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: It is possible to filter a suspension or emulsion in a filter bed of particulate filter medium by allowing the suspension to flow upwards through the filter bed simultaneously as the medium flows downwards through a filtering tank wherein filtration takes place. Filtration thus takes place during counterflow between suspension and filter medium. The supply of suspension takes place in the lower part of the filter bed and the filtered liquid phase is taken away from a zone above the filter bed. The polluted filter medium close to the bottom of the filter tank is taken out for conveyance to a washing apparatus above the filter bed and after washing is returned to the upper side of the filter bed. For providing a filter which has a considerably lower construction height for a given and unchanged volume of the filter medium, the washing apparatus is lowered so that its lower part is at a level below the upper surface of the filter bed.

Abstract: An apparatus for filtering liquids, such as fiber suspensions or polluted water, includes a hollow rotating filter body adapted to receive the liquid to be filtered within the body. A plurality of guide members are attached to the filter body and distributed around the latter to receive cloudy filtrate penetrating the filter body at the descending side. A basin is arranged at the descending side of the filter body to collect cloudy filtrate poured from the guide members. As a result, the cloudy filtrate is prevented from mixing with the clear filtrate.

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 liquid filter comprises a filter rotor with filtering elements and a container for the filtrate. The filtrate is divided in two fractions, a coarse pre-filtrate derived from that side, where the rotor dives into the liquid, and a clear filtrate derived from the opposite side. The pre-filtrate fraction is extracted from the filtrate space such that the filtrate at the side of the container is forced to pass through a number of openings lying close to the liquid surface of the filtrate and leading to a pre-filtrate outlet, whose openings are spaced apart relative to each other and distributed along the rotor.

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.