How to Filter 1 Litre of Water for 9 Cents

Aerogel Stress Balls for Industrial Wastewater Filtration

Laura Gao
19 min readApr 30, 2021

You are extremely lucky to be reading this sentence right now.

I often hear talk about the role that luck plays in success — as part of the classic hard work vs luck debate. However, what is less often talked about is how lucky we all already are. If you never have to worry about where your next drink’s water will come from, then you are luckier than two-thirds of the world’s population. If you have reliable Internet access (which you probably do if you’re reading this), then you are luckier than 3.6 billion people. If you have a running faucet 365 days of the year, then you have a higher chance of success than the average person on Earth.

This is because two-thirds of the world does not have a reliable water source for at least one month in the year. Two-thirds. That’s the majority!

If you never worry about your drinking water, you are in the minority!

This is not just a quirk of the developing world — in the United States, 140 000–200 000 people died last year from lead poisoning in water alone. That’s hundreds of thousands of people who never got to have their hopes and dreams realized due to a problem that never should’ve happened in the 21st century. This is not to mention the loved ones of those impacted.

Although the luck factor can never be eradicated when talking about success, I can work to minimize it. I am only here today out of luck. It is with this belief that Samantha, Harsehaj, Bernice, and I developed AeroPure — a solution to allow individuals to access to industrial-waste-free water at a 77x cost reduction.

There aren’t too many people working in this field right now, but I am a strong believer in this technology and what it has to offer. In terms of creating your aerogel idea for individual water filtration, now there’s definitely a market for that. I think this is a really cool idea, especially since you’re able to produce it at such a low cost.

— George Gould, VP of R&D at Aspen Aerogels

Problem: Industrial Wastewater

The most important problems usually have many layers and cannot be explained simply. Industrial wastewater is no exception.

Layer 1: Industrial Waste Kills

Clean water changes everything. Not only does it improve the health of entire communities, it also gives women freedom to earn an income and children time to go to school, when they don’t have to spend hours walking miles every day just to gather water.

— Joanne Lu,

For 850 million people globally, their daily routine consists of worrying about how they’ll get their next drink. Unsafe water has killed more people than any other cause over the last century than anything else— with one person dying every 10 seconds from unclean water.

I want my family to breathe some fresh air and drink some good water. I want to see our future generations have the time to grow up and not have to deal with young kids dying and sicknesses and illnesses.

Vivian Milligan, a resident of Ringwood, New Jersey

The majority of water quality problems are not caused by bacteria and parasites, but instead, by factory runoff, intense agriculture, mining, urban wastewater, and other contaminants that fall into the broad category of “industrial wastes,” according to UN-Water, 2011. Just like the smell of your socks — these wastes don’t go away. In Picher, Oklahoma, lakes and groundwater aquifers held water with dangerous levels of lead and heavy metals 60 years after the zinc and lead mining stopped. To this day, their water looks like this:


No one is immune — not even me, a Torontonian. One third of tests in Canadian cities measured lead exposures that exceed the national safety guideline of 5 parts per billion, according to a 2014 investigation from 9 universities.

Layer 2: Water Projects in Developing Countries do not Address Industrial Wastewater

There are many levels of clean water:

The unsolved Level 4 — No accessible method to get rid of heavy metals?

The most popular water projects (done by major water charities such as Charity: Water) are wells and pumps. Even in the western world, the U.S. Geological Survey showed that 15% of Americans drink untreated groundwater from private wells. Although underground water is less polluted than surface water, well water still contains bacteria as well as industrial wastes.

This situation can be improved by boiling water, which some communities do (ex. 90.6% of households in Indonesia boil), but boiling still does not remove industrial wastes.

Due to a lack of public information, some people may boil their well water and think it’s fine. Others may know that their boiled well water isn’t great, but they have no better choice. Either way, boiling your water does not solve the problem of industrial wastes — high temperatures can kill the bacteria and parasites that cause cholera, but you can’t boil lead out of water.

Currently, there isn’t a widespread solution to remove industrial wastes. Thus, in order to drink safe water, people in some places have no choice but to drink bottled water. Picher, Oklahoma, is one of these places.

Can you believe that for some people, the best solution for industrial-waste-free drinking water is bottled water?

Layer 3: Current Industrial Wastewater Filtration Methods are High-Maintenance and Costly

Because most water projects are pumps and wells, they are difficult to maintain. Because of this, close to half of water projects break within 2–5 years.


