A circular economy for salt that keeps rivers clean
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0:01 - 0:03Growing up in northern Wisconsin,
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0:03 - 0:07I've naturally developed a connection
to the Mississippi River. -
0:07 - 0:08When I was little,
-
0:08 - 0:13my sister and I would have contests
to see who could spell -
0:13 - 0:16"M-i-s-s-i-s-s-i-p-p-i" the fastest.
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0:17 - 0:19When I was in elementary school,
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0:19 - 0:23I got to learn about the early explorers
and their expeditions, -
0:23 - 0:27Marquette and Joliet, and how they used
the Great Lakes and the Mississippi River -
0:27 - 0:30and its tributaries
to discover the Midwest, -
0:30 - 0:33and to map a trade route
to the Gulf of Mexico. -
0:34 - 0:36In graduate school,
-
0:36 - 0:38I was fortunate to have
the Mississippi River -
0:38 - 0:41outside my research laboratory window
-
0:41 - 0:43at the University of Minnesota.
-
0:44 - 0:47During that five-year period,
I got to know the Mississippi River. -
0:47 - 0:50I got to know its temperamental nature
-
0:50 - 0:53and where it would flood
its banks at one moment, -
0:53 - 0:55and then shortly thereafter,
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0:55 - 0:57you would see its dry shorelines.
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0:58 - 1:01Today, as a physical organic chemist,
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1:01 - 1:03I'm committed to use my training
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1:03 - 1:06to help protect rivers,
like the Mississippi, -
1:06 - 1:09from excessive salt
that can come from human activity. -
1:10 - 1:12Because, you know,
-
1:12 - 1:16salt is something that can contaminate
freshwater rivers. -
1:16 - 1:22And freshwater rivers,
they have only salt levels of .05 percent. -
1:23 - 1:26And at this level, it's safe to drink.
-
1:26 - 1:30But the majority of the water
on our planet is housed in our oceans, -
1:30 - 1:34and ocean water has a salinity level
of more than three percent. -
1:34 - 1:38And if you drank that,
you'd be sick very quick. -
1:38 - 1:43So, if we are to compare
the relative volume of ocean water -
1:43 - 1:46to that of the river water
that's on our planet, -
1:46 - 1:49and let's say we are able
to put the ocean water -
1:49 - 1:52into an Olympic-size swimming pool,
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1:52 - 1:57then our planet's river water
would fit in a one-gallon jug. -
1:57 - 2:00So you can see it's a precious resource.
-
2:00 - 2:03But do we treat it
like a precious resource? -
2:03 - 2:05Or rather, do we treat it
like that old rug -
2:05 - 2:08that you put in your front doorway
and wipe your feet off on it? -
2:09 - 2:13Treating rivers like that old rug
has severe consequences. -
2:13 - 2:15Let's take a look.
-
2:15 - 2:19Let's see what just one teaspoon
of salt can do. -
2:20 - 2:22If we add one teaspoon of salt
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2:22 - 2:25to this Olympic-size
swimming pool of ocean water, -
2:25 - 2:28the ocean water stays ocean water.
-
2:28 - 2:30But if we add that same
one teaspoon of salt -
2:30 - 2:33to this one-gallon jug
of fresh river water, -
2:33 - 2:36suddenly, it becomes too salty to drink.
-
2:37 - 2:38So the point here is,
-
2:38 - 2:44because rivers, the volume is so small
compared to the oceans, -
2:44 - 2:47it is especially vulnerable
to human activity, -
2:47 - 2:49and we need to take care to protect them.
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2:50 - 2:52So recently, I surveyed the literature
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2:53 - 2:56to look at the river health
around the world. -
2:56 - 2:59And I fully expected to see
ailing river health -
2:59 - 3:04in regions of water scarcity
and heavy industrial development. -
3:04 - 3:07And I saw that
in northern China and in India. -
3:08 - 3:12But I was surprised
when I read a 2018 article -
3:12 - 3:17where there's 232 river-sampling sites
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3:17 - 3:19sampled across the United States.
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3:19 - 3:21And of those sites,
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3:21 - 3:2537 percent had increasing salinity levels.
