WO2003037805A1

WO2003037805A1 - Small capacity waste water treatment plant

Info

Publication number: WO2003037805A1
Application number: PCT/CZ2002/000058
Authority: WO
Inventors: Svatopluk Mackrle; Vladimir Mackrle; Oldrich Dracka
Original assignee: Svatopluk Mackrle; Vladimir Mackrle; Oldrich Dracka
Priority date: 2001-10-29
Filing date: 2002-10-29
Publication date: 2003-05-08

Abstract

A plant for waste water treatment, in particular sewage water from small sources, for activation treatment by unified suspended activated sludge, created by a tank (1) wherein three functional spaces are provided, and namely an aerated oxic activation space (11), an anoxic de-nitrification space (9) and a separation space (10), the waste water inlet (19) being introduced into the anoxic de-nitrification space (9), the purified water discharge (21) being installed in the upper part of the separation space (10), the anoxic de-nitrification space (9) being connected with the oxic activation space (11), the oxic activation space (11) being connected with the separation space (10), and the plant being provided with a device for pumping the activated sludge from the separation space (10) into the anoxic de-nitrification space (9). Tank (1) has a shell coat (2) smoothly passing over onto shell bottom (3) of saucer shape, the tank (1) having downwardly decreasing horizontal cross section, and the functional spaces in the tank being created by inserting and fixing at least one separate innder structure (5) that is at least partially adjacent to the inner surface of coat (2) and-or bottom (3) of tank (1), for creating the division between at least two functional spaces, all functional spaces (9, 10, 11) having concave bottom shape.

Description

Small Capacity Waste Water Treatment Plant

Field of the invention

The invention relates to a plant for waste water treatment, in particular sewage water from small sources, for activation treatment by unified suspended activated sludge, created by a tank wherein three functional spaces are provided, and namely an aerated oxic activation space, an anoxic de-nitrification space and a separation space, the waste water inlet being introduced into the anoxic de-nitrification space, the purified water discharge being installed in the upper part of the separation space, the anoxic de-nitrification space being connected with the oxic activation space, the oxic activation space being connected with the separation space, and the plant being provided with a device for pumping the activated sludge from the separation space into the anoxic denitrification space.

Description of the prior art

Ever more often also the smallest plants for the treatment of waste water, especially sewage water, use the technology of activation treatment by unified activated sludge in suspension, with nitrification and de- nitrification and simultaneous aerobic stabilisation of the activated sludge. It is an advantage that the impurities in the waste water serve as carbon source for the de-nitrification. In such case the raw water flows into the de- nitrification, i.e. the anoxic space where it is mixed with the returning mixed liquor. Then the mixed liquor flows from the anoxic space to the nitrification area, i.e. into the aerated oxic space wherefrom it proceeds to the separation space where the treated water gets separated from the activated sludge. The separated activated sludge returns into the anoxic space whereto also the water from the oxic space returns that contains also nitrates originating in the oxic space by oxidation of nitrogen containing substances. These nitrates get then biologically reduced to gazeous nitrogen in the anoxic space, and for this purpose the bacteria in the activation sludge make use of the biologically oxidable carbonaceous substances from the inflowing waste water.

As a rule, a plant for water treatment by the above technology has separated functional spaces for the various described processes. The de- nitrification is carried out under the absence of oxygen and, accordingly, the corresponding functional activation anoxic space should be arranged so as to maintain the activated sludge in suspended condition without using any aeration. This can be achieved either by mechanical mixing or by fluidisation of the suspension of activated sludge. Sufficient concentration of dissolved oxygen being indispensable for the nitrification process, the corresponding functional activation space is an oxic one and is provided with a device for air inlet that usually serves also for achieving the suspension of activated sludge. An advanced separation method is fluid filtration in a fluidized layer of a sludge blanket allowing the mixed liquor from the oxic space to be transferred to the bottom part of the separation space, while the activated sludge from the upward flow of the mixed liquor gets caught in the fluidized layer of the sludge blanket. The separated concentrated activation sludge is then pumped from the separation space back into the anoxic space. Such re-pumping is simultaneously utilised also for the re-circulation of water with nitrates from the oxic space into the anoxic one. As a rule, all functional spaces are created in one integrated plant that is supplied to the user as one unit to be connected to the sewage mouth. Such tank is usually buried into the ground next to the facility from which the waste water is discharged, and then both the onflow and outflow of water are solved by gravity.

