NOVELTY - The collector or system comprises a vessel that comprises surfaces for collecting a biomass from a fluid directed through the vessel and internal impellers in fluid communication with the surfaces through a circulatory fluid flow path, where the internal impellers facilitate a flow of the fluid through the fluid flow path, and an external impeller coupled to the internal impellers, where the external impeller is disposed external to the vessel and adapted to provide rotational energy to the internal impeller upon fluid flow through or adjacent to the external impeller.    USE - The collector or system is useful for collecting and/or harvesting biomass (claimed) such as algae biomass, which is useful for the production of bio fuels, green chemicals and nutraceuticals.    ADVANTAGE - The collector or system collects or harvests the biomass with high yield in an economical and energy efficient manner thus producing the bio fuels in an eco-friendly manner.    DETAILED DESCRIPTION - The collector or system comprises a vessel that comprises surfaces for collecting a biomass from a fluid directed through the vessel and internal impellers in fluid communication with the surfaces through a circulatory fluid flow path, where the internal impellers facilitate a flow of the fluid through the fluid flow path, and an external impeller coupled to the internal impellers, where the external impeller is disposed external to the vessel and adapted to provide rotational energy to the internal impeller upon fluid flow through or adjacent to the external impeller. The surfaces are part of plates (407). The vessel further comprises a magnet or electromagnet that is partially enclosed by an exterior wall of the vessel, a first module, and a second module. The collector further comprises a self-orienting mechanism capable of orienting a direction of the vessel with respect to a direction of a current flow when the vessel is positioned in a current, a movable gate that partially isolates the fluid flow path, a membrane/sieve in the first module, a third module, a fourth module located between the first and second modules, and a nutrient concentrator. The second module is located in downstream of the first module along fluid flow path extending from the first module to the second module, and the first module includes internal impellers for facilitating the fluid flow through the first and second modules. The membrane/sieve is included in the fluid flow path. The surface and internal impellers are disposed in separate modules. The first module is adapted to accept a fluid stream, where the first module includes a gate that is adapted to regulate the flow of the fluid stream. The second module accepts the fluid from the first module, and directs a portion of the fluid to the first module. The third module is located in downstream of the second module, and includes surfaces for retaining microorganisms upon the flow of a portion of the fluid stream through the third module. The first module and second module are separable from one another. The second module and third module are separable from one another. The external impeller is external to the first, second and third modules. The fourth module extends a length of the fluid flow path from the first module to the second module, and includes an optical window for permitting electromagnetic radiation for coming in contact with the portion of the fluid stream. The nutrient concentrator is located in upstream of the first module, is adapted to concentrate nutrients in the fluid stream before entering to the first module, and includes a magnetic field source that is adapted to induce a magnetic force that concentrates the nutrients. An INDEPENDENT CLAIM is included for a method for collecting and/or harvesting biomass.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic side view of a system for collecting biomass.    Upstream module (401)    Extension module (402)    Divider (405)    Plates (407)    Lid. (412)