Title of Invention	"WASTEWATER TREATMENT SYSTEM AND METHOD FOR THE TREATMENT OF WASTEWATER"
Abstract	The invention relates to a wastewater treatment installation, in which a mechanical purification apparatus is incorporated into a biological purification reaction vessel, to an effluent treatment plant comprising such wastewater treatment installations and to a method of purifying "wastewater. By arranging the mechanical purification apparatus over the ground plan area of the biological purification reaction vessel the floor area and space requirements of the installation are reduced.

Title of Invention

"WASTEWATER TREATMENT SYSTEM AND METHOD FOR THE TREATMENT OF WASTEWATER"

Abstract

The invention relates to a wastewater treatment installation, in which a mechanical purification apparatus is incorporated into a biological purification reaction vessel, to an effluent treatment plant comprising such wastewater treatment installations and to a method of purifying "wastewater. By arranging the mechanical purification apparatus over the ground plan area of the biological purification reaction vessel the floor area and space requirements of the installation are reduced.

Full Text	Description Wastewater treatment installation and method of treating wastewater The invention relates to a wastewater treatment installation, in which a mechanical purification apparatus is incorporated into a biological purification reaction vessel, and to a method of purifying wastewater. Background of the invention Wastewater is understood to mean both water contaminated by domestic, commercial and industrial use and rainwater from built-up areas. The direct introduction of wastewater into natural watercourses disturbs their ecological equilibrium and restricts the potential for utilization thereof, for example with regard to drinking water production. To keep such disturbances and restrictions to a minimum, wastewater needs to be purified before such introduction. Municipal and industrial wastewater contaminated with organic substances is primarily purified in effluent treatment plants, in which the wastewater is treated firstly mechanically and then biologically. For mechanical purification, the wastewater is here conveyed for example by means of raking installations and sand/fat traps at a low flow rate into large-volume primary settling tanks, also known as sedimentation basins, in which primary settling proceeds by sedimentation and/or flotation of suspended matter and/or with the assistance of chemicals. Wastewater screening may also take place as a replacement for a primary settling tank in specially constructed tanks or channels. The primary sludge, which consists of suspended matter contained in the wastewater and arises in the primary settling tanks or during wastewater screening, is removed, further processed and, after dewatering to increase its solids content, which is initially only around 2-5 wt.%, finally disposed of by composting, landfilling or incineration. Once it has passed through such mechanical purification systems, the wastewater enters the reaction vessels of biological purification apparatuses. EP1568662, for example, discloses an effluent treatment plant in which a filter means for removing hair and similar residues by means of a fine screen with a mesh size of less than 1 mm is connected upstream of a membrane bioreactor activated-sludge tank. This filter means connected upstream of the membrane bioreactor activated-sludge tank is arranged in its own tank, from which filtered wastewater is fed to the membrane bioreactor activated-sludge tank. Optionally, further wastewater treatment stages, such as a sand trap or fat separator, may be provided between the filter means and the membrane bioreactor activated-sludge tank. Such effluent treatment plants have large floor area and space requirements, since the sometimes large-volume apparatuses, in which the individual mechanical and biological purification steps are performed, are arranged next to one another. In addition, the low solids content of the primary sludge means that it arises in large volumes and requires correspondingly large further processing and dewatering apparatuses. Object of the invention It is the object of the present invention to provide a wastewater treatment installation and effluent treatment plants comprising such wastewater treatment installations for purifying wastewater which have smaller floor area and space requirements than the prior art. Detailed description of the invention This object is achieved by a wastewater treatment installationaccording to claim 1. The biological purification reaction vessel of the wastewater treatment installation may for example be a tank or a reactor. It may be a reaction vessel for performing non-aerated stages or aerated stages of an activated-sludge method. Moreover, it may be part of an apparatus for performing an aerobic activated-sludge method, an apparatus for performing an anaerobic phosphorus elimination method, an apparatus for performing a denitrification method or an apparatus for performing a biological treatment in a support-immobilized fluidized bed. The mechanical purification apparatus of the wastewater treatment installation may comprise one or more individual devices for mechanical purification, namely one or more screening drums or belt screens. These may be connected for example in parallel or in series. The number of devices for mechanical purification and the connection thereof may be selected depending on the nature and quantity of the wastewater constituents to be removed and the quantity of wastewater arising. The mechanical purification apparatus is arranged at least in part over the ground plan area of the reaction vessel for biological purification. The ground plan area of the reaction vessel is understood to mean the vertical projection of the reaction vessel onto a horizontal surface. In this arrangement, the area required for construction of the mechanical purification apparatus is smaller than the ground plan area thereof, since the mechanical purification apparatus is arranged at least in part within the area on which the biological purification reaction vessel is anyway already constructed. The larger the part of the mechanical purification apparatus arranged over the ground plan area of the reaction vessel, the greater the saving in area. The means for feeding wastewater to the biological purification reaction vessel may take the form, for example of a pipe, channel or duct. Since the feed means leads into the mechanical purification apparatus, when the wastewater treatment installation is in operation wastewater arrives at the biological purification reaction vessel only after passing through the mechanical purification apparatus and passage through the screen openings in the boundary surfaces thereof. Accordingly, only wastewater which has been mechanically purified on passing through the mechanical purification device and/or passage through the screen openings enters the biological purification reaction vessel. In