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3:25 - 3:27What was more surprising
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3:27 - 3:30is that the ones
with the highest increases -
3:30 - 3:33were found on the east part
of the United States, -
3:33 - 3:35and not the arid southwest.
-
3:35 - 3:38The authors of this paper postulate
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3:38 - 3:43that this could be due
to using salt to deice roads. -
3:44 - 3:46Potentially, another source of this salt
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3:46 - 3:50could come from salty
industrial wastewaters. -
3:50 - 3:55So as you see, human activities
can convert our freshwater rivers -
3:55 - 3:58into water that's more like our oceans.
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3:58 - 4:01So we need to act and do something
before it's too late. -
4:02 - 4:04And I have a proposal.
-
4:05 - 4:09We can take a three-step
river-defense mechanism, -
4:09 - 4:14and if industrial-water users
practice this defense mechanism, -
4:14 - 4:19we can put our rivers
in a much safer position. -
4:19 - 4:21This involves, number one,
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4:21 - 4:24extracting less water from our rivers
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4:24 - 4:28by implementing water recycle
and reuse operations. -
4:28 - 4:30Number two,
-
4:30 - 4:34we need to take the salt
out of these salty industrial wastewaters -
4:34 - 4:37and recover it and reuse it
for other purposes. -
4:38 - 4:42And number three,
we need to convert salt consumers, -
4:42 - 4:45who currently source our salt from mines
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4:45 - 4:49into salt consumers that source our salt
from recycled salt sources. -
4:50 - 4:53This three-part defense mechanism
is already in play. -
4:53 - 4:56This is what northern China
and India are implementing -
4:56 - 4:59to help to rehabilitate the rivers.
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4:59 - 5:01But the proposal here
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5:01 - 5:05is to use this defense mechanism
to protect our rivers, -
5:05 - 5:07so we don't need to rehabilitate them.
-
5:08 - 5:12And the good news is,
we have technology that can do this. -
5:12 - 5:13It's with membranes.
-
5:14 - 5:17Membranes that can separate
salt and water. -
5:18 - 5:21Membranes have been around
for a number of years, -
5:21 - 5:26and they're based on polymeric materials
that separate based on size, -
5:26 - 5:28or they can separate based on charge.
-
5:28 - 5:32The membranes that are used
to separate salt and water -
5:32 - 5:35typically separate based on charge.
-
5:35 - 5:38And these membranes
are negatively charged, -
5:38 - 5:40and help to repel the negatively
charged chloride ions -
5:40 - 5:43that are in that dissolved salt.
-
5:44 - 5:48So, as I said, these membranes
have been around for a number of years, -
5:48 - 5:55and currently, they are purifying
25 million gallons of water every minute. -
5:55 - 5:57Even more than that, actually.
-
5:58 - 5:59But they can do more.
-
6:00 - 6:05These membranes are based
under the principle of reverse osmosis. -
6:05 - 6:10Now osmosis is this natural process
that happens in our bodies -- -
6:10 - 6:12you know, how our cells work.
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6:12 - 6:16And osmosis is where you have two chambers
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6:16 - 6:19that separate two levels
of salt concentration. -
6:19 - 6:21One with low salt concentration
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6:21 - 6:24and one with high salt concentration.
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6:24 - 6:28And separating the two chambers
is the semipermeable membrane. -
6:28 - 6:30And under the natural osmosis process,
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6:30 - 6:34what happens is the water naturally
transports across that membrane -
6:34 - 6:36from the area of low salt concentration
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6:36 - 6:39to the area of high salt concentration,
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6:39 - 6:41until an equilibrium is met.
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6:42 - 6:46Now reverse osmosis,
it's the reverse of this natural process. -
6:46 - 6:48And in order to achieve this reversal,
-
6:48 - 6:53what we do is we apply a pressure
to the high-concentration side -
6:53 - 6:57and in doing so, we drive the water
the opposite direction. -
6:57 - 7:01And so the high-concentration side
becomes more salty, -
7:01 - 7:02more concentrated,
-
7:02 - 7:06and the low-concentration side
becomes your purified water. -
7:06 - 7:11So using reverse osmosis,
we can take an industrial wastewater -
7:11 - 7:16and convert up to 95 percent of it
into pure water, -
7:16 - 7:20leaving only five percent
as this concentrated salty mixture. -
7:21 - 7:24Now, this five percent
concentrated salty mixture -
7:24 - 7:26is not waste.
