METHOD AND APPARATUS FOR WATER TREATMENT

Abstract

A method for water treatment, wherein the water for treatment is conducted by a conveying device from an inlet to an outlet via multiple treatment stages, wherein at least one of the treatment stages is an oxidation stage in which foreign matter situated in the water is oxidized by an oxidant which is added to the water in or upstream of the oxidation stage, and at least one of the treatment stages to which the water is fed after the processing by the at least one oxidation stage is a separation stage in which foreign matter situated in the water after processing in the at least one oxidation stage is precipitated and separated off by addition of at least one separating agent, in particular of a flocculant and/or of activated carbon.

Claims

1. A method for water treatment, wherein the water for treatment is conducted by means of a conveying device from an inlet to an outlet via multiple treatment stages, wherein at least one of the treatment stages is an oxidation stage in which foreign matter situated in the water is oxidized by means of an oxidant which is added to the water in or upstream of the oxidation stage, and at least one of the treatment stages to which the water is fed after the processing by means of the at least one oxidation stage is a separation stage in which foreign matter situated in the water after processing in the at least one oxidation stage is precipitated and separated off by addition of at least one separating agent, in particular of a flocculant and/or of activated carbon.

2. The method according to claim 1, wherein, in the oxidation stage or in at least one of the oxidation stages, an electrolysis of the water is performed by means of an electrolysis device.

3. The method according to claim 1, wherein a tenside is admixed to the water, in particular before said water is fed to the oxidation stage or to the oxidation stages.

4. The method according to claim 1, wherein, after the treatment of the water in the separation stage or at least one of the separation stages, a proportion of the water that contains an elevated concentration of precipitated foreign matter is conducted by means of the conveying device back to the oxidation stage or to one of the oxidation stages.

5. The method according to claim 1, wherein, in the oxidation stage or in at least one of the oxidation stages and/or in the separation stage or in at least one of the separation stages, the water is held for a specified time interval in a respective buffer vessel before said water is conducted by means of the conveying device to a subsequent treatment stage.

6. The method according to claim 5, wherein, at least in one of the buffer vessels, there is arranged an agitator which is operated during a part of the time interval and which is at rest during a part of the time interval.

7. The method according to claim 1, wherein, downstream of the separation stage or one of the separation stages and upstream of the outlet, the water is conducted through a fine filter with a pore size of between 50 μm and 0.5 μm or between 30 μm and 20 μm.

8. The method according to claim 7, wherein, as a fine filter, use is made of a cup-shaped fine filter which is arranged, in particular so as to be rotatable about a vertical axis, in a fine filter vessel, wherein the water from the separation stage or from at least one of the separation stages is fed to the fine filter via an open top side of the fine filter.

9. The method according to claim 8, wherein the fine filter vessel has multiple lateral openings to which water extracted through the fine filter vessel is fed by means of a pump in order to purge the fine filter.

10. The method according to claim 1, wherein a proportion of the water is extracted from the fine filter vessel or from the interior space of the fine filter and fed to the oxidation stage or to at least one of the oxidation stages.

11. The method according to claim 1, wherein additional separating agent is added to the water in the oxidation stage or in at least one of the oxidation stages by means of a dosing device.

12. The method according to claim 1, wherein at least one of the treatment stages is a pressing stage in which a pressing device is used in order to press the water through a filter device before said water is fed to the oxidation stage.

13. The method according to claim 12, wherein separating agent is added to the water in, or before said water reaches, the oxidation stage or at least one of the oxidation stages, wherein, after the treatment of the water in the respective oxidation stage, a proportion of the water that contains an elevated concentration of precipitated foreign matter is conducted by means of the conveying device back to the pressing stage or to one of the pressing stages.

14. The method according to claim 12, wherein, as the pressing stage or one of the pressing stages, use is made of a filter press which has a housing to which the water is fed, wherein the pressing device is arranged in the housing and rotates about a vertical axis, wherein the pressing device has at least one pressing element which rotates about an axis of rotation which is at an angle with respect to the vertical axis, which pressing element is of circular cross section and has an outer shell formed from an elastic material, with which outer shell the pressing element rolls on the filter device, wherein the filter device comprises a filter medium and a filter plate which is positioned upstream of the filter medium and which has multiple apertures which are open toward the pressing element, wherein each of the apertures has a cross section which decreases toward the filter medium.