this way, the biological purification stage has to break down fewer organic impurities which bring about a biological oxygen demand, defined as BOD5, or chemical oxygen demand (COD), which allows a smaller design and smaller floor area and space requirements for the biological purification reaction vessel compared to reaction vessels without an integral mechanical purification apparatus. The mechanical purification apparatus may even be arranged wholly over the ground plan area of the reaction vessel for biological purification. According to one embodiment, the mechanical purification apparatus is located at least in part within the space defined by the walls of the reaction vessel for biological purification. According to a further embodiment, the mechanical purification apparatus is located at least in part below the operational filling level of the reaction vessel for biological purification. The operational filling level is an installation-related parameter which indicates the level up to which the biological purification reaction vessel has to be filled during operation in order to ensure optimum purification with maximum efficiency. The mechanical purification apparatus is a fine screen apparatus. A fine screen is understood to be a screen with screen openings of a clear width of 5 mm and below. Fine screening achieves extensive removal of undissolved constituents of the wastewater and greatly reduces the content of suspended matter. Depending on the nature and quantity of the constituents of the wastewater, the clear width of the screen openings may vary, the lower limit being 0.005 mm. According to the invention, the clear width of the screen openings amounts to at least 0.1 mm, preferably at least 0.25 mm, and at most 1 mm, preferably at most 0.5 mm. With such small clear widths, particularly extensive purification of the wastewater is achieved and even fat is largely screened out, while at the same time filter performance, measured in filtered volume of wastewater/unit time, is acceptable. The fine screen apparatus comprises one or more screening drums or belt screens. In the presence of a plurality of screening drums or belt screens, it is possible, depending on the quantity of wastewater arising and the wastewater load on an individual screening drum or an individual belt screen, to feed the wastewater to individual or several or all of the screening drums or belt screens. The wastewater treatment installation according to the invention also comprises an outlet means for removing wastewater treated in the biological purification reaction vessel from the reaction vessel, this possibly being for example a channel, a duct or a pipe. The mechanical purification apparatus comprises an apparatus for discharging separated-out screenings consisting of undissolved constituents of the wastewater. These screenings may be discharged in various ways, for example with a conveying screw in a perforated conveying trough. Preferably, the screenings are dewatered upon discharge, the solids content of the screenings thereby being increased, for example to up to 35 wt.% in the case of municipal wastewater. The present invention also provides an effluent treatment plant, which is characterized in that it comprises one or more wastewater treatment installations as claimed in one of claims 1-4 together with one or more apparatuses for mechanical, biological or chemical wastewater treatment arranged up- or downstream thereof. The wastewater treatment installations according to the invention may be installed during construction of new effluent treatment plants. Depending on the nature and quantity of the wastewater constituents to be removed, an effluent treatment plant comprises various combinations of apparatuses for mechanical, biological and/or chemical wastewater treatment, these being put together to match the purification tasks arising. In an effluent treatment plant according to the invention, one or more apparatuses for mechanical, biological or chemical wastewater treatment may be connected up- or downstream of the wastewater treatment installation according to the invention. Apparatuses connected upstream are for example mechanical purification apparatuses such as for instance rakes and sand traps. Apparatuses connected downstream are for example biological purification apparatuses such as for instance apparatuses for carrying out non-aerated stages or aerated stages of an activated-sludge method, such as for example of an aerobic activated-sludge method, apparatuses for carrying out an anaerobic phosphorus elimination method, apparatuses for carrying out a denitrification method or apparatuses for carrying out a biological treatment in a support-immobilized fluidized bed. The floor area and space requirements of an effluent treatment plant comprising wastewater treatment installations according to the invention is smaller than that of a conventional effluent treatment plant for fulfilling the same purification task with the same biological efficiency. In most cases, in an effluent treatment plant according to the invention it is possible to dispense with space-consuming primary settling tanks for settling or flotation of suspended matter, since suspended matter is removed by fine screening in the wastewater treatment installation according to the invention. This significantly reduces the floor area requirements of the effluent treatment plant relative to conventional effluent treatment plants. It is possible to dispense with the construction of aerated sand/fat traps if fat is also largely screened out in the wastewater treatment installation according to the invention. Instead, it is sufficient in an effluent treatment plant according to the invention to construct non-aerated sand traps which may be simpler from the point of view of construction and equipment and more compact and space-saving, since the size of aerated sand/fat traps is determined by the process engineering problem of fat separation. Additional savings in floor area may be achieved if screenings are dewatered upon discharge from the mechanical purification apparatus. Discharged screenings may be classified as primary sludge from primary settling tanks. Extensive dewatering of the separated screenings upon discharge and an increase in the degree of elimination of wastewater constituents influence the floor area and space requirements of an effluent treatment plant, since anaerobic or aerobic sludge stabilization installations and/or other disposal and dewatering means may be of smaller dimensions. Wastewater treatment installations according to the invention may also be used when extending existing wastewater treatment installations and be installed in existing effluent treatment plants, in order to allow improved purification results with identical floor area requirements or to eliminate bottlenecks in the existing effluent treatment plant. If, in an effluent treatment plant according to the invention, biological wastewater treatment also takes place in further apparatuses in addition to wastewater