-
7:26 - 7:29So scientists have also
developed membranes -
7:29 - 7:33that are modified to allow
some salts to pass through -
7:33 - 7:34and not others.
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7:35 - 7:36Using these membranes,
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7:36 - 7:39which are commonly referred to
as nanofiltration membranes, -
7:39 - 7:43now this five percent
concentrated salty solution -
7:43 - 7:46can be converted
into a purified salt solution. -
7:47 - 7:52So, in total, using reverse osmosis
and nanofiltration membranes, -
7:52 - 7:54we can convert industrial wastewater
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7:54 - 7:58into a resource of both water and salt.
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7:59 - 8:00And in doing so,
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8:00 - 8:05achieve pillars one and two
of this river-defense mechanism. -
8:06 - 8:10Now, I've introduced this
to a number of industrial-water users, -
8:10 - 8:13and the common response is,
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8:13 - 8:16"Yeah, but who is going to use my salt?"
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8:16 - 8:19So that's why pillar number three
is so important. -
8:19 - 8:23We need to transform folks
that are using mine salt -
8:23 - 8:26into consumers of recycled salt.
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8:26 - 8:29So who are these salt consumers?
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8:29 - 8:31Well, in 2018 in the United States,
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8:31 - 8:36I learned that 43 percent of the salt
consumed in the US -
8:36 - 8:40was used for road salt deicing purposes.
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8:40 - 8:44Thirty-nine percent
was used by the chemical industry. -
8:44 - 8:46So let's take a look
at these two applications. -
8:47 - 8:50So, I was shocked.
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8:50 - 8:53In the 2018-2019 winter season,
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8:53 - 8:56one million tons of salt
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8:56 - 9:00was applied to the roads
in the state of Pennsylvania. -
9:01 - 9:03One million tons of salt is enough
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9:03 - 9:06to fill two-thirds
of an Empire State Building. -
9:07 - 9:11That's one million tons of salt
mined from the earth, -
9:11 - 9:13applied to our roads,
-
9:13 - 9:16and then it washes off
into the environment and into our rivers. -
9:18 - 9:21So the proposal here
is that we could at least -
9:21 - 9:25source that salt from a salty
industrial wastewater, -
9:25 - 9:27and prevent that
from going into our rivers, -
9:27 - 9:30and rather use that to apply to our roads.
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9:30 - 9:33So at least when the melt happens
in the springtime -
9:33 - 9:36and you have this high-salinity runoff,
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9:36 - 9:38the rivers are at least
in a better position -
9:38 - 9:41to defend themselves against that.
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9:42 - 9:43Now, as a chemist,
-
9:43 - 9:48the opportunity though
that I'm more psyched about -
9:48 - 9:52is the concept of introducing
circular salt into the chemical industry. -
9:53 - 9:57And the chlor-alkali industry is perfect.
-
9:58 - 10:01Chlor-alkali industry
is the source of epoxies, -
10:02 - 10:04it's the source of urethanes and solvents
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10:04 - 10:08and a lot of useful products
that we use in our everyday lives. -
10:09 - 10:13And it uses sodium chloride salt
as its key feed stack. -
10:14 - 10:16So the idea here is,
-
10:16 - 10:19well, first of all,
let's look at linear economy. -
10:19 - 10:22So in a linear economy,
they're sourcing that salt from a mine, -
10:22 - 10:24it goes through this chlor-alkali process,
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10:24 - 10:26made into a basic chemical,
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10:26 - 10:29which then can get converted
into another new product, -
10:29 - 10:31or a more functional product.
