Activated sludge degassing process and device

A waste water purification process, in particular a continuous waste water purification process is disclosed, as well as a waste water purification plant system, in particular for continuous waste water purification. Waste water is purified in that an aerated mixture of waste water with activated sludge is degassed before being discharged into the secondary settling basin. The waste water purification system has a venting device that connects the aerating container or a separate chamber thereof to the secondary settling basin or a separated chamber thereof. The venting device is designed as a U-shaped tube. One of its branches forms the supply collecting pipe and the second branch forms the discharge collecting pipe, whereas the section that interconnects its two top ends delimits the intermediate chamber that contains a separate gas suction chamber.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a waste water continuous purification
 process, as well as to a waste water continuous purification plant system.
 2. Related Art
 Known waste water purification processes use active sludge. The mixture of
 the active sludge is held in suspension in the treated wastes and aerated.
 After leaving the aeration tanks the aerated mixture is directed to a
 secondary sedimentation tank in which sedimentation is continued by sludge
 precipitation. The precipitated sludge is used once more in the
 purification process, and the decanted liquid directed to a receptacle as
 the cleaned waste water. The active sludge recirculated in the
 purification process maintains its ability to clean new quantities of raw
 wastes which are introduced continuously or in batches.
 Purification processes of this kind, especially if carried out in aeration
 chambers formed as deep tanks (e.g. deeper than 5 m), or in multi-storey
 processes, have certain disadvantages. Because active sludge has a
 relatively low sedimentation capacity, coupled with the disadvantageous
 feature of sludge flocs coming up to the surface during the purification
 process, it is virtually impossible to carry out the sedimentation in the
 secondary sedimentation tank.
 In order to eliminate this effect, existing waste treatment processes use
 an additional operation consisting of flocculating and mixing the aerated
 wastes before their flow into the sedimentation tank. However, this causes
 the treatment process to be lengthy, and to frequently run in a chimerical
 fashion.
 Flocs of the active sludge generated during the known waste treatment
 processes have undesirable features resulting in limited effectiveness and
 capacity of these processes.
 SUMMARY OF THE INVENTION
 In accordance with a preferred embodiment of the invention, there is
 provided a waste water purification process, comprising the steps of:
 (a) mixing waste water together with active sludge;
 (b) aerating the resultant mixture in a tank;
 (c) discharging the aerated mixture into a secondary sedimentation tank
 while degassing; and
 (d) recovering the sludge in said secondary tank,
 wherein said recovered sludge in step (d) is recirculated as active sludge
 in step (a), and wherein said aerated mixture of waste in step (b) is
 brought into a state of turbulent flow directly before being vacuum
 degassed and before being discharged into said secondary sedimentation
 tank.
 In accordance with another preferred embodiment of the invention, there is
 provided a waste water purification plant system for continuous waste
 water treatment, comprising:
 an aeration tank for aerating a mixture of wastes and active sludge, said
 aeration tank having a separated chamber (7);
 a secondary sedimentation tank (10) having a separated chamber (8);
 an inverted U-shaped pipe conduit member comprising a supply collecting
 pipe (2) with lower and upper ends, a discharge collecting pipe (3) with
 lower and upper ends, and a segment connecting the upper ends of said
 supply and discharging collecting pipes, said segment having a
 cross-section greater than that of said supply and discharging collecting
 pipes, wherein said lower end of supply collecting pipe (2) is submerged
 in said aeration tank or its separated chamber (7), and said lower end of
 discharge collecting pipe (3) is submerged in said secondary sedimentation
 tank (10) or its separated chamber (8) such that said inverted U-shaped
 pipe conduit member provides a one-way, recirculating connection between
 said aeration tank or its separated chamber (7) and said secondary
 sedimentation tank (10) or its separated chamber (8);
 a vacuum degassing means (1) disposed within said segment of said inverted
 U-shaped pipe conduit member, said vacuum degassing means (1) comprising
 an intermediate chamber (4) having a gas suction chamber (5) contained
 therein; and
 means (6) for generating a turbulent flow of said aerated mixture of waste.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Flocs of the active sludge generated during the known waste treatment
 processes have undesirable features resulting in limited effectiveness and
 capacity of said processes. Based on this statement, operations and
 technical means have been devised according to the present invention to
 provide enhanced effectiveness and capacity of waste water treatment
 processes.
 In accordance with one aspect of the present invention, there are provided
 new features achieved with flocs of the recovery sludge, acting as the
 active sludge in the recirculation process, thereby allowing an increase
 in the effectiveness and capacity of waste water treatment.
 In accordance with a preferred embodiment of the invention, there is
 provided a waste water purification process, comprising the steps of:
 (a) mixing waste water together with active sludge;
 (b) aerating the resultant mixture in a tank;
 (c) discharging the aerated mixture into a secondary sedimentation tank
 while degassing; and
 (d) recovering the sludge in said secondary tank
 wherein said recovered sludge in step (d) is recirculated as active sludge
 in step (a), and wherein said aerated mixture of waste in step (b) is
 brought into a state of turbulent flow directly before being vacuum
 degassed and before being discharged into said secondary sedimentation
 tank.
 In one preferred embodiment, the vacuum degassing is advantageously carried
 out by creating negative pressure.
 In one preferred embodiment, the turbulent flow is caused by supplying an
 additional amount of air to said mixture.