15. The method according to claim 1, wherein, in the or at least one of the oxidation stages, a roll assembly is used for enlarging the surface area of the water, which roll assembly has at least one shaft bearing in each case at least one roll, a drive for the at least one shaft, a water feed arranged above the respective roll, and a collecting trough, assigned to the respective roll, for the water, wherein the roll has two cylinder-shell-shaped lateral surfaces which are spaced apart in a radial direction and which are each in the form of a mesh and which, at the bottom side of the roll, project into the collecting trough, wherein the water is conducted through the respective water feed to the respective roll, wherein the respective roll is driven by means of the drive.

16. The method according to claim 15, wherein the oxidation stage that comprises the roll assembly comprises a water vessel to which the water is fed via a vessel inlet and from which the water is discharged through a vessel outlet, wherein the water is drawn in via an intake opening of the water vessel, in particular by means of a pump, and fed to the respective water feed of the respective roll, wherein a water drain of the roll assembly, to which water that passes over a side wall of at least one of the collecting troughs is fed, opens out in the water vessel.

17. The method according to claim 1, wherein at least two or at least three of the oxidation stages and/or at least two of the separation stages and/or at least two of the pressing stages are used, through which the water is conducted in each case sequentially by means of the conveying device.

18. The method according to claim 1, wherein a proportion of the water is recirculated from at least one of the oxidation stages into an oxidation stage that has been passed through previously.

19. The method according to claim 1, wherein, in the event of a triggering condition, which is in particular dependent on the water quality at the outlet, being satisfied, the inlet to a buffer vessel is shut off, and instead water from a water reservoir is processed.

20. An apparatus for water treatment, comprising an inlet for the feed of water for treatment, an outlet for the discharge of treated water, and a conveying device for conveying the water from the inlet to the outlet, wherein the fluid is conducted through multiple treatment stages, wherein at least one of the treatment stages is an oxidation stage for the oxidation of foreign matter situated in the water by means of an oxidant which is added to the water in or upstream of the oxidation stage, and at least one of the treatment stages to which the water is fed after the processing by means of the oxidation stage is a separation stage for the precipitation of foreign matter situated in the water downstream of the oxidation stage, wherein a control device of the apparatus is configured for controlling the conveying device and the treatment stages.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0066] In the drawing:

[0067] FIG. 1 shows an exemplary embodiment of an apparatus according to the invention for water treatment, by means of which an exemplary embodiment of the method according to the invention is implemented, and

[0068] FIGS. 2 to 4 show detail views of various components of the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0069] FIG. 1 shows an apparatus for water treatment 1, which apparatus comprises an inlet 92 for the feed of water for treatment, an outlet 11 for the discharge of treated water, and a conveying device 2 for conveying the water from the inlet 92 to the outlet 11, wherein the water is conducted through multiple treatment stages. Here, three of the treatment stages are oxidation stages 5, 6, 7, in which foreign matter situated in the water is oxidized by means of an oxidant 12 which is added to the water. By means of a dosing device 13, in the example a pump, the oxidant 12 is introduced from a reservoir into the water in the first oxidation stage 5, and also remains in said water in the subsequent oxidation stages 6, 7, such that oxidant that has not yet been consumed can also oxidize foreign matter in the further oxidation stages 6, 7.

[0070] The two treatment stages are separation stages 8, 9, to which the water is fed after said water has passed through the oxidation stages 5, 6, 7. In the separation stages 8, 9, separating agent 14, which may for example be a mixture of flocculant and activated carbon, is fed to the water from a reservoir by means of a respective dosing device 15, in the example by means of a conveying screw. This has the effect that foreign matter situated in the water flocculates owing to the flocculant, or are bound to the activated carbon.

[0071] Here, the problem commonly arises that high concentrations of large organic molecules can greatly inhibit such a physical separation by means of separating agents 14, such that a long standstill time and high material usage would be necessary in the separation stages 8, 9. In the apparatus 1 and in the discussed method, this is avoided in that, by means of the oxidation stages 5, 6, 7 that have been passed through beforehand, corresponding molecules have already been oxidized or destroyed in some other manner, such that primarily relatively small molecules, which can be easily precipitated, are present in the separation stages 8, 9.

