Reactor plant and process for culturing phototropic microorganisms with a reactor vessel and a photosynthetic module, which are connected with one another in a circulation circuit by a pump and can be controlled via a control unit, where in the circulation circuit or in the reactor vessel, a homogenizer is provided, where a light-intensity control of the photosynthetic module is provided, and where a bypass of the circulation circuit or of the reactor vessel with a filter device which is arranged externally of the reactor vessel for separating off extracellular products during the fermentation is provided.