 In accordance with another preferred embodiment of the invention, there is
 provided a waste water purification plant system for continuous waste
 water treatment, comprising:
 an aeration tank for aerating a mixture of wastes and active sludge, said
 aeration tank having a separated chamber (7);
 a secondary sedimentation tank (10) having a separated chamber (8);
 an inverted U-shaped pipe conduit member comprising a supply collecting
 pipe (2) with lower and upper ends, a discharge collecting pipe (3) with
 lower and upper ends, and a segment connecting the upper ends of said
 supply and discharging collecting pipes, said segment having a
 cross-section greater than that of said supply and discharging collecting
 pipes, wherein said lower end of supply collecting pipe (2) is submerged
 in said aeration tank or its separated chamber (7), and said lower end of
 discharge collecting pipe (3) is submerged in said secondary sedimentation
 tank (10) or its separated chamber (8) such that said inverted U-shaped
 pipe conduit member provides a one-way, recirculating connection between
 said aeration tank or its separated chamber (7) and said secondary
 sedimentation tank (10) or its separated chamber (8);
 a vacuum degassing means (1) disposed within said segment of said inverted
 U-shaped pipe conduit member, said vacuum degassing means (1) comprising
 an intermediate chamber (4) having a gas suction chamber (5) contained
 therein; and
 means (6) for generating a turbulent flow of said aerated mixture of waste.
 It has been determined that the active sludge gathered in the secondary
 tank, after being vacuum outgassed, and directed once more to the aeration
 process as the recovery sludge, is characterised by an increased absorbing
 capacity for contamination in wastes to be treated. This substantially
 accelerates the treatment of wastes and also provides for binding to
 phosphorus contamination.
 It has also been determined that said active sludge has a higher resistance
 to sudden overloading by contamination.
 The invention will be described in more detail in its embodiments shown in
 the drawings. FIG. 1 represents a waste treatment device in a schematic
 partial view. FIG. 2 represents the same device used in a waste treatment
 plant arrangement having a multi-storey tank.
 Venting device 1 comprises an inverted U-shaped pipe conduit member
 comprising a supply collecting pipe (2) with lower and upper ends, a
 discharge collecting pipe (3) with lower and upper ends, and a segment
 connecting the upper ends of said supply and discharging collecting pipes,
 said segment having a cross-section greater than that of said supply and
 discharging collecting pipes, wherein said lower end of supply collecting
 pipe (2) is submerged in said aeration tank or its separated chamber (7),
 and said lower end of discharge collecting pipe (3) is submerged in said
 secondary sedimentation tank (10) or its separated chamber (8) such that
 said inverted U-shaped pipe conduit member provides a one-way,
 recirculating connection between said aeration tank or its separated
 chamber (7) and said secondary sedimentation tank (10) or its separated
 chamber (8). (FIG. 1).
 The supply collecting pipe 2 is provided with an opening 6 located above
 the "a" level of the waste water to be aerated, filling the waste water
 tank or the chamber 7 separated in it.
 The gas suction chamber 5 is connected to a vacuum source, e.g. a vacuum
 pump not shown in the drawings.
 In FIG. 2 there is shown the venting device 1 located between the last
 uppermost chamber 9 in the multi-storey system for aerating the active
 sludge in the waste water to be treated, and the secondary sedimentation
 tank 10.
 The movement and the turbulent flow of the formerly aerated mixture of
 waste water and active sludge is forced in the described venting device 1
 by causing an additional quantity of air to flow through the opening 6
 located above the level of the liquid filling the chamber 7 of the
 aeration tank. A mammoth pump may be used in order to achieve that flow.
 The additionally introduced quantity of air is vacuumed together with
 gases contained in that mixture, thereby causing the required reduction in
 the specific gravity of the mixture.
 EXAMPLE
 Waste water having a contamination load of 30 kg O.sub.2 per hour, and
 introduced in a quantity of 100 m.sup.3 /h into a typical municipal wastes
 purification plant, comprising a container for the mixture consisted of
 wastes and active sludge, was effectively and efficiently treated. The
 active sludge sedimentation capacity has been substantially increased by
 installing the venting device according to the present invention, thus
 making it possible to increase the sludge quantity in the treatment
 system. This achieves an effective and efficient waste water treatment
 process with a capacity at least 50% greater without the necessity of
 using additional aeration tanks.
 This effect is achieved after venting the previously aerated mixture
 consisting of wastes and active sludge under vacuum conditions by the
 venting device of the present invention. Because of surrounding
 micro-bubbles of gas present in the flocks of active sludge, the flocs are
 freed of that gas which, in the above mentioned vacuum conditions, expands
 to many times its volume. As a result the micro-bubbles are disconnected
 from a floc while its flocculate structure is almost entirely degraded.
 Afterwards, during the further flow through the venting device, under
 conditions of a gradually decreasing negative pressure value, individual
 sludge flocs attain a much greater specific gravity after the venting
 operation. As a result, the sedimentation capacity of the sludge flocs is
 substantially increased and they quickly rebound together.
 Thus, one may advantageously treat substantially more process quantities of
 filiform micro-organisms comprised in the sludge without disturbing the
 sludge sedimentation capacity. This cannot be achieved by using the known
 processes.
 Furthermore, active sludge flocs produce, as a result of intrafloccule
 processes during degassing, a gas that does not create microbubbles in a
 sludge floc, but which is instead dissolved in a previously outgassed
 mixture.