NOVELTY - The small wastewater treatment system for domestic wastewater, comprises a buffer memory (8) for unfiltered or roughly filtered domestic wastewater, a photocatalytic collector (10), which has photocatalytically coated surfaces on which the wastewater is flowed and cleaned. The photocatalytic collector comprises glass- and/or plastic tubes by which the wastewater flows and whose inner side forms the photocatalytic active coated surface. The photocatalytic collector comprises a glass- and/or plastic plate, which covers a tube- or channel system through which the wastewater flows.    USE - Small wastewater treatment system useful for domestic wastewater.    ADVANTAGE - The small wastewater treatment system is effective.    DETAILED DESCRIPTION - The small wastewater treatment system for domestic wastewater, comprises a buffer memory (8) for unfiltered or roughly filtered domestic wastewater, a photocatalytic collector (10), which has photocatalytically coated surfaces on which the wastewater is flowed and cleaned. The photocatalytic collector comprises glass- and/or plastic tubes by which the wastewater flows and whose inner side forms the photocatalytic active coated surface. The photocatalytic collector comprises a glass- and/or plastic plate, which covers a tube- or channel system through which the wastewater flows, where the glass- and/or the plastic plate part is provided with the tube- or the channel system, which forms the inner side facing the glass- and/or the plastic plate of the photocatalytic coated surface. The photocatalytic collector comprises the tube- or the channel system by which the wastewater flows, where the tube- or the channel system comprises glass- or plastics beads and/or glass- or plastic splitter, which forms the photocatalytic coated surface. The photocatalytic collector comprises mirror systems for bundling and/or concentrating and/or canalization and/or steering of incident radiation. The photocatalytic collector module is formed from collector modules, which comprise a carrier plate on which all other collector components are mounted. The small wastewater treatment system comprises a clean water reservoir such as a cold water reservoir and/or a hot water reservoir. The photocatalytic collector is arranged in such a way that the flow of the wastewater is evoked by the photocatalytic collector of a free convection current by heating the wastewater entering into the collector or roughly filtered wastewater by the incident electro magnetic solar radiation in the photocatalytic collector. The small wastewater treatment system comprises a circulation pump, which is arranged in such a way that the pump promotes in operation of the wastewater by the photocatalytic collector, and comprises a photovoltaic system for the energy supply of the circulation pump, a coarse material filter unit (2), which is arranged in such a way that roughly filtered wastewater is guided into the photocatalytic collector and comprises a thermal composter for deteriorating solids (4) such as filtered solids from the wastewater, where the thermal composter comprises a hot water-heating device, which is guided by cleaning and heating water into the photocatalytic collector. An INDEPENDENT CLAIM is included for a domestic water system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of a small wastewater treatment system for domestic wastewater.    Coarse material filter unit (2)    Solids (4)    Buffer memory (8)    Photocatalytic collector (10)    Hot water storage. (13)