Abstract: The invention provides a method of inhibiting biological damage to a cellulosic structural element exposed to environmental moisture, said method comprising applying a pulsed asymmetric electrical voltage to a decay-prone region of a said element over a prolonged time period.

Abstract: A method for biological purification of wastewater is disclosed, wherein the wastewater is purified in a biofilm process followed by an activated sludge process. The biological degradation in the biofilm process is performed under limitation of one of the nutrient salts nitrogen or phosphorous, and the surplus sludge from the biofilm process is allowed to pass to the activated sludge process.

Abstract: The invention refers to a carrier element to be used as a carrier for a microbial film in a biological water or waste water purification process in which the carrier elements are kept moving in the water. The surface of the carrier element is partly protected against collision with the surfaces of the other carrier elements. The carrier element has flow passages therethrough and is moreover designed to allow good flow of water therethrough also after a microbial film having been established on the surfaces. The carrier element has a length, width and/or height which exceeds 1.5 cm, and the protected area is larger than 100 m.sup.2 /m.sup.3 of the volume of the carrier element. The cross-sectional area of the passage opening in the boundary surface towards the surroundings of the element comprises at least 35% of the boundary surface towards the surroundings of a homogenous body having the same dimensions.

Abstract: A method for water purification in which waste water is fed into a reactor containing carriers having a biofilm which promotes a desired conversion of impurities, using carriers which are particulate elements having a larger surface than smooth elements of the same dimension and having a density in the range 0.90 to 1.20, normally 0.92 till 0.98, particularly 0.92 to 9.96 kg/dm.sup.3, wherein the carriers with biofilm are kept suspended in the water in a reactor for aerobic, anoxic or anaerobic water purification, comprising inlet and outlet tubes and optionally mixing means, and containing a large number of carriers for biofilm. This reactor is also comprised by the present invention.

Abstract: A method for water purification in which waste water is fed into a reactor containing carriers having a biofilm which promotes a desired conversion of impurities, using carriers which are particulate elements having a larger surface than smooth elements of the same dimension and having a density in the range 0.90 to 1.20, normally 0.92 till 0.98, particularly 0.92 to 0.96 kg/dm.sup.3, wherein the carriers with biofilm are kept suspended in the water in a reactor for aerobic, anoxic or anaerobic water purification, comprising inlet and outlet tubes and optionally mixing means, and containing a large number of carriers for biofilm. This reactor is also comprised by the present invention.