The known types of small integrated plants with unified activated sludge in suspension have tanks of prismatic or cylindrical shape and flat bottoms. The various operation spaces in the inside are created either by rigidly attached partition walls that are usually welded to the coat of the tank, or the de-nitrification space and the separation space can be inserted as separate component parts into the tank. In case of an inserted separate part the space between such part and the coat of the tank can serve as an aerating oxic activation space. Inserted parts are known having the form of a prism on whose one side an inverted truncated semi-cone is accommodated, or in form of an inverted truncated cone that is divided in two parts. The semi-cone serves as the separation space for fluid flotation, the prism or the other semi-cone serves as the anoxic de-nitrification space. In case of a prismatic shape the anoxic de-nitrification space is provided with a mechanical mixer for maintaining the activated sludge in suspension, in case of a semi-cone the suspension of activated sludge in the anoxic de-nitrification space is maintained by way of fluidization of the suspension of activated sludge.

All these known and used solutions are burdened by a number of drawbacks. The main disadvantage of all known types of the above plants is the clumsiness of these reactors in view of their mass shipment from the factory to the local distribution site wherefrom they are transported to various customers. The plants with welded internal partition walls can be shipped as a unit only. A standard transport container of 6 meter length, e.g., allows to load five plants with 4 to 5 persons capacity, or 3 plants with 8 to 10 persons capacity. In case of reactors with inserted de-nitrification and separation spaces a certain saving of loading capacity can be achieved by putting a smaller plant into the tank of a larger one, instead of its inner structure, provided plants of various sizes are hauled at a time, however, the saving is not a substantial one. Experience teaches us that the shipment cost of small plants over longer distances are exceedingly high, reaching up to scores of percent of the product price in case of long distance shipment. Another disadvantage of all hitherto known integrated plants are problems concerning the strength of the bottom and of the tank walls that can not be economically manufactured so rigid as to withstand all pressures and strains to which the tank may be exposed. A flat bottom of the tank requires a reinforced substrate on which the tank is buried in the soil. As a rule, a concrete foundation plate is used as substrate, which results in additional costs of the plant installation. Also its walls, irrespective of whether they are cylindrical or flat, are unable to withstand considerable pressures of the soil, or possibly of ground water, especially if the tank is empty and, accordingly, they also require reinforcement, such as with concrete rings or inner struts, which further raises the material cost, as well as the manufacturing and installation expenses.

The mentioned drawbacks are thus reflected in high investment, transport and installation costs, which stand in the way of mass production and broad utilisation of this advanced technology for the solution of individual small sources of sewage pollution. Substance of the invention

The above disadvantages are eliminated by a plant according to the invention characterised in that the tank creating the plant has a shell coat smoothly passing over into a shell bottom that is saucer-shaped, the tank having downwards decreasing horizontal cross section, the functional spaces in the tank being created by inserting and fixing at least one separate inner structure adjacent at least partly to the inner side of the coat and/or the bottom of the tank, in order to create a division between at least two functional spaces, all functional spaces having concave bottom. It is also preferable, regarding the installation, if the horizontal cross section of the inner structure decreases in the downward direction.

Concerning the constructional embodiment, it is preferable to create the inner structure of at least two rigidly connected partition walls, whose edges are adjacent to the coat and to the bottom of the tank, the first partition wall creating a division between the anoxic de-nitrification space and the oxic activation space, and the second partition wall creating a division between the oxic activation space and the separation space, the oxic activation space being located between the anoxic de-nitrification space and the separation space. Another preferable embodiment resides in that the inner structure is created by at least three rigidly interconnected partition walls, whose edges are adjacent to the coat and to the bottom of the tank, the first partition wall creating a division between the anoxic de- nitrification space and the oxic activation space, the second partition wall dividing the oxic activation space from the separation space, and the third partition wall dividing the anoxic de-nitrification space from the separation space. Concerning the accumulation of the separated sludge, and also concerning the storage, transportability and ease of manufacture, it is a contribution that the tank has the shape of a downward narrowing down rotary body terminated by a bottom substantially in form of a spherical, or possibly elliptical canopy.

Considering the design and the treatment effect of the plant it is a contribution that the waste water inlet is connected to the mixing chamber that is connected with the bottom part of the anoxic de-nitrification space, the connection between the anoxic de-nitrification space and the oxic activation space being provided in their upper part, the connection of the oxic activation space with the separation space mouthing in the lower part of the separation space, and at the bottom of the separation space accommodating the inlet to the device for pumping the activated sludge from the separation space to the anoxic de-nitrification space, the latter being created, e.g., by a re-circulation air-lift pump.

An important manufacturing aspect is the fact that the tank is made of fibreglass.

Due to manufacturing and installation considerations it is further beneficial that the inner structure comprises a centrally accommodated mixing chamber bearing all partition walls. It is also preferable to provide a mixing chamber in form of a prismatic tube with quadrangular or triangular cross section.

