Abstract: Aqueous liquid having an oxygen demand flows into a treatment vessel where it is treated by suspended aerobic bacterial solids in the presence of dissolved oxygen. A pressurised flow of the treated liquid passes to a clarifying membrane separator effective to separate the flow into a discharge stream of clear liquid and a pressurised recycle stream concentrated in the aerobic bacterial solids. A first oxic gas is employed to scour the membranes and is conveyed away from the membrane separator in the pressurised recycle stream. The pressurised recycle stream is returned to under the surface of the liquid in the treatment vessel. A second oxic gas is introduced either into the pressurised recycle stream or into a further pressurised stream of aqueous liquid flowing into the same volume. The rate of introduction of the oxic gases is controlled with reference to the pH and dissolved oxygen concentration of the liquid in the vessel.

Abstract: In a method and apparatus for operating and regenerating ion exchange material a wash fluid or elution solution for rinsing the ion exchange material (1) is prepared, there is collected as a by-product of said preparation a first waste stream including cationic species to be eliminated, the ion exchange material (1) is subjected to a wash step in which there is eluted from the ion exchange material by the wash fluid or solution an anionic species to be eliminated and a second waste stream including the anionic species to be eliminated is obtained, the first waste stream (12) and the second waste stream (14) are combined to form a precipitate SW comprising a reaction product of said cationic species and said anionic species, and the precipitate is removed. The method provides an efficient means of eliminating undesired species from a circuit containing an ion exchange material to be regenerated.