DE2800035C2 - Process and device for wastewater purification - Google Patents

Description

30th

The invention relates to a method for wastewater purification in which the wastewater has a cover equipped fumigation zone in which oxygen-rich gas is absorbed via the surface of the wastewater, and then an open zone in which the surface of the waste water is exposed to the atmosphere is flowed through. The invention also relates to a wastewater purification device for implementation this process, with a basin that covers part of the water surface in the basin in a gas-tight manner Has cover, and with a device for supplying pure oxygen or with oxygen enriched air under the cover.

Such a method and a device for carrying it out is known from DE-OS 22 12 715. The cleaning process according to this publication is a straight-ahead process in which the waste water only passes through the treatment device once and in which the cleaning process must then be completed. To the consumption ai. pure Lower O2 or oxygen-rich gas without affecting the To have to forego the cleaning intensity caused thereby, is the supply in the known method of oxygen-rich gas is limited to the first phase of the cleaning process. In the second phase, when the cleaning is relatively advanced, the remainder of the cleaning is done with normal ventilation carried out. The supply of oxygen-rich gas must therefore be as long as possible at the beginning of the treatment be maintained until a predominant part of the total oxygen demand of the wastewater is met, the cleaning process has already run to a large extent and that is only then apparent to him the less important remaining part of the cleaning process can be switched to normal ventilation.

In contrast, the invention has the object of creating a method of the type mentioned above, which with particularly economical use of oxygen or the oxygen-rich gas enables an optimal cleaning effect

This object is achieved according to the invention in that the wastewater is circulated in a horizontal circuit is, with at least a partial flow of the total circulated waste water volume with the cover provided gassing zone and the open zone flows through several times

The advantage of achieving better cleaning in a shorter time with even lower consumption of pure O2 is achieved in the invention in that the repeated rapid change between intensive oxygenation and staying under normal air prevents the _{accumulation of larger amounts of CO 2 dissolved in the water} would shift the pH of the wastewater to the acidic range and impair the activity of the bacteria that break down the pollutants. Each phase with the supply of oxygen-rich gas, in which CO _{2 is formed to} an increased extent as a metabolic product of the microorganisms, is immediately followed in rapid alternation by a phase with normal ventilation in which the CO2 is expelled again.

This avoids the disadvantage occurring in the known method, namely that during the relatively long initial phase with the supply of oxygen-rich gas a very large amount of CO ₂ inevitably dissolves in the wastewater, which the activity of the microorganisms due to the pH shift and thereby decisively reduces the benefits of the supply of oxygen-rich gas in this long initial phase.

In the process according to the invention, a reaction equilibrium can be achieved with optimal purification conditions while maintaining a relatively low oxygen concentration in the wastewater (including in the As a rule, a wastewater activated sludge mixture is always to be understood). Another special advantage of the process is its great flexibility and adaptability to changing feed quantities and degrees of pollution of the treated wastewater.

Further advantageous features of the method according to the invention emerge from the subclaims 2-9. In particular, they concern a bubble-free and thus energy-saving circulation of the Wastewater, and on the other hand, a process management in which, depending on the amount and nature of the wastewater to be treated can be switched between oxygen gassing at atmospheric pressure and oxygen gassing at overpressure and / or conventional surface aeration without oxygen gassing. The oxygen supply can be regulated within each of these operating modes or ventilation performance take place in such a way that the oxygen concentration in the wastewater within a economically optimal range is maintained, and both the switching and the control can be in Dependence on limit values for the oxygen concentration in the wastewater and / or the oxygen content in the Gas space under the cover.

As already mentioned, the invention also relates to a waste water purification device for carrying out the above-described method with a basin, which is a part of the water surface in the basin gas

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Has tightly covering cover, and with a device for supplying pure oxygen c <the oxygenated air under the cover.

In such a cleaning device known from DE-OS 22 12 715, the above-described The advantage is that a considerable saving in pure oxygen is possible without any loss of cleaning effect is achieved in that the cover (15, 16) having the basin as an annular basin with circulating devices is designed to generate a horizontal cycle of wastewater.