[0072] The conveying device 2 serves for transporting the water between the inlet 92, the outlet 11 and the individual treatment stages. Said conveying device is formed by a multiplicity of line network sections 17, through which water is transported either by means of pumps 19 or by gravitational force. In order to prevent or enable transport by gravitational force, and/or for selection between multiple possible conveying paths, a multiplicity of valves 18 are also provided.

[0073] The pumps 19 and valves 18, like the various treatment stages, are controlled by means of a control device 16 of the apparatus 1, which control device is merely schematically illustrated. The control may be implemented for example by means of one or more microcontrollers, or the like. The provision of control signals and the receipt of sensor signals may take place directly digitally or by means of corresponding transducers.

[0074] If relatively large items of foreign matter are present in the fed water, for example long fibers, such as occur in slurry, fermentation residue from biogas plants or the like, it is advantageous to utilize at least one pressing stage 3, 4 as a further treatment stage upstream of the oxidation stages 5, 6, 7 in order to separate off solid and fibrous matter.

[0075] In the exemplary embodiment shown, as a first pressing stage 3, use is made of a coarse press which can for example press fed material against a screen by means of a screw, in order for the pressed water to subsequently be processed further. Here, as indicated by the arrow 20, the solid matter is conducted out of the apparatus 1 or is stored there until it is removed. The pressed water is firstly accumulated in a buffer vessel 21, wherein, in the buffer vessel 21, a tenside 22, in particular in the form of a tenside solution, is added from a reservoir 96 by means of the dosing device 23.

[0076] Tensides 22 lead in the first instance to better solubility of organic molecules, or of other molecules with low polarity, in water, such that an addition of tensides 22 for the purposes of improving a precipitation of foreign matter appears in the first instance to be counterintuitive. It has however been identified that, through addition of tensides, there is a tendency for a separation of foreign matter to be achieved, whereby reactions, that is to say in particular an oxidation or hydrolysis of said molecules, in order to split them up into smaller molecule residues, can take place considerably more quickly than in situations in which colloids, in particular of hydrophobic molecules, are present in clustered form as suspended particles, or the like.

[0077] From the buffer vessel 21, the water with added tensides 22 is conducted into the housing 24 of a second pressing stage 4, which will be discussed in more detail further below with reference to FIG. 2. This can allow filtering of particles up to a size of between 1 μm and 50 μm, preferably up to a size of between 1 μm and 25 μm. By means of the refinement discussed in more detail further below, it is nevertheless possible for clogging of the filter to be avoided even in the case of water that is heavily laden with suspended matter.

[0078] The water purified by means of the two pressing stages 3, 4 is conducted into the buffer vessel 25 of the first oxidation stage 5, in the example by means of the same pump that has already been used to conduct the water to the second pressing stage 4. In said buffer vessel, as discussed above, oxidant 12 is added from the vessel 95. The water remains in the buffer vessel 25 for a certain time interval specified by the control device 16, wherein, for a part of this time interval, the agitator 34 is operated in order to accelerate reactions in the water.

[0079] Further to the addition of oxidant 12, a breakdown of in particular organic molecules is also realized by virtue of an electrolysis of the water in the buffer vessel 25 being performed by means of an electrolysis device 30, of which only the electrodes are illustrated schematically in FIG. 1. In this way, the ozone and oxygen content of the water and of the surrounding air increase, which on its own contributes to the oxidation of foreign matter. Furthermore, there are resulting elevated OH.sup.− and H.sub.3O.sup.+ concentrations at least in the immediate vicinity of the electrodes, whereby the hydrolysis of foreign matter can be accelerated, because, for this, no activation energy for the breakdown of water molecules is required.

