Scientists have invented a wild way to remove plastic pollution from our oceans with egg whites: ‘99% efficiency’

Link to article

(Click on pictures below for larger view.)

The Earth's oceans contain 97% of all water, but it's unsuitable for drinking, agriculture, or most industrial uses. The remaining 3% is freshwater, but most of that (2.5%) is unavailable because it is part of glaciers or the polar ice caps, atmosphere, and soil, and may be very polluted or is too far underground to be extracted economically. That leaves 0.5% of all water on the planet as freshwater we have access to and that is usable for consumption or agriculture. Researchers have found a way that could potentially remove salt and microplastic pollution from seawater and make it usable for humans.

What microplastics look like in water

Why is the ocean salty? Rainwater dissolves carbon dioxide from the atmosphere to make it slightly acidic in the form of carbonic acid. This strips ions off rocks and carries them to the oceans. Also, heat from the magma that comes up from the volcanoes and seafloor vents breaks down minerals which get dissolved in the atmosphere and seawater. The two commonest elements in ocean water are sodium and chloride (which are what make up table salt).

From Why Is The Ocean Salty? website

A lot of recent news talks about the problem of microplastics in the ocean. Basically, they are pieces smaller than 5 mm (0.2 inches, about as big as a sesame seed) long that form as UV from sunlight, wave action, and washing break down bigger pieces. Some are called microbeads and are less than 1 mm in diameter; they are made specifically for scrubbing compounds and cosmetic face cleaners. Here's a short video about the topic to show two problems that microplastics create.

What is a microplastic? (YouTube)

This article is not about cleaning up the oceans for the sake of the environment. Rather, this is to report on research done at Princeton University to develop a material to remove salt and microplastics so that the cleaned water can be used in homes and industry.

Activated carbon/charcoal is a cheap material used to remove unwanted chemicals from water. Its tiny particles are full of pores with many convoluted channels to trap organic molecules, and its own chemical nature breaks down chlorine to chloride and carbon dioxide. But because it doesn't remove all unwanted chemicals, water purification systems use it as only a first step, often followed by reverse osmosis (RO). RO systems pressurize dirty water through a membrane with pores that allow only water to pass. But it's also more expensive than activated carbon filtration.

Powdered activated carbon and diagram of one particle in action

Reverse osmosis process (YouTube 2:00)

So, what's cheaper than RO but more effective than activated carbon?  Eggs.

The Princeton University researchers conceived of a material that would be porous like activated carbon. They took egg whites (albumin), which contain a lot of protein, and treated them as follows.

1. Egg whites are freeze-dried to remove liquid. The material forms strands of proteins bonded together.
2. The freeze-dried material is heated in a nitrogen atmosphere to 900 degrees C (1,650 F). This burns away everything but the carbon and changes the structure into an aerogel matrix of carbon which is very lightweight, porous, and strong.

You can see the actual changes in the diagrams and photos below from the original research paper.

Process of making aerogel material from egg whites (Ozden et al, 2022, Materials Today)

Aerogels are materials made from gels and into these sorts of lattice-like networks. They can be made from various starting materials like silica or tin or carbon. The carbon ones made at Princeton University are about 4 cm (1.6 inches) long and 2 cm (0.8 inches) in diameter. When sliced in half, you can see the dense yet porous network of carbon.

Aerogel from silica (left) and from egg whites (right)

The Princeton University researchers took their aerogel from egg whites and shaped it into a 5-mm-thick (0.2 inches) filter and allowed seawater to flow through it by simple gravity (no added pressure) 50 times. They measured the purity each time.

From Ozden et al., 2022 report

As the seawater passes through the egg white aerogel, water travels unevenly through the carbon matrix, and ions stick to it to let only purified water come through. After 50 purification cycles, 98.2% of the ions were removed.

(h) dry aerogel, (i) water [blue] flowing through,

(l and m) saltwater ions being trapped [green = chlorine, orange = sodium, violet = magnesium,

blue = nitrogen, red = oxygen] (From the Ozden et al., 2022 report)

They then tested their egg white aerogel for its ability to remove microplastics (147 nm and 400 nm diameter) and compared it to an activated carbon filter.

• In the first purification cycle, egg white aerogel removed 93.2% of the smaller plastic and 98.5% of the larger, while activated carbon removed 82% of the smaller particles.
• After 15 cycles, egg white aerogel removed 99.986% of the smaller plastic and 99.995% of the larger, while activate carbon removed 98.2% (standard for other industry materials).

So, on a small scale, the egg white aerogel outperformed activated carbon. Obviously, this has to be scaled up, as the researchers noted. Before you wonder whether industry will consume a large portion of the egg supplies in the world and cause prices to rise,  it is good to see what Professor Craig Arnold of the Princeton team said:

"Because other proteins also worked, the [aerogel] material can potentially be produced in large quantities relatively cheaply and without impacting the food supply."