Abstract: A process for the biological purification of effluent which is contaminated with nitrogen in the form of ammonium, nitrite or nitrate ions or in the form of organic compounds, by oxidizing the nitrogen under aerobic conditions and reducing the nitrogen under anaerobic conditions, wherein the sewage to be treated, mixed with activated sludge, is subjected, in an aeration basin, to oxygen-containing gas bubbles introduced from below and is thereby simultaneously enriched with dissolved oxygen, to oxidize carbon compounds and nitrogen compounds, and transported upward, by the buoyancy of the gas bubbles, releases gas at the surface of the liquid and, due to the higher average density of the mixture of lower gas content, in part automatically again flows downward in the aeration basin, to undergo further aeration, while in part it overflows into a denitrification basin which communicates with the aeration basin through an opening at the liquid surface, and an opening at the bottom of the partition, is mixed, in t

Abstract: Treatment of waste water produced in the manufacture of expandable polystyrene, comprising passing a stream of fine gas bubbles through the waste water and removing the resulting foam containing a high concentration of impurities from the aqueous phase. In a special embodiment of the invention, the aqueous phase can then be subjected to further treatment.

Abstract: Method of biologically treating waste water with gasifying nozzles producing a screw-type flow in the activated sludge system. The method provides a maximum partial pressure gradient for the transfer of oxygen to the mixture of waste water and activated sludge.