treatment installations according to the invention, it is advantageous for the wastewater treatment installations according to the invention to be arranged upstream of the further apparatuses for biological wastewater treatment when viewed in the flow direction of the wastewater. In this way it rs ensured that only wastewater already treated in a wastewater treatment installation according to the invention is introduced into the further apparatuses for biological wastewater treatment. This treated wastewater entrains only a small amount of matter requiring biological degradation, and accordingly the further apparatuses for biological wastewater treatment may be of small dimensions, which reduces the floor area and space requirements of the effluent treatment plant. The method according to the invention for treating wastewater is described in claim 6. Preferably, biological purification takes place by means of an aerobic activated-sludge method, an anaerobic phosphorus elimination method, a denitrification method, or biological treatment in a support-immobilized fluidized bed. The invention is explained with reference to the attached exemplary, schematic figures 1, 2, 3, 4a and 4b and the following descriptions. Fig. 1 shows a diagram of an effluent treatment plant according to the prior art Fig. 2 shows a diagram of an embodiment of an effluent treatment plant according to the invention with a wastewater treatment installation according to the invention, which comprises a mechanical purification apparatus incorporated into an aerobic activated-sludge tank. Fig. 3 is a schematic diagram of the arrangement of a belt screen in a tank for an aerobic biological activated-sludge method. Figs. 4a and Fig. 4b are schematic diagrams of a front view and a side view of the arrangement according to the invention of a screening drum in an activated-sludge tank. Fig. 1 shows how wastewater 1 from different sources, for example domestic wastewater 2, rainwater from built-up areas 3, or commercial or industrial wastewater 4, is treated firstly mechanically and then biologically in an effluent treatment plant according to the prior art. The apparatuses in which the individual mechanical and biological purification steps are performed are arranged next to one another but spatially separated from one another and the wastewater 1 flows through them in succession. First of all, coarse solids 6 are removed by raking 5. Then sand 8 and fats 9 and oils 10 are separated out in an aerated sand/fat trap 7. Next, suspended matter is separated out in the sedimentation basin 11 and removed as primary sludge 12. Then the wastewater treated mechanically in this way is fed to an aerobic activated-sludge tank 13. The aerobic activated-sludge tank 13 is followed by a secondary settling tank 14, from which surplus sludge 15 is removed. The purified wastewater is discharged from the secondary settling tank 14 into a receiving stream 16. Apparatuses for treating the primary and surplus sludge which arise are not shown. The effluent treatment plant according to the invention illustrated in Fig. 2 differs from the effluent treatment plant in Fig. 1 in that the aerobic activated-sludge tank 13 has been replaced by a wastewater treatment installation 17 according to the invention, the aerated sand/fat trap 7 has been replaced by a non-aerated sand trap 18, and the sedimentation basin 11 has been dispensed with, which markedly reduces the floor area requirements of the effluent treatment plant relative to the effluent treatment plant illustrated in Fig. 1. After passing through the non-aerated sand trap 18, the wastewater treated mechanically by means of rakes 5 and a non- aerated sand trap 18 is passed through a pipe 19 into the mechanical purification apparatus 20 of the wastewater treatment installation 17 according to the invention, which is arranged within an aerobic activated-sludge tank 21. From the mechanical purification apparatus 20, the wastewater passes through screen openings in its boundary surfaces into the aerobic activated-sludge tank, this being indicated by arrows. Separated-out screenings 22, which contain suspended matter, fats and oils, are discharged from the mechanical purification apparatus 20. The wastewater treatment installation 17 according to the invention is followed by a secondary settling tank 14, from which surplus sludge 15 is removed. From the secondary settling tank 14, the purified wastewater is discharged into a receiving stream 16. Apparatuses for treating the screenings and surplus sludge which arise are not shown. In Figs. 1 and 2, the arrows indicate the direction of movement of the wastewater or of the substances discharged from the various apparatuses, such as coarse solids, sand, fats, oils, primary sludge, surplus sludge and screenings. Fig. 3 is a schematic diagram of the arrangement of a fine screen apparatus 23 in a tank 24 for an aerobic biological activated-sludge process. The fine screen apparatus 23 comprises an endless belt screen 25, which is guided around deflection sheaves 26. The belt screen 25 is in part immersed in the activated-sludge suspension 27 contained in the tank 24. The space enclosed by the belt screen 25 is sealed at its end faces, such that the wastewater can only flow through the screen openings in the belt screen 25 into the tank 24. The space enclosed by the belt screen 25 is designated the inside of the belt screen. The face of the belt screen 25 facing the inside is designated the inner face of the belt screen, while the other face of the belt screen 25 is designated the outer surface of the belt screen. For clarity's sake, the screen openings of the belt screen 25 are not shown. Wastewater flows into the inside of the belt screen through a feed line 28, which is guided through one of the end faces. Apart from the passage opening of the feed line 28, the end faces do not have any openings. The wastewater flows from the inside of the belt screen through the screen openings of the belt screen 25 into the tank 24, indicated by arrows. If screen openings become blocked by separated-out screenings, wastewater builds up inside the belt screen, and a stagnation pressure builds up inside the belt screen as a result of the level of the wastewater 30 then hying above the level of the activated-sludge suspension 29. The magnitude of the stagnation pressure is used as a measure of how blocked up the screen openings of the belt screen are. If the stagnation pressure exceeds a selected limit value, the belt screen 25 is moved by apparatuses, not shown, in such a way that parts of the belt screen 25 previously immersed in the activated-sludge suspension 27 and blocked by separated-out screenings are brought to above the level of the activated-sludge suspension 29. At the same time, parts of the belt screen 25 previously lying above the level of the activated-sludge suspension 29 and not blocked by separated-out screenings are immersed in the activated-sludge suspension 27. The direction of movement of the belt screen 25 is indicated by arrows 