The plant according to the invention offers numerous benefits. The tank shape with shell coat in form of a body narrowing down in vertical direction and terminated with a concave shell bottom offers advantages for the treatment technology using suspended activated sludge. The saucer shape of the tank bottom creates a focussed narrowing down of the bottom parts of the functional spaces that is favourable for the processes of anoxic de-nitrification and separation of the suspension, whereas the principle of fluidization in the upward flow is used for keeping the activated sludge in suspension, the fluidized layer being created in the broadening part of the functional space and supported from the bottom by the broadening walls of this space. The mentioned shape is also preferable for the withdrawal of separated activation sludge in one spot from the bottom of the separation. The saucer shape of the tank bottom is favourable also for the oxic activation space, allowing to concentrate the aeration on one central aeration element. All above advantages are reflected in the improved efficiency of treatment accompanied by lower power consumption and substantial simplification of the plant design, resulting in lower operation and investment costs.

Another advantage of the chosen tank shape of the plant consists in its suitability for advanced series manufacturing technology, such as integrally wound fibreglass tanks. This ensures both the necessary design rigidity for accommodating the plant in the ground, and material savings due to the application of thin-walled shell design. Yet another advantage resides in the possibility of stacking a plurality of tanks by inserting them into one another. This allows to achieve substantial savings during the shipment of the plants. In combination with the modular concept of the technological inner structure this provides excellent storage aspects of the product, resulting in cost savings during long distance container shipment. The transport cost can thus drop to a few percent of the total price of the plant, creating prerequisites for meeting also the demand of distant markets, and thus also enabling centralized large capacity production applying the most advanced manufacturing technology. Another benefit of the shell coat and bottom and the saucer shape of the latter resides in the possibility of burying the plant in the ground without the necessity of any reinforced foundation plate for depositing the plant as well as eliminating the necessity of reinforcing the coat of the plant for being buried in the soil, thus offering savings related to its installation.

The above benefits make the plant for the treatment of small sources of sewage pollution a reliable, efficient and economically very beneficial option of separate house treatment plants representing an effective replacement of expensive, centralized solutions with a central treatment plant in case of scattered type of estate.

Brief description of the drawings

Examples of embodiments are illustrated in the drawings where Fig. 1 is a diagrammatical representation of the vertical cross section of the plant and Fig. 2 a diagrammatical representation of a horizontal cross section of the plant according to Fig. 1, Fig. 3 a diagrammatical representation of another embodiment of the plant in axonometrical view and Fig. 4 a diagrammatical representation of a horizontal cross section of the plant according to Fig. 3.

Exemplifying embodiments of the invention

Example 1

An exemplifying embodiment of the invention is illustrated in Figs. 1 and 2. The plant consists of tank I having a fibreglass shell coat 2 in form of a slightly downward narrowing truncated cone smoothly passing over into a shell bottom 3 that is saucer-shaped, e.g. having the shape of spherical canopy. In general the shape of bottom 3 can be described as focussed, in other words the surface of bottom 3 is orientated to one point that is the lowest point of the whole tank L

The upper edge of the tank is reinforced by ring 4 created by double bend of coat 2. The horizontal cross section of tank I is decreasing in the downward direction and the shape of tank \ allows to insert such tanks into one another. The mentioned tank I accommodates a separate inner structure 5 that is at least partly adjacent to the inner surface of coat 2 and/or of bottom 3 of tank I. The inner structure 5 is created by two partition walls, and namely by first partition wall 6 and second partition wall 7 that are rigidly attached to one another and, after the insertion, their edges abut the inner surfaces of coat 2 and bottom 3 of tank L Both these partition walls 6 and 7 and their connection are made of fibreglass as one unit of the illustrated embodiment, and the resulting inner structure 5 has substantially the form of a partial tank that is inserted as one unit into the outer tank 1 creating the plant. The design of this inner structure 5 ensures also a vertically narrowing down horizontal cross section of inner structure 5, enabling the single inner structures 5 to be stacked_^too. The upper edge of inner structure 5 is reinforced by frame 8 that is created by bending both partition walls 6 and _. including their connections. A part of this frame 8, after the inner structure 5 has been inserted into tank I, snaps into ring 4 and is fixed in place after the insertion, e.g. by bolts. By inserting the inner structure 5 into tank 1 an anoxic de-nitrification space 9 and a separation space JO are created at the sides of tank I, whereas the inside of structure 5 serves as the oxic activation space JJ.. The first partition wall 6 creates thus a division between the anoxic de-nitrification space 9 and the oxic activation space ϋ, whereas the second partition wall 7 creates a division between the oxic activation space 11 and the separation space JO, so that the oxic activation space H is accommodated between the anoxic de-nitrification space 9 and the separation space 10. The first partition wall 6 is provided with a hole 12 connecting the upper part of the anoxic de-nitrification space 9 and the oxic activation space JJ,, whereas the second partition wall 7 is provided with hole 13 connecting the oxic activation space JJ, with the bottom part of separation space 10. Between coat 2 and bottom 3 of tank 1 and the adjacent part of the inner structure 5 a not illustrated sealing is inserted, that fully prevents any direct communication between the anoxic de- nitrification space 9 and the separation space JJ), as soon as the inner structure 5 has been installed. The inner structure 5 bears further minor parts of the plant: a mixing chamber 14 in shape of a broader perpendicular pipe, re-circulation air-lift pumps 15 and 16 and the screening wall J 7 in the inner activation area close to hole 13. From the bottom part of the mixing chamber 14 a connecting tube 18 is seen to project which passes through the first partition wall 6 and proceeds to the bottom part of the anoxic de-nitrification space 9 where it mouths tangentially at the wall of bottom 3 at a certain height above the lowest place of the bottom of the anoxic de-nitrification space 9. The upper part of mixing chamber 4 is provided with waste water inlet 19, passing over through the mixing chamber \4 and the connecting tube 18 to the anoxic de-nitrification space 9. The mixing chamber J4 has, under the waste water inlet 19, a removable sifter 20 with holes that are substantially smaller than the diameter of connecting tube 18. The sifter is provided with a handle for removing shown in Fig. 1.

