Patent EA-003629-B1 (EA)
Title: Method for biological effluent treatment
IPC: C02F3/12
Filed: 2000-11-30
Abstract: 1. Method for biological purification of wastewater by means of activated sludge, wherein the wastewater is introduced first into an aerated activated sludge tank (B tank) and then, by turns, into one of several sedimentation and recirculation tanks (SU tanks), which are permanently hydraulically linked with said B tank and in which, several times a day an operating cycle proceeds comprising a stirring phase (R phase), a pre-settling phase (V phase) and a discharge phase (A phase), wherein in turns in the R phase the activated sludge is remixed with the water, in the V phase the activated sludge settles down and in the A phase clear water is drawn off, and wherein the cycles in the SU tanks are phase displaced to each other, the A phases are adjacent, only in the A phases the SU tanks are flown through, an approximately constant water level is present, thus causing an outflow from the purification plant corresponding to its inflow (throughflow principle), characterized in that after the V phases and before the R phases settled and thickened activated sludge is reintroduced from the SU tank into the B tank (S phase). 2. Method according to claim 1, characterized in that the reintroduction of settled activated sludge occurs during or preferable after the A phase. 3. Method according to claim 2, characterized in that the volume displaced in the B tank during the S phase with less dry substance than the introduced settled activated sludge is returned via openings near to the surface into the SU tanks, and the surface near openings allow a throughflow only in the S and R phases and are closed in the V and A phases. 4. Method according to any one of claims 1 to 3, characterized in that the stirring in the SU tanks (R phase) is done by injecting air, by means of electrically driven stirring apparatuses or by means of air jet lifts. 5. Method according to any one of claims 1 to 4, characterized in that for reintroducing settled activated sludge and for stirring in the SU tanks (S and R phases) a combined air jet lift (duplex siphon) is used, which allows a transport of fluid in both directions and provides a permanent hydraulic connection between the B tank and SU tanks in the V and A phases, wherein the stirring effect in the SU tanks is produced by generating a strong jet of water which whirls up activated sludge sedimented on the bottom, generates a water roll with homogenizing effect and transports possibly developing floating sludge via the surface-near openings into the B tank. 6. Method according to any one of claims 1 to 5, characterized in that the aeration of the B tank is intermittent in the R phases, in the S phases or in both. 7. Method according to any one of claims 1 to 6, characterized in that a B tank is hydraulically connected with two SU tanks and the cycle times are chosen based on approx. 140 min (S phase approx. 5 min; R phase approx. 5 min; V phase approx. 60 min and A phase approx 70 min); or, with three SU tanks the cycle times are chosen based on approx. 105 min (S phase approx. 5 min; R phase approx. 5 min; V phase approx. 60 min; A phase approx. 35 min). 8. Method according to any one of claims 1 to 7, characterized in that the outlet is realized as a pneumatic closure having a horizontal tube and at least one drainage socket oriented downward, wherein into the horizontal tube pressured air can be injected. 9. Method according to any one of claims 1 to 8, characterized in that at the end of the V phase the sludge concentration is measured at a predefined depth of approx.1.0 to 1.5 m below the water level, and at the end of the A phase thickened surplus sludge is drawn off for a short time (a few minutes) if the measurement of the sludge concentration revealed a sludge level lying above the measuring position. 10. Method according to any one of claims 1 to 9, characterized in that the B tank is permanently connected hydraulically with the SU tanks via one or more openings in the middle region, in the S phase thickened sludge is led from the bottom of the SU tank into the upper region of the B tank and the content of the B tank thereby displaced is returned via the openings in the middle region of the tanks, in the R phase the content of the SU tank is whirled up and homogenized without generation of a circulating current over the B tank, and in the A phase the flow from the B tank into the SU tanks occurs via the openings in the middle region as well.