31. The part of the belt screen 25 which is brought above the level of the activated-sludge suspension 29 by movement of the belt screen is cleaned by a cleaning means 32 using a jet of water and/or air directed towards the outer face of the belt screen. Separated-out screenings then fall into the inside of the belt screen and are discharged therefrom via an apparatus, not shown, for discharging screenings. The wastewater treated biologically in the tank 24 is discharged from the tank 24 via an outlet line 33. Fig. 4a and Fig. 4b show how a cylindrical screening drum 34 is arranged within an activated-sludge tank 35. The activated-sludge tank 35 is filled up to the operational filling level 36 with activated-sludge suspension 37. The screening drum 34 is located within the activated-sludge tank 35 and is immersed in part in the activated-sludge suspension 37. The wastewater is introduced by a feed line 38, which passes through one of the two outer faces into the inside of the screening drum 34. Apart from the passage opening of the feed line 38, the outer faces do not have any openings. The shell 39 of the cylindrical screening drum 34 is partially constructed as a fine screen. The wastewater flows through the fine screen upon passage from the inside of the screening drum 34 into the activated-sludge tank 35. A stagnation pressure is necessary for this purpose, this being built up inside the screening drum when the level of the wastewater 40 inside the screening drum 34 is higher than the level of the activated-sludge suspension 41 in the activated-sludge tank 35. This difference in levels is known as differential head. The differential head varies depending on the quantity of wastewater introduced per unit time and the extent to which the fine screen is blocked. The possible differential head is predetermined by the local installation situation; ideally, however, it amounts to no more than 50 cm. The flows within the activated-sludge tank 35 filled with activated-sludge suspension 37 do not influence fine screening, since the flow direction of the wastewater is clearly set by the accumulating stagnation pressure. The maximum planned differential head is detected by level measurement, not shown, within the screening drum 34. If a set filling level limit value is exceeded, rotary motion of the screening drum 34 about its longitudinal axis is automatically triggered, as is cleaning of the area of the fine screen which is located above the level of the activated-sludge suspension 41. Apparatuses for moving the screening drum are not shown. Cleaning proceeds while the drum is rotating by means of a cleaning means 42 with an air jet and by means of a cleaning means 43 with a water jet. The screenings separated out using the fine screen are blown off by the air jet and drop into a discharge apparatus 44, which is installed below the cleaning means 42. The discharge apparatus 44 comprises a perforated receiving channel 45 for screenings which fall down during cleaning and a conveying screw 46. The conveying screw 46 removes the screenings from the receiving channel 45 and dewaters them at the same time. In the embodiment illustrated in Fig. 4a and Fig. 4b, It is advantageous for the screenings not to be suspended in the wastewater after cleaning of the fine screen until they are discharged from the screening drum 34. In this way, thorough dewatering may be performed during discharge. Areas of the screening drum 34 which have been cleaned by the air jet of the cleaning means 42 move by rotation of the screening drum away from the cleaning means 42 and are finally struck by the water jet of the cleaning means 43 and cleaned. Since the cleaning means 43 is arranged laterally offset relative to the cleaning means 42, the spray water does not enter the receiving channel 45. The spray water is not collected separately but rather mixes with the wastewater inside the screening drum 34. The wastewater treated biologically in the activated-sludge tank 35 is discharged from the activated-sludge tank 35 via an outlet line 47. The screenings dewatered upon discharge are removed from the discharge apparatus 44 as filter cake 48. We Claims:- Patent claims:- 1. A wastewater treatment installation (17), comprising at least one biological purification reaction vessel with a mechanical purification apparatus (20) arranged at least in part over the ground plan area thereof and with a wastewater feed means leading into the mechanical purification apparatus (20), the mechanical purification apparatus (20) comprising screen openings in at least one of its boundary surfaces, whereas the reaction vessel is designed for performing an aerobic activated-sludge method, an anaerobic phosphorus elimination method, a denitrification method, or a biological treatment in a support- immobilized fluidized bed, and whereas the mechanical purification apparatus (20) is a fine screen apparatus (23), and whereas the fine screen apparatus (23) comprises one or more screening drums (34) or one or more belt screens (25), and whereas the clear width of the screen openings of the fine screen apparatus (23) amounts to at least 0.1 mm, preferably at least 0.25 mm, and at most 1 mm, preferably at most 0.5 mm. 2. The wastewater treatment installation as claimed in claim 1, characterized in that the mechanical purification apparatus (20) is arranged wholly over the ground plan area of the biological purification reaction vessel. 3. The wastewater treatment installation as claimed in claim 1 or 2, characterized in that the mechanical purification apparatus (20) is located at least in part within the space defined by the walls of the biological purification reaction vessel. 4. The wastewater treatment installation as claimed in one of claims 1-3, characterized in that the mechanical purification apparatus (20) is located at least in part below the operational filling level of the biological purification reaction vessel. 5. An effluent treatment plant, characterized in that it comprises one or more wastewater treatment installations (17) as claimed in one of claims 1-4 together with one or more apparatuses for mechanical, biological or chemical wastewater treatment arranged up- or downstream thereof. 6. A method for treating wastewater, characterized in that the wastewater is purified mechanically by means of a fine screen apparatus, which is located at least in part over the ground plan area of a biological purification reaction vessel, and passes therefrom into the biological purification reaction vessel and is there purified biologically by an aerobic activated-sludge method, by an anaerobic phosphorus elimination method, by a denitrification method or by a biological treatment in a support-immobilized fluidized bed, whereas the fine screen apparatus (23) comprises one or more screening drums (34) or one or more belt screens (25), and whereas the clear width of the screen openings of the fine screen apparatus (23) amounts to at least 0.1 mm, preferably at least 0.25 mm, and at most 1 mm, preferably at most 0.5 mm .

