Planting trees in forests is a commonly used strategy for companies and governments to lower CO2 in the air. But what can we do in dense cities where there’s barely any space for a bush? After all, these urban sites are where the pollution is concentrated. Fortunately, a group of Serbian scientists has come up with an ingenious solution: a liquid tree.
According to the IHME Global Health Data Exchange Tool, “pollution kills three times as many people a year as HIV/AIDS, tuberculosis, and malaria combined”.
Because of two very large coal power plants, Belgrade is one of the most polluted cities in Serbia. In fact, these two power plants are so intense, they were included in the 2019 Health and Environment Alliance (HEAL)’s list of 10 dirtiest plants in Europe.
Overall, Serbia ranked 28 in the world for worst air quality in 2020. Currently, the nation has a PM 2.5 concentration, which is 4.9 times above the WHO annual air quality guideline value. It is then no surprise that the country’s citizens suffer from intense side effects of such pollution. In 2019, the Global Alliance for Health and Pollution published the Global, Regional, and Country Analysis of Pollution and Health Metrics. In the report, Serbia was placed as the #1 country in Europe with the highest pollution-related deaths: 175 per 100,000 people, followed by Georgia and Bulgaria. Some activists in the country have even stated that the pollution can be seen, smelt, and tasted during the winter.
Ms. Francine Pickup, Resident Representative of the United Nations Development Program (UNDP) in Serbia, explained that: “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”. She later continued to explain that 59% of the Serbian population lives in urban areas and that the number is constantly increasing. Because the population density is so high, creating green areas and planting trees – which represent natural air purification in urban areas– is a complex goal to achieve, as there is a lack of free areas for landscaping.
Dr. Ivan Spasojevic, Ph.D. in Biophysical sciences, and one of the authors on the project from the Institute for Multidisciplinary Research at the University of Belgrade, developed an innovative tool for reducing greenhouse gas emissions and improving air quality: the liquid tree. Also dubbed LIQUID 3, the novel creation is Serbia’s first urban photo-bioreactor, a solution in the fight for clean air. It contains six hundred litres of water and works by using microalgae to bind carbon dioxide and produce pure oxygen through photosynthesis.
The microalgae replace two 10-year-old trees or 200 square meters of lawn. The function of the LIQUID 3 is practically an imitation of it. Both trees and grass perform photosynthesis and bind carbon dioxide. However, the advantage of microalgae is that it is 10 to 50 times more efficient than trees. The team behind LIQUID 3 has stated that their goal is not to replace forests or tree planting plans but to use this system to fill those urban pockets where there is no space for planting trees. In conditions of intense pollution, such as Belgrade, many trees cannot survive, while algae do not have a problem with the great levels of pollution.
The LIQUID 3 is placed in front of the Municipality of Stari Grad in Makedonska Street in Belgrade, a busy urban area where CO2 emission where the concentrations are highest.
“The photobioreactor is a completely new biotechnological solution for air purification and the production of oxygen. In an aquarium of six hundred liters of water, we have algae that bind carbon dioxide and produce pure oxygen through photosynthesis. The project is designed to be multifunctional. 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”, said Bojan Bojić, head of the Department for Social Affairs and Development Projects in Stari Grad.
Dr. Ivan Spasojevic also explained that “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. 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. This project aims to popularize and expand the use of microalgae in Serbia, because they can be used in wastewater treatment, as compost for green areas, for the production of biomass and biofuels, as well as for air purification from exhaust gases from the factories”.
Because of its creative, practical, and innovative design, LIQUID 3 was awarded one of the 11 best innovative and climate-smart solutions by the Climate Smart Urban Development project, created by the UNDP, the Ministry of Environmental Protection, and sponsored by the Global Environment Facility (GEF).
The LIQUID 3 comes to show that the promotion of climate-smart urban development is as important as ever. By engaging the civil society, the public, and businesses to come up with new and innovative ideas on how to contribute to this in practice, we can ensure better solutions for climate change mitigation, which will overall have a positive effect across all areas.