Abstract: In a process for the biological purification of wastewater, the wastewater is mixed with activated sludge in an aeration basin in the presence of carrier particles for microorganisms and is aerated with an oxygen-containing gas. Treated wastewater and free activated sludge are discharged from a discharge zone of the aeration basin downstream of an initial zone at least 20% up to 70% of the length of the aeration basin.

Abstract: In the treatment of wastewater, the mixture of wastewater and the sludge is transported through a treatment zone, and then through a filter zone containing a bed of support particles, e.g., particles of polyurethane foam, to deposit the biomass onto the support particles. The loaded support particles are subsequently regenerated within the filter zone by means of a regenerating means in the same area as the filter zone, e.g., by strong aeration or by being compressed between press-rolls, whereby the system requires neither additional land for regeneration of the support particles nor a secondary settling tank.

Abstract: In an activated sludge process for the biological purification of wastewater wherein undesirable bulking sludge is formed in addition to normal activated sludge, the improvement which comprises mechanically destroying the microorganisms causing the bulking sludge without substantially destroying the microorganisms required for the normal activated sludge.

Abstract: In a process for the biological purification of wastewater wherein the wastewater is treated in a purification plant comprising at least one storage tank and at least one biological treatment stage, the improvement wherein the entering wastewater, in case of normal load, is introduced directly into the biological treatment stage and, during the time period of peak loads, is introduced at least partially into the storage tank; and that, after the subsiding of the peak loads, the wastewater is transferred from the storage tank into the biological treatment stage. A process variable associated with the biological treatment stage, such as oxygen, or one associated with incoming wastewater such as BOD, is used to automatically regulate the timing of the flows.

Abstract: An apparatus for introducing gas, e.g. atmospheric oxygen, into a liquid such as waste water or sewage comprises a plurality of ribs of airfoil cross-section and forming venturi nozzles which are first constricted and then widened in the direction of liquid flow. The ribs are formed with minute passages for introducing the gas into the liquid perpendicular to the direction of liquid flow across the ribs.

Abstract: An apparatus for introducing gas, e.g. atmospheric oxygen, into a liquid such as waste water or sewage comprises a plurality of ribs of airfoil cross-section and forming venturi nozzles which are first constricted and then widened in the direction of liquid flow. The ribs are formed with minute passages for introducing the gas into the liquid perpendicular to the direction of liquid flow across the ribs.