Full Text

Description
Wastewater treatment installation and method of treating wastewater
The invention relates to a wastewater treatment installation, in which a mechanical purification apparatus is incorporated into a biological purification reaction vessel, and to a method of purifying wastewater.
Background of the invention
Wastewater is understood to mean both water contaminated by domestic, commercial and industrial use and rainwater from built-up areas. The direct introduction of wastewater into natural watercourses disturbs their ecological equilibrium and restricts the potential for utilization thereof, for example with regard to drinking water production. To keep such disturbances and restrictions to a minimum, wastewater needs to be purified before such introduction.
Municipal and industrial wastewater contaminated with organic substances is primarily purified in effluent treatment plants, in which the wastewater is treated firstly mechanically and then biologically.
For mechanical purification, the wastewater is here conveyed for example by means of raking installations and sand/fat traps at a low flow rate into large-volume primary settling tanks, also known as sedimentation basins, in which primary settling proceeds by sedimentation and/or flotation of suspended matter and/or with the assistance of chemicals. Wastewater screening may also take place as a replacement for a primary settling tank in specially constructed tanks or channels. The primary sludge, which consists of suspended matter contained in the wastewater and arises in the primary settling tanks or during wastewater screening, is removed, further processed and, after dewatering to increase its solids content, which is initially only around 2-5 wt.%, finally disposed of by composting, landfilling or incineration. Once it has passed through such mechanical purification systems, the wastewater enters the reaction vessels of biological purification apparatuses.
EP1568662, for example, discloses an effluent treatment plant in which a filter means for removing hair and similar residues by means of a fine screen with a mesh size of less than 1 mm is connected upstream of a membrane bioreactor activated-sludge tank. This filter means connected upstream of the membrane bioreactor activated-sludge tank is arranged in its own tank, from which filtered wastewater is fed to the membrane bioreactor activated-sludge tank. Optionally, further wastewater treatment stages, such as a sand trap or fat separator, may be provided between the filter means and the membrane bioreactor activated-sludge tank.
Such effluent treatment plants have large floor area and space requirements, since the sometimes large-volume apparatuses, in which the individual mechanical and biological purification steps are performed, are arranged next to one another. In addition, the low solids
content of the primary sludge means that it arises in large volumes and requires correspondingly large further processing and dewatering apparatuses.
Object of the invention
It is the object of the present invention to provide a wastewater treatment installation and effluent treatment plants comprising such wastewater treatment installations for purifying wastewater which have smaller floor area and space requirements than the prior art.
Detailed description of the invention
This object is achieved by a wastewater treatment installationaccording to claim 1.
The biological purification reaction vessel of the wastewater treatment installation may for example be a tank or a reactor. It may be a reaction vessel for performing non-aerated stages or aerated stages of an activated-sludge method. Moreover, it may be part of an apparatus for performing an aerobic activated-sludge method, an apparatus for performing an anaerobic phosphorus elimination method, an apparatus for performing a denitrification method or an apparatus for performing a biological treatment in a support-immobilized fluidized bed.
The mechanical purification apparatus of the wastewater treatment installation may comprise one or more individual devices for mechanical purification, namely one or more screening drums or belt screens. These may be connected for example in parallel or in series. The number of devices for mechanical purification and the connection thereof may be selected depending on the nature and quantity of the wastewater constituents to be removed and the quantity of wastewater arising.
The mechanical purification apparatus is arranged at least in part over the ground plan area of the reaction vessel for biological purification. The ground plan area of the reaction vessel is understood to mean the vertical projection of the reaction vessel onto a horizontal surface. In this arrangement, the area required for construction of the mechanical purification apparatus is smaller than the ground plan area thereof, since the mechanical purification apparatus is arranged at least in part within the area on which the biological purification reaction vessel is anyway already constructed.
The larger the part of the mechanical purification apparatus arranged over the ground plan area of the reaction vessel, the greater the saving in area.
The means for feeding wastewater to the biological purification reaction vessel may take the form, for example of a pipe, channel or duct. Since the feed means leads into the mechanical purification apparatus, when the wastewater treatment installation is in operation wastewater arrives at the biological purification reaction vessel only after passing through the mechanical purification apparatus and passage through the screen openings in the boundary surfaces thereof. Accordingly, only wastewater which has been mechanically purified on passing through the mechanical purification device and/or passage through the screen openings enters the biological purification reaction vessel. In this way, the biological purification stage has to break down fewer organic impurities which bring about a biological oxygen demand, defined as BOD5, or chemical oxygen demand (COD), which allows a smaller design and smaller floor area and space requirements for the biological purification reaction vessel compared to reaction vessels without an integral mechanical purification apparatus.
The mechanical purification apparatus may even be arranged wholly over the ground plan area of the reaction vessel for biological purification.
According to one embodiment, the mechanical purification apparatus is located at least in part within the space defined by the walls of the reaction vessel for biological purification.
According to a further embodiment, the mechanical purification apparatus is located at least in part below the operational filling level of the reaction vessel for biological purification. The operational filling level is an installation-related parameter which indicates the level up to which the biological purification reaction vessel has to be filled during operation in order to ensure optimum purification with maximum efficiency.
The mechanical purification apparatus is a fine screen apparatus. A fine screen is understood to be a screen with screen openings of a clear width of 5 mm and below. Fine screening achieves extensive removal of undissolved constituents of the wastewater and greatly reduces the content of suspended matter.
Depending on the nature and quantity of the constituents of the wastewater, the clear width of the screen openings may vary, the lower limit being 0.005 mm.
According to the invention, the clear width of the screen openings amounts to at least 0.1 mm, preferably at least 0.25 mm, and at most 1 mm, preferably at most 0.5 mm. With such small clear widths, particularly extensive purification of the wastewater is achieved and even fat is largely screened out, while at the same time filter performance, measured in filtered volume of wastewater/unit time, is acceptable.
