Carrier element, biological water treatment system and their use, and method for biologically treating waste water

Biological water treatment system comprising a treatment reactor, which has a reactor volume defined by reactor wall(s) and bottom, which reactor volume comprises freely moving carrier elements, each carrier element having—a first end and a second end at a distance from each other, the length of the carrier element, measured from the first end to the second end, being 11.0-14.9 mm, the maximum diameter of the first end being larger than the maximum diameter of the second end,

• growing surface structures, configured to support the growth of a biofilm, which are internal walls that extend from the first end to the second end and from inner part of the element towards periphery of the element, wherein at least one of said internal walls is triangular shaped, and at least one of said internal walls is quadrangular shaped, the triangular shaped wall having a side at the second end, and a vertex at its first end,
• a solid longitudinal central axis to which the internal walls are attached, and,—at least two support structures that encircle the growing surface structures at the periphery of the element and connect the growing surface structures to each other, the support structures defining the outer boundary surface of the carrier element, whereby the support structures are spaced from each other so that apertures allowing access to the biofilm growing surface structures are formed only between the support structures and the internal walls, the density of the carrier element being 0.92-0.99 kg/dm3.

Method for biologically treating waste water by—leading water to be treated or purified to a treatment reactor comprising carrier elements which are freely moving, suspended in the water, in the treatment reactor and on which a biofilm is grown,

• feeding air or oxygen to the treatment reactor, and
• leading treated or purified water away from the treatment reactor, characterized in using carrier elements in the treatment reactor, each carrier element having—a first end and a second end at a distance from each other, the length of the carrier element, measured from the first end to the second end, being 11.0-14.9 mm, the maximum diameter of the first end being larger than the maximum diameter of the second end,
• growing surface structures, configured to support the growth of a biofilm, which are internal walls that extend from the first end to the second end and from inner part of the element towards periphery of the element, wherein at least one of said internal walls is triangular shaped, and at least one of said internal walls is quadrangular shaped, the triangular shaped wall having a side at the second end, and a vertex at its first end,
• a solid longitudinal central axis to which the internal walls are attached, and,—at least two support structures that encircle the growing surface structures at the periphery of the element and connect the growing surface structures to each other, the support structures defining the outer boundary surface of the carrier element, whereby the support structures are spaced from each other so that apertures allowing access to the biofilm growing surface structures are formed only between the support structures and the internal walls, the density of the carrier element being 0.92-0.99 kg/dm3.