The World Bank estimates that less than 5% of water projects are visited at all after implementation, and less than 1% are monitored long term. NGOs are unaware or wilfully ignorant when a project breaks down or is unused. This is donor money spent on projects that aren’t maintained!

I don’t need to report on what happens after my project ends, and I’m not accountable if or when the pump breaks down. Why would I want to report the breakdown of a pump to our donors? It could jeopardise future funding. It would also pose a question for which there is no clear answer: who is responsible for fixing the broken pump?

By designing and managing projects the way I do, I am doing my job.

Ajay Paul, thematic coordinator for the sustainable services initiative at Welthungerhilfe

Often, NGOs install a pump with a group of local people dubbed “water-user committee” and call it a day, leave to do other projects, expecting the community to operate and fix the system without future support! However, from the local people’s perspective, it’s the NGO’s responsibility to fix the pump if it breaks down. This is a good reminder that all initiatives will fail if one does not consider perspective, to humanize the people you’re trying to help.

Similarly, industrial wastewater filtration complexes in western countries are capital-intensive, costly, and impractical for setup in developing countries and expecting local people to maintain well. The World Bank sets out these criteria to assess whether a solution meets the “maintenance” standard:

  • Is the system easy to use and maintain?
  • Can the technology be used anywhere in the world?
  • Are the spare parts affordable and available locally?

Alongside pumps and wells, current industrial wastewater filtration methods don’t meet these criteria.

Aside from maintenance, the second bottleneck in current industrial wastewater filtration methods is cost. People are living off of a few dollars a day, and can’t pay the $7000 initial capital cost of chlorine systems.

This is the 21st century, so why use 20th century technology? When tackling the water crisis, one need not think in terms of pumps and wells.

Capturing drinkable water from atmospheric humidity is one such 21st century novel tech

If we could develop any technology, the best case scenario would be one that tackles all three layers. It would need to:

  1. Provide safe drinking water by effectively filter out industrial wastes — this tackles the issue of the unsolved Level 4. (Pathogens can be removed via boiling)
  2. Be cheap
  3. Be easy to maintain

Lucky for us, such a technology exists.

Aerogel — A Piece of the Sky in Your Hands


Using a combination of cellulose and aerogel beads (the chemical details for which I’ll break down in a minute), we are able to achieve effective filtration of 99% heavy metals and 99.4% organic compounds with a reusable, biodegradable product that costs $4.04 per person per 10 days.

How is this possible? Here are the table of contents for the next section:

  1. What is aerogel?
  2. How do cellulose and alginate aerogels work?
  3. How is AeroPure manufactured?
  4. How do I use AeroPure?
  5. Cost breakdown

What is Aerogel, and Why Does it Look Like a Piece of the Sky?

Aerogel is a solid material with an extremely low density in between 0.001 and 0.2 g/cm3, high porosity ( ≥ 90%) with pores on the size of the nanoscale, and high specific surface area (200–600 m2/g) produced by the substitution of liquid inside a gel with the gas.

In English, aerogel is the world’s lightest solid, sitting at 99.98% air by volume.

Jelly (yes, the one in peanut butter and jelly), is made up of a solid structure with holes on the nanoscale and liquid suspended inside those holes. (This is why my Grade 9 science teacher called it a “suspension” instead of a “homogeneous mixture!”) Aerogel was invented when Dr. Samuel Stephens Kistler held an informal competition with a colleague about who can first get rid of the liquid while keeping the solid structure.

There’s one catch: if you just evaporate the water, the solid structure shrinks, and the pores collapse in on themselves. This is called capillary action. But what he and his colleague found out is that you can replace the solvent with any other solvent by immersing the gel in the liquid, and diffusion will work its magic. This way, you can turn, for example, a water-based gel into an alcohol-based one easily.

The second breakthrough discovery came with the usage of a funky “state of matter” known as supercritical fluid.

If you’re curious, the next section is a tanget about how supercritical fluid works. If not, feel free to skip the section.

Tanget — Supercritical Fluid — the Intersection of Liquid and Gas?


If you heat any liquid under high pressure to a certain temperature known as the supercritical point, the liquid becomes a supercritical fluid.

In a Veritasium YouTube video, liquid CO2 is heated up until it reaches supercritical point. In the following diagrams, you can see the progression of liquid as it slowly turns supercritical — as the temperature increases, the line between liquid and gas becomes blurry until it disappears altogether.

The progression of liquid CO2 heated under high pressure until it reaches the supercritical temperature

The breakthrough discovery was that you can heat the aerogel under high pressure until the liquid inside its pores turns supercritical. At this point, the supercritical fluid can be removed without damaging the solid structure. In place of the liquid comes gas, and now, you have aerogel!