The purified water discharge 21 is installed in the upper part of separation space JO, it leads out through the coat 2 of tank 1, its position determining water level 22 in tank 1. This water level 22 passes through hole 12 in the first partition wall 6 so as to ensure that the upper edge of this hole 12 is above the water level 22 and the bottom edge underneath the same. Also the sifter 20 in mixing chamber 14 is under the water level 22. The inlet 23 to the re-circulation air-lift pump 15 is at the bottom of separation space JJ), and outlet 24 of re-circulation air-lift pump lδ passes through both partition walls 6 and 7 mouthing at the side tangentially at the wall of coat 2 into the central part of anoxic de-nitrification space 9. The inlet 25 to re-circulation air-lift pump J 6 is arranged in the upper part of anoxic de-nitrification space 9 under the water level 22 and passes through the first partition wall 6. The air-lift pump 16 is introduced from the bottom into the mixing chamber J4, its outlet 26 being accommodated under sifter 20 and screened from above against the falling of gross impurities. The bottom part of the first partition wall 6 is provided at both sides with one way reflux valves 27 and 28. The inner structure 5 also contains elements for aerating the suspension, such as aeration element 34-

Minor parts mounted onto the separate inner structure 5 as well as purified water discharge 21 mounted on tank can be easily removed and installed again and, accordingly, for distance shipment in a container the separate tank J. , the separate element 5 and minor parts, such as the mixing chamber 14 with sifter 20 and the re-circulation air-lift pump 16 and the connecting tube 18, the re-circulation air-lift pump !_5 with outlet 24, the screening wall 17, the purified water discharge 21, reflux valves 27 and 28 and, possibly, also the waste water inlet, can be loaded separately, while putting tanks into one another, similar stacking of inner structures 5_^ and depositing the mentioned minor parts into the remaining gaps in the container can result in high numbers of plants shipped at a time. It has been shown by calculation that one standard 6 meter shipment container is sufficient for transporting 30 knocked-down plants for 4-5 persons capacity from the factory to the local distribution place where the plants are assembled and distributed by one to various customers In case of burying into the ground the plant can be provided with a non illustrated attachment having a coat in shape of a truncated cone and provided with a ring at the bottom that is seated on ring 4 of tank of the plant. The waste water inlet 19 passes through the attachment. The attachment can be also provided with a not illustrated saucer shaped lid closing the plant from above. The attachments and the lids can be preferably inserted into one another for shipment.

