NOVELTY - The wastewater treatment system comprises a main reactor (1) containing a material of granular filter bed (2), a device (4) to discontinuously inject the wastewater disposed into the main reactor above the filter bed so that downdraft wastewater passes to a recovery tank (3) through the bed, and a device (7) to discontinuously inject oxygen or air in the filter bed. The material is fixed and based on a recovery tank of treated water. A first reactor (5) is arranged for initial temporary storage of wastewater to be treated for one day before injecting in the filter bed.    USE - The system is useful for treatment of wastewater such as domestic sewage and wastewater obtained from agri-food industry and/or agro-industrial sector.    ADVANTAGE - The system is compact and easy to install, ensures simple and energy efficient treatment of wastewaters with improved performance, and allows to discharge the wastewater into the natural medium without affecting the quality of water and the environment.    DETAILED DESCRIPTION - The wastewater treatment system comprises a main reactor (1) containing a material of granular filter bed (2), a device (4) to discontinuously inject the wastewater disposed into the main reactor above the filter bed so that downdraft wastewater passes to a recovery tank (3) through the bed, and a device (7) to discontinuously inject oxygen or air in the filter bed. The material is fixed and based on a recovery tank of treated water. A first reactor (5) is arranged for initial temporary storage of wastewater to be treated for one day before injecting in the filter bed, and comprises an enzyme bed to accelerate and facilitate the development of bacterial mass contained in wastewater. The wastewater injection device comprises nozzles arranged above the filter bed to ensure an even distribution of wastewater in the bed. The oxygen or air injection device is arranged at the bottom of the filter bed or inside a core of the filter bed so that aerobic wastewater is aerated throughout its passage. The oxygen or air is injected at the same time as the wastewater. The first reactor is either connected to or independent of the main reactor, and is equipped with a level sensor so that a unit of a pumping device allows to bring the bacteria enriched wastewater from the first reactor into the main reactor when the wastewater reaches a predetermined level. The oxygen or air injection device comprises injection nozzles at the core of the filter bed, where the nozzles are connected to an air pump coupled to a set of photovoltaic cells for providing electrical supply. The granular filter bed material consists of a grit with a particle size of 15-20 mm, and is made of non-calcareous siliceous sand having a particle size of 2-5 mm. The recovery tank is separated from the filter bed with a grill or a grating. An INDEPENDENT CLAIM is included for a process for treating the wastewater.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic sectional view of a wastewater treatment system.    Main reactor (1)    Filter bed (2)    Recovery tank (3)    Wastewater injection device (4)    First reactor (5)    Oxygen or air injection device. (7)