This was the original aerogel.

Note: Carbon dioxide is typically used because it has a low supercritical temperature and pressure at 31.0 °C and 1,070 psi. (Compared to water’s 373.946 °C and 3,200.1 psi.)

This high porosity is what gives aerogel all of its unique properties — ranging from insulating your hand as it’s held next to a blowtorch, to diffusing blue photons faster than red ones, giving them a distinct blue color (this is the same reason that the sky is blue!)


Most notably for us, crazy large number of pores gives it a heck ton of room to absorb things.

And absorb things they do!

The original aerogel, silica aerogel, is brittle and once it absorbs water, it’s done. If you pinch it, it breaks. There is no hope of getting the liquid out. Since the original invention, people have developed different alternatives to combat this. Cellulose aerogel is one — compared to silica aerogels which are extremely fragile, bio-aerogels do not break under compression.

Cellulose and Alginate Aerogels — The Chemistry

Cellulose aerogel is a biodegradable natural material made up of hydroxyl (-OH), methoxyl (-CH2OH), and ether (C-O-C) groups.

Hydroxyl groups are amphiphilic, meaning they attract both water and organic compounds (substances that contain carbon), such as oils and dyes. We only want the aerogel to absorb the organic compounds however, so we make it hydrophobic by adding a silane coupling agent. Doing this allows the removal of oils, dyes, pesticides, pharmaceuticals, and organic solvents.

The functionality of cellulose aerogel. Note: this is not what our product looks like, this is for visualisation purposes only 😉

However, the removal of organic compounds is not enough.

The Other Culprit — Heavy Metals

In order to filter out metals, the most important functional groups are carboxyl/carboxylate (COOH/COO-).

Alginate aerogels have hydroxyl groups and also carboxylate groups, giving them a high affinity for metals.

As alginate is anionic, this allows them to attract the cationic heavy metals.

And so, these two aerogels combined filter out both organic contaminants (meaning oils, dyes, pharmaceuticals, and pesticides) and heavy metals! That takes care of all our industrial waste.

Level 4 is what our solution is targeting.

The most shocking fact about cellulose aerogel (other than how well it can absorb oils and dyes) is that it is completely made from organic waste, such as paper and orange peels. Yea, you heard that right — this is the ultimate transformation of trash into treasure.

How to Turn Trash Into Treasure — le Mânufacturiñg Prôçess

The production of polysaccharide aerogels can generally be summed up by the following procedures:

  1. Dissolution
  2. Gelation and pore formation
  3. Solvent exchange
  4. Drying


The manufacturing of cellulose aerogel differs from silica in many ways. For one, paper waste doesn’t come neatly bundled in packets of gel, and thus we have to convert our biomass into gel before drying. An appropriate solvent must be chosen to dissolve the polysaccharide, with the ability to release and untwine the polymeric chains. One method discovered in 2011 by Lina Zhang involved dissolving the cellulose in a sodium hydroxide/urea (NaOH/urea) aqueous solution with cooling, and this new pathway in cellulose dissolution was deemed “a milestone in the history of cellulose processing technology.”

To disperse the cellulose from the recycled cellulosic fibers of the paper waste, sonication is used for about 6 mins on the NaOH/urea solution. Sonication is the act of applying sound energy to agitate particles in a sample, and this allows for the compounds to be extracted. The solution is then placed into a refrigerator to allow for the cooling aspect of the procedure.

Polysaccharide aerogels can also be made from biowaste, typically using plant material. There’s a whole other process in extracting those fibers out however, in order to remove the other components such as hemicellulose and lignin.

Gelation and Pore Formation

Unlike silica aerogels, the starting material for polysaccharide aerogels isn’t a suspension, but rather, a solution of what we call “ready” polymer. The solidification of the solution typically occurs through a mechanism called phase separation, namely “liquid-liquid demixing” typically with an ethanol coagulation system that forms polymer-rich and polymer-poor areas in the solution. The polymeric chains then form physical or chemical cross-links with each other to create a 3D interconnected network filled with liquid — in other words, a gel.

The gelation process takes approximately 853 seconds, and you’ll know when it has formed if you can turn the container upside down and not be rained on.

Solvent Exchange

The next step is solvent exchange, where the solvent that was used for dissolving the cellulose is replaced by a non-solvent, typically deionized water. Because this process occurs by diffusion, a relatively slower process as the solvent has to diffuse out and the water has to diffuse in, it can last quite some time — up to 2 days. Diffusion does occur faster however from the gelation step, which sometimes isn’t used.

