New 'Liquid Trees' Divide the Internet

Large tanks full of green, gunky algae, dubbed "liquid trees," are being promoted as a possible solution to air pollution issues in big cities, sparking an online debate.

Posts on Twitter sharing photos and videos of the algae tanks have gone viral this week, with one post by @yupthtexists amassing 18,000 likes and millions of views.

"Scientists create Liquid Trees; a tank full of water and micro-algae that could be an alternative to trees in urban areas," the caption read.

The "liquid trees" actually emerged in late 2021, having been developed by scientists from the University of Belgrade in Serbia. Named "LIQUID 3," the tanks were said to be the first urban photo-bioreactor in Serbia, designed to remove carbon dioxide (CO2) from city air.

The 600-liter (around 158-gallon) tank is filled with microalgae, which use photosynthesis to convert CO2 to oxygen in the same process as trees and other plants do, harvesting energy from sunlight using chlorophyll.

"The microalgae replaces two 10-year-old trees or 200 square metres of lawn," Ivan Spasojevic, one of the scientists working on the project from the Institute for Multidisciplinary Research at the University of Belgrade, said in a statement from the United Nations Development Programme in 2021.

"The system is the same because both trees and grass perform photosynthesis and bind carbon dioxide."

The algae is also more efficient than trees at removing CO2 from the atmosphere, acting between 10 to 50 times faster. One species of algae, Chlorella vulgaris, is up to 400 times more effective at harvesting CO2 than trees, according to biotechnology company Hypergiant Industries.

Twitter users haven't taken well to the suggestion that these tanks are an alternative to trees, however.

"Before Atlanta gets any ideas, liquid trees don't reduce erosion, enrich soil, prevent flooding, and improve the quality of groundwater," tweeted Atlanta Community Press Collective, @atlanta_press.

""Liquid trees" THERES ALREADY FREE AIR!!!! FROM REAL TREES!!!!" tweeted @nightmeir_1.

Spasojevic said that the tanks were never supposed to replace trees, but to be a space-efficient supplement for cities with particularly bad air quality, like Belgrade, which is the fourth-most polluted city in Serbia as it has two large coal power plants nearby. Serbia had Europe's highest level of pollution-related deaths in 2019, according to a GAHP study.

"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," Spasojevic said.

Additionally, in some cities, the air pollution is so bad that trees actually struggle to grow, while algae tends to be more resilient.

"In certain conditions of great pollution, trees cannot survive, while algae do not mind that pollution," he said.

According to the statement, over 59 percent of Serbians live in urban areas, with high densities of people, buildings and vehicles. With little space to plant trees, these liquid trees provide an efficient way to deal with pollution.

The algae they have used are single-celled freshwater algae that can be found in ponds and lakes in Serbia. They are resilient to the conditions of a city, being able to grow in tap water and weather high and low temperatures. The tanks also don't require much maintenance, with the extra algae being created by the growing algal bloom only needing to be removed around every 45 days, followed by adding fresh water and minerals. The excess algae can also be used as fertilizer, in wastewater treatment, or for biofuel production.

The "liquid trees" are also designed to be multifunctional in a city space, providing a sitting down space, solar-powered lighting at night, and a charging port.

"LIQUID3 is also a bench, it has chargers for mobile phones, as well as a solar panel, thanks to which the bench has lighting during the 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," Bojan Bojić, head of the department for social affairs and development projects in the Municipality of Stari Grad, said in the statement.

The United Nations Development Programme, in partnership with the Ministry of Environmental Protection, selected "LIQUID 3" as one of the 11 best innovative and climate-smart solutions within their Climate Smart Urban Development project.

In classic internet fashion, however, most users' main concern was how tempted they would be to drink the liquid trees in the dead of night when nobody else is watching.

"Wish i hadn't drunk the liquid in the liquid tree, now i can't stop photosynthesizing at inappropriate moments," tweeted @GutturalSounds, while @puckdotnet said, "i'm gonna get arrested for drinking the liquid trees."

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