- a grid of effluent gutters, extending horizontally between opposing sides of the reactor vessel wall, at such a vertical distance from the reactor vessel bottom that, during use, a row of inlet holes comprised by the effluent gutters is arranged for discharging relatively clean water from an upper layer of the water contained in the reactor vessel as effluent.

Background of the invention

Aerobic granular sludge technology for treating wastewater is known and commercially available as Nereda® waste water treatment technology, supplied to the market by the present applicant. The Nereda® technology comprises the purification of wastewater by controlling the growth and formation of micro-organisms. Therein, a three-step approach is adopted: during a first step, the reactor vessel is filled with wastewater from a relatively low point in the reactor vessel and relatively clean water (or effluent) from the upper layer is 'pushed out' through the inlet holes of the effluent gutter. During a second step, the waste water is brought into contact with sludge particles comprising the micro-organisms, while an oxygen-comprising gas is fed to the reactor vessel to allow purification of the wastewater. During a third step, a settling step, the sludge granules are allowed to settle. This cycle is continuously repeated.

A problem with the present reactor vessels is that it is rather difficult to maintain a proper vertical plug flow in the reactor vessel, especially in cases with a limited influent flow.

Another problem with the present reactor vessels is that sludge granules may be recirculated, which is highly undesirable. An object of the present invention is thus to provide a reactor vessel, wherein a proper vertical plug flow can be maintained in the reactor vessel, especially in cases with a limited influent flow.

Another object of the present invention is thus to provide a reactor vessel for treating wastewater by means of aerobic granular sludge technology, wherein sludge is prevented from being recirculated.

Summary of the invention Hereto, according to the invention, the reactor vessel is characterized by:

a grid of recirculation gutters, extending horizontally between opposing sides of the reactor vessel wall at substantially the same height as the grid of effluent gutters, wherein the recirculation gutters are integrated with the effluent gutters in such a way, that the vertical plug flow is kept intact.

Due to the recirculation gutters being arranged at a relatively high position in the reactor vessel (as far away from the sludge bed as possible), the relatively clean water from the upper layer of the wastewater is allowed to be recirculated without sludge entering the recirculation gutter. At the same time, due to the specific integration of the recirculation gutters with the effluent gutters, the flow patterns in the upper layer of the water body are only minimally disturbed. This holds in particular for the flow of relatively clean water to the effluent gutter and for the vertical plug flow, especially in cases with a limited influent flow. This improves formation of granules and improves separation of settling sludge. Also, recirculation allows nitrate to be recirculated back to the sludge bed, allowing extensive denitrifi cation to occur, therein improving effluent quality. Furthermore, the present effluent gutter construction can be advantageously used for mounting the recirculation gutter, saving on construction costs and facilitating only minimal use of available space.

Purely by means of example, the height difference between the grid of effluent gutters and the grid of recirculation gutters preferably is less than 1 m, more preferably less than 0,5 m, even more preferably less than 0,2 m. Most preferably, the grid of recirculation gutters is attached to the grid of effluent gutters.

An embodiment relates to an aforementioned reactor vessel, wherein each effluent gutter extends along an effluent gutter axis, the effluent gutter having a bottom wall as well as opposite side walls extending along the effluent gutter axis, wherein at least one of the side walls of the effluent gutter, preferably both side walls, comprises the row of inlet holes extending along the effluent gutter axis.

An embodiment relates to an aforementioned reactor vessel, wherein at least one recirculation gutter is arranged adjacent to an underside of the effluent gutter, therein extending along the effluent gutter axis.

An embodiment relates to an aforementioned reactor vessel, wherein at least one recirculation gutter has a tubular shape.

An embodiment relates to an aforementioned reactor vessel, wherein at least one recirculation gutter has a bottom wall and a top wall, and two opposing side walls extending along the effluent gutter axis, the recirculation gutter thus for example having a square or rectangular cross-section.

An embodiment relates to an aforementioned reactor vessel, wherein the recirculation gutter comprises a row of inlet holes extending along the effluent gutter axis for allowing the relatively clean water from the upper layer of the water in the reactor vessel to be recirculated.

An embodiment relates to an aforementioned reactor vessel, wherein recirculation tubes are fluidly connected to the recirculation gutters for recirculating the relatively clean water towards the bottom of the reactor vessel.

An embodiment relates to an aforementioned reactor vessel, wherein waste removal means are provided for removing floating waste from the wastewater. Therein, a separate floating waste collection point may be used for getting rid of the floating waste.

An embodiment relates to an aforementioned reactor vessel, wherein at least one effluent gutter is provided with a baffle for preventing floating waste from entering the inlet holes of the effluent gutter. Thus, the relatively clean water entering the effluent gutter keeps on entering the inlet holes at the required flow rate and simultaneously enters the effluent gutter without any unwanted matter, such as floating waste or debris.