Fun fact: once water has completely filled the pores, it becomes a “wet-gel” or “hydrogel.”


The last step in the process is drying the hydrogel — in other words, replacing the water in the pores with air so that it’s able to become an aerogel. You might think — couldn’t you just wait for the water to evaporate out? The reason why that doesn’t work is due to something called capillary action. Essentially, the pores would collapse on themselves.

What has to be done instead is supercritical drying, which involves substituting the water with a supercritical fluid, typically CO2, applying a pressure of about 10 MPa, then gradually depressurizing it over 20 to 60 mins, bringing the CO2 to its gaseous phase.

Although CO2 has a suitable supercritical point, supercritical drying still has problems: it’s expensive AND it’s not very environmentally friendly as we need big bulky special equipment of being able to immerse the gel into a high pressure sealed contraption.

Luckily, another way to dry aerogel exists: freeze drying.

The freeze-drying process occurs with 3 steps: decreasing the temperature in an isobaric process (pressure held constant) past the triple point (aka to a very low temperature), the use of a vacuum to bring the pressure down, and lastly increasing the temperature again to sublimate it into its gaseous phase.

To get it to such a low temperature, the gel can be submerged in liquid nitrogen (-196 C) for a fast cooling and thus smaller pores.

The cons to freeze-drying are that it usually results in slightly larger pores, though still < 100 nm, and prolongs the processing time.

Note: freeze-dried gels are also referred to as cryogels.

And there you have it. Voila, we have successfully created our cellulose aerogels!

All in all, the entire aerogel manufacturing process takes a few days, with the majority of that time spent on solvent exchange and freeze drying. Here’s the full process together:

Although we can stop here, there are some extra processes that can be done to improve our product:


For our cellulose aerogels, we have to go through a process of hydrophobization in order to ensure the selective absorption of the organic compounds rather than the water as well. This is typically done through a silylation reaction with methyltrimethoxysilane (MTMS), which creates a coating on the aerogel. In order to maintain the biodegradability of our aerogels however, we will use MTES which is much less harmful for the environment. To facilitate this reaction, the aerogel is heated at 70°C in an oven for about 2 hours, then placed in a vacuum oven to remove the excess reagent until the pressure reaches 0.03 mbar.

Shaping — Why Towels Aren’t Balls

It’s 2000 BC. Your cotton plantation has a drought, making it difficult for your family to sell enough cotton to purchase food. You want your family’s towels to absorb as much water as possible, while using as little cotton as possible. How would you shape your towel?

If it is shaped like a ball, the outer parts of cotton will absorb water, but look at all that inside cotton wasted!

Just because round wheels are nice, doesn’t mean making everything round is nice.

To save costs, we want to use as little aerogel as possible. To maximize the amount of contaminant we can absorb using a single piece of aerogel, we want to maximize the surface area to volume ratio.

Think about it yourself — what shape has the highest surface area using the least volume?

Towels are flat sheets. So one way we can shape our aerogel is to shape it as a flat sheet.

This shape is called a “monolith”.

Yay! Problem solved! That’s our aerogel!

Not so fast. For one, a single flat sheet would assume that everyone has a container with an opening size that fits the one sheet.

How to keep a high surface area to volume ratio while allowing compatibility? Mathematicians would tell you that spheres have the highest surface area to volume ratio out of all shapes.

Furthermore, using beads removes the need to superglue the alginate and cellulose aerogels together.

Turns out, towels can be balls! That is, if you’re willing to wash your face with 7 mm sized beads.

Our beads will be 7 cm in diameter.

How is shaping done?

While this is an optional step, as the gel will take the shape of whatever container it was made in, we formed aerogel beads in order to maximize the surface area and hence the absorption/adsorption capabilities of our aerogels, as well as provide more customizability for the user.

Forming beads can easily be done by dropping the polysaccharide solution into a cross-linking solution. For alginate aerogel beads, the alginate solution would be added dropwise into a solution of CaCl2 (calcium chloride), upon which hydrogel spheres are immediately formed. For cellulose aerogel beads, the same thing can be done but with silicone oil. The cross-linking solutions can then be filtered off to obtain the hydrogel beads.

How do I use AeroPure?

1: Fill

Fill your reusable mesh bag with one packet of cellulose aerogel beads and one packet of alginate aerogel beads.

2: Soak

Place your AeroPure in the unfiltered water for 1 to 2 hours to allow the contaminants to be uptaken by the beads.

