Belgrade, Belgrade (FUA), Serbia
City population: 1685563
Duration: 2021 – 2024
Implementation status: Completed
Scale: Sub-microscale: Street scale (including buildings)
Project area: 6 m2
Type of area: Central Business District / City Centre
Last updated: May 2025

Liquid 3 is the first urban photo-bioreactor in Serbia, developed by an interdisciplinary team at the Institute for Multidisciplinary Research at the University of Belgrade (Ref. 1,2,3). Prompted by an appeal of the United Nations Development Programme (UNDP), the team was eager to find novel approaches to combat the city's severe air pollution issues while being space efficient and providing year-round benefits (Ref. 3). The key to the bioreactor are algae which are very efficient in sequestering carbon and filtering heavy metals from the air (Ref. 2). A Liquid 3 feature can be quickly set and occupies a plot of only 3 m². Some of its benefits include its ability to withstand high levels of air pollution and its ease of installation on surfaces like walkways and other sealed infrastructure (Ref. 2,3). Additionally, by design, Liquid 3 integrates amenities such as power outlets, a bench, and nighttime lighting (Ref. 1). The selected strain of algae can tolerate temperatures between 5-35°C making it deployable all year. However, monthly maintenance is required, during which the water and algae are replaced—both of which can be repurposed, for example, as fertilizers (Ref. 6).The project has received global media coverage as well as a prize for the best innovative and climate-smart solution in Serbia. Its success has prompted the installation of two more such bioreactors in Serbia, with interest coming from other countries such as Hungary and the UAE (Ref. 1,4).

Installed Liquid 3
Installed Liquid 3
https://www.undp.org/serbia/news/first-algae-air-purifier-serbia

Overview

Nature-based solution

  • Nature on buildings (external)
  • Green walls or facades

Key challenges

  • Environmental quality
  • Air quality improvement
  • Health and well-being (SDG 3)
  • Creation of opportunities for recreation
  • Improving physical health

Principal problems in Functional Urban Area (FUA)

  • Environmental Degradation
  • Air pollution
  • Health, Well-being and Social cohesion
  • Physical health harm (from pollution, wildfire, extreme temperature)

Key priorities

Social Justice and community

Focus

Creation of new green areas, Creation of any other green urban spaces, Knowledge creation and awareness raising, Scientific research of biodiversity or ecosystems, Other

Project objectives

- Provision of an innovative solution to combat air pollution (Ref.1), with delivery of year-round benefits (since it is operational during the winter months) (Ref. 3) - Popularize and expand the use of microalgae in Serbia by drawing attention to their co-benefits, such as water purification or biomass application as fertilizer (Ref. 2) - Increase awareness of innovative urban greening and environmental protection (Ref. 1) - Offer other functional amenities - i.e. integrated street light, power outlets, bench (Ref. 2,3)

Implementation activities

1) Development Phase (3 years): Identify the most suitable stain of algae for the project purpose (i.e. resistance to heat and cold) (Ref. 6, 1:05) 2) Installation: "The bioreactor consists of a glass tank filled with 600 litres of water and microalgae and a solar panel, which supplies electricity to a small pump." (Ref. 3), "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 (Ref. 2).", "The microalgae need heating if temperatures drop below five degrees. Therefore, the photo-bioreactor is also connected to the city grid in addition to the solar panel" (Ref. 3) 3) Maintenance: "Every month, the amount of water with microalgae has to be changed almost entirely, and the biomass has to be taken out. (Ref. 3), "The Public Utilities Company Greenery Belgrade could use it to fertilise lawns and flowerbeds" ( Ref. 6, 1:30) 4) Knowledge Dissemination: "Our team member delivered a lecture on Liquid3 at the Technical University of Munich" (Ref. 1)

Main beneficiaries

  • Researchers/University
  • Citizens or community groups

Governance

Management set-up

  • Led by non-government actors

Type of initiating organisation

  • Researchers/university
  • Multilateral organisation

Participatory approaches/ community involvement

  • Unknown

Details on the roles of the organisations involved in the project

"Lead institution: University of Belgrade – Institute for Multidisciplinary Research" (Ref. 1) "The first urban photo-bioreactor in Serbia [...] was implemented by the UNDP in partnership with the Ministry of Environmental Protection, with the financial support of the Global Environment Facility (Ref. 4) "The municipality of Stari Grad, provided the location and allowed the installation of the system. (Ref. 1) Regarding the other two intallations "The action is part of a wider regional initiative, within which all member banks of the NLB Group will support various associations" (Ref. 4)

Project implemented in response to ...

... an EU policy or strategy? Unknown
... a national policy or strategy? Unknown
... a local policy or strategy? Unknown

Type of enablers

Technological innovations, Support from transitional governance actors, NBS research project (e.g., H2020, Urban Living Labs, national research projects)

Financing

Total cost

Less than €10,000

Source(s) of funding

  • Multilateral funds/international funding
  • Commercial banks

Type of funding

  • Direct funding (grants, subsidies, or self-financed projects by private entities)
  • Donations

Non-financial contribution

Unknown

Impacts and Monitoring

Environmental impacts

  • Climate change
  • Enhanced carbon sequestration
  • Achieved enhanced carbon sequestration
  • Environmental quality
  • Improved air quality
  • Achieved improved air quality
  • Other

Economic impacts

  • Other

Socio-cultural impacts

  • Health and wellbeing
  • Improved prevention of respiratory problems
  • Expected improved prevention of respiratory problems
  • Education
  • Increased support for education and scientific research
  • Achieved increased support for education and scientific research
  • Increased awareness of NBS and their benefits
  • Achieved increased awareness of NBS and their benefits
  • Other

Type of reported impacts

Presence of formal monitoring system

Yes

Presence of indicators used in reporting

Yes

Presence of monitoring/ evaluation reports

No evidence in public records

Availability of a web-based monitoring tool

No evidence in public records

Potential risks of implementation and trade-offs

Other

References

1.
Spasojević, I. (n.d.). Liquid 3 Urbani fotobioreaktor | Urban Photo-Bioreactor. Accessed on August 24, 2024, [Source link];
2.
UNDP (2021). The first algae air purifier in Serbia. Accessed on August 24, 2024, [Source link];
3.
Krieger, B. (2022). Liquid tree to combat air pollution in Belgrade. Balkan Green Energy News, Accessed on August 24, 2024, [Source link];
4.
EKOlist (2023). Donacija inovativnog domaćeg patenta „tečnog drveća“ najzagađenijim opštinama u Srbiji. Accessed on August 24, 2024, [Source link];
5.
FoNet (2022). Bojić: Postavljeno prvo „tečno drvo“ u Srbiji ispred SO Stari Grad. N1, Accessed on August 24, 2024, [Source link];
Illustration of the design, processes and functions of the Liquid 3
Liquid 3 Illustration
https://liquid3.rs/about/
naturescapes bannerInformation about this nature-based solution was collected as part of the Naturescapes project funded by the European Union under Grant Agreement No 101084341.