[0080] Aside from the water fed from the pressing stage 4, water from the separation stages 8, 9 is also fed to the oxidation stage 5. Since said water is extracted via intake openings 33 that are arranged at or close to the base of the respective buffer vessel 28, 29, said water comprises a high concentration of foreign matter, which has been precipitated in the separation stage, and of the one or more separating agents, on which the foreign matter has been adsorbed. This results in numerous advantages. Firstly, in this way, separating agent is additionally already introduced into the first oxidation stage 5, such that foreign matter that has bound to corresponding separating agents can be precipitated already in the oxidation stage 5 and can be extracted via the extraction opening 48 in the vicinity of the base of the buffer vessel 25. For this purpose, the agitator 34 is deactivated for a part of the time interval for which the water remains in the buffer vessel 25. For example, the agitator 34 may be active for 10 seconds and may subsequently remain at rest for 30 seconds in order to allow a sedimentation of foreign matter that has bound to separating agents 14. Through the multiple use of the one or more separating agents 14, it is firstly the case that the required material usage is reduced. Secondly, it is for example the case that the flocculation in a respective separation stage 8, 9, on the one hand, and in the oxidation stage 5, on the other hand, results in relatively large flocculates, which can be separated off effectively by means of the pressing stage 3.

[0081] The water is subsequently conducted by means of the conveying device 2 into the buffer vessel 26 of the second oxidation stage 6. There, it is likewise the case that an electrolysis of the water is performed by means of the electrolysis device 31. Like the agitator 34, the agitator 35 is operated in a time-offset manner. Thus, substantially the same processes take place in the second oxidation stage 6 as in the oxidation stage 5. Through the addition of activated carbon and flocculants from the reservoir 97 by means of the dosing device 37 which is in the example in the form of a feed screw, the COD value of the water can be influenced and controlled, wherein the concentration of foreign matter, in particular of foreign matter that have still to be oxidized, is already reduced as a result of the preprocessing in the first oxidation stage 5. With sufficient addition of oxidants 12 from the vessel 95 in the first oxidation stage 5, there is still sufficient unconsumed oxidant 12 present, such that no further addition of oxidant is necessary.

[0082] Information regarding the salt content of the water in the buffer vessel 26 can be obtained from the electrical current flowing at the electrolysis device 31. In a manner dependent on said salt content or the electrical current, a dosing device 37, in the example a conveying screw, can be controlled by the control device 16 so as to introduce further separating agent 36 from a reservoir 97 into the water in the buffer vessel 26.

[0083] The third oxidation stage 7 is, by contrast, of somewhat different construction. There, use is likewise made of a buffer vessel 27, in which the water remains for a certain time interval in order to adapt the water treatment in said oxidation stage 7 to the cyclic passage of water through the other treatment stages. Furthermore, as discussed above, it is also the case in the buffer vessel 27 that an electrolysis is performed by means of the electrolysis device 32 in order to achieve the discussed advantages.

[0084] The buffer vessel 27 is however, in a preparatory manner, filled with water that is removed via an opening 46 at a base of a fine filter 43 which is arranged between the separation stages 8, 9 and the outlet 11. In other words, water that contains a low concentration of still-unprocessed foreign matter is used for the pre-filling of the buffer vessel 27. It has been found that, for the subsequent water treatment by means of the roll assembly 40, use is preferably made, already at the inlet side, of relatively low concentrations of foreign matter for processing.

[0085] In the flow path between the buffer vessel 27 and the buffer filter 28 of the first separation stage 8, as part of the third oxidation stage 7, there is arranged a sub-stage 69, which will be discussed in more detail further below with regard to FIGS. 3 and 4. Said sub-stage serves generally for generating large water surface areas in a roll assembly 40 and, in this way, in particular in conjunction with the added tensides, achieving good molecule separation and thus very good reaction rates.

[0086] Since, as discussed above, owing to the recirculation of a proportion of the water from the separation stages 8, 9 into the oxidation stage 5, it is also the case in the oxidation stages 5, 6, 7 and thus also in the sub-stage 69 that the water contains separating agents 14 and, furthermore, certain residues of foreign matter precipitate of their own accord after an oxidation, for example hydroxides of metals which result in the case of an oxidation of organometallic compounds, extraction openings 49, 50 are arranged at the base on the buffer vessel 27 and on the water vessel 38 of the sub-stage 69, via which extraction openings water that comprises a high concentration of said precipitated foreign matter can be conducted back to the first oxidation stage 5, which can, as discussed above, result in relatively large flocculates, which can be separated out for example in the pressing stage 3.

