PURPOSE: To perform self-system internal treatment near to a closed cycle treatment by mounting a water impermeable sheet, a drain conduit, a storage tank, a water sprinkling conduct equipped with nozzles and a main pipe containing a pump supplying sewage to the water sprinkling conduit under pressure.

CONSTITUTION: Rain falling on a reclaimed land is guided by a water impermeable sheet to be accumulated on a bottom part and passes through the drain conduit 4 communicating with the bottom part of the reclaimed land to reach a storage tank 7 to be stored therein. A pipe equipped with a large number of nozzles 15 is suspended above the reclaimed land and the water stored in the storage tank 7 is pressurized by a pump 8 to be injected in a mist form from the nozzle 15 through respective water guide pipes. The greater part of the stored water injected from the respective nozzles 15 is evaporated in space. By this constitution, since the greater part of sewage accumulated in the storage tank 7 can be evaporated in space, the efficiency of sewage treatment is markedly enhanced and the sewage scattering-uniform control means of a conventional discharge gun can be dispensed with.