Abstract: Method for harvesting microalgae in a culture medium, includes passing the medium through a set of consecutive concentrators; each including a passive filtering unit separating the inner space of the concentrator into an upper and lower volume; the upper volume having an inlet (16) and an outlet (18) arranged at a lower position with respect to the inlet for extracting a more concentrated culture medium from the upper volume; the lower volume having an outlet (32) for extracting a liquid from the lower volume; the inlet (16) of a downstream concentrator being connected to the outlet (18) of the upper volume of the upstream concentrator; and harvesting a concentrated culture medium at the outlet (18) of the upper volume of a concentrator. Preferably, the inlet of the upper volume of an upstream concentrator is located at a greater height than the inlet of the upper volume of the downstream concentrator.

Abstract: A photobioreactor, especially for the growth and development of photosynthetic microorganism such as microalgae or cyanobacteria. The photobioreactor includes at least one reflector (101) placed on one side of the photobioreactor and tubes arranged in a plurality of layers following one after another along a direction (N) normal to the reflector taken at a central region thereof, each layer including a plurality of tubes. Preferably, the tubes (1, 16, etc.) are straight and extend along a direction orthogonal to the normal direction (N), the reflector is cylindrical of circular or oval cross section, and the layers are cylindrical, of circular or oval cross section, and concentric.