An embodiment relates to an aforementioned reactor vessel, wherein at least one effluent gutter is configured in such a way, that, during filling of the reactor, the rows of inlet holes are located below water level to prevent floating waste from being mixed with the relatively clean effluent. An embodiment relates to an aforementioned reactor vessel, wherein at least one effluent gutter is provided with a top wall, such that a tubular effluent gutter is created, for instance having a square or rectangular cross-section.

An embodiment relates to an aforementioned reactor vessel, wherein the inlet holes of the recirculation gutter are arranged at the lowermost position of the side wall, adjacent to the bottom wall. This also facilitates any sludge that may have entered the recirculation flow to be flushed out of the recirculation gutter again via the inlet holes, such as via air or water flushing, or by alternatingly flushing with water and air.

An embodiment relates to an aforementioned reactor vessel, wherein the inlet holes of the recirculation gutter are sized to allow sludge (granules) to leave the recirculation gutter.

An embodiment relates to an aforementioned reactor vessel, wherein the recirculation tubes extend in a horizontal direction.

An embodiment relates to an aforementioned reactor vessel, wherein the recirculation tube extends in a direction perpendicular to the effluent gutter axis. More preferably, the recirculation tube and the recirculation gutter are arranged in such a way, i.e. when multiple effluent gutters and multiple recirculation gutters and recirculation tubes are used, a square or rectangular grid pattern is formed, when seen in top view.

An embodiment relates to an aforementioned reactor vessel, wherein the top wall of the recirculation gutter is attached to the underside of the effluent gutter as to achieve minimal flow interference and allow for a relatively simple mounting construction.

An embodiment relates to an aforementioned reactor vessel, wherein at least one recirculation gutter has a width (W) of 400 - 600 mm, or even up to 1000 mm, and/or a height (H) of 300 - 600 mm.

An embodiment relates to an aforementioned reactor vessel, wherein a sludge tube is arranged at a vertical distance from an underside of the recirculation gutter, extending along the effluent gutter axis, wherein a sludge transport tube is fluidly connected to the sludge tube for transporting sludge (the sludge variant that hardly settles) away from the reactor vessel. The vertical distance is preferably so chosen that the sludge removal process does not interfere with the recirculation process. In order to remove sludge granules from the sludge tube, the sludge tube may for instance be flushed with water or air, or may be flushed alternatingly with water and air. An embodiment relates to an aforementioned reactor vessel, wherein the sludge tube is suspended from the effluent gutter, for instance via suspension beams. Preferably, in the direction of the effluent gutter axis, multiple opposite pairs of suspension beams are used to properly support the sludge tube.

An embodiment relates to an aforementioned reactor vessel, wherein the sludge tube is provided with one or more curved inlet pipes extending downwards from a bottom part of the sludge tube, wherein sludge is allowed to enter the curved inlet pipes and subsequently the sludge tube through a respective inlet opening of the curved inlet pipes, wherein the inlet opening is arranged to cause the sludge to enter in a horizontal direction. Therein, the curved inlet pipes are preferably configured to prevent sludge granules from entering the inlet opening. Additionally, the curved inlet pipes are preferably used to maintain an airlock and a compressed air supply can be used to achieve this.

Brief description of the drawings

Embodiments of a reactor vessel according to the invention will by way of non- limiting example be described in detail with reference to the accompanying drawings. In the drawings:

Figure 1 shows a perspective view of an exemplary embodiment of a reactor vessel according to the invention;

Figure 2 shows a cross-sectional view of an exemplary embodiment of an effluent gutter and a recirculation gutter according to the invention;

Figure 3 shows a cross-sectional view of a further exemplary embodiment of an effluent gutter and a recirculation gutter according to the invention.

Detailed description of the invention

Figures 1 and 2 will be discussed in conjunction. Figure 1 shows a reactor vessel 1, i.e. a typical prior art Nereda® reactor design, for treating wastewater 2 by means of aerobic granular sludge technology. The reactor vessel 1 comprises a reactor vessel bottom 3 and a generally circular reactor vessel wall 4 delimiting the reactor vessel bottom 3, although the reactor vessel 1 could having a square or rectangular shape. The reactor vessel 1 is provided with a grid of multiple effluent gutters 5, such as three or five, extending horizontally and in a parallel fashion between opposing sides of the reactor vessel wall 4, each along an effluent gutter axis 6.

As shown in figure 2, an effluent gutter 5 has a horizontally extending bottom wall 7 as well as opposite, vertical side walls 8 extending along the effluent gutter axis 6. At least one of the side walls 8 - but preferably both of the side walls 8 of the effluent gutter 5 - comprises a row of inlet holes 9 extending along the effluent gutter axis 6. As indicated in figures 1 and 2, the grid of effluent gutters 5 is arranged at such a vertical distance D from the reactor vessel bottom 3 that, during use, the horizontally extending row of inlet holes 9 is arranged for discharging relatively clean water from an upper layer 10 of the water 2 contained in the reactor vessel 1 as effluent 11.