[0087] After flowing through the sub-stage 69, the water is in turn accumulated in the buffer vessel 28, which is part of the separation stage 8, in which, as discussed above, additional separating agent 14 is fed from the reservoir. This results in a high separating agent concentration there and, after brief operation of the agitator 41, the latter can be stopped in order to realize a rapid precipitation of the foreign matter that has bound to the one or more separating agents 14.

[0088] The same approach is subsequently repeated in a further separation stage 9 in the buffer vessel 29, which has the agitator 42. Since the oxidation stages 5, 6, 7 used beforehand have already oxidized large organic molecules or destroyed these in some other way, there are no remaining obstructions to precipitation, such that, even with short standstill times of 30 seconds, for example, substantially complete precipitation of the foreign matter can be achieved.

[0089] In order to retain the few remaining foreign matter flocculates and activated carbon particles, which are relatively small and have thus not necessarily sunk, the water, after passing through the separation stages 8, 9, is conducted into a cup-shaped fine filter 43 which forms the final treatment stage 10 and which is mounted, so as to be rotatable by means of a motor 45, in a fine filter vessel 44. This may for example have a pore size of 25 μm, wherein use may also be made of considerably smaller pore sizes of for example 1 μm. The cup shape of the fine filter 43 results in a relatively large filter surface area, wherein, as a result of the rotation of the fine filter 43, different parts of said filter surface are primarily involved in the filtering process in alternating fashion, such that clogging of the filter surface takes considerably longer than in the case of a static filter.

[0090] Since such clogging can nevertheless not be completely avoided, purging of the fine filter 43 is performed after every cycle of the processing or after a certain number of cycles or the like. For this purpose, it is firstly the case that pure water is removed from the filter vessel 44 via the outlet 11, and at least a major proportion of the water that remains in the fine filter 43 is extracted via the opening 46 and, as already discussed above, is utilized to completely fill the buffer vessel 27. In this way, the side wall of the fine filter 43 is substantially completely exposed. Water removed from the fine filter vessel 44 can subsequently be fed through lateral openings 47 to the fine filter 43 by means of a pump, in order to purge the fine filter. Here, the fine filter 43 preferably rotates in order to achieve cleaning of substantially the entire surface area of the fine filter 43. Since, during the purging, the water passes through the fine filter 43 in the opposite direction to that during the filtering, the filter pores can be reliably opened again.

[0091] Over relatively long periods of operation of the apparatus 1, deposits may form on certain components of the apparatus 1, which deposits have the effect that increasingly larger proportions of the foreign matter or of decomposition products of the foreign matter reach the outlet. It can thus be expedient for the water quality at the outlet 11 to be periodically or continuously monitored, wherein it may suffice for samples to be taken at relatively large time intervals. If unsatisfactory water quality is detected, and if for example the COD value overshoots a threshold value, it would be possible, in principle, to perform maintenance of the apparatus 1 as a whole.

[0092] It has however been identified that, in many cases, it suffices to operate the apparatus 1 for one or more cycles with relatively clear water rather than with slurry or fermentation waste, for example, in order to achieve considerably improved levels of water quality at the outlet 11 during subsequent renewed operation with these starting materials. It is thus possible, in particular in automated fashion by means of the control device 16, for the inlet to the buffer vessel 21 to be shut off, and instead for water from a water reservoir 51 to be processed, in the event of a triggering condition being satisfied, for example in the event of an excessively high COD value being detected. As can be seen from the illustration in FIG. 1, the water in the water reservoir 51 may in particular be removed from the fine filter vessel 44 during the course of normal operation, that is to say may correspond to the treated water extracted via the outlet 11 during normal operation.

[0093] By means of the described construction of the apparatus 1 for water treatment and the described method, a very compact construction of the apparatus 1 is achieved. For example, the components shown can be arranged in two stacked 40-foot ISO containers, as is schematically illustrated in FIG. 1 by the boxes surrounding the components. This makes it possible for the apparatus to be delivered to an installation site with little outlay and to be set in operation there with little installation outlay by connecting a small number of lines. By means of the combination of oxidation and physical separation, in particular in conjunction with preceding pressing stages and a final stage of fine filtering, it is possible, with relatively low energy expenditure of 10 kW, for example, and by means of an apparatus of correspondingly small construction, to achieve relatively high throughputs of for example 18,000 tonnes of slurry per year. By means of the discussed multiple use of the separating agent and the use of the oxidant in multiple treatment stages, it is furthermore the case that very little usage of material is required.

