The use of fluidized-bed bioreactors in waste and drinking water treatment has several advantages, the most significant of which is the specific removal rate, which is an order of magnitude higher than that of equivalent activated sludge processes. In this paper, the usual concept of nitrification-denitrification in separated units is replaced by a new concept in which the two processes are performed together in a single high-performance fluidized-bed. Based on the former nitrifying reactor, new equipment was designed. This reactor contained a fluidized bed with separated aerobic and anoxic sections for nitrification and denitri fication respectively. This was accomplished by the use of different-diameter sand as carrier material and appropriate reactor shape, recirculation, feed and aeration conditions. The reactor (20 L fluidized-bed volume) was operated for 3 months. It was fed with synthetic waste water (50 L/h) containing 25-40 mg NH₄ ⁺-N/L. Propionic acid and ethanol in a 1:4 ratio were used as the carbon source (2.3 g C/L) for deni trification, fed in at different points of the reactor. Ammonium removal reached 50%, while denitrification was 75%. The total nitrogen removal rate was 0.8-1.2 kg N/m ³.d. A new simple hydrostatic pressure method was used to monitor biofilm thickness in the fluidized bed. During the experiments the oxidation-reduc tion potential (ORP) was tested as a tool to monitor reactor performance; its use for the control of the process was found to be limited.

A computer-controlled pressurising system enabling large aquatic organisms like marine fishes to be maintained for long periods is described. The paper presents a system that is capable not only of maintaining constant hydrostatic pressures but also of producing any desired cyclic variations of that parameter, allowing the close and reliable simulation of vertical migrations that many species of fishes and other aquatic animals perform during some stages of their life cycles. | Es descrito un sistema de presurización controlado por computador que permite realizar experiencias de larga duración con animales acuáticos de considerable tamaño, manteniéndolos siempre en óptimas condiciones. Este artículo presenta un sistema que es capaz, no solo de mantener presiones hidrostáticas constantes sinó también de producir variaciones cíclicas de dicho parámetro permitiendo realizar una riguorosa simulación de las condiciones que se dan en las migraciones verticales que muchas especies de peces y otros animales acuáticos realizan durante algunas etapas de su ciclo vital.