The described plant operates as follows. Waste water flows through inlet 19 into mixing chamber JA Gross impurities get caught on sifter 20. The mixed liquor from the anoxic de-nitrification space 9 is sucked through inlet 25 by re-circulation air-lift pump 16 and flows through outlet 26 under sifter 20 into mixing chamber H. The stream of outflowing mixed liquor together with air bubbles from the re-circulation air-lift pump 16 rinse sifter 20 and disintegrate, both mechanically and biologically, the caught gross impurities that are biodegradable, such as toilet paper. The continuous rinsing prevents clogging of the sifter by caught impurities. The gross impurities that are not biodegradable, such as polyethylene bags, nylon underwear etc., are left on the sifter and should be removed during periodical revisions of the plant; for this purpose sifter 20 is arranged removably. The inflowing waste water gets mixed with re-circulated mixed liquor in the mixing chamber 14 and flows through connecting tube 8 to the bottom part of the anoxic de-nitrification space 9. Due to the tangential mouthing of the connecting tube 18 at the wall of bottom 3 and the shape of this bottom 3 the outflow of water gets curved so as to create circular upward flow in the bottom part of the anoxic de-nitrification space 9. On the other hand, solid impurities having passed through holes in sifter 20 enter the anoxic de-nitrification space 9 through the connecting tube 18 and settle at the bottom and, accordingly, the area of the anoxic de-nitrification space 9 under the level of the mouthing of connecting tube !_8 serves as accumulation space 33 for smaller solid impurities, e.g. from kitchen crushers. The biodegradable settled impurities get de-composed in the stream of activated sludge rinsing them, whereas the not biodegradable ones, such as sand, remain in the accumulating space 33 and should be removed from the latter, e.g. by a portable sludge pump or gulley sucker. The waste water to be treated is mixed with activated sludge from the anoxic de-nitrification space 9, creating, in the bottom part of this space, anaerobic environment, assisting the biological removal of phosphorus. The upward flow of the mixture of waste water with activated sludge is mixed with the mixed liquor that is re-circulated from the oxic activation space JJ, and the activated sludge that is re-circulated from the separation space JjO by action of the air-lift pump 15. The outlet 24 of the air-lift pump 15 mouthing tangentially from the side at the wall of coat 2, the inflowing liquid enhances the circular upward flow in the anoxic de-nitrification space 9, which compensates for the slowing down of this stream due to the fact that the diameter of the anoxic de-nitrification space 9 is widening in the upward direction, so that the suspension of activated sludge in the upward flow of liquid is maintained. The nitrates brought to the anoxic de- nitrification space 9 by the mixed liquor re-circulated from the oxic activation space JJ, get reduced to gazeous nitrogen in the anoxic de- nitrification space 9 under simultaneous oxidation of a certain part of organic compounds from the incoming waste water. The mixed liquor from the upper part of the anoxic de-nitrification space 9 then flows through hole 12 into the upper part of the oxic activation space JJ_.. The activated sludge re-circulated into the anoxic de-nitrification space 9 from the separation space 0 compensates for the withdrawal of sludge in the mixed liquor through hole 12 into the oxic activation space 1J The mixed liquor having come to the oxic activation space JJ, is then saturated by oxygen due to aerating. Under the presence of oxygen the oxidation of ammonia and organically bound nitrogen results in nitrates and biodegradation of remaining organic pollutants, with the end result of water purification. The concentration of nitrates in treated water is maintained on a low level by de-nitrification in the re-circulated water, as described above. If the ratio of re-circulated and outflowing amount of water equals r, the concentration of nitrates in the outflowing treated water will decrease in the ratio l/(l+r). The aeration also maintains the activated sludge in the oxic activation space 11 in suspended state, and also simultaneous aerobic stabilization of sludge takes place there. The mixed liquor containing purified water and activated sludge flows over through hole J from the oxic activation space JJ, to the bottom part of separation space JJ). The screening wall 17 deflects the stream prior to arriving to hole 13, thus preventing the transfer of turbulence and air bubbles from the oxic activation space JJ, to the separation space JJ). With respect to the interconnection of all functional spaces within the plant and maintaining constant water level 22, the waste water incoming through waste water inlet 19 will displace the same amount of purified water into the purified water discharge 21. This purified water flows through the separation space JJ) upward from hole 13 to the purified water discharge 21. The separation space JJ) widens in the upward 037805

15

direction, and that is why in the upward flow of water with the suspension a fluidized layer of sludge blanket is created, catching the activated sludge by way of filtration, and the purified water that is free from activated sludge flows out through purified water discharge 21. The trapped sludge will then drop to the bottom of separation space JO wherefrom it is returned by re- circulation air-lift pump 15 into the treatment process, as described above. Example 2

An exemplifying embodiment of the invention is illustrated in Figs. 3 and 4. The plant consists of tank having a fibreglass shell coat 2 in form of a slightly downward narrowing truncated cone smoothly passing over into a shell bottom 3 that is saucer-shaped, e.g. having the shape of spherical canopy. In general the shape of bottom 3 can be described as focussed, in other words the surface of bottom 3 is orientated to one point that is the lowest point of the whole tank 1 and that is located in the central area of the ground plan.

The upper edge of the tank is reinforced, e.g., by ring 4 created by double bend of coat 2. The horizontal cross section of tank 1 is decreasing in the downward direction and the shape of tank I allows to insert such tanks into one another. The mentioned tank accommodates a separate inner structure 5 the edges of which are adjacent to the inner surface of coat 2 and/or of bottom 3 of tank 1. The inner structure 5 is created by a mixing chamber H in form of a broader perpendicular prismatic tube with quadrangular cross section to which three substantially vertical partition walls 6, 7 and 35 are attached, whose edges are adjacent to the inner surface of coat 2 and bottom 3 of tank 1. Thus all three functional spaces are created, each of them being delimited by two partition walls and a part of coat 2 and bottom 3 of tank . The mixing chamber J can also have triangular or polygonal cross section.