Further advantageous features of the device according to the invention emerge from the subclaims 11 to 26.

Embodiments of the invention are explained in more detail with reference to the drawings.

F i g. 1 schematically shows a plan view of a device for carrying out the invention Method according to one embodiment.

FIG. 2 shows the device according to FIG. 1 in section according to the line H-II with an additional scheme of the regulation and control device.

F i g. 3 schematically shows a longitudinal section through a gassing basin with a bubble-free propulsion device.

4 and 5 show a plan view of the ring basin with other embodiments for bubble-free propulsion devices.

F i g. 6 shows schematically in plan view the flow diagram of a modified embodiment of the invention Procedure.

F i g. 7 shows, in longitudinal section, a gassing basin with a cover according to another embodiment the invention.

F i g. 8 shows in a representation similar to FIG. 3 another embodiment.

The device shown in Fig. 1 and 2 for performing the method consists essentially from an annular basin 1 with a central wall 3 in the manner of the usual activation or oxidation ditches. By doing Basins are two horizontal-axis surface containers 5, 7 arranged in the basin a horizontal one Generate circulation according to arrows 9. The inflow of the wastewater to be treated is not shown, the drain is located at 11 and is equipped with a height-adjustable weir 13 so that the height the water level in basin 1 and thus the immersion depth of the surface container 5, 7 can be regulated can.

On part of the route that the waste water travels in its circulation through basin 1 is the Water surface covered gas-tight by a cover 15, which with its longitudinal edges on the pool wall or the central partition 3 is seated and has movable flaps 17 at their transverse edges, which immerse in the sewage. These flaps 17 can od sealing lips at their ends. The like. For a gas-tight Have system on the pool walls. The flaps 17 can either be by hand or by a drive (not shown) can be brought into a position in which they are not immersed in the water and thus allow air to enter under the cover 15. In this case, the one under the cover 15 located surface aerator 5 perform a surface ventilation with ambient air, as well as the Surface aerators located outside the cover 7. The flaps can also be used as rigid transverse walls be designed in which access openings for ambient air that can be closed by doors or hatches are provided are. It is also possible to divide the transverse walls into rigid parts and foldable sections.

From a container 19 for pure oxygen leads a line 20 with flow meter 22 and Valves 24, 26, 28 in the space under the cover 15 in order to supply this pure oxygen, which through the surface aerator 5 can be entered into the water. This registered in the form of gas bubbles Some of the oxygen will dissolve, and some of the gas bubbles will after a certain length of stay to come back to the surface. The cover 15 extends from the surface aerator 5 in Direction of the flow generated by this (arrow 30), preferably at least as far as the length of stay the amount of gas bubbles in the water. A discharge line 32 with a shut-off valve 34 extends from the cover 15. to release excess gas into the atmosphere.

A measuring probe arranged in the water for the oxygen content is connected via a measuring signal amplifier 38 a working in the manner of a two-point controller threshold level 40 connected, which the of the Measuring probe compares the measured value with adjustable upper and lower limit values and sends it to a central control and switching device 42 emits different signals, depending on the oxygen content in the water exceeds the upper limit value or falls below the lower limit value. Likewise, an im Gas chamber under the cover 15 arranged sensor 44 for the oxygen content or partial pressure Via a measuring signal amplifier 46 to a threshold value stage operating in the manner of a two-point controller 48 connected, which supplies the central control unit with different signals, depending on the Oxygen content in the gas space under the cover 15 is below a lower limit or an upper limit Exceeds limit. A pressure measuring probe 45 is also arranged in the gas space under the cover 15, which controls the valve 26 in such a way that the oxygen through the line 20 when the valves 24, 28 are open at a constant Pressure is applied.

From the central control and switching device 42 control lines go to the valves 24, 28,34, to a display unit 50, which shows the position of the movable Prescribes flaps 17, as well as an adjusting motor 52 for the weir 13.