The fine screen apparatus comprises one or more screening drums or belt screens. In the presence of a plurality of screening drums or belt screens, it is possible, depending on the quantity of wastewater arising and the wastewater load on an individual screening drum or an individual belt screen, to feed the wastewater to individual or several or all of the screening drums or belt screens.
The wastewater treatment installation according to the invention also comprises an outlet means for removing wastewater treated in the biological purification reaction vessel from the reaction vessel, this possibly being for example a channel, a duct or a pipe.
The mechanical purification apparatus comprises an apparatus for discharging separated-out screenings consisting of undissolved constituents of the wastewater. These screenings may be discharged in various ways, for example with a conveying screw in a perforated conveying trough. Preferably, the screenings are dewatered upon discharge, the solids content of the screenings thereby being increased, for example to up to 35 wt.% in the case of municipal wastewater.
The present invention also provides an effluent treatment plant, which is characterized in that it comprises one or more wastewater treatment installations as claimed in one of claims 1-4 together with one or more apparatuses for mechanical, biological or chemical wastewater treatment arranged up- or downstream thereof.
The wastewater treatment installations according to the invention may be installed during construction of new effluent treatment plants. Depending on the nature and quantity of the wastewater constituents to be removed, an effluent treatment plant comprises various combinations of apparatuses for mechanical, biological and/or chemical wastewater treatment, these being put together to match the purification tasks arising. In an effluent treatment plant according to the invention, one or more apparatuses for mechanical, biological or chemical wastewater treatment may be connected up- or downstream of the wastewater treatment installation according to the invention. Apparatuses connected upstream are for example mechanical purification apparatuses such as for instance rakes and sand traps. Apparatuses connected downstream are for example biological purification apparatuses such as for instance apparatuses for carrying out non-aerated stages or aerated stages of an activated-sludge method, such as for example of an aerobic activated-sludge method, apparatuses for carrying out an anaerobic phosphorus elimination method, apparatuses for carrying out a denitrification method or apparatuses for carrying out a biological treatment in a support-immobilized fluidized bed.
The floor area and space requirements of an effluent treatment plant comprising wastewater treatment installations according to the invention is smaller than that of a conventional effluent treatment plant for fulfilling the same purification task with the same biological efficiency. In most cases, in an effluent treatment plant according to the invention it is possible to dispense with space-consuming primary settling tanks for settling or flotation of suspended matter, since suspended matter is removed by fine screening in the wastewater treatment installation according to the invention. This significantly reduces the floor area requirements of the effluent treatment plant relative to conventional effluent treatment plants. It is possible to dispense with the construction of aerated sand/fat traps if fat is also largely screened out in the wastewater treatment installation according to the invention. Instead, it is sufficient in an effluent treatment plant according to the invention to construct non-aerated sand traps which may be simpler from the point of view of construction and equipment and more compact and space-saving, since the size of aerated sand/fat traps is determined by the process engineering problem of fat separation.
Additional savings in floor area may be achieved if screenings are dewatered upon discharge from the mechanical purification apparatus. Discharged screenings may be classified as primary sludge from primary settling tanks. Extensive dewatering of the separated screenings upon discharge and an increase in the degree of elimination of wastewater constituents influence the floor area and space requirements of an effluent treatment plant, since anaerobic or aerobic sludge stabilization installations and/or other disposal and dewatering means may be of smaller dimensions.
Wastewater treatment installations according to the invention may also be used when extending existing wastewater treatment installations and be installed in existing effluent treatment plants, in order to allow improved purification results with identical floor area requirements or to eliminate bottlenecks in the existing effluent treatment plant.
If, in an effluent treatment plant according to the invention, biological wastewater treatment also takes place in further apparatuses in addition to wastewater treatment installations according to the invention, it is advantageous for the wastewater treatment installations according to the invention to be arranged upstream of the further apparatuses for biological
wastewater treatment when viewed in the flow direction of the wastewater. In this way it rs ensured that only wastewater already treated in a wastewater treatment installation according to the invention is introduced into the further apparatuses for biological wastewater treatment. This treated wastewater entrains only a small amount of matter requiring biological degradation, and accordingly the further apparatuses for biological wastewater treatment may be of small dimensions, which reduces the floor area and space requirements of the effluent treatment plant.
The method according to the invention for treating wastewater is described in claim 6.
Preferably, biological purification takes place by means of an aerobic activated-sludge method, an anaerobic phosphorus elimination method, a denitrification method, or biological treatment in a support-immobilized fluidized bed.
The invention is explained with reference to the attached exemplary, schematic figures 1, 2, 3, 4a and 4b and the following descriptions.
Fig. 1 shows a diagram of an effluent treatment plant according to the prior art
Fig. 2 shows a diagram of an embodiment of an effluent treatment plant according to the
invention with a wastewater treatment installation according to the invention, which
comprises a mechanical purification apparatus incorporated into an aerobic activated-sludge
tank.
Fig. 3 is a schematic diagram of the arrangement of a belt screen in a tank for an aerobic
biological activated-sludge method.
Figs. 4a and Fig. 4b are schematic diagrams of a front view and a side view of the
arrangement according to the invention of a screening drum in an activated-sludge tank.
Fig. 1 shows how wastewater 1 from different sources, for example domestic wastewater 2, rainwater from built-up areas 3, or commercial or industrial wastewater 4, is treated firstly mechanically and then biologically in an effluent treatment plant according to the prior art. The apparatuses in which the individual mechanical and biological purification steps are performed are arranged next to one another but spatially separated from one another and the wastewater 1 flows through them in succession. First of all, coarse solids 6 are removed by raking 5. Then sand 8 and fats 9 and oils 10 are separated out in an aerated sand/fat trap 7. Next, suspended matter is separated out in the sedimentation basin 11 and removed as primary sludge 12. Then the wastewater treated mechanically in this way is fed to an aerobic activated-sludge tank 13. The aerobic activated-sludge tank 13 is followed by a secondary settling tank 14, from which surplus sludge 15 is removed. The purified wastewater is discharged from the secondary settling tank 14 into a receiving stream 16. Apparatuses for treating the primary and surplus sludge which arise are not shown.
