Title of Invention	A PROCESS FOR LIQUOR-PARTICULARLY WASTEWATER - AGITATION AND/OR AERATION
Abstract	The invention relates to a method for stirring and/or aerating fluids, particularly sewage, having the following cyclically repeated steps: aerating the fluid by means of an immersed aerator for a predetermined first period of time (t1) using an aeration device (1) disposed on a carrier (3, 43) designed as a floodable hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought into the fluid by the aeration device, whereby the potential for nitrification is created in the fluid; stirring the fluid by means of the immersed aerator for a predetermined second period of time (t2), the air infeed by the aeration device (1) being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body (2, 42) with gas or air, the immersed aerator assuming the function of a mixing device in which fluid rises upward, thus mixing the fluid, wherein the potential for denitrification is created in the fluid; and an immersed aerator.

Title of Invention

A PROCESS FOR LIQUOR-PARTICULARLY WASTEWATER - AGITATION AND/OR AERATION

Abstract

The invention relates to a method for stirring and/or aerating fluids, particularly sewage, having the following cyclically repeated steps: aerating the fluid by means of an immersed aerator for a predetermined first period of time (t1) using an aeration device (1) disposed on a carrier (3, 43) designed as a floodable hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought into the fluid by the aeration device, whereby the potential for nitrification is created in the fluid; stirring the fluid by means of the immersed aerator for a predetermined second period of time (t2), the air infeed by the aeration device (1) being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body (2, 42) with gas or air, the immersed aerator assuming the function of a mixing device in which fluid rises upward, thus mixing the fluid, wherein the potential for denitrification is created in the fluid; and an immersed aerator.