The operation of this device is described using the following example method.

example
1. Surface ventilation with ambient air

It is initially assumed that the wastewater to be treated is relatively little polluted, ie has a low chemical and / or biological oxygen demand (COD ₅ or BOD ₅ ). In this case, the flaps 17 of the cover 15 are open (which, for example, can be indicated to the operator by lighting up a green lamp on the display unit 50), and the valve 24 in the oxygen line is closed. The wastewater is cleaned by surface ventilation with ambient air, the sensor 36 via the threshold value stage 40, the control and switching device 42 and the motor 52 die

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Position of the weir 13 and thus the immersion depth of the surface aerators 5, 7 controls so that through the Aeration an oxygen content in the sewage z. B. between 1.8 mg / 1 and 2.2 mg / 1 is observed.

2. Oxygen gassing without excess pressure

If, for surface ventilation with ambient air, even with the greatest immersion depth of the ventilation rotors the O2 content in the wastewater z. B. 15 minutes smaller than z. B. 1.8 mg / 1 remains, is over the probe 36, the threshold level 40 and the regulating and switching device 42, the display unit 50 is controlled in such a way that that a second, z. B. red lamp lights up, which indicates to the clarifier that the flaps 17 are closed should be. Of course, the regulating and handling device 42 can also be used instead automatic closing of the flaps 17 can be effected. In addition, the control and switching device 42 initiated the following processes in this case:

Or content in wastewater e.g. B. drops below 1.8 mg / 1, and is closed when it z. B. rises above 2.2 mg / l.

4. Return to L_r oxygen gassing without excess pressure 5

If the degree of pollution of the wastewater decreases again in such a way that with the oxygen gassing with overpressure the oxygen concentration in the water longer than z. B. 15 minutes z. B. is above 2.2 mg / 1, so causes the control and switching device 42 a return to oxygen gassing without excess pressure by the Exhaust valve 34 is now constantly open and the oxygen supply valve 28 is opened in the sense of a two-point control or closed to keep the oxygen content! 5 in the wastewater between the two limit values (e.g. 1.8 and 2.2 mg / l).

5. Return to surface ventilation with ambient air

a) setting the weir 13 by means of the drive 52 to an optimal height for oxygen gassing;

b) opening the oxygen shut-off valve 24;

c) opening the exhaust valve 34;

d) rules, d. H. open and close the oxygen valve 28 as a function of the oxygen content measured by the sensor 36 in the wastewater such that this oxygen content z. B. is kept between 1.8 and 2.2 mg / l.

In order to maintain these oxygen concentrations in the wastewater, depending on the degree of pollution of the Wastewater larger or smaller values of the oxygen concentration in the gas space under the cover 15 are required. If the sensor 44 indicates that the necessary oxygen input is already in place with an oxygen content of 21% or less takes place, then shut off the oxygen supply and open the flaps 17 on Surface ventilation with ambient air can be switched back.

3. Oxygen gas supply with positive pressure

If, however, the sensor 44 indicates that to maintain the desired oxygen concentration an oxygen content or partial pressure in the gas space under the cover 15 is necessary in the water, which is higher than z. B. 35%, then so much oxygen would escape through the exhaust pipe 32 that this is uneconomical were. Therefore, if the oxygen content in the gas space under the cover 15 is longer than z. B. 15 minutes z. B. is over 35%, via the sensor 44 and the threshold stage 48 such a signal given to the control and switching device 42 that it closes the exhaust valve 34 and the oxygen valve 28 opens continuously (valve 24 is also open). Oxygen will now flow under the cover for so long 15 until the pressure set at the pressure control valve 26 and measured by the pressure measuring probe 45 is reached and the oxygen supply then ceases. All of the supplied oxygen is then taken from the wastewater recorded. In this operating mode, too, the oxygen content in the wastewater is regulated the sensor 36 in such a way that the threshold value stage 40 via the control and switching device 42, the exhaust valve 34 controls in such a way that it is opened when the with further decreasing pollution of the As already mentioned above, waste water can be removed by switching off the oxygen supply and opening the flaps 17 can be switched back to surface ventilation with ambient air, which is then raised and lowered of weir 13 is regulated.

Of course, the invention is not restricted to the details of the exemplary embodiment. In particular the limit values in the wastewater or in the gas space that are relevant for control and switchover can also be changed depending on the circumstances, and / or other criteria, such as e.g. B. the Inflow amount of wastewater, the return sludge ratio, or z. B. also external conditions, such as annual and time of day, temperature, etc., are included in the switchover and control.

