As is well known, trees and plants are essential in any ecosystem, since they play a crucial role in purifying the air that surrounds us. Its function of converting CO2 into oxygen manages, to a large extent, to moderate the pollution that reaches the atmosphere.

However, modern cities barely leave room for vegetation beyond a few parks and gardens, making it difficult to naturally control the quality of what we breathe on a daily basis.

Developed by a group of researchers from the University of Belgrade - and currently running on some streets in Serbia - Liquid3 bills itself as an 'urban photo-bioreactor', basically consisting of a tank housing a massive population of microalgae, diluted in 600 liters of water that acquires the characteristic green color of those.

Like other plant species, microalgae capture the CO2 present in the nearby air and, through photosynthesis, produce clean oxygen that they return to the environment. Sunlight, another key component of the process, penetrates directly through the tank glass walls.

Along with oxygen, the photosynthesis of microalgae leaves a certain amount of biomass as residue that can also be used as fertilizer. This biomass is extracted when carrying out maintenance and cleaning of the tank, something that can be done once a month.

Thus, with no more electronics than some solar panels on top (necessary, for example, to illuminate it at night), this 'liquid tree' is a natural machine whose design also allows it to be integrated into street furniture, since it includes a space to sit and even USB terminals to charge mobile devices.

The system requires no special maintenance - just remove the biomass created by splitting algae, which can be used as an excellent fertilizer, in a month and a half pour in new water and minerals, and the algae continues to grow indefinitely. It is self-supplied with solar energy during the periods of more radiation and is connected to the electrical network during winter.

The goal is not to replace forests, but to use this system to fill those urban areas where there is no space to plant trees. It is especially useful in highly polluted conditions where trees cannot survive, but microalgae can thrive without being affected by the pollution.

Liquid3 captures as much CO2 as a mature tree and releases as much oxygen as 200 square meters of lawn and is an innovative solution in cities that have more and more people, vehicles and industry, and fewer green areas.