[0094] FIG. 2 shows further details of the fine press used as pressing stage 4 in the apparatus 1. Here, the figure shows a cut-away perspective view. The treatment stage 4 comprises a housing 24, into which the water is introduced via an inlet 55. In the housing 24, there are arranged a fine filter device 52 and a pressing device 53, which, in the example shown, has three pressing elements 54. The housing 24 is closed off upwardly by means of a cover 56, on which there is seated a drive motor 57, which drive motor drives a shaft 59 which forms a vertical axis 58 and to which the pressing elements 54 are connected. The pressing elements 54 roll on the filter device 52 and press the water through the filter device 52, whilst a major proportion of the foreign matter, which has a certain particle size, remains stuck in the filter device 52. The purified water accumulates in an accumulating vessel 60, which is in the form of an annular space and which is positioned downstream of the filter device 52. Via an outlet 61, the filtered water can be drawn off and fed to the oxidation stage 5.

[0095] In the housing interior, there is furthermore provided an accumulating vessel 62, which is positioned downstream of a central opening 63 of the filter device 52. Pressed-out filter cakes accumulate in said accumulating vessel 62, which filter cakes are firstly formed in the filter device 52, by virtue of the pressing elements 54 rolling over the filter device 52, but are secondly also drawn out of the apertures of the filter device 52 again by means of said pressing elements, such that said filter cakes, suspended in the liquid, can accumulate in the accumulating vessel 62 and can be extracted therefrom via the extraction opening 68. In the apparatus shown in FIG. 1, the water extracted via the extraction opening 68 is fed to the first pressing stage 3.

[0096] The filter device 52 has a frustoconical or funnel shape and is screw-connected to the housing by way of the annular flange 64. The pressing elements 54 are of frustoconical form, such that they lie on the filter device 52. Each pressing element 54 comprises a hollow element body 65, to the outside of which an outer shell 67 composed of an elastic material is applied.

[0097] The filter device 52 comprises a filter plate which forms the apertures already discussed above, into which the filter cakes are pressed. At that side of the filter plate which is averted from the pressing elements 54, there is arranged a filter medium, for example a perforated film or a nonwoven, which has very small apertures, for example in the range between 1 μm and 25 μm. The filter medium retains the material of the filter cake and allows only water and very small particles to pass through.

[0098] By means of the approach discussed above, in which the filter cake is drawn out of the corresponding apertures again as the pressing elements 54 roll onward, it can be achieved that, in relation to conventional filters, in which the water is pressed through a filter medium, no or at least considerably fewer residues accumulate on the filter surface, whereby the corresponding pressing stage 4 can be operated over relatively long periods of time without maintenance, even if a very fine-pore filter medium is used.

[0099] FIG. 3 shows a detail view of the sub-stage 69 of the oxidation stage 7 shown in FIG. 1. Said sub-stage comprises a water vessel 38, to which water for processing is fed via a vessel inlet 70. After the processing, the water is discharged from the water vessel 38 via the vessel outlet 71.

[0100] In the exemplary embodiment, the water that flows in via the vessel inlet 70 firstly passes electrodes of an electrolysis device 73, to which electrodes a voltage is applied by means of said electrolysis device. The electrolysis of the water has the effect, on the one hand, that a high oxygen content and also a significant content of ozone or oxygen radicals are present in the air situated above the water surface, which, as will be discussed in more detail further below, can contribute to the breakdown of foreign matter in the roll assembly 40. Furthermore, at least locally in the region of the respective electrodes, a higher concentration of H3O+ and OH− radicals than would otherwise be present in the water is achieved. This can locally contribute to the hydration of foreign matter, because it is for example no longer necessary to separate a hydrogen atom from the water molecule in order to utilize an OH− group for the hydration of a molecule.

[0101] If the circulation of the water via the roll assembly 40, discussed in more detail further below, results in a flow speed that is sufficiently high, the elevated H3O+ and OH− concentrations can also be present in the roll assembly 40, because the transport of water can take place more quickly than a neutralization of H3O+ and OH− radicals by diffusion processes.