Full Text	Method for stirring and/or aerating fluids, particularly wastewater, particularly with a floodable aerator The present invention relates to a process for liquor, particularly wastewater, agita- tion, particularly with a floodable immersed aerator and with at least one diffuser dis- posed on a carrier. Modern wastewater/sewage plants need to denitrify the wastewater to attain the specified capped nitrate values. Denitrification - in other words dissociating the oxy- gen bound to the nitrate to thus liberate the molecular nitrogen - requires several bio- logical phases by bacteria suitable for the purpose in the anoxic milieu, i.e. in the absence of dissolved oxygen in the reactor. Optimizing denitrification requires, for one thing, intensive agitation of the biomass (bacteria) with the wastewater to increase the interface and accelerate discharge of the denitrified medium, for another, the existence of degradable carbon compounds. For, it is the aerobic C degradation that firstly ,,forces" - to put it simply - denitrifica- tion to fetch the oxygen from the nitrate. Doing this is currently performed by a variety of phases in processing, all of which, however, are characterized by the creation of an anoxic milieu. Depending on how high the concentration is in the nitrogen supply, anoxic volumes as high as 50% of the total reactor volume are needed and usual. But wastewater/sewage treatment in general (oxidation of carbon products, oxidation of the ammonia) always necessitates an oxic milieu in which treatment (degradation of C and ammonia) is mainly aerobic, whereas in any reactor having a predominantly oxic milieu denitrification is impossible. This has resulted in a variety of ways of getting round this problem, including, for ex- ample, simultaneous denitrification, and upstream and downstream denitrification. In upstream denitrification the return sludge (a mixture of biomass and richly nitrated wastewater) is separately basined where it is mixed with a highly carbonated flow of water. In simultaneous denitrification the phases in the process are performed all at the same time in a reactor involving separation of oxic/anoxic volumina either spatially (by zoning the basin by throttling aeration definedly) or in time (cyclic ON/OFF of aeration), combinations of these phases also being possible. In downstream denitrification, as the name suggests, denitrification occurs after ac- tual aeration. All three of these processes have their specific advantages and disad- vantages, especially downstream denitrification having since become outdated. In summary it can be said that simultaneous denitrification offers the most benefits, this prompting the following considerations: When a basin is aerated, C and ammonia degradation (oxidation) is normal. But when denitrification is needed at the same time, either the aeration needs to be throt- tled locally or shut off completely. However, to circulate a certain reactor volume a critical minimum air feed is needed to keep the balance of the biomass to make deni- trification possible in the first place and in preventing the plant from become fouled up. In other words, when shutting off aeration completely, agitators are needed to agitate the basin contents to ensure the necessary interfacial mass transfer as is usual in practice. But if aeration is simply throttled it may happen that the oxygen introduced is still too high, resulting in no anoxic zones materializing, thus ruining the chances of effective denitrification being achieved. This is especially the case when the waste- water feed has a low C concentration, resulting in the air flow needed for circulation still exceeding the air flow (or oxygen requirement) needed for oxidation by the bac- teria. Known from European patent EP 0 249 172 B1 (von Nordenskjold) is a process for aerating and circulating wastewater and activated sludge for the purpose of nitrifica- tion and denitrification by means of a plurality of diffusers moved over the bottom of the basin in a cyclic sweeping action. For this purpose certain bottom diffusers are supplied with a reduced air feed to form slightly aerated zones in the wastewater or activated sludge to achieve the anoxic conditions in making zoned denitrification possible. The drawback of this system is its many components such as squeeze valves sus- ceptible to failure. For aerating and agitating wastewater a wealth of different means and processes are known from prior art. Known from DE 196 21 116 C2 (Invent) e.g. is a bottom distributor for gas to which at least one flexible perforated tube can be connected for gas charging, including, communicatingly connected to a diffuser, a hollow base body provided as a bottom distributor for the diffuser supply. To maintain such a device operative near to the bottom, when used in water treatment plants, suitable weights have to be provided to compensate the flotation tendency caused by the cavities in the bottom distributor. Known from DE 40 01 201 C1 (von Nordenskjold) is a floating aerator for introducing air to aerate a body of water in supplying air thereto via connecting lines via bottom diffusers employed as a so-called immersed aerator. The problem here is that bot- tom diffusers have a limited lifetime with the nuisance of requiring regular cleaning maintenance and inspection. This requires, as a rule, the bottom diffusers to be lifted out of the basin during operation of water or wastewater treatment plant. And, here again, these regularly require weights to weigh the system to compensate a float tendency of the bottom diffusers in operation. Lifting a bottom diffuser out of the ba- sin is not simple, it needing to be lifted to the water surface of an activated sludge basin of a wastewater treatment plant (for cleaning, inspection, and possibly repair) and then to be returned in place. All this is highly complicated and costly and even a hazard for personnel doing the work. Apart from this the corresponding parts of the floating or bottom diffusers or also immersed aerators are stressed to the extreme. Especially when the aerators include membranes, damage to these sensitive items can hardly be avoided. Known from US 5,906,774 (Parkson) is a surface aerator connected by a rod to a submerged (immersed) aerator in the region of which additional inflatable buoyant members are arranged to help get round the aforementioned problem of lifting an immersed aerator to the surface of the water which is a great help in servicing it. However, this system has the serious drawback that the inflatable buoyant members add to the components in the vicinity of the immersed aerator which are a nuisance to handle, both non-inflated and inflated, whilst being prone to damage by becoming punctured and thus useless. Surface aerators are employed in the operation of wastewater treatment plants, i.e. floats to which the surface aerators are attached submerged in the water body. It is especially in wastewater treatment plants that such devices are used to aerate the activated sludge basin. Another use serves to oxygenate water bodies. The way these work, known in principle, involves a pressurized aeration system in which air is sucked in from the atmosphere by compressors and distributed by a feeding system to the so-called immersed aerators engineered, as a rule, to discharge the drawn-in air in fine bubbles which rise to the surface of the water from the immersed aerator, giving off oxygen to the water on their way. In anaerobic systems these devices are likewise employed as gas injectors on the same principle, especially for circulation. As compared to diffuser members secured to the bottom of the basin as in classic wastewater treatment plants surface aeration has special advantages, this being the reason why surface aerators have since become very popular. The increase in the size of individual systems also adds to the number of diffuser members per system, these very quickly amounting to several thousand such mem- bers within a system. Known are devices in which so-called diffuser tubes are grouped together into aerators attached to floating air distribution tubing for sub- mersed operation at the bottom of the basin. Known diffuser tubes are made of poly- ester or ceramics and perforated membrane materials which, as a rule, are lifted to the surface on supporting members. Particularly perforated membrane diffusers have become popular in recent years since their oxygen exploitation is greatly supe- rior to that of other diffuser materials. In addition to these, plate aerators find applica- tion. The increase in size of such plants has called for ever-larger individual basins and water depths, nowadays often six meters deep, necessitating grouping together more and more diffuser tubes to form an aerator assembly. One salient feature of a func- tionable ,,floating" immersed aerator is that its submersed components have a stable working depth wo excessive buoyancy which would otherwise render the immersed aerator useless, i.e. becoming unstable, resulting in the diffuser members becoming partly floated, entangled, and endangering effective aeration, or even bringing the system to a standstill. In addition to this, it will readily be appreciated that such ran- dom movements of the diffuser members can be damaging. This is why any opti- mally designed immersed aerator has just enough dead weight to, on the one hand, maintain the aerator in stable operation, whilst, on the other, keeping the weight down sufficiently to assist handling by assembly and operating personnel. The diffuser assemblies described hitherto are exposed to high wear and tear in op- eration, they needing to be cleaned regularly and the membranes replaced new after a certain lifetime. This necessitates lifting the diffuser assembly or immersed aera- tors to the water surface, done, as a rule, without halting plant operation. Lifting aera- tors out of the water is a difficult operation prone to damage, usually involving an ex- perienced crew of workers. A particular nuisance to safe handling is the ..biological" slime fouling of the many normally submersed surfaces rendering them slippy to handle. In addition to this, the aerators and their ancillary facilities are often stressed when lifted out of the water, risking damage such as tube kinking, tube connector breakage and diffuser membrane rupture. Lengthy handling of individual surface or immersed aerators poses the particular drawback of the activated sludge in the water zone worked by a particular immersed aerator becoming imbalanced to negatively affecting the biological process as a whole. It is thus an object of the invention to propose a process with which the cited draw- backs of prior art are avoided or at least greatly reduced, and to propose an im- mersed aerator which can now be employed to advantage in the proposed process. This object is achieved by a process for liquor - particularly wastewater - agitation and/or aeration having the following cyclically repeated steps a) and b): a) aerating the liquor by means of an immersed aerator for a predetermined first pe- riod of time (t1) using a diffuser disposed on a carrier designed as a floodable hollow body, the hollow body being flooded and air being brought into the liquor by the dif- fuser, making it possible to create nitrification in the liquor; b) agitating the liquor by means of the immersed aerator for a predetermined second period of time (t2), the air feed by the diffuser being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body with gas or air, the immersed aerator assuming the function of an agitator in which liquor rises upward, thus agitating the liquor, making denitrification possible in the liquor. The advantages of the process in accordance with the invention consist inter alia of aeration, after a certain period of time, now being followed by a period of non- aeration in which an anoxic zone is created in the corresponding zone of the liquor, since aeration is totally ceased therein. Instead, an agitation phase is set by the hol- low body being cyclically flooded and evacuated. It is this cyclic flooding and evacua- tion of the hollow body which causes the aerator to continually bob up and down, agitating the liquor. Any air escaping during this highly agitated agitating of the liquor is immaterial to the oxygen content of the liquor since, on the one hand, the volume of air involved is much less than that in normal aeration and, on the other, the escaping air has such large bubbles that there is hardly any transfer of oxygen, i.e. with no risk of endan- gering the anoxic phase. As detained above, the person skilled in the art is aware that anoxic phases need to be present for denitrification, which, however, have to be replaced by oxic phases to achieve nitrification. In one advantageous further embodiment of the process the first and second periods of time (t1, t2) are timed by a controller with the advantage of this now making it pos- sible to precisely define denitrification to the corresponding load on the liquor. The object is achieved furthermore by an immersed aerator comprising at least one diffuser disposed on a carrier, the immersed aerator being characterized by it com- prising at least one floodable hollow body formed by the carrier. The device in accor- dance with the invention has numerous benefits. The carrier configured as a flood- able hollow body to carry the diffuser is of decisive assistance in reducing the buoy- ancy tendency of the immersed aerator when filled with water in operation, thus do- ing away with, or at least minimizing, the need for ballast weights to compensate buoyancy so that the aerator is stationed stabilized, in thus avoiding an excessive dead weight of the immersed aerator. In one advantageous aspect of the invention the floodable hollow body is configured as an elongated tube with the advantage that low-cost standard parts can now be used in producing the immersed aerator in accordance with the invention. In another advantageous aspect of the invention the immersed aerator carrier con- figured as a floodable hollow body is configured as a tube of rectangular, round or elliptic cross-section. Thus now makes it possible to individualize the immersed aera- tor to preferred diffusers. In yet another advantageous aspect of the invention the floodable hollow body is equipped with a compressed air feeder for filling the hollow body with gas or air, this device making it easy to surface the device in accordance with the invention in the water simply by feeding the compressed air to remove the water in the floodable hol- low body, prompting the immersed aerator to surface since the hollow body is no longer flooded. As an alternative, the compressed air feed can be made by a source of compressed air on a maintenance boat, by a feeder specifically included for this purpose in the plant or by making corresponding use of the air for aerating the water. In still another advantageous aspect of the invention the carrier of the immersed aerator in accordance with the invention is equipped at least partly with a perforated membrane enveloping the latter and a means for feeding gas between the carrier and the membrane. This now makes it possible to advantage to achieve the diffusers as known substantially from prior art, particularly in combination with the invention by much simpler means. The carrier configured as an elongated tube forms by its outer wall a wall of the air feeder of the diffuser, the other wall of which is formed by a per- forated membrane which except for the pores is sealed off gas-tight from the carrier. In another advantageous aspect of the invention the hollow body of the immersed aerator comprises at least one first end part disposed in a first end portion of the hol- low body with a first passageway for feeding compressed air to the diffuser and a second passageway for feeding compressed air to fill the hollow body with gas or air. There is a whole series of methods known from prior art for maintaining air injectors at a constant level below the water surface. As compared to these, however, the configuration of the device in accordance with the invention now makes for a design requiring fewer parts and more friendly installation, all of which makes for enormous cost savings and saving time both in installing and servicing the immersed aerator. In another particularly advantageous aspect of the invention the immersed aerator is characterized by it comprising a second end part with a passageway for feeding the diffuser with gas or air and an outlet passageway disposed in a second end portion opposite the first end portion of the hollow body. This now makes it possible to added advantage to increase, e.g. double the air feed in the same time with the same speed. In yet another advantageous aspect of the invention the immersed aerator is charac- terized by it being suspended by at least two suspension devices which now makes it possible to set it precisely level in harmonizing bubble formation in aeration. In still a further advantageous aspect of the invention the immersed aerator is char- acterized by at least one of the suspension devices being configured as a feeder for the diffuser with the advantage of making for a simplified arrangement whilst reduc- ing the risk of suspension devices and feeders becoming entangled. In yet another advantageous aspect of the invention the immersed aerator is charac- terized by the outlet passageway being disposed near to the bottom of the hollow body operationally. This facilitates evacuating fluid still therein when evacuating the immersed aerator to advantage in preventing a short-circuit flow of the evacuating gas above the bottom of the hollow body. In a further advantageous aspect of the invention the first passageway of the end part is provided with non-return valves preventing a liquor flow, for instance of the wastewater through the first passageway from the hollow body, advantageously mak- ing sure that no unwanted materials have access to the air feed of the diffuser. In still another advantageous aspect of the invention the immersed aerator is charac- terized by a ballast weight enabling the device in accordance with the invention to be individualized to the necessary conditions or marginal circumstances as dictated by the wastewater and also by the situation in operating the immersed aerator in each case. In another advantageous aspect of the invention the immersed aerator is character- ized by a hollow body configured as a shallow cylinder whose circumferential wall forms a hub mounting the spoked arrangement of the diffusers, for example, in the form of of diffuser tubes and the like. Configuring the immersed aerator in accor- dance with the invention in this way permits making use of the operating