Thus the first partition wall 6 creates a division between the anoxic de-nitrification space 9 and the oxic activation space JJ,, whereas the second partition wall 7 creates a division between the oxic activation space JJ. and the separation space JJ), and the partition wall 35 serves as division between the anoxic de-nitrification space 9 and the separation space JJ). The partition walls 6 and 35 are vertical, the partition wall 7 is attached to mixing chamber J4 slightly askew, with an inclination resulting in an offset of its bottom edge from the upper edge that is less than the width of the adjacent side of mixing chamber 14. For sealing off the contact of partition walls 6, 7 and 35 with coat 2 and bottom 3 of tank the edges of these partition walls and the bottom of mixing chamber 14 are provided with a not illustrated seal. The upper edges of all partition walls are provided with clips 36 serving to fix the inner structure 5 to coat 2 or ring 4 after installation into tank 1. Inside the separation space 10, at its bottom, insert 37 in shape of a part of conical coat is accommodated, which is supported with strut 38 and is closely adjacent with its edges to coat 2 and bottom 3 of tank 1 and partition walls 7 and 35 ■ The first partition wall 6 is provided with hole 12 connecting the upper parts of the anoxic de-nitrification space 9 and the oxic activation space JJ,, and the second partition wall 7 has hole 13 connecting the oxic activation space H with the bottom part of separation space JJ). The third partition wall 35 has no hole. The upper part of mixing chamber J4, under the water level 22 in tank 1, is provided with a removable sifter 20 for catching gross impurities, that is provided with a handle for lifting. The bottom part of mixing chamber J is provided at one of its sides with hole 39 serving as inlet to the anoxic de-nitrification space 9, and at the other side of mixing chamber 14 the anoxic de-nitrification space 9 accommodates the inlet 25 of the re-circulation air-lift pump 16 that is located inside the mixing chamber 4 and whose outlet 26 mouths under sifter 20. Within the separation space JJ) the mixing chamber 14 carries another re-circulation air lift pump Jj5 whose inlet 23 is accommodated at the bottom of separation space JO and whose outlet 24 terminates in the mixing chamber 14 above water level 22 in tank L On partition wall 7 the shielding wall 17 is attached that shields the hole 13 at the side of the oxic activation space JJ_.. In front of shielding wall J 7 the partition walls 6 and 7 carry the aeration element 34 that is thus accommodated inside the oxic activation space JJ,. The waste water inlet 19 mouths from above into the mixing chamber 14. The purified water discharge 2J, is installed in the upper part of separation space JJ), passing to the outside through coat 2 of tank 1, its position determining water level 22 in tank 1. This water level 22 passes through hole 12 in the first partition wall 6 so as to leave the upper edge of this hole 12 above water level 22 and its bottom edge under this level. The bottom part of the first partition wall 6 is provided with one way reflux valves 27 and 28 at both sides.

One of partition walls 6, 7, 35_. is rigidly attached to mixing chamber 14 with which also both re-circulation air-lift pumps 15 and J 6 are rigidly connected, the remaining partition walls are bolted to the mixing chamber 14 so as to allow their easy removal and mounting. Also shielding wall 17 and aeration element 34 are bolted to partition walls 6 and 7. Due to this design the inner structure 5 can be shipped in knocked-down condition and easily assembled at the site prior to the installation into tank 1. This allows easy and expedient container shipment of large numbers of plants, various parts of the plants being loaded separately, as putting the tanks 1 into one another and depositing the knocked-down inner structures 5 into the remaining gaps in the container. It enables large number of plants to be shipped at a time. It has been shown by calculation that one standard 6 meter shipment container is sufficient for transporting 30 knocked-down plants for 4-5 persons capacity from the factory to the local distribution place where the plants are assembled and distributed by one to various customers.

