Photobioreactors for culturing microalgae at aquaculture and at wastewater treatment. They can be applied in reactors fields, aquaculture of microalgae or in the WWTP as tertiary refining process (last treatment processes before the algae are removed from the water). The reactors contain microalgae, that filter residual polluting particles with the use of photosynthesis. The bioreactors are placed in series and their amount can be adapted to the needs of the customer. The bioreactors can also be sold separately to be used in other WWTP or aquaculture.