LIQUID3 represents alternative concept of greening that was developed for urban environments which cannot accomodate traditional greening due to the lack of space, high value of land, and excessive air pollution. It relies on photo-bioreactor technology and high efficiency of microalgae in CO2 fixation and O2 production. According to carbon fixation rate, it is equivalent to one adult tree or to 200 m2 of lawn. It is compatible with urban space through multifunctionality, contemprorary design, and safe construction. LIQUID3 enables smart use of city space and promotes environmental awareness.