[0102] A deflector plate 74 is arranged in the water vessel 38 such that the vessel inlet 70 and a water outlet of the roll assembly 40, discussed again further below, are arranged on the same side of said deflector plate 74, whereas the vessel outlet 71 of the water vessel 38 is arranged on the other side of the deflector plate 74. This has the effect that water that is fed via the vessel inlet 70 cannot flow directly to the vessel outlet 71, but is mixed with the water that has already been treated in the roll assembly 40, whereby the concentration of still-unprocessed foreign matter in the water is considerably reduced.

[0103] Since the water mixed in this way is furthermore, on its flow path to the vessel outlet 71, conducted past an intake opening 93 via which it is drawn in by means of the pump 39 and conveyed to the roll assembly 40, it can be achieved, through corresponding setting of the conveying rate of the pump 39 in relation to the water quantity that is fed via the vessel inlet 70 and discharged by the vessel outlet 71, that fed water is, on average, conducted through the roll assembly 40 several times before being discharged via the vessel outlet 71. In this way, for the water in the water vessel 38 and in particular for the water that is discharged via the vessel outlet 71, a very low concentration of still-unprocessed foreign matter can be achieved.

[0104] The oxidation stage 7 or the sub-stage 69 serves primarily for processing foreign matter in the water such that said foreign matter can subsequently be precipitated in an effective manner in the separation stages 8, 9. Proportions of the foreign matter may nevertheless precipitate already in the sub-stage 69 itself. For example, in the case of the treatment of water that has been recovered from fermented slurry, for example from a biogas plant, relatively high pH values are encountered, such that, after a break-up of organometallic compounds, hydroxides of the metals are precipitated in most cases. Furthermore, as discussed above, it is also the case in the oxidation stages 5, 6, 7 that separating agents 14, 36 are already present in the water. A sediment with a high concentration of precipitated foreign matter can thus form in the water vessel 38, which sediment can be extracted via a pumping-out opening 50 situated close to the base, or the pipe 72.

[0105] In order to achieve high throughputs with relatively compact dimensions of the apparatus 1, on the one hand, and a low level of remaining unprocessed foreign matter in the water, on the other hand, the roll assembly 40 is utilized to enlarge the size of the surface area of the water and generally increase the dynamics of reactions for the treatment. A detailed view of the roll assembly 40 is illustrated in FIG. 4. In the example, the roll assembly 40 comprises six rolls 81, 81′, which are supported by a housing 94 of the roll assembly 40 and which are driven by a common drive 83. The drive 83 is merely schematically illustrated in FIG. 2. The drive 83 may for example be an electric motor. The drive 83 may for example be coupled directly to the shaft 87 of one of the rolls 81, 81′. The shafts 87 of the various rolls 81, 81′ may be coupled to one another in terms of movement, for example by means of V-belts.

[0106] The water that is drawn in by the pump 39 via the intake opening 93 is conducted to respective apertures 78 of the housing 94 of the roll assembly 40, which apertures are adjoined by water feeds 79 which conduct the inflowing water axially along the roll 81, 81′ and cause said water to flow through a gap 80 or some other opening onto an outer lateral surface 86 of the respective roll 81, 81′.

[0107] The respective rolls 81, 81′ comprise, as can be seen in particular in FIG. 4, two cylindrical lateral surfaces 85, 86 which are spaced apart from one another in a radial direction and which are each formed by a mesh. Below the roll 81, 81′, there is arranged a respective collecting trough 82, 82′ which collect the water fed via or by means of the roll 81, 81′. Here, the dimensions of the lateral surfaces 85, 86 are selected such that they project into the collecting trough 82, 82′ at the bottom side of the roll 81, 81′. Furthermore, radially within the inner lateral surface 85, there is situated a cylindrical inner shell 84, which is likewise connected rotationally conjointly to the shaft 87. As indicated by the arrow 88, the respective shaft 87 and thus the rolls 81, 81′ are rotated with a relatively high rotational speed of, for example, 1000 rpm.

