NOVELTY - A bioreactor (100) for cultivating microorganisms (150) comprises: at least one liquid permeable layers (110) comprising a first surface (111) and a second surface (112), where microorganisms are cultivatable on the first surface of the liquid permeable layer and the second surface is connectable in fluid communication with a fluid source, and where the liquid permeable layer is rotatable. The bioreactor further comprises a rotation member (130) for rotating the liquid permeable layer; fluid reservoir (160); and housing (200).    USE - For cultivating microorganisms. The microorganisms are photosynthetic microorganisms, methanotrophic microorganisms, yeast and/or benthic microorganisms. The photosynthetic microorganisms are algae, microalgae and/or cyanobacteria (all claimed) such as Scenedesmus obliquus (Chlorophyta), Isocrysis glabana (haptophyta), Nannochloropsis sp. (Eustigatophya), Tetraselmis Suecica (Chlorophyta), Phaeodactylum tricornutum (Bacillariophyta), Botryococcus braunii (Chlorophyta) and Spirulina (Cyanobacteria). Also used for the production of biomass, biofuels, animal feed, waste water remediation, the production of high value compounds (e.g. oils), CO2 remediation and/or the production of fertilizer.    ADVANTAGE - The bioreactor exhibits increased and uniform microorganism growth and productivity for generating high density cultivated biomass, specifically photosynthetic microorganisms, such as algae, as well as reduced contamination of the microorganisms and reduced harvesting time when compared to existing technologies.    DETAILED DESCRIPTION - A bioreactor (100) for cultivating microorganisms (150), comprises: at least one liquid permeable layers (110) comprising a first surface (111) and a second surface (112), where microorganisms are cultivatable on the first surface of the liquid permeable layer and the second surface is connectable in fluid communication with a fluid source, and where the liquid permeable layer is rotatable. The bioreactor further comprises a rotation member (130) for rotating the liquid permeable layer; fluid reservoir (160); and housing (200). The fluid source comprises a fluid conducting layer. The fluid conducting layer comprises a fluid conducting material. The fluid source is selected from water, nutrients, growth media, waste water and secondary treated sewage. INDEPENDENT CLAIMS are included for the following:    (1) method for cultivating microorganisms involving rotating the liquid permeable layers comprising a first surface and a second surface, where the second surface is in fluid communication with a fluid source; and cultivating the microorganisms on the first surface; and    (2) a system for cultivating microorganisms comprising liquid permeable layers comprising a first surface comprising microorganisms and a second surface in fluid communication with a fluid source; and a rotation member for rotating the liquid permeable layer, to facilitate microorganism growth.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of the bioreactor.    Bioreactor (100)    Liquid permeable layer (110)    First surface (111)    Second surface (112)    Rotation member (130)    Stand (140)    Microorganisms (150)    Fluid reservoir (160)    Central axis (180)    Housing (200)