It is a compact unit where sand and oil removal occurs in a single stage during pre-treatment. When wastewater enters the compact unit, it first passes through the grate channel. The waste accumulated on the grill surface is discharged through the grill press. Wastewater passing through the grid channel is transferred to the sand and oil trap section. The sand in the wastewater settles on the bottom of the tank, where it is dewatered and removed from the system by a screw conveyor. The oil accumulated on the surface is removed by a scraper or sluice system depending on the operating needs.