It is a compact unit where sand and oil removal during pre-treatment takes place in a single stage. When the waste water enters the compact unit, it first passes through the grid channel. The wastes accumulated on the grating surface are discharged by passing through the grating press. Waste water passing through the grating channel is transferred to the sand and oil trap section. The sand contained in the waste water is deposited on the tank bottom and dewatered by a spiral conveyor and removed from the system. Oil accumulated on the surface is removed by a scraper or sluice system according to the operating needs.