Liquid3
Liquid 3 is an urban photobioreactor tank full of water and micro-algae installed as way to produce oxygen in cities that have high  in the air. They also have sitting benches and solar energy panel next to them and can be used to fill urban pockets.
They may replace function of an adult tree. They have been used in Serbian cities, such as Belgrade. They are developed through UNDP. It contains 600 liters (159 gallons) of water and works by photosynthesis.

References

External links
https://liquid3.rs/

Belgrade
Bioreactors