Carrier element, biological water treatment system and their use, and method for biologically treating waste water
The invention relates to a carrier element for an aerobic biological water treatment system. The carrier element has a first end and a second end at a distance from each other, the maximum diameter of the first end being larger than the maximum diameter of the second end. It also has biofilm growing surface structures that extend from the first end to the second end and from inner part of the element towards periphery of the element 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 define 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 between the support structures. The invention relates also to a water treatment system employing the carrier elements.
1. Carrier element for an aerobic biological water treatment system, the 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.
2. Carrier element according to claim 1 , characterized in that the first end has a diameter in the range of 11.0-13.6 mm.
3. Carrier element according to claim 1 characterized in that the second end has a diameter in the range of 8.5-11.3 mm.
4. Carrier element according to claim 1 , characterized in that the ratio of the diameter of the first end and the diameter of the second end is over 1.2.
5. Carrier element according to claim 1 , characterized in that the apertures in the outer boundary surface of the carrier element against the cross sectional area of a similar solid element boundary surface are over 42%.
6. Carrier element according to claim 1 , characterized in that it is made of hard plastic material.
7. Carrier element according to claim 1 , characterized in that the cross-sections of the first and second ends are circular.
8. Carrier element according to claim 1 , characterized in that the carrier element is made of injection molded plastic.
9. 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.
10. Biological water treatment system according to claim 9 , characterized in that the filling degree of carrier elements in the reactor is between 14-28 volume-%, of the total reactor volume.
11. Biological water treatment system according to claim 9 , characterized in that the reactor comprises a bottom aeration system comprising one or more grid-like aeration elements.
12. Biological water treatment system according to claim 11 , characterized in that the grid-like aeration elements comprise a main air feed pipe and a number of air diffusers arranged perpendicularly to the air feed pipe.
13. Biological water treatment system according to claim 11 , characterized in that the aeration elements comprise one or several air diffusers that are made of plastic material.
14. Biological water treatment system according to claim 11 , characterized in that the aeration system is arranged self-flushing.
15. Biological water treatment system according to claim 9 , characterized in that it comprises two or more treatment reactors arranged in parallel or in series.
16. Biological water treatment system according to claim 9 , characterized in that it comprises a clarifier, selected from the group consisting of a gravity settler, dissolved air flotation (DAF), and lamella clarifier, arranged after the treatment reactor and connections for recycling sludge from clarifier back to treatment reactor.
17. Biological water treatment system according to claim 16 , characterized in that in the upper part of the treatment reactor is arranged an output connection, which is connected to the clarifier.
18. Biological water treatment system according to claim 9 , characterized in that it comprises an oxygen sensor that is arranged in connection with the treatment reactor to measure oxygen concentration in the reactor and an adjustment means for adjusting the aeration of the reactor according to the measured oxygen concentration.
19. 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.
20. Method according to claim 19 , characterized in leading treated or purified water to a clarifier, and recycling sludge from the clarifier back to treatment reactor.
21. Method according to claim 20 , characterized in that the volume of the recycled sludge flow is 2-15 volume-% of the incoming flow of water to be treated or purified.
22. Method according to claim 19 , characterized in leading treated or purified water away from the upper part of the treatment reactor.
23. Method according to claim 19 , characterized in rotating the carrier elements in a counterclockwise direction against the incoming feed flow in the treatment reactor.
24. Method according to claim 19 , characterized in leading the sludge from the treatment reactor to an activated sludge process located between the treatment reactor and clarifier.