The University of Belgrade's Institute for Multidisciplinary Research has developed an urban photo-bioreactor called Liquid 3, which serves as a bench and cleans the air in Belgrade city centre. Serbia has one of the highest air pollution death rates in Europe, and Liquid 3 was created in response to an appeal from the Development Program of the United Nations to tackle air pollution.
The device uses microalgae to bind carbon dioxide while also serving as an urban design feature. It was installed in September 2021 in front of the Municipality of Stari Grad in Belgrade.
Air pollution is a major problem in Serbia, with at least 75% of Serbian citizens breathing air polluted by particular airborne matter (PM) throughout the year.
The microalgae perform photosynthesis and convert water and CO2 into oxygen, which is released into the atmosphere, with biomass produced as a byproduct. Microalgae are also more resistant to heavy metals than trees, making them an effective way to remove PM particles from the air.
Liquid 3 is intended for densely populated urban areas where it is not possible to establish green zones or where single trees cannot sufficiently clean the air. One Liquid 3 unit can replace one adult tree in terms of its capacity to bind carbon dioxide, but it is not a replacement for trees and parks in the city, which have an important social function and improve the quality of life.
The device requires more maintenance than regular trees, with the amount of water with microalgae needing to be changed almost entirely every month and the biomass needing to be removed.