Abstract: Dual-flow filter for the biological purification of effluents, particularly water, comprising at least two filtration cells, arranged in series, in fluid communication, with one another so that the effluent to be treated passes through them successively, these two cells being separated by an intermediate box provided with aeration means, wherein the first filtration cell is of the ascending flow type and the second filtration cell is of the descending flow type, and the aeration in the intermediate box takes place countercurrentwise with respect to the liquid flow moving through the box, with a movement of the flows guided with the aid of a siphon partition.

Abstract: The present invention relates to a filtering apparatus and the method of washing such an apparatus. The filtering apparatus with an upward flow of a fluid to be treated in an enclosure (7) closed at least at one end (15) and containing a fixed floating bed of filtering particles (16) of a density less than that of the fluid to be treated, is characterized in that the pipe (3) for discharging the filtered materials in suspension has the form of a lyre with vent (5) and dimensions allowing the column of fluid contained in the enclosure to be emptied at a speed higher than the minimum fluidization speed, the filtering particles having a characteristic mass per unit volume between 5 kg/m.sup.3 and 500 kg/m.sup.3 and a pipe (1) for intake of the fluid to be treated is disposed in a zone at the lower end of the enclosure situated below the lower level of the fixed floating bed and above the upper level (30) of the waste discharge pipe (3).

Abstract: The present invention concerns an oxidation and biological reduction reactor for liquid to be treated by upwards circulation and recirculation including, within a longitudinal vertical enclosure 5 accessible by an admission 9, a lower layer 1 of biomass fixation made of material whose density is lower than that of the liquid and an upper layer of fixation 3 of biomass made of material whose density is higher than that of the liquid, characterized in that the lower layer 1 is separated from the upper layer 3 by a transverse wall 2 preventing the passage of filtration materials between a lower zone located under the wall 2 and an upper zone above the wall 2, an oxidation gas input 8 under the upper layer 3 and above the wall 2, an outlet 10 for the treated liquid is recycled by a pump 12 and an outer pipe 11 on the inlet 9.