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10:31 - 10:34But during that conversion process,
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10:34 - 10:38oftentimes salt is regenerated
as the by-product, -
10:38 - 10:40and it ends up
in the industrial wastewater. -
10:41 - 10:46So, the idea is that we can
introduce circularity, -
10:47 - 10:51and we can recycle the water and salt
from those industrial wastewater streams, -
10:51 - 10:53from the factories,
-
10:53 - 10:57and we can send it to the front end
of the chlor-alkali process. -
10:58 - 11:00Circular salt.
-
11:00 - 11:02So how impactful is this?
-
11:02 - 11:05Well, let's just take one example.
-
11:05 - 11:08Fifty percent of the world's
production of propylene oxide -
11:08 - 11:11is made through the chlor-alkali process.
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11:11 - 11:17And that's a total of about five million
tons of propylene oxide -
11:17 - 11:19on an annual basis, made globally.
-
11:20 - 11:24So that's five million tons of salt
mined from the earth -
11:24 - 11:28converted through the chlor-alkali process
into propylene oxide, -
11:28 - 11:30and then during that process,
-
11:30 - 11:34five million tons of salt
that ends up in wastewater streams. -
11:35 - 11:36So five million tons
-
11:36 - 11:39is enough salt to fill
three Empire State Buildings. -
11:40 - 11:42And that's on an annual basis.
-
11:42 - 11:48So you can see how circular salt
can provide a barrier -
11:48 - 11:52to our rivers from this excessive
salty discharge. -
11:52 - 11:54So you might wonder,
-
11:54 - 11:58"Well, gosh, these membranes
have been around for a number of years, -
11:58 - 12:02so why aren't people implementing
wastewater reuse? -
12:03 - 12:05Well, the bottom line is,
-
12:05 - 12:08it costs money to implement
wastewater reuse. -
12:08 - 12:10And second,
-
12:10 - 12:13water in these regions is undervalued.
-
12:13 - 12:15Until it's too late.
-
12:15 - 12:20You know, if we don't plan
for freshwater sustainability, -
12:20 - 12:22there are some severe consequences.
-
12:22 - 12:25You can just ask one of the world's
largest chemical manufacturers -
12:25 - 12:29who last year took
a 280-million dollar hit -
12:29 - 12:33due to low river levels
of the Rhine River in Germany. -
12:34 - 12:38You can ask the residents
of Cape Town, South Africa, -
12:38 - 12:42who experienced a year-over-year drought
drying up their water reserves, -
12:42 - 12:45and then being asked
not to flush their toilets. -
12:46 - 12:48So you can see,
-
12:48 - 12:50we have solutions here, with membranes,
-
12:50 - 12:55where we can provide pure water,
-
12:55 - 12:57we can provide pure salt,
-
12:57 - 12:59using these membranes, both of these,
-
12:59 - 13:02to help to protect our rivers
for future generations. -
13:03 - 13:04Thank you.
-
13:04 - 13:07(Applause)
- Title:
- A circular economy for salt that keeps rivers clean
- Speaker:
- Tina Arrowood
- Description:
-
During the winter of 2018-2019, one million tons of salt were applied to icy roads in the state of Pennsylvania alone. The salt from industrial uses like this often ends up in freshwater rivers, making their water undrinkable and contributing to a growing global crisis. How can we better protect these precious natural resources? Physical organic chemist Tina Arrowood shares a three-step plan to keep salt out of rivers -- and create a circular salt economy that turns industrial byproducts into valuable resources.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TEDTalks
- Duration:
- 13:19
Brian Greene edited English subtitles for A circular economy for salt that keeps rivers clean | ||
Brian Greene edited English subtitles for A circular economy for salt that keeps rivers clean | ||
Brian Greene edited English subtitles for A circular economy for salt that keeps rivers clean | ||
Brian Greene approved English subtitles for A circular economy for salt that keeps rivers clean | ||
Brian Greene edited English subtitles for A circular economy for salt that keeps rivers clean | ||
Krystian Aparta accepted English subtitles for A circular economy for salt that keeps rivers clean | ||
Krystian Aparta edited English subtitles for A circular economy for salt that keeps rivers clean | ||
Krystian Aparta edited English subtitles for A circular economy for salt that keeps rivers clean |