3: Wash and squeeze

The mighty stress ball o’ science

Squeeze your AeroPure to remove the organic compounds, and wash it in a vinegar solution to remove the metals and prevent biofouling. Inspired by stress balls, cellulose and alginate aerogel beads will be packaged in mesh-like containers, so the ball can be squeezed to remove oil and heavy metals.

Wang et al. (2019) demonstrated that the same beads can be reused 10–30 times without decrease in absorption capabilities:

Why vinegar: To remove heavy metals, squeezing isn’t enough. An acid must be used to remove heavy metals. According to Jens Mroszczok, Associate Research Fellow Low Cost Carbon Fibre at Deakin University, submerging the alginate in vinegar is effective at removing heavy metals.

4: Throwing Out and Biodegrading

Alginate aerogel takes 1 year to biodegrade; cellulose aerogel takes six months. Both these materials environmentally friendly. We do not create more waste by trying to clean water — if we did, that would be like swallowing a horse to eat a fly!

Cost Breakdown


100 mg of alginate aerogel is able to successfully remove 99% of heavy metal ions from a 50 mL sample of 1.5 mmol/L concentration.

100 mg x (1 g/1000 mg) = 0.1 g
50 mL x (1 L/1000 mL) = 0.050 L
0.1 g/0.050 L = 2 g of alginate aerogel/L of polluted water

Alginate aerogels have a density of 2.15 g/cm³.

Producing 100 cm³ of aerogel costs approximately $6.

2.15 g/cm³ = 215 g/100 cm³

Thus, it costs approximately $6 to produce 215 g of alginate aerogel.

215 g/(2 g/L) = 107.5 L can be filtered for $6
$6/107.5 L =
$0.056 / L of polluted water


10 mg of cellulose aerogel is able to absorb 99.4% of oils from a 50 mL sample consisting of 5 mL of the oil.

10 mg x (1 g/1000 mg) = 0.01 g
50 mL x (1 L/100 mL) = 0.050 L
0.01 g/0.050 L = 0.2 g of cellulose/L of polluted water

Cellulose aerogels have a density of 0.04 g/cm³.

Producing 100 cm³ of aerogel costs approximately $6.

0.04 g/cm3 = 40 g/100 cm³

Thus, it costs approximately $6 to produce 40 g of cellulose aerogel.

40 g/(0.2 g/L) = 200 L can be filtered for $6
$6/200 L =
$0.03 /L of polluted water

Add up the cellulose and alginate components:

$0.056/L + $0.03/L = 9 cents per litre

Cost per Person

The average person uses 47 L of water per day in Africa.

$0.056/L x 47 L = $2.63 for alginate aerogel
$0.03/L x 47 L = $1.41 for cellulose aerogel
$2.63 + $1.41 =
$4.14 per person, per day

If the 47 L of water used per person per day in Africa were clean and drinkable, this would cost them $31.33 a day. For many individuals living near coal-fired power plants or similar facilities, they must resort to relying on bottled water given the high levels of certain chemicals in their well water.

It costs approximately $1 for a 1.5 L bottle of water in Africa.

$1/1.5 L = $31.33/47 L

Our aerogels can easily be reused 10 times (and up to 30 times) without a significant decrease in absorption or adsorption capabilities (<1% drop).

Therefore, while it would cost $2.63 to filter 47 L with the alginate aerogel and $1.41 to filter 47 L with the cellulose aerogel, the cost would remain the same for 10 times the volume of water. However, the cost for the bottled water would be 10 times more.

$31.33 x 10 = $313.30

Thus, as a final comparison of cost:

$313.30/($4.14) = 77.5 x less using AeroPure

AeroPure — Bringing Power Back to Consumers

Definitely the idea is very fine and there is potential, and you should go your way with it. I will put my thumb on it!

— Björn Schulz, studied cellulose aerogels in a PhD at RWTH Aachen University

From the ever-growing influence of big tech to the fact that you can’t spend 5 minutes online without seeing an ad, we’ve seen how much corporations have a say in our lives. Don’t let them control your water too.

If we don’t have water, we cannot live. So when you have companies coming into your neck of the woods, contaminating your water, what are we going to do? What are we going to do? We can’t live like that.

Tracey Edwards of Walnut Cove, North Carolina.

Our vision is a world where anyone who wants toxin free water can have sanitary water, where no one has to have their life robbed from them due to a system that failed to protect them. AeroPure empowers individuals to take their health into their own hands, by providing cheap and easy-to-maintain technology that allows anyone to filter their own water.

Now, that’s a world I want to live in.

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