Belgrade’s LIQUID 3 uses microalgae to clear the air in dense urban jungle
Trees are natures great air filters. They take in CO2 and churn out oxygen, a boon to living things all around them. They beautify landscapes and help make cities livable. There are pushes to plant as many trees as possible, trillions of them, to fight climate change and pollution-related disease. But there are some settings where planting a tree isn’t the best course of action and there’s a better weapon to clean up the air. The Serbian capital, Belgrade, is one such place, and there the city is deploying what its creators call LIQUID 3 and what others have dubbed a “liquid tree.”
The LIQUID 3 system, designed by researchers at the Institute for Multidisciplinary Research at the University of Belgrade, consists of a 600-liter tank of water with a microalgae that takes in carbon dioxide and produces oxygen through photosynthesis much like trees do, but anywhere from 10 to 50 times more efficiently. A single tank can yield as much O2 as two decade-old trees or 200 square meters (2,150 square feet) of grass.
“The Institute used single-celled freshwater algae, which exist in ponds and lakes in Serbia and can grow in tap water, and are resistant to high and low temperatures, said Dr. Ivan Spasojevic, one of LQUID 3’s creators. “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, pour new water and minerals, and the algae continue to grow indefinitely.”
That’s not all the urban bioreactor does. It also comes equipped with a bench and charging outlets so Belgradians can sit and enjoy a moment of peace under the liquid tree. A solar panel soaks up sunshine during the day and provides light for the bench at night.
“The municipality of Stari Grad has decided to support this project which directly contributes to improving the quality of life of our fellow citizens, public health and cleaner environment through using smart and innovative solutions,” said Bojan Bojić, head of the Department for Social Affairs and Development Projects in Stari Grad.
The Perfect Testing Ground
The necessity that mothered the invention of the LIQUID 3 is the notoriously poor air quality in Serbia, and in Belgrade in particular. The city is home to two large coal-fired power plants that rank among the 10 dirtiest in Europe. Serbia’s pollution concentration is nearly five times the World Health Organization’s guidelines for air quality, and the country has the highest rate of pollution-related deaths in Europe.
“More than half of the population of Serbia lives in urban settlements, even 59%, and that number is constantly increasing,” said Francine Pickup, resident representative of the United Nations Development Program (UNDP) in Serbia. “This greatly affects the density of settlements, the quality of life, the increase in the number of vehicles on the streets, pollution and the increase of harmful greenhouse gas emissions.”
While local authorities would love to plant more trees in Belgrade, there’s simply not room for enough trees to thoroughly clean the city’s air. As Spasojevic explained, LIQUID 3 is not intended as a ubiquitous substitute for trees.
“Our goal is not to replace forests, but to use this system to fill those urban pockets where there is no space for planting trees. In certain conditions of great pollution, trees cannot survive, while algae do not mind that pollution,” he said.
Where it Might Work
Trees aren’t going anywhere, and they’re still great allies and friends of humans in both rural and urban areas. Some cities, however, need a bit more help. Belgrade isn’t the only one. As population trends toward even more densely packed urban cores, emissions will be even more concentrated.
“It is estimated that cities are the source of as much as 75% of total CO2 emissions in the world, of which the largest percentage comes from traffic and cooling and heating in buildings,” Pickup said.
Many cities with legacy power systems throughout the world have dangerously low levels of air quality. India, home to 39 of the world’s 50 most polluted cities, springs to mind. Areas of lower income tend to have the worst air quality and lack room for trees, which take years to reach maturity. “Liquid trees” like LIQUID 3 – recognized as one of 11 innovative solutions in the UNDP’s Climate Smart Urban Development Project – can step in right away and begin scrubbing the air in places where trees might fail. It’s a relatively simple solution that can join the all-hands-on-deck action plan against climate change and pollution.