principle in accordance with the invention also with immersed aerators figured otherwise, espe- cially including such immersed aerators employed decentralized as single aerators. In yet a further advantageous aspect of the immersed aerator in accordance with the invention it is again characterized by a hollow body configured as a shallow cylinder but here with the diffusers topping the cylinder. Here too, the same as in the example aspect as described before, the device in accordance with the invention can be indi- vidualized to comply with given, possible already existing systems, now with the spe- cial advantage afforded by the device in accordance with the invention of, namely, in surfacing an immersed aerator with no problem. In still a further advantageous aspect of the invention an immersed aerator is charac- terized by the floodable hollow body being configured as an elongated tube, from the outer wall of which diffusers extend substantially perpendicular thereto, here again with the advantages of the aspects as just described, namely adapting and integrat- ing the device in accordance with the invention to/in already existing systems or combining the device in accordance with the invention with the other possible advan- tages of the variants, hollow bodies and diffusers as already described. Further features and advantages of the invention read from the sub-claims. For a better appreciation of the invention it will now be detained by way of a few ex- amples with reference to the drawing in which: FIG. 1 is a very simplified diagrammatic view of one example aspect of an immersed aerator in accordance with the invention shown partially sectioned. FIG. 2 is a view in perspective of the immersed aerator as shownin FIG. 1. FIG. 3 is again a very simplified diagrammatic view of another example aspect of the immersed aerator in accordance with the invention shown in perspective. FIG. 4 is again a very simplified diagrammatic view of yet another example aspect of the an immersed aerator in accordance with the invention shown in perspective. FIG. 5 is a diagrammatic view of the immersed aerator as shown in FIG. 4 shown sectioned. FIG. 6 is a view of still another example aspect of an immersed aerator in accor- dance with the invention. FIG. 7 is a view of a further example aspect of an immersed aerator in accordance with the invention. FIG. 8 is a view in perspective of the salient features of the immersed aerator as shown in FIG. 7. FIG. 9 is a view of still a further example aspect of an immersed aerator in accor- dance with the invention. FIG. 10 is a view of another example aspect of an immersed aerator in accor- dance with the invention. Referring now to FIG. 1 there is illustrated in a very simplified diagrammatic view an immersed aerator 4 including a carrier 3 mounting a diffuser 1. The carrier 3 is con- figured as a floodable hollow body 2 in which the cavity 10 of the floodable hollow body 2 here and otherwise is depicted cross-hatched for a better appreciation. Via a gas feeder 6, for example, air is fed in the direction of the arrow L into the immersed aerator ported via the carrier 3 of the diffuser 1. The path of the air bubbles ascend- ing from the diffuser 1 to the surface of the water is in the direction of the arrows B. Referring now to FIG. 2 in additon to FIG. 1 there is illustrated how the carrier 3 con- figured as a floodable hollow body 2 has the shape of an elongated cube. The sur- face area depicted cross-hatched in the hollow body 2 can be filled or flooded with liquor in operation of the immersed aerator, reducing the buoyancy of the immersed aerator in accordance with the invention to the extent in which the hollow body 2 is flooded with the intention of maintaining it at a stable level preferably near to the bot- tom 7 as depicted diagrammatically. Referring now to FIG. 3 there is illustrated a further example aspect of the invention, depicting in this case a carrier 13 configured integrated with a shallow cylindrical hol- low body as a floodable hollow body 12. Mounted on a cross-beam 18, which as shown in FIG. 3 is carried by the carrier 13 as an air feeder, are diffusers 11 with conventional diffuser tubes 15 as depicted diagrammatically. The special advantage afforded by this arrangement is that a single floodable hollow body 12 serves for a whole battery of diffuser tubes 15. In principle the air feed into the diffusers 11 is the same as the gas feed as shown in the example aspects of FIG. 1 and FIG. 2. Thus, each of the diffusers 11 has an air feed in the direction of the arrows L again via a gas feeder 16, here again the direction of the air bubbles ascending from the diffus- es 11 to the water surface being symbolized in the direction of the arrows B. Referring now to FIG. 4 there is illustrated another example aspect of an immersed aerator 24 comprising a central carrier 23 or central hollow body 22 mounting a spoked arrangement of the diffusers 21 receiving a spoked gas feed via a gas feeder 26. Referring now to FIG. 5 there is illustrated for a better appreciation of the aspect as shown in perspective in FIG. 4 the diffuser in a diagrammatically sectioned view. Via the gas feeder 26 air is fed via an air passageway 29 into the diffusers 21 which ascends to the surface of the water in the direction of the arrows B. Referring now to FIG. 6 there is illustrated yet another example aspect of the inven- tion in the form of a spoked arrangement of the immersed aerator 36 in which the functioning of the various components is in principle the same as already described with reference to FIGs. 3 and 4. Here too, there is depicted the advantage of the configuration as shown in FIG. 3 involving a plurality of diffusers in combination with a single floodable hollow body 32. Referring now to FIG. 7 there is illustrated still a further example aspect of an im- mersed aerator 44 in accordance with the invention including a carrier 43 doubling in function as a hollow body 42. The passageway 46 ports via a coupling (not shown) into an end part 401 sealing off the left-hand side of the immersed aerator 41 as shown in FIG. 7 in the interior portion of the carrier 43 also forming the hollow body 42. The end part 401 has a gas feeder passageway 49 via which air is directed through drillings 402 in the carrier 43 between the outer wall 413 of the carrier 43 and a membrane 403 surrounding the outer wall 413 through which air can escape via pores 404 to ascend to the surface of the water in the direction of the arrows B. Clamps 405 clamp the membrane 403 to the outer shell of the carrier 43 respectively hollow body 42 configured, for example, cylindrical. In the cavity 410 of the hollow body 42 the floodable portion is depicted cross-hatched. A feeder 406 ports likewise in the end part 401 into the gas feeder passageway 409 via which the cavity 410 of the hollow body 42 can be filled with compressed air. The liquor in the cavity 410 is evacuated via an outlet passageway 411 disposed on the right-hand side of the im- mersed aerator 41 as shown in FIG. 7 in an end part 412. When compressed air is directed in the direction of the arrows DL via the feeder 406 and the gas feeder pas- sageways 409 into the end part 401 in the cavity 410 of the immersed aerator 41, the liquor in the cavity 410 is evacuated by an outlet passageway 411 evacuating the cavity 410, increasing the buoyancy of the immersed aerator 41 to such an extent that it ascends to the surface of the water. By means of this design of the immersed aerator in accordance with the invention by using compressed air to „pump up" or drain the floodable hollow body it can be caused to ascend to the surface of the water for maintenance with no problem, after which the immersed aerator is returned in the water where it automatically becomes flooded to sink back down to its operating level. Indicated diagrammatically furthermore in FIG. 7 is the basin bottom 47 in the vicinity of which the immersed aerator 41 has its operating level. Depending on the thick- ness 414 and weight of the wall of the hollow body 42 or also the material of the hol- low body 42 and the volume of the cavity 410 the immersed aerator 41 can be set to ascend as desired. Greatly simplified in FIG. 7 is the position of the membrane 403' „in aeration opera- tion" at the underside of the immersed aerator 41 used to set the compressed air feed in this situation by reason of the overpressure building up between the outer wall 413 of the hollow body 42 and the membrane 403. The pores 404 of the elastic membrane 403 open to release air in the direction of the arrows B from the im- mersed aerator 41. Non-return valves 407 and/or 408 are optional on gas feeder passageways 409 and 49 of the end part 401 to prevent a backflow of liquor from the cavity 410 into the gas feeder passageways 409 and 49 respectively to prevent the corresponding air feed- ers 406 and 46 from becoming fouled up. Referring now to FIG. 8 there is illustrated the salient features of the immersed aera- tor 41 as shown in in FIG. 7 in a view in perspective. It is understood, of course, that the principle in accordance with the invention can be used just as well with plate aerators achieved in accordance with the design features as detained for the example aspect as shown in FIG. 7. Making use of of the principle of the immersed aerator in accordance with the invention permits a wealth of possi- ble variants. Thus, it is understood that the invention and the scope of its claims is not restricted to the aspects shown herein by way of example. Referring now to FIG. 9 there is illustrated how the immersed aerator comprises on the left-hand side of the drawing a feeder 521 normally directed upwards, for exam- ple for an air feed (not shown) in the direction of the arrow L. A compressed air feeder 506 feeds air to the cavity to fill it with gas or air to cause the immersed aera- tor to ascend and to evacuate the liquor contained therein. Although it is possible to suspend the immersed aerator by a suspension device 502 shown in bold or broken lines, it is also just as possible to arrange for the immersed aerator to be carried solely by the feeder 521 and a suspension device 520 or just by two feeders 521. Referring now to FIG. 10 there is illustrated still a further immersed aerator - de- picted halved to save space - which as compared to the immersed aerator as shown in FIGs. 7 and 8 ends on both sides in a passageway 46 with an air feed L. Outlet passages for the fluid to be evacuated can be suitably provided at one end, e.g. as shown in FIGs. 7 and 8 and as described. It is, of course, just as possible to provide suspension devices (not shown) on this immersed aerator as shown in FIG. 10 as described before. Agitation and aeration are alternated as follows: When after aeration, orchestrated as known, is to be followed by a denitrification phase, introducing an anoxic phase in a zone to set aeration by the immersed aera- tor is done by shutting off the air feed via passageways 46, 49 via the feeder(s) 521, after which the cavity 410 is filled by feeding compressed air via feeders 406 and 409 to evacuate the fluid therein, usually a liquid, such as water or wastewater via the outlet passageway 411, 511. This causes the immersed aerator to tilt in the direction of the air feeder on the immersed aerator, to tilt further until it is standing upright on ascending to the surface of the water. This is the same procedure as performed while inspecting an immersed aerator. On it surfacing, the compressed air feed is shut off in the hollow body, resulting in the hollow body being refilled with liquor via the outlet passageway 411, 511 in thus becoming heavier to sink with reduced buoy- ancy. Once the immersed aerator has sunk to its lowestmost position as restricted by the suspension devices, the procedure is repeated, i.e. the cavity 410 again being evacuated, causing the immersed aerator to re-ascend. The anoxic phase for denitrification is thus created in accordance with the invention by alternating flooding and evacuation of the hollow body of the immersed aerator causing it to continuously bob up and down in it thus being changed in function to that of an agitator. It is this bobbing up and down action of the immersed aerator, actually functioning as an agitator, that agitates the liquor, preventing the system from sludging up. To terminate denitrification this procedure is ceased, the immersed aerator flooded and recharged with air to aerate the liquor in „down" position of the aerator. List of Reference Numerals 1,11,21,31 diffuser 2, 12, 22, 32, 42 floodable hollow body 3,13,23,33 carrier 4, 14, 24, 34, 41, 44 immersed aerator 5, 15, 25, 35 diffuser tubes or membrane aerator 6,16,26,36,46 gas feed 7,47 bottom 9, 29 air passageway 10 cavity 18 cross-beam 49 first feeder passageway 59 second feeder passageway 401 first end part 402 passageway 403,403' membrane 404 pore 405 clamp 406 compressed air feeder 407 non-return valve 408 non-return valve 409 passageway 410 Cavity 411 outlet passageway 412 end part 413 cylindrical outer wall 414 wall thickness 415 bottom 501 end part 502 passageway 509 passageway 511 outlet passageway 515 bottom 520 suspension device 521 feeder B arrow, bubble movement direction L arrow, air feed direction DL arrow, compressed air feed direction CLAIMS 1. A process for liquor - particularly wastewater - agitation and/or aeration having the following cyclically repeated steps a) and b): a) aerating the liquor by means of an immersed aerator for a predetermined first pe- riod of time (t1) using a diffuser (1) disposed on a carrier (3, 43) designed as a flood- able hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought into the liquor by the diffuser, making it possible to create nitrification in the liquor; b) agitating the liquor by means of the immersed aerator for a predetermined second period of time (t2), the air feed by the diffuser (1) being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body (2, 42) with gas or air, the immersed aerator assuming the function of an agitator in which liquor rises upward, thus agitating the liquor, making denitrification possible in the liquor. 2. The process as set forth in claim 1, characterized in that the first and the sec- ond period of time (t1, t2) are timed by a controller. 3. An immersed aerator for implementing the process as set forth in claim 1 or 2 comprising at least one diffuser (1) disposed on a carrier (3, 43), characterized in that the immersed aerator (1) comprises at least one floodable hollow body (2, 42) as formed by the carrier (3, 43). 4. The immersed aerator as set forth in claim 3, characterized in that the flood- able hollow body (2, 42) is configured as an elongated tube. 5. The immersed aerator as set forth in claim 4, characterized in that the flood- able hollow body (2) is configured as a tube of rectangular, round or elliptic cross- section. 6. The immersed aerator as set forth in any of the claims 3 to 5, characterized in that the floodable hollow body (2)is equipped with a compressed air feeder for filling the hollow body (2) with gas or air. 7. The immersed aerator as set forth in any of the claims 3 to 6, characterized by a perforated membrane (403) enveloping the carrier (3, 43) at least partly and a gas feeder (402) for feeding gas between the carrier (42) and the membrane (403). 8. The immersed aerator as set forth in claim 7, characterized in that it com- prises a first end part (401) disposed in a first end portion of the hollow body (2), a first passageway (49) for feeding compressed air to the diffuser (1) and a second passageway (409) for feeding compressed air to fill the hollow body (2, 42) with gas or air as well as an outlet passageway (411) disposed in a second end portion oppo- site the first end portion for evacuating the liquor contained in the hollow body. 9. The immersed aerator as set forth in claim 8, characterized in that it com- prises, disposed in a second end portion opposite the first end portion of the hollow body (2), a second end part with a feeder passageway (59) for feeding the diffuser (1) with gas or air and an outlet passageway (511). 10. The immersed aerator as set forth in claim 8 or 9, characterized in that the immersed aerator is suspended by at least two suspension devices (520). 11. The immersed aerator as set forth in claim 10, characterized in that at least one of the suspension devices is configured as a feeder (521) for the diffuser (1). 12. The immersed aerator as set forth in any of the claims 9 to 11, characterized in that the outlet passageway (411) is disposed near to the bottom of the hollow body operationally. 13. The immersed aerator as set forth in any of the claims 8 to 12, characterized in that the first passageway (49) and/or the second passageway (409) is provided with non-return valves (407, 408) preventing a liquor flow through the first or second passageway (409) from the hollow body (2). 14. The immersed aerator as set forth in any of the claims 3 to 13, characterized by a ballast weight. 15. The immersed aerator as set forth in any of the claims 3 to 14, characterized by a hollow body (2) configured as a shallow cylinder whose circumferential wall forms a hub mounting the spoked arrangement of the diffusers. 16. The immersed aerator as set forth in any of the claims 3 to 15, characterized by a hollow body (2) configured as a shallow cylinder with diffusers topping the cylin- der. 17. The immersed aerator as set forth in any of the claims 4 to 15, characterized in that the floodable hollow body is configured as an elongated tube, from the outer wall of which diffusers (11) extend substantially perpendicular thereto. 18. A process for liquor as herein described and illustrated in claims 1 and 2. 19. An immersed aeratoras as herein described and illustrated. The invention relates to a method for stirring and/or aerating fluids, particularly sewage, having the following cyclically repeated steps: aerating the fluid by means of an immersed aerator for a predetermined first period of time (t1) using an aeration device (1) disposed on a carrier (3, 43) designed as a floodable hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought into the fluid by the aeration device, whereby the potential for nitrification is created in the fluid; stirring the fluid by means of the immersed aerator for a predetermined second period of time (t2), the air infeed by the aeration device (1) being throttled or turned off, and the previously flooded hollow body being evacuated in order to fill the hollow body (2, 42) with gas or air, the immersed aerator assuming the function of a mixing device in which fluid rises upward, thus mixing the fluid, wherein the potential for denitrification is created in the fluid; and an immersed aerator.