In Fig. 3 denotes 60 the bottom of a ring basin, which is partially provided by a cover 15 with oxygen supply line 20 and gas discharge line 32 is. There is no surface aerator or other gas inlet element under the cover 15, but rather the uptake of the oxygen at the water surface 61 should only take place at a sufficiently rapid rate and turbulent movement of this surface can be achieved. To do this, the water in the ring basin must be included be circulated at a speed that is significantly higher than the usual, only for prevention the velocities required for sludge sedimentation. The flow rate is particular greater than 1 m / sec and is preferably it. 2 m / ssc

To generate the flow and circulation of the wastewater, it is advantageous if the propulsion through a device is made that works in a medium that is as free of gas bubbles as possible, since a medium that is free of gas bubbles can be circulated with less energy than a bubble containing. To this end, a whole is shown in FIG A propulsion device working under water is shown, which consists of a number of paddle surfaces 63 which extend essentially over the entire width of the basin and pivotable at one end are hinged to a bracket 65, which by means of a drive, not shown, according to the double arrow 67 is constantly moving up and down. Stops 69 provided on the holder 65 ensure that the paddle surfaces 63 during the downward movement of the holder 65 in the drawn drawn, upwards set directed position 63 while at the

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Upward movement of the holder 65 assume the downwardly directed position 63 'shown in dashed lines. As a result, the paddle surfaces cause one with every up and down movement in the manner of fish fins completely bubble-free propulsion according to the arrows 71, so that the sewage with sufficient speed is passed under the cover 15.

To increase the speed in the area under the cover cross-section-narrowing fixtures can be provided in this arm of the ring trench, the z. B. are formed as a (dot-dash line) elevation 60 'of the bottom 60 and / or as projections extending from the side walls. Instead of this or in addition, disruptive bodies for generating turbulence can be arranged in the area of the surface. For example, the lower edge 62 of the front transverse wall of the cover 15 can be designed as a comb or the like, or such combs or other disruptive bodies can be provided elsewhere under the cover.

Other possibilities, the water with completely submerged propulsion devices essentially To circulate bubble-free, FIG. 4 and FIG. 5 show. According to FIG. 4 is an annular basin 70 through a partition 72 divided into two straight sections, and at the bend of the basin is a circulating device designed as a rotor 73 arranged, which consists essentially of a single vertical paddle surface that the Cross-section of the basin is essentially completely filled and can be rotated about the vertical axis 75. the Partition 72 extends to the periphery of the outer edge of the paddle surface of the circulating device 73 described circle 77. This is the circulation movement generated by the paddal surface (Arrow 79) converted into a straight movement (arrows 31) along the ring basin. Of course you can the rotor also have several paddle surfaces. These paddle surfaces can also be extended vertically be formed narrow strips, which are arranged at regular intervals on a circumference. Around To improve their effectiveness, the paddle surfaces can be rotated about a vertical longitudinal axis on one Support cage attached and be movable via steering levers and control cams so that they are during each revolution Radial in the circular arc section of the trench measuring 180 ° and in the two remaining quadrants are aligned transversely to the longitudinal flow. As a result, you are always with your full, and not just with yours projected area effective. It is essential that the rotor is arranged under water and therefore only as Propulsion organ and not works as a surface aerator.

The same effect is achieved according to FIG. 5 rnii a circulating device 83 designed as a rotor, which is rotatable around the axis 85 from a center mounted and driven paddle surface, which is in a gap in the partition 72 of the ring basin 70 is arranged, revolves in the direction of arrow 87 and also generates a circulation flow Another possibility for intensifying and equalizing the circulation flow is to use the close to the rotor end portion of the partition 72 to bend or kink so that the partition ends approximately tangentially on the circumference of the rotor, preferably in the opposite direction to the direction of rotation of the rotor, d. H. on its downstream side.

