Abstract: In the biological purification of sewage water or drinking water, it is known to purify the water in a filter bed of granular filter medium, wherein the filter medium is transported from the bottom of the bed to its upper side with the aid of air, so as to obtain a continuously working filter. It is suggested in accordance with the invention that the amount of filter medium to be transported is divided into two or more parts which are transported in parallel, so as to prevent the flow conditions in the transport tube having a negative effect on the reactivity of the filter bed by decreasing the bacteria strain.

Abstract: A suspension is delivered to a filter bed comprised of granular filter medium in a continuously working filter at the lower part of the bed and is then permitted to flow upwards through the bed. With the intention of optimizing the capacity of the filter, the suspension is now guided into a central region of the bed. The suspension is divided from this region into at least two specific proportional quantities which are each led from the filter bed in a respective ring-shaped pattern at mutually different heights in relation to the extension of the bed, these ring-shaped patterns having different diameters and each being adapted to the extension of the filter medium in the direction of the diameter.

Abstract: A filtering process for and apparatus separating air bubbles and granular filter medium from a filtrate contaminated by the filter medium and bubbles when passing through a filter bed formed by the filter medium for treatment of a suspension or liquid solution, a gas being passed through the filter medium in contact therewith, includes providing a treated filtrate zone (3) above the filter bed (2), collecting the treated filtrate in the filtrate zone, conducting granular filter medium from the filter bed (2) upwardly through a conveying pipe (4) to a position above the filter bed and thereafter downwardly through a washing apparatus (5) from which the filter medium is precipitated onto a plate (11) above the filter bed.

Abstract: A gas is blown into a filter (1) having a granular filter bed such that the gas flows into the bed along at least one elongate free edge disposed in the bed.

Abstract: A method of reducing nitrogen, phosphor, and excessive biological oxygen demand (BOD) in wastewater supplied to and passing through a granular filter bed activated with bacteria includes in the flow direction of the wastewater through the bed simultaneously precipitation of phosphorous, denitrification and reduction of the excessive BOD in a single process step. The reduction of excess BOD is produced by blowing in an oxygen-containing gas, preferably air. Immediately before the wastewater enters the filter bed a precipitation/flocculation agent may be added for precipitation of phosphor.

Abstract: The invention relates to a heat transfer from waste water from a building back to the building. The waste water is supplied to a waste pipe (2) in such a way that it is forced to flow downwardly in the pipe along its inner wall. Heat from the waste water is transmitted to a medium flowing on the outside of the pipe.