Full Text

Method for stirring and/or aerating fluids, particularly wastewater,
particularly with a floodable aerator
The present invention relates to a process for liquor, particularly wastewater, agita-
tion, particularly with a floodable immersed aerator and with at least one diffuser dis-
posed on a carrier.
Modern wastewater/sewage plants need to denitrify the wastewater to attain the
specified capped nitrate values. Denitrification - in other words dissociating the oxy-
gen bound to the nitrate to thus liberate the molecular nitrogen - requires several bio-
logical phases by bacteria suitable for the purpose in the anoxic milieu, i.e. in the
absence of dissolved oxygen in the reactor.
Optimizing denitrification requires, for one thing, intensive agitation of the biomass
(bacteria) with the wastewater to increase the interface and accelerate discharge of
the denitrified medium, for another, the existence of degradable carbon compounds.
For, it is the aerobic C degradation that firstly ,,forces" - to put it simply - denitrifica-
tion to fetch the oxygen from the nitrate.
Doing this is currently performed by a variety of phases in processing, all of which,
however, are characterized by the creation of an anoxic milieu. Depending on how
high the concentration is in the nitrogen supply, anoxic volumes as high as 50% of
the total reactor volume are needed and usual.
But wastewater/sewage treatment in general (oxidation of carbon products, oxidation
of the ammonia) always necessitates an oxic milieu in which treatment (degradation
of C and ammonia) is mainly aerobic, whereas in any reactor having a predominantly
oxic milieu denitrification is impossible.