The effluent treatment plant according to the invention illustrated in Fig. 2 differs from the effluent treatment plant in Fig. 1 in that the aerobic activated-sludge tank 13 has been replaced by a wastewater treatment installation 17 according to the invention, the aerated sand/fat trap 7 has been replaced by a non-aerated sand trap 18, and the sedimentation basin 11 has been dispensed with, which markedly reduces the floor area requirements of the effluent treatment plant relative to the effluent treatment plant illustrated in Fig. 1. After passing through the non-aerated sand trap 18, the wastewater treated mechanically by means of rakes 5 and a non-
aerated sand trap 18 is passed through a pipe 19 into the mechanical purification apparatus 20 of the wastewater treatment installation 17 according to the invention, which is arranged within an aerobic activated-sludge tank 21. From the mechanical purification apparatus 20, the wastewater passes through screen openings in its boundary surfaces into the aerobic activated-sludge tank, this being indicated by arrows. Separated-out screenings 22, which contain suspended matter, fats and oils, are discharged from the mechanical purification apparatus 20.
The wastewater treatment installation 17 according to the invention is followed by a secondary settling tank 14, from which surplus sludge 15 is removed. From the secondary settling tank 14, the purified wastewater is discharged into a receiving stream 16. Apparatuses for treating the screenings and surplus sludge which arise are not shown.
In Figs. 1 and 2, the arrows indicate the direction of movement of the wastewater or of the substances discharged from the various apparatuses, such as coarse solids, sand, fats, oils, primary sludge, surplus sludge and screenings.
Fig. 3 is a schematic diagram of the arrangement of a fine screen apparatus 23 in a tank 24 for an aerobic biological activated-sludge process. The fine screen apparatus 23 comprises an endless belt screen 25, which is guided around deflection sheaves 26. The belt screen 25 is in part immersed in the activated-sludge suspension 27 contained in the tank 24. The space enclosed by the belt screen 25 is sealed at its end faces, such that the wastewater can only flow through the screen openings in the belt screen 25 into the tank 24. The space enclosed by the belt screen 25 is designated the inside of the belt screen. The face of the belt screen 25 facing the inside is designated the inner face of the belt screen, while the other face of the belt screen 25 is designated the outer surface of the belt screen. For clarity's sake, the screen openings of the belt screen 25 are not shown. Wastewater flows into the inside of the belt screen through a feed line 28, which is guided through one of the end faces. Apart from the passage opening of the feed line 28, the end faces do not have any openings. The wastewater flows from the inside of the belt screen through the screen openings of the belt screen 25 into the tank 24, indicated by arrows. If screen openings become blocked by separated-out screenings, wastewater builds up inside the belt screen, and a stagnation pressure builds up inside the belt screen as a result of the level of the wastewater 30 then hying above the level of the activated-sludge suspension 29. The magnitude of the stagnation pressure is used as a measure of how blocked up the screen openings of the belt screen are. If the stagnation pressure exceeds a selected limit value, the belt screen 25 is moved by apparatuses, not shown, in such a way that parts of the belt screen 25 previously immersed in the activated-sludge suspension 27 and blocked by separated-out screenings are brought to above the level of the activated-sludge suspension 29. At the same time, parts of the belt screen 25 previously lying above the level of the activated-sludge suspension 29 and not blocked by separated-out screenings are immersed in the activated-sludge suspension 27. The direction of movement of the belt screen 25 is indicated by arrows 31. The part of the belt screen 25 which is brought above the level of the activated-sludge suspension 29 by movement of the belt screen is cleaned by a cleaning means 32 using a jet of water and/or air directed towards the outer face of the belt screen. Separated-out screenings then fall into the inside of the belt screen and are discharged therefrom via an apparatus, not shown, for discharging screenings. The wastewater treated biologically in the tank 24 is discharged from the tank 24 via an outlet line 33.
Fig. 4a and Fig. 4b show how a cylindrical screening drum 34 is arranged within an activated-sludge tank 35. The activated-sludge tank 35 is filled up to the operational filling level 36 with activated-sludge suspension 37. The screening drum 34 is located within the activated-sludge tank 35 and is immersed in part in the activated-sludge suspension 37. The wastewater is introduced by a feed line 38, which passes through one of the two outer faces into the inside of the screening drum 34. Apart from the passage opening of the feed line 38, the outer faces do not have any openings. The shell 39 of the cylindrical screening drum 34 is partially constructed as a fine screen. The wastewater flows through the fine screen upon passage from the inside of the screening drum 34 into the activated-sludge tank 35. A stagnation pressure is necessary for this purpose, this being built up inside the screening drum when the level of the wastewater 40 inside the screening drum 34 is higher than the level of the activated-sludge suspension 41 in the activated-sludge tank 35. This difference in levels is known as differential head. The differential head varies depending on the quantity of wastewater introduced per unit time and the extent to which the fine screen is blocked. The possible differential head is predetermined by the local installation situation; ideally, however, it amounts to no more than 50 cm. The flows within the activated-sludge tank 35 filled with activated-sludge suspension 37 do not influence fine screening, since the flow direction of the wastewater is clearly set by the accumulating stagnation pressure. The maximum planned differential head is detected by level measurement, not shown, within the screening drum 34. If a set filling level limit value is exceeded, rotary motion of the screening drum 34 about its longitudinal axis is automatically triggered, as is cleaning of the area of the fine screen which is located above the level of the activated-sludge suspension 41. Apparatuses for moving the screening drum are not shown. Cleaning proceeds while the drum is rotating by means of a cleaning means 42 with an air jet and by means of a cleaning means 43 with a water jet. The screenings separated out using the fine screen are blown off by the air jet and drop into a discharge apparatus 44, which is installed below the cleaning means 42. The discharge apparatus 44 comprises a perforated receiving channel 45 for screenings which fall down during cleaning and a conveying screw 46. The conveying screw 46 removes the screenings from the receiving channel 45 and dewaters them at the same time.
In the embodiment illustrated in Fig. 4a and Fig. 4b, It is advantageous for the screenings not to be suspended in the wastewater after cleaning of the fine screen until they are discharged from the screening drum 34. In this way, thorough dewatering may be performed during discharge.
Areas of the screening drum 34 which have been cleaned by the air jet of the cleaning means 42 move by rotation of the screening drum away from the cleaning means 42 and are finally struck by the water jet of the cleaning means 43 and cleaned. Since the cleaning means 43 is arranged laterally offset relative to the cleaning means 42, the spray water does not enter the receiving channel 45. The spray water is not collected separately but rather mixes with the wastewater inside the screening drum 34.
The wastewater treated biologically in the activated-sludge tank 35 is discharged from the activated-sludge tank 35 via an outlet line 47. The screenings dewatered upon discharge are removed from the discharge apparatus 44 as filter cake 48.

