Abstract: A method for the secondary treatment of sewage (and apparatus therefor) having a step in which sewage is circulated in a system having a riser and a downcomer communicating with each other at their upper and lower ends and in which an oxygen-containing gas is supplied to the sewage as it passes through the downcomer. The method is intended for use in the aeration and/or digestion steps of the secondary treatment of sewage. The riser and downcomer are preferably located in a shaft extending into the ground for at least 40 meters below a basin containing the sewage.

Abstract: A method for the secondary treatment of sewage (and apparatus therefor) having a step in which sewage is circulated around a system having a riser and a downcomer communicating with each other at their upper and lower ends and in which an oxygen-containing gas is supplied to the sewage as it passes through the downcomer. The method is intended for use in the aeration and/or digestion steps in the secondary treatment of sewage. The riser and downcomer are preferably located in a shaft extending into the ground for at least 40 meters below a basin containing the sewage.

Abstract: Process and apparatus for treating waste water by circulating it, together with oxygen-containing gas, through communicating downflow and upflow pipes enclosed in a treatment chamber, the pipes being open at their bottom ends, and controlling the flow of waste water/gas mixture from the downflow pipe to cause gas bubbles to escape downwardly, or part downwardly and part upwardly, in the treatment chamber.

Abstract: Solids-liquid separation, wherein a solids-liquid mixture containing dissolved oxygen-containing gas is circulated around a circulatory system comprising a downcomer and a riser, part of the mixture in the riser being introduced into a flotation chamber in which the hydrostatic pressure gradually decreases as the mixture flows upwards, with consequent release from solution of gas bubbles which carry solid particles to the top of the mixture.

Abstract: Method for treating sewage, wherein sewage is circulated around a system comprising a downcomer and a riser communicating with each other at their upper and lower ends, the downcomer having an upper portion of enlarged cross-section and the riser having a lower portion of enlarged cross-section.

Abstract: A method and apparatus for continuously circulating a mixture comprising a liquid and a gas around a system comprising a riser and a downcomer and a gas disengagement section in which liquid flows downwardly at a velocity which does not exceed 0.2 meters per second and is being injected into a lower section of the riser. The method and apparatus are particularly useful for conducting aerobic fermentations.