[0108] The described arrangement has the effect that, in the case of the collecting trough 82, 82′ being filled to a sufficient level with water, the two lateral surfaces 85, 86 dip into the water and, owing to the lateral surfaces 85, 86 being in the form of meshes and owing to the relatively fast rotation of the rolls 81, 81′, intensely swirl said water and entrain said water at least over a certain distance. Thus, in the intermediate spaces between the lateral surfaces 85, 86 and between the inner shell 84 and the lateral surface 85, which may for example have an extent of 1 to 1.5 cm in a radial direction, there is resulting hydrodynamic water movement and swirling of the water. This leads, on the one hand, to an acceleration of treatment processes within the water, that is to say for example of a hydration of foreign matter.

[0109] On the other hand, in particular because tensides 22 are present in the water, there is resulting intense foam formation, wherein the lateral surfaces 85, 86 in the form of meshes however simultaneously act as mechanical foam breakers, such that the foam or individual air bubbles in the foam have a very short lifetime of for example only approximately 2 ms. The interaction of the intense foam formation with the simultaneous rapid breakdown of the foam has the effect that very large surface areas are briefly provided, but at the same time a high throughput can be achieved.

[0110] The formation of large surface areas leads on the one hand to foreign matter in the water interacting much more intensely with fed air, which, as discussed above, may in particular have high oxygen and ozone contents. On the other hand, tensides 22 present in the water are adsorbed on said surface and can thus form a large filter surface area in order at to kill foreign matter, for example organic residues of oxidized molecules or viruses or bacteria.

[0111] As a result of the rotation of the rolls 81, 81′, water situated in the respective collecting trough 82, 82′ tends to be accelerated to the right in FIG. 4, such that, for the collecting trough 82, the water is sloshed or conveyed over the side wall 89 of the collecting trough 82, following which said water can fall vertically through the cavity, situated to the right of the collecting troughs 82, of the housing 94 of the roll assembly 40, which cavity forms the water outlet of the roll assembly 40, back into the water vessel 38, specifically on the left-hand side of the deflector plate 74. This results in the mixing with freshly fed water, as already discussed above.

[0112] Here, water that is situated in the collecting trough 82′ is firstly conveyed into the collecting trough 82, because the side walls 89 of the collecting troughs 82, 82′ are connected to one another in water-tight fashion. This has the effect, on the one hand, that water that is initially fed to the rolls 81′ can be processed twice in the roll assembly, specifically once by the roll 81′ and once by the roll 81. At the same time, this has the effect that the water that is fed to the roll 81 is diluted with the pre-processed water fed from the roll 81′, such that a lower concentration of still-unprocessed foreign matter is present in the region of the roll 81 than is the case for the roll 81′. It has been identified that this combination between series and parallel processing of the water is particularly advantageous.

[0113] The mesh that forms the lateral surfaces 85, 86 may thus be designed so as to result in a sawtooth structure of the roll surface. This leads overall, in conjunction with a small spacing between the outer lateral surface 86 and the base of the collecting trough 82, 82′, to a good break-up of hydrate shells and water clusters, which can suppress a reaction of foreign matter in the water. The water is hereby initially intensely compressed in the region 90 and subsequently suddenly expanded in the region 91. Together with the shear forces that arise in the constriction, water clusters can be broken up in this way. A corresponding sawtooth structure for meshes results for example in the case of production of a rhomboidal mesh as an expanded mesh.

[0114] In order to firstly further assist the foam formation within the roll assembly and secondly achieve the high oxygen and ozone concentration, which occurs owing to the electrolysis of the water, also in the region of the rolls 81, 81′, use is made of gas feed lines 75 which are fed through a gas discharge opening at the top side of the water vessel 38. Since in particular the operation of the roll assembly 40 can have the effect that a foam layer forms on the surface of the water in the water vessel 38, and it is advantageously sought to prevent the gas discharge opening or the gas feed lines 75 from being covered with foam, which would restrict a feed of gas to the roll assembly 40, a foam breaker 76 is arranged in the region of the gas discharge opening, which foam breaker, in the example, is driven by an electric motor 77. As a foam breaker 76, use may for example be made of a disk with rods attached thereto, as is illustrated schematically in FIG. 3. Here, the rods are led rapidly through the foam and thus connect air bubbles, leading to the break-up of the foam. In addition or alternatively, baffle plates may be used, against which the air bubbles burst.

[0115] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.