only would this method find a better use for the salt than
being dumped, but it would turn a profit which could help pay
for the power required to operate a desalination plant. An
example of a place in the world where the problem of brine
disposal is a pressing issue is in Saudi Arabia, in which 70%
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Sam Cooke
At our next meeting with our investors, he is going to
assure them that the way we will be disposing of the brine will
not have a negative impact on marine life in any way. John
firmly believes that the small amount of brine compared to the
large amount of seawater will not have any noticeable impact
on underwater ecosystems near the dump site. This places the
engineering team, myself included, in a very tough position.
In our contracts, we agreed that we would not disclose
information regarding the project without the project
manager’s consent. There are lots of factors to take into
consideration while making a decision on what to do. We
desperately need our investors support in order to fund this
project, so if we were to disclose the fact that we plan to dump
brine into the ocean, we would need to delay completion for
several months at least, until we can find another method of
dealing with the waste. As stated in the American Society of
Mechanical Engineers’ code of ethics, as engineers, we need
to minimize harm to the environment and “consider
environmental impact in the performance of their professional
duties” [8].
However, we also need to look at the situation from a
purely ethical standpoint. Should we delay this product
further by taking the environment into consideration, at the
cost of delaying the desalination of water for people who
desperately need clean water? This ethical problem begs the
question: is it better to risk more people dying of thirst, or to
destroy a variety of undersea ecosystems by using
unsustainable methods? To decide on the latter by pumping
brine into the ocean would demonstrate speciesism, which is
defined as “a bias in favor of one’s own species” [10].
Examples of this can be seen everywhere in human society,
such as how we kill animals for food. This is not normally
considered morally wrong by society, but it can be
questionable when it comes to damaging the Earth which
could have a negative impact on future generations. Doing so
would also violate the ASME code of ethics which states that
engineers shall act “as faithful agents or trustees, and shall
avoid conflicts of interest of the appearance of conflicts of
interest” [8]. As the engineers responsible for the
development of the development this product, it is part of our
responsibilities to ensure that harm to the environment is not
caused by something we have helped create, which is stated
in the second professional obligation of the National Society
of Professional Engineers’ code of ethics [9]. My team and I
meet to discuss possible courses of action for dealing with this
situation in a professional manner, and come to the conclusion
that we will meet with John and inform him that he is being
untruthful to our investors, and that serious legal
consequences could occur if our company went forward with
our current plan. Our reasoning behind this plan is that
although it will take longer for the product to be completed, it
is better to wait for a more sustainable method to become
available so that we do not have to redesign this product in the
future to lessen our impact on the environment, after damage
has already been done.
CONCLUSION
I would advise any engineers who find themselves in a
similar situation to talk to the project head and inform him or
her of the consequences of the course of action being taken.
We need to make it a priority to preserve the Earth and its
resources with sustainable development. This situation is a
good example of how we need to take many very different
factors into account when making important decisions that
have an impact on people and the environment. If we
disregard the environment while designing solutions to the
world’s problems, damage will be done before we eventually
make the decision to make the technology sustainable. My
engineering instructor in high school, Michael Boyer always
lectured us about ethics and professionalism and would teach
us that being honest and professional may not be the most
popular decision among your teammates or employers, but
integrity comes before all. My mother is also a very strong
advocate for sustainable development and preserving the
environment while progressing technologically, and she
would choose to take action to help stop the degradation of
the ocean and the life that inhabits it. As engineers, it is our
duty to help people around the world with our ideas, and to
also make sure that they do not leave a negative mark on the
world. This way we can work toward a world in which we can
help our fellow human beings as well as our home, the Earth.
REFERENCES
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Sam Cooke
Single-Layer Graphene Membranes.” Nano Letters. (journal
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ADDITIONAL SOURCES
M. Boyer. (2013). Lecture.
[5] D. Cohen-Tanugi, R. K. McGovern, S. H. Dave, J. H.
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L. Hubbard-Cooke. (2014). Conversation.
ACKNOWLEDGEMENTS
I would like to thanks Ben Stutz and Jay Murray for
discussing ideas on what to write about. I would also like to
thanks my parents for supporting me in all my endeavors and
my high school engineering teacher Mr. Boyer for helping
inspire me to pursue engineering.
[6] M. Meneses, J. C. Pasqualino, R. Cespedes-Sanchez, and
F. Castells. (2010). “Alternatives for Reducing the
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article). DOI: 0.1111/j.1530-9290.2010.00225.x
[7] V. Badescu, A. Ciocanea, R. B. Cathcart, and C. W. Finkl,
et al. (2013). “Desalination Brine Disposal by Submerged
Pipes in the Red Sea.” Journal of Coastal Research. (online
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www.onlineethics.org/Resources/Cases/Toxic.aspx
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salination_pros_and_cons_of_a_typically_thorny_issue.html
[13] R. Bucknam. (2002). “What’s the Angle? (Case 1010).”
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[14] National Society of Professional Engineers. (2013).
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