This urban algae canopy displayed at the Expo Milano is capable of producing oxygen equivalent to that produced by 4 hectares of dense woodland. Since microalgae organisms normally are 10 times more effective in the process of photosynthesis than grass or large trees, they are super-efficient when it comes to producing oxygen.
https://truththeory.com/2019/11/03/this-algae-canopy-produces-the-same-amount-of-oxygen-as-four-hectares-of-woodland/