Abstract: The invention relates to a process for the biological treatment of waste water, in which a mixture of activated sludge and waste water is treated with gas in an activation stage and the activated sludge is separated off from the treated waste water by flotation, wherein the concentration of the activated sludge in the activation stage is .gtoreq.6 g/l and wherein the flotation is a pressure-relief flotation.

Abstract: The invention relates to a device, in particular for the treatment of low-viscosity polymer melts, containing a vessel (1) with a stirrer element, the stirrer element (6) essentially comprising a support structure which passes through the vessel and on which surface formers (8) are arranged. According to the invention, the support structure is designed as a cage-like rod frame (7).This results in the following advantages:1. Owing to the now possible continuous wetting or wiping of the surfaces, encrustations and inhomogeneities are avoided.2. Due to enhanced cascading with weir plates, the residence time spectrum can be controlled, which likewise improves the product quality.3. The flexing of the stirrer element is reduced.

Abstract: A polycondensation reactor for polyesters, polyamides or polyarylates, for example, in which a low viscosity material is introduced into the reactor and a relative high viscosity polymer exits the reactor. The reactor has at least two longitudinally intersecting cylindrical interior chambers, each with a rotating shaft through its length. Each shaft has a plurality of stirrers and spacers designed to wipe all interior surfaces of the reactor. The stirrers can be shaped as a cycloid or involute profile, for example. Generally the stirrers on each shaft are indexed from one another preferably by 90.degree. and intermesh with stirrers on the adjacent shaft. Stirring the low viscosity material by rotating the stirrers (on the shafts) spreads the material into a plurality of thin films. At the temperature and vacuum conditions of the reactor, a volatile component is removed, thus causing the material to polymerize, by condensation, forming a relatively high viscosity polymer.

Abstract: A polycondensation reactor for processing low viscosity polyester or another polymer into relatively highly viscosity polymer comprises a substantially cylindrical horizontal reactor vessel with a polymer inlet and a polymer outlet adjacent its opposite ends and a vapor exhaust opening in the upper side of the vessel at its outlet end. A polymer agitator is rotated axially within the chamber and includes plural alternating annular overflow and underflow baffles and multiple perforated film-forming screens disposed therebetween in parallel spaced relation to one another. The overflow baffles are in peripheral polymer-sealing relation to the vessel while the underflow baffles have multiple underflow recesses in their outer peripheries, whereby the baffles define a tortuous polymer flow path alternately through their respective polymer overflow and underflow openings to control residence time, distribution and viscosity growth as the polymer flows between the baffles.