This has resulted in a variety of ways of getting round this problem, including, for ex-
ample, simultaneous denitrification, and upstream and downstream denitrification.
In upstream denitrification the return sludge (a mixture of biomass and richly nitrated
wastewater) is separately basined where it is mixed with a highly carbonated flow of
water.
In simultaneous denitrification the phases in the process are performed all at the
same time in a reactor involving separation of oxic/anoxic volumina either spatially
(by zoning the basin by throttling aeration definedly) or in time (cyclic ON/OFF of
aeration), combinations of these phases also being possible.
In downstream denitrification, as the name suggests, denitrification occurs after ac-
tual aeration. All three of these processes have their specific advantages and disad-
vantages, especially downstream denitrification having since become outdated.
In summary it can be said that simultaneous denitrification offers the most benefits,
this prompting the following considerations:
When a basin is aerated, C and ammonia degradation (oxidation) is normal. But
when denitrification is needed at the same time, either the aeration needs to be throt-
tled locally or shut off completely. However, to circulate a certain reactor volume a
critical minimum air feed is needed to keep the balance of the biomass to make deni-
trification possible in the first place and in preventing the plant from become fouled
up.
In other words, when shutting off aeration completely, agitators are needed to agitate
the basin contents to ensure the necessary interfacial mass transfer as is usual in
practice. But if aeration is simply throttled it may happen that the oxygen introduced
is still too high, resulting in no anoxic zones materializing, thus ruining the chances of
effective denitrification being achieved. This is especially the case when the waste-
water feed has a low C concentration, resulting in the air flow needed for circulation
still exceeding the air flow (or oxygen requirement) needed for oxidation by the bac-
teria.
Known from European patent EP 0 249 172 B1 (von Nordenskjold) is a process for
aerating and circulating wastewater and activated sludge for the purpose of nitrifica-

tion and denitrification by means of a plurality of diffusers moved over the bottom of
the basin in a cyclic sweeping action. For this purpose certain bottom diffusers are
supplied with a reduced air feed to form slightly aerated zones in the wastewater or
activated sludge to achieve the anoxic conditions in making zoned denitrification
possible.
The drawback of this system is its many components such as squeeze valves sus-
ceptible to failure.
For aerating and agitating wastewater a wealth of different means and processes are
known from prior art.
Known from DE 196 21 116 C2 (Invent) e.g. is a bottom distributor for gas to which
at least one flexible perforated tube can be connected for gas charging, including,
communicatingly connected to a diffuser, a hollow base body provided as a bottom
distributor for the diffuser supply. To maintain such a device operative near to the
bottom, when used in water treatment plants, suitable weights have to be provided to
compensate the flotation tendency caused by the cavities in the bottom distributor.
Known from DE 40 01 201 C1 (von Nordenskjold) is a floating aerator for introducing
air to aerate a body of water in supplying air thereto via connecting lines via bottom
diffusers employed as a so-called immersed aerator. The problem here is that bot-
tom diffusers have a limited lifetime with the nuisance of requiring regular cleaning
maintenance and inspection. This requires, as a rule, the bottom diffusers to be lifted
out of the basin during operation of water or wastewater treatment plant. And, here
again, these regularly require weights to weigh the system to compensate a float
tendency of the bottom diffusers in operation. Lifting a bottom diffuser out of the ba-
sin is not simple, it needing to be lifted to the water surface of an activated sludge
basin of a wastewater treatment plant (for cleaning, inspection, and possibly repair)
and then to be returned in place. All this is highly complicated and costly and even a
hazard for personnel doing the work. Apart from this the corresponding parts of the
floating or bottom diffusers or also immersed aerators are stressed to the extreme.
Especially when the aerators include membranes, damage to these sensitive items
can hardly be avoided.
Known from US 5,906,774 (Parkson) is a surface aerator connected by a rod to a
submerged (immersed) aerator in the region of which additional inflatable buoyant

members are arranged to help get round the aforementioned problem of lifting an
immersed aerator to the surface of the water which is a great help in servicing it.
However, this system has the serious drawback that the inflatable buoyant members
add to the components in the vicinity of the immersed aerator which are a nuisance
to handle, both non-inflated and inflated, whilst being prone to damage by becoming
punctured and thus useless.
Surface aerators are employed in the operation of wastewater treatment plants, i.e.
floats to which the surface aerators are attached submerged in the water body. It is
especially in wastewater treatment plants that such devices are used to aerate the
activated sludge basin. Another use serves to oxygenate water bodies. The way
these work, known in principle, involves a pressurized aeration system in which air is
sucked in from the atmosphere by compressors and distributed by a feeding system
to the so-called immersed aerators engineered, as a rule, to discharge the drawn-in
air in fine bubbles which rise to the surface of the water from the immersed aerator,
giving off oxygen to the water on their way. In anaerobic systems these devices are
likewise employed as gas injectors on the same principle, especially for circulation.
As compared to diffuser members secured to the bottom of the basin as in classic
wastewater treatment plants surface aeration has special advantages, this being the
reason why surface aerators have since become very popular.
The increase in the size of individual systems also adds to the number of diffuser
members per system, these very quickly amounting to several thousand such mem-
bers within a system. Known are devices in which so-called diffuser tubes are
grouped together into aerators attached to floating air distribution tubing for sub-
mersed operation at the bottom of the basin. Known diffuser tubes are made of poly-
ester or ceramics and perforated membrane materials which, as a rule, are lifted to
the surface on supporting members. Particularly perforated membrane diffusers
have become popular in recent years since their oxygen exploitation is greatly supe-
rior to that of other diffuser materials. In addition to these, plate aerators find applica-
tion.
The increase in size of such plants has called for ever-larger individual basins and
water depths, nowadays often six meters deep, necessitating grouping together more
and more diffuser tubes to form an aerator assembly. One salient feature of a func-
tionable ,,floating" immersed aerator is that its submersed components have a stable
working depth wo excessive buoyancy which would otherwise render the immersed

aerator useless, i.e. becoming unstable, resulting in the diffuser members becoming
partly floated, entangled, and endangering effective aeration, or even bringing the
system to a standstill. In addition to this, it will readily be appreciated that such ran-
dom movements of the diffuser members can be damaging. This is why any opti-
mally designed immersed aerator has just enough dead weight to, on the one hand,
maintain the aerator in stable operation, whilst, on the other, keeping the weight
down sufficiently to assist handling by assembly and operating personnel.
The diffuser assemblies described hitherto are exposed to high wear and tear in op-
eration, they needing to be cleaned regularly and the membranes replaced new after
a certain lifetime. This necessitates lifting the diffuser assembly or immersed aera-
tors to the water surface, done, as a rule, without halting plant operation. Lifting aera-
tors out of the water is a difficult operation prone to damage, usually involving an ex-
perienced crew of workers. A particular nuisance to safe handling is the ..biological"
slime fouling of the many normally submersed surfaces rendering them slippy to
handle. In addition to this, the aerators and their ancillary facilities are often stressed
when lifted out of the water, risking damage such as tube kinking, tube connector
breakage and diffuser membrane rupture. Lengthy handling of individual surface or
immersed aerators poses the particular drawback of the activated sludge in the water
zone worked by a particular immersed aerator becoming imbalanced to negatively
affecting the biological process as a whole.
It is thus an object of the invention to propose a process with which the cited draw-
backs of prior art are avoided or at least greatly reduced, and to propose an im-
mersed aerator which can now be employed to advantage in the proposed process.
This object is achieved by a process for liquor - particularly wastewater - agitation
and/or aeration having the following cyclically repeated steps a) and b):
a) aerating the liquor by means of an immersed aerator for a predetermined first pe-
riod of time (t1) using a diffuser disposed on a carrier designed as a floodable hollow
body, the hollow body being flooded and air being brought into the liquor by the dif-
fuser, making it possible to create nitrification in the liquor;
b) agitating the liquor by means of the immersed aerator for a predetermined second
period of time (t2), the air feed by the diffuser being throttled or turned off, and the
previously flooded hollow body being evacuated in order to fill the hollow body with

