Our team at the University of Belgrade has developed a microalgae-based alternative concept of urban greening named urban photo-bioreactor LIQUID3. This concept represents a nature-based solution that targets urban areas and pockets, which cannot accommodate traditional greening due to the lack of space, high value of land, excessive air pollution, or harsh climate, such as squares and pedestrian areas, streets with intensive traffic, public indoor spaces, and cities in the regions with arid climate. The solution relies on the high efficiency of photosynthetic microalgae in CO2 fixation and O2 production and their capacity to sequester heavy metals from particulate matter of highly polluted air (Spasojević and Stojiljković 2021). Microalgae are grown in a combination of flat-panel and airlift bioreactors, which are integrated with a bench, solar USB charger, and a night light and may also serve as a translucent urban barrier or info panel.