In case of burying into the ground the plant can be provided with a non illustrated attachment, having a coat in shape of a truncated cone and provided with a ring at the bottom that is seated on ring 4 of tank 1 of the plant. The waste water inlet 19 passes through the attachment. The attachment can be also provided with a not illustrated saucer shaped lid closing the plant from above. The attachments and the lids can be preferably inserted into one another for shipment. The described plant operates as follows. Waste water flows through inlet 19 into mixing chamber JA There the activated sludge flowing through outlet 24 is delivered from the separation space 10 by the re- circulation air-lift pump 15. The sifter 20 traps gross particles of impurities. The mixed liquor from the anoxic de-nitrification space 9 is sucked by re- circulation air-lift pump J_6 through inlet 25 and flows out through outlet 26 under sifter 20 into the mixing chamber JA The stream of outflowing mixed liquor together with air bubbles leaving the re-circulation air-lift pump 16 rinse the sifter 20 and desintegrate the caught gross biodegradable impurities, such as toilet paper, and namely mechanically and biologically. The continuous rinsing prevents the sifter from getting clogged by caught impurities. The trapped gross impurities that are not biodegradable, such as polyethylene bags, nylon underwear etc, remain on the sifter and should be removed during periodical revisions of the plant; for this purpose sifter 20 has been arranged removably. The delivered waste water gets mixed with the re-circulated mixed liquor in mixing chamber J4 and flows through hole 39 into the bottom part of the anoxic de-nitrification space 9. Due to the shape of bottom 3 the discharge of water is curved so as to create circular upward flow in the bottom part of the anoxic de-nitrification space 9. This flow is sufficient for maintaining the suspension of the activated sludge in the de-nitrification space 9. The re-circulating air-lift pump 15 delivers, through the outlet 24 and through the mixing chamber 14 into the anoxic de-nitrification space 9, in addition to the activated sludge that has been separated from waste water in the separation space 10, also the mixed liquor from the oxic activation space JJ, that is sucked-in by inlet 24 through hole J_3. This liquid contains nitrates originated in the oxic activation space JJ,. The nitrates brought to the anoxic de-nitrification space 9 through the mixed liquor, that is re-circulated from the oxic activation space H, get reduced to gaseous nitrogen in the anoxic de- nitrification space 9, and namely under simultaneous oxidation of a certain part of organic compounds from the onflowing waste water. Then the mixed liquor flows from the upper part of the anoxic de-nitrification space 9 into the upper part of the oxic activation space JJ_.. The activated sludge, that has been re-circulated into the anoxic de-nitrification space 9 from the separation space JJ), compensates for the discharge of sludge in the mixed liquor through hole J2 into the oxic activation space U,. The mixed liquor having come to the oxic activation space U, is saturated by oxygen by way of aeration. Under the presence of oxygen the oxidation of ammonia and of organically bound nitrogen to nitrates as well as biodegradation of remaining organic pollutants take place, resulting in water purification. The concentration of nitrates in purified water is maintained on a low level by de-nitrification in the re-circulated water, as described above. If the ratio of re-circulated and outflowing amount of water equals r, the concentration of nitrates in the outflowing treated water will decrease in the ratio l/(l+r). The aeration also maintains the activated sludge in the oxic activation space 11 in suspended state, and also simultaneous aerobic stabilization of sludge takes place there. The mixed liquor containing treated water and activated sludge flows over through hole J_3 from the oxic activation space JJ_. to the bottom part of separation, space JO. The screening wall J7 deflects the stream prior to its arrival to hole ϋ, thus preventing the transfer of turbulence and of air bubbles from the oxic activation space JJ, to separation space JO. With respect to the interconnection of all functional spaces within the plant and maintaining constant water level 22, the raw water incoming through waste water inlet J9 will displace the same amount of treated water into the purified water discharge 21- This purified water flows through the separation space JJ) upward from hole J_3 to the purified water discharge 2L The separation space JJ) widens in the upward direction, and that is why in the upward flow of water with the suspension a fluidized layer of sludge blanket is created, trapping the activated sludge by filtration, and the purified water freed from activated sludge flows out through purified water discharge 21- The trapped sludge will then drop to the bottom of separation space JJ) wherefrom it is returned by re-circulation air-lift pump 15 into the treatment process, as described above. The insert 37 in the bottom part of separation space JO prevents the formation of sediments of activated sludge from settling down on the bottom of separation space JO. The invention is not restricted solely to the described embodiments, but covers all types of equipment having the basic general characteristics of the invention, as described in claim 1, and possibly also some further claims, while they may also differ from some auxiliary claims. The inserted inner structure 5 according to example 1, e.g., can be created by two separate partition walls 6 and 7 that are connected with each other by struts during the assembly, and these walls can get apart from each other in the downward direction. It is also possible to use two separate inner structures created by the first partition wall 6 and the second partition wall 7 that can be inserted into the tank 1 of the plant separately, for this purpose they would be fixed, in addition to the attachment at the top, also by appropriate lugs in coat 2 and/or bottom 3, while these lugs would of course be shaped so as not to prevent putting a plurality of tanks into one another.