gas or air, the immersed aerator assuming the function of an agitator in which liquor
rises upward, thus agitating the liquor, making denitrification possible in the liquor.
The advantages of the process in accordance with the invention consist inter alia of
aeration, after a certain period of time, now being followed by a period of non-
aeration in which an anoxic zone is created in the corresponding zone of the liquor,
since aeration is totally ceased therein. Instead, an agitation phase is set by the hol-
low body being cyclically flooded and evacuated. It is this cyclic flooding and evacua-
tion of the hollow body which causes the aerator to continually bob up and down,
agitating the liquor.
Any air escaping during this highly agitated agitating of the liquor is immaterial to the
oxygen content of the liquor since, on the one hand, the volume of air involved is
much less than that in normal aeration and, on the other, the escaping air has such
large bubbles that there is hardly any transfer of oxygen, i.e. with no risk of endan-
gering the anoxic phase. As detained above, the person skilled in the art is aware
that anoxic phases need to be present for denitrification, which, however, have to be
replaced by oxic phases to achieve nitrification.
In one advantageous further embodiment of the process the first and second periods
of time (t1, t2) are timed by a controller with the advantage of this now making it pos-
sible to precisely define denitrification to the corresponding load on the liquor.
The object is achieved furthermore by an immersed aerator comprising at least one
diffuser disposed on a carrier, the immersed aerator being characterized by it com-
prising at least one floodable hollow body formed by the carrier. The device in accor-
dance with the invention has numerous benefits. The carrier configured as a flood-
able hollow body to carry the diffuser is of decisive assistance in reducing the buoy-
ancy tendency of the immersed aerator when filled with water in operation, thus do-
ing away with, or at least minimizing, the need for ballast weights to compensate
buoyancy so that the aerator is stationed stabilized, in thus avoiding an excessive
dead weight of the immersed aerator.
In one advantageous aspect of the invention the floodable hollow body is configured
as an elongated tube with the advantage that low-cost standard parts can now be
used in producing the immersed aerator in accordance with the invention.

In another advantageous aspect of the invention the immersed aerator carrier con-
figured as a floodable hollow body is configured as a tube of rectangular, round or
elliptic cross-section. Thus now makes it possible to individualize the immersed aera-
tor to preferred diffusers.
In yet another advantageous aspect of the invention the floodable hollow body is
equipped with a compressed air feeder for filling the hollow body with gas or air, this
device making it easy to surface the device in accordance with the invention in the
water simply by feeding the compressed air to remove the water in the floodable hol-
low body, prompting the immersed aerator to surface since the hollow body is no
longer flooded. As an alternative, the compressed air feed can be made by a source
of compressed air on a maintenance boat, by a feeder specifically included for this
purpose in the plant or by making corresponding use of the air for aerating the water.
In still another advantageous aspect of the invention the carrier of the immersed
aerator in accordance with the invention is equipped at least partly with a perforated
membrane enveloping the latter and a means for feeding gas between the carrier
and the membrane. This now makes it possible to advantage to achieve the diffusers
as known substantially from prior art, particularly in combination with the invention by
much simpler means. The carrier configured as an elongated tube forms by its outer
wall a wall of the air feeder of the diffuser, the other wall of which is formed by a per-
forated membrane which except for the pores is sealed off gas-tight from the carrier.
In another advantageous aspect of the invention the hollow body of the immersed
aerator comprises at least one first end part disposed in a first end portion of the hol-
low body with a first passageway for feeding compressed air to the diffuser and a
second passageway for feeding compressed air to fill the hollow body with gas or air.
There is a whole series of methods known from prior art for maintaining air injectors
at a constant level below the water surface. As compared to these, however, the
configuration of the device in accordance with the invention now makes for a design
requiring fewer parts and more friendly installation, all of which makes for enormous
cost savings and saving time both in installing and servicing the immersed aerator.
In another particularly advantageous aspect of the invention the immersed aerator is
characterized by it comprising a second end part with a passageway for feeding the
diffuser with gas or air and an outlet passageway disposed in a second end portion
opposite the first end portion of the hollow body. This now makes it possible to

added advantage to increase, e.g. double the air feed in the same time with the
same speed.
In yet another advantageous aspect of the invention the immersed aerator is charac-
terized by it being suspended by at least two suspension devices which now makes it
possible to set it precisely level in harmonizing bubble formation in aeration.
In still a further advantageous aspect of the invention the immersed aerator is char-
acterized by at least one of the suspension devices being configured as a feeder for
the diffuser with the advantage of making for a simplified arrangement whilst reduc-
ing the risk of suspension devices and feeders becoming entangled.
In yet another advantageous aspect of the invention the immersed aerator is charac-
terized by the outlet passageway being disposed near to the bottom of the hollow
body operationally. This facilitates evacuating fluid still therein when evacuating the
immersed aerator to advantage in preventing a short-circuit flow of the evacuating
gas above the bottom of the hollow body.
In a further advantageous aspect of the invention the first passageway of the end
part is provided with non-return valves preventing a liquor flow, for instance of the
wastewater through the first passageway from the hollow body, advantageously mak-
ing sure that no unwanted materials have access to the air feed of the diffuser.
In still another advantageous aspect of the invention the immersed aerator is charac-
terized by a ballast weight enabling the device in accordance with the invention to be
individualized to the necessary conditions or marginal circumstances as dictated by
the wastewater and also by the situation in operating the immersed aerator in each
case.
In another advantageous aspect of the invention the immersed aerator is character-
ized by a hollow body configured as a shallow cylinder whose circumferential wall
forms a hub mounting the spoked arrangement of the diffusers, for example, in the
form of of diffuser tubes and the like. Configuring the immersed aerator in accor-
dance with the invention in this way permits making use of the operating principle in
accordance with the invention also with immersed aerators figured otherwise, espe-
cially including such immersed aerators employed decentralized as single aerators.

In yet a further advantageous aspect of the immersed aerator in accordance with the
invention it is again characterized by a hollow body configured as a shallow cylinder
but here with the diffusers topping the cylinder. Here too, the same as in the example
aspect as described before, the device in accordance with the invention can be indi-
vidualized to comply with given, possible already existing systems, now with the spe-
cial advantage afforded by the device in accordance with the invention of, namely, in
surfacing an immersed aerator with no problem.
In still a further advantageous aspect of the invention an immersed aerator is charac-
terized by the floodable hollow body being configured as an elongated tube, from the
outer wall of which diffusers extend substantially perpendicular thereto, here again
with the advantages of the aspects as just described, namely adapting and integrat-
ing the device in accordance with the invention to/in already existing systems or
combining the device in accordance with the invention with the other possible advan-
tages of the variants, hollow bodies and diffusers as already described.
Further features and advantages of the invention read from the sub-claims.
For a better appreciation of the invention it will now be detained by way of a few ex-
amples with reference to the drawing in which:
FIG. 1 is a very simplified diagrammatic view of one example aspect of an immersed
aerator in accordance with the invention shown partially sectioned.
FIG. 2 is a view in perspective of the immersed aerator as shownin FIG. 1.
FIG. 3 is again a very simplified diagrammatic view of another example aspect of the
immersed aerator in accordance with the invention shown in perspective.
FIG. 4 is again a very simplified diagrammatic view of yet another example aspect of
the an immersed aerator in accordance with the invention shown in perspective.
FIG. 5 is a diagrammatic view of the immersed aerator as shown in FIG. 4 shown
sectioned.
FIG. 6 is a view of still another example aspect of an immersed aerator in accor-
dance with the invention.

