Abstract: A carrier for biofilm to be used in wastewater purification plants, comprising a cup-shaped body that is formed by a substantially circular bottom, by a perimetric wall that has substantially a cylindrical symmetry and by an opening that is arranged opposite the bottom for the access of the wastewater; a helical wing runs along the inner side of the perimetric wall and accordingly has a portion of surface that is undercut with respect to the opening. Advantageously, the carrier is constituted by an ordinary screw cap for bottles, which is made of plastics, or by a reject from the production of screw caps for bottles.