Sand trappers are used for separating inorganic substances like sand or pebbles from water, and avoiding wear of pumps and similar equipments in treatment facilities and occlusion at settlement pools. These structures might not be needed for removal of industrial waste waters which do not contain sands and similar substances. Sand trappers are used for trapping solid substances with density higher than 2650 kg/m³ and a particle diameter larger than 0.1-0.2 mm. Removel of the mud settled at the base is ensured through a pump which shuttles on the bridge.