FIG. 7 is a view of a further example aspect of an immersed aerator in accordance
with the invention.
FIG. 8 is a view in perspective of the salient features of the immersed aerator as
shown in FIG. 7.
FIG. 9 is a view of still a further example aspect of an immersed aerator in accor-
dance with the invention.
FIG. 10 is a view of another example aspect of an immersed aerator in accor-
dance with the invention.
Referring now to FIG. 1 there is illustrated in a very simplified diagrammatic view an
immersed aerator 4 including a carrier 3 mounting a diffuser 1. The carrier 3 is con-
figured as a floodable hollow body 2 in which the cavity 10 of the floodable hollow
body 2 here and otherwise is depicted cross-hatched for a better appreciation. Via a
gas feeder 6, for example, air is fed in the direction of the arrow L into the immersed
aerator ported via the carrier 3 of the diffuser 1. The path of the air bubbles ascend-
ing from the diffuser 1 to the surface of the water is in the direction of the arrows B.
Referring now to FIG. 2 in additon to FIG. 1 there is illustrated how the carrier 3 con-
figured as a floodable hollow body 2 has the shape of an elongated cube. The sur-
face area depicted cross-hatched in the hollow body 2 can be filled or flooded with
liquor in operation of the immersed aerator, reducing the buoyancy of the immersed
aerator in accordance with the invention to the extent in which the hollow body 2 is
flooded with the intention of maintaining it at a stable level preferably near to the bot-
tom 7 as depicted diagrammatically.
Referring now to FIG. 3 there is illustrated a further example aspect of the invention,
depicting in this case a carrier 13 configured integrated with a shallow cylindrical hol-
low body as a floodable hollow body 12. Mounted on a cross-beam 18, which as
shown in FIG. 3 is carried by the carrier 13 as an air feeder, are diffusers 11 with
conventional diffuser tubes 15 as depicted diagrammatically. The special advantage
afforded by this arrangement is that a single floodable hollow body 12 serves for a
whole battery of diffuser tubes 15. In principle the air feed into the diffusers 11 is the
same as the gas feed as shown in the example aspects of FIG. 1 and FIG. 2. Thus,
each of the diffusers 11 has an air feed in the direction of the arrows L again via a

gas feeder 16, here again the direction of the air bubbles ascending from the diffus-
es 11 to the water surface being symbolized in the direction of the arrows B.
Referring now to FIG. 4 there is illustrated another example aspect of an immersed
aerator 24 comprising a central carrier 23 or central hollow body 22 mounting a
spoked arrangement of the diffusers 21 receiving a spoked gas feed via a gas feeder
26. Referring now to FIG. 5 there is illustrated for a better appreciation of the aspect
as shown in perspective in FIG. 4 the diffuser in a diagrammatically sectioned view.
Via the gas feeder 26 air is fed via an air passageway 29 into the diffusers 21 which
ascends to the surface of the water in the direction of the arrows B.
Referring now to FIG. 6 there is illustrated yet another example aspect of the inven-
tion in the form of a spoked arrangement of the immersed aerator 36 in which the
functioning of the various components is in principle the same as already described
with reference to FIGs. 3 and 4. Here too, there is depicted the advantage of the
configuration as shown in FIG. 3 involving a plurality of diffusers in combination with
a single floodable hollow body 32.
Referring now to FIG. 7 there is illustrated still a further example aspect of an im-
mersed aerator 44 in accordance with the invention including a carrier 43 doubling in
function as a hollow body 42. The passageway 46 ports via a coupling (not shown)
into an end part 401 sealing off the left-hand side of the immersed aerator 41 as
shown in FIG. 7 in the interior portion of the carrier 43 also forming the hollow body
42. The end part 401 has a gas feeder passageway 49 via which air is directed
through drillings 402 in the carrier 43 between the outer wall 413 of the carrier 43
and a membrane 403 surrounding the outer wall 413 through which air can escape
via pores 404 to ascend to the surface of the water in the direction of the arrows B.
Clamps 405 clamp the membrane 403 to the outer shell of the carrier 43 respectively
hollow body 42 configured, for example, cylindrical. In the cavity 410 of the hollow
body 42 the floodable portion is depicted cross-hatched. A feeder 406 ports likewise
in the end part 401 into the gas feeder passageway 409 via which the cavity 410 of
the hollow body 42 can be filled with compressed air. The liquor in the cavity 410 is
evacuated via an outlet passageway 411 disposed on the right-hand side of the im-
mersed aerator 41 as shown in FIG. 7 in an end part 412. When compressed air is
directed in the direction of the arrows DL via the feeder 406 and the gas feeder pas-
sageways 409 into the end part 401 in the cavity 410 of the immersed aerator 41, the
liquor in the cavity 410 is evacuated by an outlet passageway 411 evacuating the

cavity 410, increasing the buoyancy of the immersed aerator 41 to such an extent
that it ascends to the surface of the water.
By means of this design of the immersed aerator in accordance with the invention by
using compressed air to „pump up" or drain the floodable hollow body it can be
caused to ascend to the surface of the water for maintenance with no problem, after
which the immersed aerator is returned in the water where it automatically becomes
flooded to sink back down to its operating level.
Indicated diagrammatically furthermore in FIG. 7 is the basin bottom 47 in the vicinity
of which the immersed aerator 41 has its operating level. Depending on the thick-
ness 414 and weight of the wall of the hollow body 42 or also the material of the hol-
low body 42 and the volume of the cavity 410 the immersed aerator 41 can be set to
ascend as desired.
Greatly simplified in FIG. 7 is the position of the membrane 403' „in aeration opera-
tion" at the underside of the immersed aerator 41 used to set the compressed air
feed in this situation by reason of the overpressure building up between the outer
wall 413 of the hollow body 42 and the membrane 403. The pores 404 of the elastic
membrane 403 open to release air in the direction of the arrows B from the im-
mersed aerator 41.
Non-return valves 407 and/or 408 are optional on gas feeder passageways 409 and
49 of the end part 401 to prevent a backflow of liquor from the cavity 410 into the gas
feeder passageways 409 and 49 respectively to prevent the corresponding air feed-
ers 406 and 46 from becoming fouled up.
Referring now to FIG. 8 there is illustrated the salient features of the immersed aera-
tor 41 as shown in in FIG. 7 in a view in perspective.
It is understood, of course, that the principle in accordance with the invention can be
used just as well with plate aerators achieved in accordance with the design features
as detained for the example aspect as shown in FIG. 7. Making use of of the principle
of the immersed aerator in accordance with the invention permits a wealth of possi-
ble variants. Thus, it is understood that the invention and the scope of its claims is
not restricted to the aspects shown herein by way of example.

Referring now to FIG. 9 there is illustrated how the immersed aerator comprises on
the left-hand side of the drawing a feeder 521 normally directed upwards, for exam-
ple for an air feed (not shown) in the direction of the arrow L. A compressed air
feeder 506 feeds air to the cavity to fill it with gas or air to cause the immersed aera-
tor to ascend and to evacuate the liquor contained therein. Although it is possible to
suspend the immersed aerator by a suspension device 502 shown in bold or broken
lines, it is also just as possible to arrange for the immersed aerator to be carried
solely by the feeder 521 and a suspension device 520 or just by two feeders 521.
Referring now to FIG. 10 there is illustrated still a further immersed aerator - de-
picted halved to save space - which as compared to the immersed aerator as shown
in FIGs. 7 and 8 ends on both sides in a passageway 46 with an air feed L. Outlet
passages for the fluid to be evacuated can be suitably provided at one end, e.g. as
shown in FIGs. 7 and 8 and as described. It is, of course, just as possible to provide
suspension devices (not shown) on this immersed aerator as shown in FIG. 10 as
described before.
Agitation and aeration are alternated as follows:
When after aeration, orchestrated as known, is to be followed by a denitrification
phase, introducing an anoxic phase in a zone to set aeration by the immersed aera-
tor is done by shutting off the air feed via passageways 46, 49 via the feeder(s) 521,
after which the cavity 410 is filled by feeding compressed air via feeders 406 and 409
to evacuate the fluid therein, usually a liquid, such as water or wastewater via the
outlet passageway 411, 511. This causes the immersed aerator to tilt in the direction
of the air feeder on the immersed aerator, to tilt further until it is standing upright on
ascending to the surface of the water. This is the same procedure as performed
while inspecting an immersed aerator. On it surfacing, the compressed air feed is
shut off in the hollow body, resulting in the hollow body being refilled with liquor via
the outlet passageway 411, 511 in thus becoming heavier to sink with reduced buoy-
ancy. Once the immersed aerator has sunk to its lowestmost position as restricted by
the suspension devices, the procedure is repeated, i.e. the cavity 410 again being
evacuated, causing the immersed aerator to re-ascend.
The anoxic phase for denitrification is thus created in accordance with the invention
by alternating flooding and evacuation of the hollow body of the immersed aerator

