Elixir of life? Belgrade installs liquid trees to combat pollution and this is how they work

• Serbia came up with the idea of ‘liquid trees’ to counter the problem of air pollution.
  
• Technically termed bioreactors, liquid trees are tanks containing six hundred litres of water and microalgae. The microalgae bind carbon dioxide and produce pure oxygen through photosynthesis.
  
• The bioreactors installed in Serbia double up as benches and even offer power outlets for charging mobile phones.

It’s a well-known fact that widespread pollution has significantly lowered the quality of life — especially in urban areas where greenery is limited and often, non-existent. To counter this problem, Serbia has come up with an innovative solution — liquid trees.

Earlier this week, liquid trees started trending on social media after the Twitter account Yup They Exist shared their image, prompting a conversation on their pros and cons. While many users remarked about technology replacing actual trees, the history behind these liquid trees support their existence.

Installed in Serbia’s capital city, Belgrade, the trees look fit to be in a science-fiction film. But in reality, these are devices that help improve and control air quality.

Technically termed bioreactors, these are tanks containing six hundred litres of water and microalgae. It works by using microalgae to bind carbon dioxide and produce pure oxygen through photosynthesis. Because of the microalgae, the tanks emit an eerie green colour.

These trees are solar-powered and capable of replacing one 10-year-old adult tree, or a full 200 square meter of lawn. Additionally, compared to trees, these bioreactors can be built and installed far more quickly, and start processing polluted air immediately.

The bioreactors installed in Serbia double up as benches and even offer power outlets for charging mobile phones.

The history of liquid trees

Serbia, especially Belgrade, has one of the worst cases of air pollution in the world. Belgrade is home to large coal plants that further contribute to the city’s severe air pollution. As per IQ Air, at the time of writing this article, the PM2.5 concentration in Belgrade was 4.3 times the WHO annual air quality guideline value.

PM 2.5 pollution refers to the presence of tiny dirt particles in the air. Among other sources, these dirt particles come from power plants, motor vehicles, and agricultural burning. They're considered dangerous because they can penetrate deep into people's lungs because of their small size.

As a solution, Dr Ivan Spasojevic, Ph.D. in Biophysical science, developed the liquid tree, also dubbed LIQUID3. The first urban photo-bioreactor was actually installed in Belgrade in September 2021. The team behind the project has shown how the tank can survive in winter and even documented the tank’s maintenance process on social media.

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