In the case of the in FIG. The device shown schematically in FIG. 6 is located in an annular basin 70 with a partition 72 the sewage-activated sludge mixture is conducted in a horizontal cycle, with the necessary propulsion equipment are not shown, e.g. B. of the construction shown in Fig.3 to 5 can be.

Of course, other propulsion organs such. B. surface aerators, propellers or the like., In Question. A partial flow of the wastewater is drawn from the annular basin 70 by means of a line 89 with a pump 91 branched off and fed to a fumigation basin 93,

ίο in which pure oxygen is supplied through a line 95 becomes, the z. B. is entered into the wastewater by means of an agitator 97. If in the gas space of the tank If a sufficiently high partial pressure of the oxygen is maintained, oxygen concentrations can be found in the wastewater of about 50 mg / l. This wastewater, which is highly saturated with oxygen, is fed back to the annular basin 70 through the line 99 and mixed with the wastewater circulated there. The ratio of the branched off partial flow to the total circulated amount of wastewater is chosen so that in the ring basin 70 for a economic cleaning sets the optimum oxygen concentration, which is approx. 2 mg / 1. This embodiment of the method has the advantage that in the ring basin 70 completely bubble-free wastewater is circulated, which saves energy, and compliance with the Desired oxygen concentration in the ringbci ia *: very simply by regulating the amount of wastewater branched off via line 89, in particular by regulating the delivery rate of the pump 91 can take place.

F i g. 7 shows how a gas-tight covering of the water surface can be realized with particularly simple and cheap means, which cover extends over a sufficiently long distance from a surface aerator. In this arrangement, which is largely similar to that according to FIG. 2, the rigid cover 15 extends only over a relatively short distance above the surface aerator 5, which introduces the oxygen supplied through the line 20 into the wastewater. The wastewater is circulated in the direction of the arrows 18. At the front end, the cover 15 has a flap 17 immersed in the water, while at the downstream end of the cover 15 a flexible film 100, e.g. B. a rubber mat is connected, which rests directly on the water surface and covers the water surface over a distance that corresponds to the length of stay of the gas bubbles in the wastewater calculated by the surface aerator 5. The lateral edges of the film or rubber mat 100 can be immersed in the wastewater by means of suitable devices, flaps, strips or the like. The rubber mat 100 can float 102 or

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auin tcuigiicii uuiuu us umciuüiu uci ruuc water escaping from uciu and accumulating gas kept floating. A suspension of the rubber mat prevents at 104 100 in that the mat at a standstill of the device sinks At the end of the film or rubber mat 100 a collecting bag 106 is provided to collect the escaping from the waste water, not gone into solution oxygen, with through a return line 108 the gas space under the cover 15 is connected.

! n F i g. 8 is similar to FIG. 3 shows the bottom 60 of an annular basin in which the wastewater is circulated by propulsion means (not shown) according to arrows 71. The cover 16 with Feed line 20 and discharge line 32 are arranged here as a diving bell under the water surface 61.

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net, and by the excess pressure of the supplied gas
a free surface 61 'is maintained below it. Because of the higher pressure, the oxygen is absorbed more intensively or at a lower flow velocity and turbulence than at the
Surface 61.

For this purpose 4 sheets of drawings

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Claims (1)

