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Redefining Arboriculture: Unveiling the Potential of Liquid Trees

Madhulika Jadon

When we think of trees, we usually imagine solid structures with roots, trunks, branches, and leaves. However, a new concept has emerged that challenges this traditional view of trees. Liquid trees, as they are called, are a fascinating and innovative idea that has captured the attention of scientists, designers, and environmentalists. Also dubbed as LIQUID 3, the novel creation is Serbia’s first urban photo-bioreactor, a solution in the fight for clean air. Liquid trees mimic the natural functions of trees. The idea is to create a network of interconnected systems that use a mixture of water, nutrients, and microorganisms to provide ecological services similar to those of trees, such as carbon sequestration and air purification.

“It all started with an appeal from the Development Program of the United Nations (UNDP Serbia) to tackle air pollution,” explains Ivan Spasojević, biophysicist and project coordinator of the LIQUID 3 project at the Institute for Multidisciplinary Research. Every year, when the heating season begins, the problem of air pollution in Serbia reaches a boiling point. Nevertheless, the nation experiences air pollution all year round. According to data from the Serbian National Ecological Association (NEA), at least 75% of Serbian citizens breathe air that is polluted by particular airborne matter (PM). Swiss air quality database IQAir ranked Belgrade as the world’s fifth most polluted major city in early November. Together with an architect and a phycologist, the scientists were attempting to find a way to integrate urban planning with microalgae's ability to effectively bind carbon dioxide. LIQUID 3, the end outcome, was introduced in Belgrade in September 2021.

The photo-bioreactor consists of a glass tank filled with 600 liters of water, microalgae, and a solar panel which supplies electricity to a small pump that brings air into the tank through tiny holes. Through photosynthesis, the microalgae produce oxygen, which is subsequently released into the atmosphere. Biomass is a byproduct of the process. The system does not require special maintenance—it is enough to remove the biomass created by dividing algae, which can be used as an excellent fertilizer. In a month and a half, new water and minerals will have to be poured, and the algae would continue to grow indefinitely.

One of the main advantages of liquid trees is their versatility. Unlike traditional trees that require specific soil conditions and climatic factors to thrive, liquid trees can be deployed in a variety of settings, from urban areas to deserts. The project is designed to be multifunctional. LIQUID 3 also acts as a bench, has chargers for mobile phones, as well as a solar panel that provides the bench with lighting during the night. The efficiency of liquid trees also makes them advantageous because they have the capability to absorb more pollutants and sequester more carbon due to their larger surface area. They are more resistant to heavy metals than trees. Through analysis of biomass, it was found that they clean 300 to 3,000 cubic meters of air from heavy metals. They can also be integrated with other green infrastructure systems such as green roofs and rain gardens in order to create a more holistic approach to urban greening.

Rather than replacing forests or tree planting initiatives, the LIQUID 3 team has indicated that their objective is to utilize this technology to fill those urban pockets where there isn't enough room for growing trees. Many trees cannot thrive in highly polluted environments, while algae are unaffected by the great levels of pollution. Perhaps the most exciting aspect of liquid trees is their potential to revolutionize the way we think about nature and technology. By merging the natural and the artificial, we can create new forms of ecological infrastructure that are more sustainable and resilient than anything we have seen before. The concept of liquid trees offers a glimpse into a future where technology and nature work together to create a more sustainable and resilient world. As we continue to grapple with the complex environmental challenges of our time, it is inspiring to see innovative ideas like liquid trees emerge and offer hope for a brighter future.


1. Daniela Castim, “A Liquid Tree? Scientists in Serbia Make Incredible Innovation”, World Bio Market Insights,

2. Benno Krieger, “Liquid tree to combat air pollution in Belgrade”, Balkan Green Energy News, 25/11/2022,


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