We Claims:-
Patent claims:-
1. A wastewater treatment installation (17), comprising at least one biological
purification reaction vessel with a mechanical purification apparatus (20) arranged at least in
part over the ground plan area thereof and with a wastewater feed means leading into the
mechanical purification apparatus (20), the mechanical purification apparatus (20) comprising
screen openings in at least one of its boundary surfaces, whereas the reaction vessel is
designed for performing an aerobic activated-sludge method, an anaerobic phosphorus
elimination method, a denitrification method, or a biological treatment in a support-
immobilized fluidized bed, and whereas the mechanical purification apparatus (20) is a fine
screen apparatus (23), and whereas the fine screen apparatus (23) comprises one or more
screening drums (34) or one or more belt screens (25), and whereas the clear width of the
screen openings of the fine screen apparatus (23) amounts to at least 0.1 mm, preferably at
least 0.25 mm, and at most 1 mm, preferably at most 0.5 mm.
2. The wastewater treatment installation as claimed in claim 1, characterized in
that the mechanical purification apparatus (20) is arranged wholly over the ground plan area
of the biological purification reaction vessel.
3. The wastewater treatment installation as claimed in claim 1 or 2, characterized
in that the mechanical purification apparatus (20) is located at least in part within the space
defined by the walls of the biological purification reaction vessel.
4. The wastewater treatment installation as claimed in one of claims 1-3,
characterized in that the mechanical purification apparatus (20) is located at least in part
below the operational filling level of the biological purification reaction vessel.
5. An effluent treatment plant, characterized in that it comprises one or more
wastewater treatment installations (17) as claimed in one of claims 1-4 together with one or
more apparatuses for mechanical, biological or chemical wastewater treatment arranged up- or
downstream thereof.
6. A method for treating wastewater, characterized in that the wastewater is
purified mechanically by means of a fine screen apparatus, which is located at least in part
over the ground plan area of a biological purification reaction vessel, and passes therefrom
into the biological purification reaction vessel and is there purified biologically by an aerobic
activated-sludge method, by an anaerobic phosphorus elimination method, by a
denitrification method or by a biological treatment in a support-immobilized fluidized bed,
whereas the fine screen apparatus (23) comprises one or more screening drums (34) or one or
more belt screens (25), and whereas the clear width of the screen openings of the fine screen
apparatus (23) amounts to at least 0.1 mm, preferably at least 0.25 mm, and at most 1 mm,
preferably at most 0.5 mm .

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Patent Number

271121

Indian Patent Application Number

4487/DELNP/2010

PG Journal Number

06/2016

Publication Date

05-Feb-2016

Grant Date

03-Feb-2016

Date of Filing

21-Jun-2010

Name of Patentee

VA TECH WABAG GMBH

Applicant Address

DRESDNER STRASSE 87-91, 1200 WIEN, AUSTRIA

Inventors:

#	Inventor's Name	Inventor's Address
1	FERDINAND KLEGRAF	LANGEGARTEN 13, DE-65345 RAUENTHAL, GERMANY

PCT International Classification Number

B01D 61/16

PCT International Application Number

PCT/EP2008/065307

PCT International Filing date

2008-11-11

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2100/2007	2007-12-21	Austria