causing it to continuously bob up and down in it thus being changed in function to
that of an agitator.
It is this bobbing up and down action of the immersed aerator, actually functioning as
an agitator, that agitates the liquor, preventing the system from sludging up.
To terminate denitrification this procedure is ceased, the immersed aerator flooded
and recharged with air to aerate the liquor in „down" position of the aerator.

List of Reference Numerals
1,11,21,31 diffuser
2, 12, 22, 32, 42 floodable hollow body
3,13,23,33 carrier
4, 14, 24, 34, 41, 44 immersed aerator
5, 15, 25, 35 diffuser tubes or membrane aerator
6,16,26,36,46 gas feed
7,47 bottom
9, 29 air passageway
10 cavity
18 cross-beam
49 first feeder passageway
59 second feeder passageway
401 first end part
402 passageway
403,403' membrane
404 pore
405 clamp
406 compressed air feeder
407 non-return valve
408 non-return valve
409 passageway
410 Cavity
411 outlet passageway
412 end part
413 cylindrical outer wall
414 wall thickness
415 bottom
501 end part
502 passageway
509 passageway
511 outlet passageway
515 bottom
520 suspension device
521 feeder
B arrow, bubble movement direction
L arrow, air feed direction
DL arrow, compressed air feed direction

CLAIMS
1. A process for liquor - particularly wastewater - agitation and/or aeration having
the following cyclically repeated steps a) and b):
a) aerating the liquor by means of an immersed aerator for a predetermined first pe-
riod of time (t1) using a diffuser (1) disposed on a carrier (3, 43) designed as a flood-
able hollow body (2, 42), the hollow body (2, 42) being flooded and air being brought
into the liquor by the diffuser, making it possible to create nitrification in the liquor;
b) agitating the liquor by means of the immersed aerator for a predetermined second
period of time (t2), the air feed by the diffuser (1) being throttled or turned off, and
the previously flooded hollow body being evacuated in order to fill the hollow body (2,
42) with gas or air, the immersed aerator assuming the function of an agitator in
which liquor rises upward, thus agitating the liquor, making denitrification possible in
the liquor.

2. The process as set forth in claim 1, characterized in that the first and the sec-
ond period of time (t1, t2) are timed by a controller.
3. An immersed aerator for implementing the process as set forth in claim 1 or 2
comprising at least one diffuser (1) disposed on a carrier (3, 43), characterized in
that the immersed aerator (1) comprises at least one floodable hollow body (2, 42) as
formed by the carrier (3, 43).
4. The immersed aerator as set forth in claim 3, characterized in that the flood-
able hollow body (2, 42) is configured as an elongated tube.
5. The immersed aerator as set forth in claim 4, characterized in that the flood-
able hollow body (2) is configured as a tube of rectangular, round or elliptic cross-
section.
6. The immersed aerator as set forth in any of the claims 3 to 5, characterized in
that the floodable hollow body (2)is equipped with a compressed air feeder for filling
the hollow body (2) with gas or air.

7. The immersed aerator as set forth in any of the claims 3 to 6, characterized by
a perforated membrane (403) enveloping the carrier (3, 43) at least partly and a gas
feeder (402) for feeding gas between the carrier (42) and the membrane (403).
8. The immersed aerator as set forth in claim 7, characterized in that it com-
prises a first end part (401) disposed in a first end portion of the hollow body (2), a
first passageway (49) for feeding compressed air to the diffuser (1) and a second
passageway (409) for feeding compressed air to fill the hollow body (2, 42) with gas
or air as well as an outlet passageway (411) disposed in a second end portion oppo-
site the first end portion for evacuating the liquor contained in the hollow body.
9. The immersed aerator as set forth in claim 8, characterized in that it com-
prises, disposed in a second end portion opposite the first end portion of the hollow
body (2), a second end part with a feeder passageway (59) for feeding the diffuser
(1) with gas or air and an outlet passageway (511).
10. The immersed aerator as set forth in claim 8 or 9, characterized in that the
immersed aerator is suspended by at least two suspension devices (520).
11. The immersed aerator as set forth in claim 10, characterized in that at least
one of the suspension devices is configured as a feeder (521) for the diffuser (1).
12. The immersed aerator as set forth in any of the claims 9 to 11, characterized
in that the outlet passageway (411) is disposed near to the bottom of the hollow body
operationally.
13. The immersed aerator as set forth in any of the claims 8 to 12, characterized
in that the first passageway (49) and/or the second passageway (409) is provided
with non-return valves (407, 408) preventing a liquor flow through the first or second
passageway (409) from the hollow body (2).
14. The immersed aerator as set forth in any of the claims 3 to 13, characterized
by a ballast weight.

15. The immersed aerator as set forth in any of the claims 3 to 14, characterized
by a hollow body (2) configured as a shallow cylinder whose circumferential wall
forms a hub mounting the spoked arrangement of the diffusers.
16. The immersed aerator as set forth in any of the claims 3 to 15, characterized
by a hollow body (2) configured as a shallow cylinder with diffusers topping the cylin-
der.
17. The immersed aerator as set forth in any of the claims 4 to 15, characterized
in that the floodable hollow body is configured as an elongated tube, from the outer
wall of which diffusers (11) extend substantially perpendicular thereto.

18. A process for liquor as herein described and illustrated in claims 1 and 2.
19. An immersed aeratoras as herein described and illustrated.

The invention relates to a method for stirring and/or aerating fluids,
particularly sewage, having the following cyclically repeated steps:
aerating the fluid by means of an immersed aerator for a predetermined
first period of time (t1) using an aeration device (1) disposed on a carrier
(3, 43) designed as a floodable hollow body (2, 42), the hollow body (2,
42) being flooded and air being brought into the fluid by the aeration
device, whereby the potential for nitrification is created in the fluid;
stirring the fluid by means of the immersed aerator for a predetermined
second period of time (t2), the air infeed by the aeration device (1) being
throttled or turned off, and the previously flooded hollow body being
evacuated in order to fill the hollow body (2, 42) with gas or air, the
immersed aerator assuming the function of a mixing device in which fluid
rises upward, thus mixing the fluid, wherein the potential for
denitrification is created in the fluid; and an immersed aerator.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=2aNOFU8frAldk8aZ7VN6Lw==&loc=wDBSZCsAt7zoiVrqcFJsRw==

« Previous Patent

Next Patent »

Patent Number

269339

Indian Patent Application Number

60/KOLNP/2010

PG Journal Number

43/2015

Publication Date

23-Oct-2015

Grant Date

16-Oct-2015

Date of Filing

05-Jan-2010

Name of Patentee

BIOWORKS VERFAHRENSTECHNIK GMBH

Applicant Address

WERNHER-VON-BRAUN-STRASSE 10, 85640 PUTZRUNN, GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	BUCH, STEPHAN	KIRCHPFAD 8, 55606 HOCHSTETTEN-DHAUN, GERMANY
2	KRÖNER, PETER	HABICHTSTR. 16, 81827 MÜNCHEN, GERMANY

PCT International Classification Number

B01F 3/04,C02F 3/20

PCT International Application Number

PCT/EP2008/005527

PCT International Filing date

2008-07-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2008 021 649.6	2008-04-30	Germany
2	10 2007 033 483.6	2007-07-18	Germany