The inner inserted structure 5 according to example 2 can be also created by a plurality of partition walls attached to the central mixing chamber 14 - so four partition walls, e.g., can create one anoxic de- nitrification space, one separation space, and two oxic activation spaces of which each is the neighbour and communicating party with the anoxic de- nitrification space from one side and with the separation space from the other side. Tank 1 can have also a different shape of coat 2 than described in the exemplifying embodiment, such as the form of an oval in horizontal cross section or of a rectangle with convex walls and rounded off edges etc., it is only substantial that the coat should be of shell type with horizontal cross section narrowing down and allowing to insert a number of tanks 1 into one another. All these described options, as well as further possible modifications of the basic specified principles are covered by this invention. 037805

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List of parts:

1 - tank

2 - outer wall

3 - bottom

5 - inner structure

6 - first partition wall

7 - second partition wall

8 - frame 9 - anoxic de-nitrification space

10 - separation space

11 - oxic activation space 12 - hole

13 - hole 14 - mixing chamber

15 - re-circulation air-lift pump

16 - re-circulation air-lift pump 17 - screening wall

18 - connecting tube 19 - waste water inlet

20 - sifter

21 - purified water discharge

22 - water level

23 - inlet 24 - outlet

25 - inlet

26 - outlet

27 - reflux valve

28 - reflux valve 33 - accumulation space

34 - aeration element

35 - third partition wall

36 - clips

37 - insert 38 - strut

39 - hole

Claims

C L A I M S

1. A plant for waste water treatment, in particular sewage water from small sources, for activation treatment by unified suspended activated sludge, created by a tank (1) wherein three functional spaces are provided, and namely an aerated oxic activation space (11), an anoxic de-nitrification space (9) and a separation space (10), the waste water inlet (19) being introduced into the anoxic de-nitrification space (9), the purified water discharge (21) being installed in the upper part of the separation space (10), the anoxic de-nitrification space (9) being connected with the oxic activation space (11), the oxic activation space (11) being connected with the separation space (10), and the plant being provided with a device for pumping the activated sludge from the separation space (10) into the anoxic de-nitrification space (9) characterised in that tank (1) has a shell coat (2) smoothly passing over onto shell bottom (3) of saucer shape, the tank (1) having downwardly decreasing horizontal cross section, and the functional spaces in the tank being created by inserting and fixing at least one separate inner structure (5) that is at least partially adjacent to the inner surface of coat 2 and/or bottom (3) of tank (1), for creating the division between at least two functional spaces, all functional spaces (9, 10, 11) having concave bottom shape.

2. Plant according to Claim 1, characterized in that the inner structure (5) is created by a structure having downwardly decreasing horizontal cross section.

3. Plant according to Claim 1, characterized in that the inner structure (5) is created by two rigidly interconnected partition walls (6,7), whose edges are adjacent to coat (2) and bottom (3) of the tank (1), the first partition wall (6) forming a division between the anoxic de-nitrification space (9) and the oxic activation space (11) and the second partition wall (7) forming a division between the oxic activation space (11) and separation space (10), the oxic activation space (11) being arranged between the anoxic de- nitrification space (9) and the separation space (10).

4. Plant according to Claim 1, characterized in that the inner structure (5) is created by at least three rigidly interconnected partition walls (6,7,35), whose edges are adjacent to coat (2) and bottom (3) of the tank, the first partition wall (6) serving as division between the anoxic de-nitrification space (9) and the oxic activation space (11), the second partition wall (7) serving as division between the oxic activation space (11) and the separation space (10), whereas the third partition wall (35) serves as division between the anoxic de-nitrification space (9) and the separation space (10).

5. Plant according to Claim 1, characterized in that the tank (1) has the shape of conical downwardly narrowing rotation body terminated by bottom (3) substantially in form of a spherical or, possibly, elliptical canopy.

6. Plant according to Claim 1, characterized in that the waste water inlet (19) is connected to mixing chamber (14), that is connected with the bottom part of the anoxic de-nitrification space (9), the connection (12) between the anoxic de-nitrification space (9) and the oxic activation space (11) being created in their upper part, whereas the connection (13) between the oxic activation space (11) and the separation space (10) mouths in the lower part of separation space (10) which is, close to the bottom of separation space (10), provided with the inlet (23) to the device for re- pumping the activation sludge from the separation space (10) into the anoxic de-nitrification space (9), such device being created, e.g., by re- circulation air- lift pump (15).

7. Plant according to Claim 1, characterized in that the tank (1) is made of fibreglass.

8. Plant according to any of Claims 1 to 4, characterized in that the inner structure (5) comprises the centrally accommodated mixing chamber (14), whereto all partition walls (6,7,35) are attached.

9. Plant according to Claim 8, characterized in that the mixing chamber (14) has the form of a prismatic tube, e.g. with quadrangular or triangular cross section.