At first glance, it looks like nothing more than a sleek glass column. But press the power button beside the built‑in bench, and this «liquid tree» hums softly, quietly ingesting the city’s polluted air and exhaling fresh oxygen. Welcome to a future where innovation meets ecology—right at the heart of our concrete forests.
A New Guardian Of Urban Air
Cities worldwide ache for green relief. Crowded pavements, crowded buildings, and surging vehicle emissions strain our lungs and wellbeing.
Traditional trees offer many benefits—shade, cooling, habitat—but they need space, years to grow, and aren’t always possible in dense concrete zones. Enter the liquid tree, also called LIQUID 3, a water‑filled bioreactor brimming with micro‑algae that promises to cleanse the air faster, smarter, and in a fraction of the space.
The Heart Of The System: Micro-Algae Magic
Inside each liquid tree is a 600‑litre tank—prism‑like—full of water and thriving microscopic algae. As polluted air is gently pumped in, the algae carry out photosynthesis, binding CO₂ and releasing oxygen. According to Dr Ivan Spasojević, the technology’s creator at the University of Belgrade, these tiny aquatic plants absorb carbon 10 to 50 times more efficiently than mature trees. Imagine the CO₂‑cleansing power of two 10‑year‑old trees—or 200 m² of lawn—all packed into that slender, urban sculpture.
But efficiency isn’t all—these liquid trees double as benches, streetlights, and mobile‑phone charging hubs, powered by solar panels. They are designed to blend into sidewalks and squares as functional, welcoming infrastructure.
Real-World Beginnings: Belgrade’s Experiment And Global Interest
Belgrade serves as the testbed. In 2021, the city installed the first urban LIQUID 3 model in Stari Grad, a neighbourhood notorious for heavy pollution—even ranking fourth worst in Serbia. United Nations Development Programme representative Francine Pickup explains that more than 59% of Serbia’s population lives in urban areas where planting traditional trees is near‑impossible due to space and pollution.
UNDP characterised this liquid “aquarium” as “a completely new biotechnological solution for air purification and the production of oxygen.” The algae, resistant to extreme temperatures and hardy conditions, work non‑stop: after about one and a half months, biomass is harvested—usable as fertilizer—refilled with nutrients, and the system resumes operation.
Interest has soared. Trending videos from EuroNews and The National Desk in Washington highlight global curiosity, calling them “simply tanks filled with water and green algae” that capture CO₂ in spaces too tight for conventional trees.
Beyond Carbon: Hidden Perks And Plumbing The Fourth Point
While carbon removal is the headline benefit, there’s a fourth aspect you must know: air pollutant capture. These photo‑bioreactors don’t just bind CO₂—they actively filter out particulate matter, heavy metals, allergens, even microplastics. Unlike passive trees, which trap some dust on leaves temporarily, liquid trees offer continuous filtration in a contained system.
UNDP and biophysicist Dr Spasojević emphasise that while liquid trees don’t aim to replace forests, they provide a targeted remedy in urban nooks where planting fails. And though a liquid tree won’t provide shade, wildlife habitat, or the cooling effects of evapotranspiration (the invisible, refreshing breath of leaves), it does offer rapid, high‑efficiency filtration—a complement, not a substitute.
Balancing Tech And Nature
Online discussion reflects both admiration and caution. A Reddit user from r/environmental_science cautioned:
“Clean air is just one of the many benefits trees in urban environments provide… it doesn’t provide shade which helps cool down… doesn’t help regulate water and probably also doesn’t bring mental relief.”
That critique strikes at the heart of why liquid trees aren’t magic bullets. They lack the cooling canopy, biodiversity support, and seasonal beauty of their leafy counterparts. Yet, championing both sides, advocates like Sam Bentley‑inspired writers note that we don’t punitively pit one against the other. Instead, we weave both into a tapestry of resilience and hope.
Promise, Scalability And Room For Improvement
Science supports the urgency. A June 2024 Reuters analysis underscores that to meet climate goals, carbon removal efforts need to roughly quadruple—from today’s 2 billion tonnes annually to 7–9 billion. While vast tree planting and oceanic algae are vital, urban innovations like liquid trees can chip away at that colossal target in the heart of our cities.
In Europe, systems like Germany’s CityTrees—vertical moss filters—have popped up in major cities, targeting particulate matter with moderate success. Unlike liquid trees, they absorb dust but not CO₂. Some have drawn criticism over effectiveness and costs. Liquid trees may offer a richer solution: CO₂, particulates, metals—packed into a compact, multifunctional structure.
A Human Pulse Amid Glass And Green
Picture Mara, a Belgrade bus driver: she rests for a moment on a liquid tree bench after a grueling morning route. As traffic thunders and dust clouds rise, she watches the sun catch iridescent algae inside the glass cylinder. It whirs quietly and Mara inhales deeply—just enough of a clean breath to remind her why she keeps coming back to this city.
One morning, a university student stops to plug in her phone at the integrated charging port. She marvels at the green glow, snaps a picture, and tweets: “City breathing tech.” Social media ignites. Soon, engineering professors and city planners tour the installation, eyes lighting up at the melding of design, biology, and public utility.
Looking Ahead With Hope
Belgrade paved the way—founded by Dr Spasojević, supported by UNDP, housed in Stari Grad, and humming in sidewalks since 2021. But this is just the beginning. Similar projects in Turkey integrate AI‑controlled systems, tackling indoor air in offices, homes, schools—and use harvested algae not just as fertilizer but raw material for bioplastics, nutraceuticals, even cosmetics.
Over time, design improvements—transparent pipework, solar autonomy, interactive displays—could make liquid trees common landmarks. They won’t dwarf real forests, but they could clean air, teach science, and spark global dialogue on rethinking our cities as ecosystems, not eyesores.
Conclusion
No single solution will fix climate chaos or urban smog. Trees remain foundational to urban health, delivering shade, habitat, and wellbeing. However, liquid trees offer a complementary tool—compact, efficient, and futuristic—especially in spaces where soil and sunlight struggle to reach.
For those heartened by innovation and uplifted by collaboration, this is a story of hope. In the soft hum of algae‑filled columns across the world, we glimpse a city breathing lighter—and a future designed to heal, steadily and together.