As shown in figure 2, according to an exemplary embodiment of the invention, a grid of recirculation gutters 12 is arranged at substantially the same height, for example adjacent to or directly below the bottom wall 7 of the effluent gutter 5, as the grid of effluent gutters 5, such as at a distance of 0 - 1000 mm, more preferably 0 - 500 mm, even more preferably 0 - 200 mm, most preferably around 0 mm. According to the embodiment as shown, the recirculation gutter 12 may have a horizontally extending bottom wall 13 and a parallel top wall 14, and two opposing, vertical side walls 15 extending along the effluent gutter axis 6, although tubular variants, such as tubes having a square, rectangular, triangular, or round cross-section, are also conceivable. At least one of the side walls 15 of the recirculation gutter 12 comprises a row of inlet holes 16 extending along the effluent gutter axis 6 (perpendicular to the plane of the paper) for allowing the relatively clean water from the upper layer 10 of the water body 2 to be recirculated. A recirculation tube 17 is fluidly connected to the recirculation gutter 12 for recirculating the relatively clean water towards the bottom 3 of the reactor vessel 1. The recirculation tubes 17 and the recirculation gutters 12 therein may be comprised by the grid of recirculation gutters.

The effluent gutter 5 as shown in figure 2 is provided with a baffle 18, for instance comprising vertically extending plates, having a height of for example 5-30 cm, such as 10-20 cm, for preventing floating waste from entering the inlet holes 9 of the effluent gutter 5 and/or for preventing wind from entering the inlet holes 9 of the effluent gutter 5. Generally speaking, the effluent gutter 5 will be provided with a top wall 19, such that a tubular effluent gutter 5 is created, for instance having a square, rectangular or round cross-section. The inlet holes 9 may be shaped as so-called V-notches. The inlet holes 16 of the recirculation gutter 12 are arranged at the lowermost position of the side wall 15, adjacent to the bottom wall 13. The inlet holes 16 of the recirculation gutter 12, preferably having a round shape, although other shapes are also conceivable, are sized to allow sludge from leaving the recirculation gutter 12. Preferably, the recirculation tube 17 extends in a horizontal direction. More preferably, the recirculation tube 17 extends in a direction perpendicular to the effluent gutter axis 6. Therein, multiple recirculation tubes 17 may intersect, i.e. fluidly connect to, the recirculation gutter 12 at spaced-apart positions along the recirculation gutter 12 to form the grid pattern. The top wall 14 of the recirculation gutter 12 is preferably attached to the bottom wall 7 of the effluent gutter 5. The recirculation gutter 12 may have a width W of 400 - 600 mm, such as around 450 mm, and/or a height H of 300 - 600 mm, such as around 350 mm.

Figure 3 shows a cross-sectional view of a further exemplary embodiment of an effluent gutter and a recirculation gutter according to the invention, in which like structures as described with regard to figure 2 are shown and referred to with like reference numerals. Additionally, a sludge tube 20 is arranged at a vertical distance, such as 600 - 1200 mm, from the bottom wall 13 of the recirculation gutter 12, extending along the effluent gutter axis 6. A sludge transport tube 22 is fluidly connected to the sludge tube 20 for transporting sludge away from the reactor vessel 1. The sludge tube 20, for instance having a circular cross-section, is suspended from the effluent gutter 5, for instance via suspension beams 23. Preferably, the sludge tube 20 intersects the sludge transport tube 22 in a lower part of the sludge transport tube 22. The sludge tube 20 as shown is provided with one or more curved inlet pipes 21, such as a pair, extending downwards from a bottom part of the sludge tube 20. Sludge is allowed to enter the curved inlet pipes 21 and subsequently the sludge tube 20 through a respective inlet opening of the curved inlet pipes 21. The inlet opening is arranged to cause the sludge to enter in a horizontal direction.

Thus, the invention has been described by reference to the embodiments discussed above. It will be recognized that the embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. In fact, applicant foresees a possible future use of the sludge tube independent of the use of recirculation gutters. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.

Reference numerals

1. Reactor vessel

2. (Waste)water

3. Reactor vessel bottom

4. Reactor vessel wall

5. Effluent gutter

6. Effluent gutter axis

7. Bottom wall of effluent gutter

8. Side wall of effluent gutter

9. Row of inlet holes of effluent gutter

10. Upper layer of water

11. Effluent

12. Recirculation gutter

13. Bottom wall of recirculation gutter

14. Top wall of recirculation gutter

15. Side wall of recirculation gutter

16. Row of inlet holes of recirculation gutter

17. Recirculation tube

18. Baffle

19. Top wall of effluent gutter

20. Sludge tube

21. Curved inlet pipe

22. Sludge transport tube

23. Suspension beam