28 OO Patent claims: 1. Process for wastewater purification in which wastewater has a fumigation zone provided with a cover, in which oxygen-rich gas is absorbed via the surface of the sewage, and following this an open zone in which the surface of the wastewater is exposed to the free atmosphere is exposed, flows through, characterized in that that the wastewater is circulated in a horizontal cycle, with at least a partial flow of the total circulated waste water volume the gassing zone provided with the cover and the open zone flows through several times. 2. A method for wastewater purification according to claim 1, characterized in that the wastewater by means of propulsion working exclusively under water, with essentially no entry of Gas bubbles is circulated. 3. A method for wastewater purification according to claim 1, characterized in that the oxygen uptake over the water surface through a surface aerator located under the cover he follows. 4. A method for wastewater purification according to claim 1, characterized in that from the open Zone branched off a waste water partial flow and only this partial flow is exposed to oxygen gassing and then admixed again to the main circuit running in the open zone. 5. A method for wastewater purification according to claim 1, characterized in that one goes through Supply of the gas under pressure to a diving bell arranged under the surface of the water Covering under this creates a free surface of the sewage for the uptake of the oxygen. 6. A method for purifying waste water according to claim 5, characterized in that the waste water at a flow rate several times that used to prevent sludge settling required speed is, can flow under the cover, so that only oxygen uptake is caused by this flow movement. 7. A method for wastewater purification according to claim 6, characterized in that the flow rate is more than 1 m / sec and preferably approx. 2 m / sec. 8. A method for wastewater purification according to claim 1, characterized in that the oxygen gassing carried out under the cover either at atmospheric pressure or with overpressure and between these two modes of operation switches depending on the amount and / or nature of the wastewater. 9. A method for wastewater purification according to claim 1, characterized in that at times the oxygen gassing ended and instead a surface aeration with ambient air performs, whereby one depends between the surface aeration and the oxygen gassing switches depending on the amount and / or nature of the wastewater. 10. Wastewater purification device for performing the method according to claim 1, with a Basin which has a cover that covers part of the water surface in the basin in a gas-tight manner, and with a device for supplying pure oxygen or air enriched with oxygen under the cover, characterized in that the cover (15, i6) having the basin as an annular basin (1,70) with circulation devices (5, 63, 73, 83) for generating a horizontal circuit of the sewage is formed 11. The device according to claim 10, characterized in that that as circulation devices one or more completely submerged essentially Bubble-free working conveying organs (63,73,83) are provided. 12. The device according to claim 11, characterized in that that as a conveyor a vertical rotor with one or more completely under Water arranged paddle surfaces (73, 83) is provided, with a partition (72) of the ring basin (70) extends to close to the circumference of the rotor 13. The device according to claim 11, characterized that a number of paddle surfaces (63) are provided as a conveyor element, which are in the wastewater vertically or horizontally reciprocable and for reciprocating movement with opposite Inclination to the direction of flow are adjustable. 14. Device according to one of claims 10 to 13, characterized in that in the area of the cover (15) cross-section narrowing and / or turbulence producing internals (60 ') or disruptive bodies are provided. 15. The device according to claim 10, characterized in that the cover (15) as a diving bell is formed and one lying under the water surface, by the pressure of the supplied Gas maintained free surface (61 ') of the waste water covered 16. The device according to claim 10, characterized in that under the cover (15) at least a surface aerator (5) is arranged for introducing the oxygen into the water. 17. The device according to claim 16, characterized that the cover (15) extends to such a distance from the surface aerator (5) than the retention distance of the gas bubbles introduced into the water by the surface aerator is equivalent to. 18. The device according to claim 10, characterized in that the cover (15) is movable Has parts (17) for releasing the access of air under the cover. 19. The device according to claim 10, characterized in that that the cover (15) or parts (100) thereof floating on the water surface are supported. 20. Apparatus according to claim 19, characterized in that that the cover (15) consists of a rigid part and an adjoining part of a flexible film formed part (100), which rests floating on the water surface and / or is carried by swimmers (102). 21. Apparatus according to claim 17 or 20, characterized in that the cover (15) with the part (100) at a distance from the surface aerator corresponding to the length of time the gas bubbles remain (5) a collecting pocket (106) for from the 28 OO Has gas bubbles escaping from waste water 2Z device according to claim 21, characterized by a return line (108) from the collecting pocket (106) into the space under the cover ('S). 23. The device according to claim 16, characterized in that the surface aerator (5) is at the same time a conveying element for circulating the wastewater in the circuit 24. Device according to one of claims 16, 17, 21 to 23, characterized in that the surface aerator (5) is a horizontal-axis aerating rotor 25. The device according to claim 10, characterized in that outside the cover (15) at least one surface aerator (7) is arranged 26. The device according to claim 10, characterized by measuring sensors (36, 44) for the oxygen content in the wastewater and for the oxygen content in the gas space under the cover (15), and through of the signals from the sensors controlled regulating and / or switching devices (42) for the oxygen supply for the cover (15), for the gas extraction from the cover, for the surface aerator (5) and / or for the moving parts (17) of the cover.