WO2006111420A1

WO2006111420A1 - Process and device for separating solids and liquids

Info

Publication number: WO2006111420A1
Application number: PCT/EP2006/003743
Authority: WO
Inventors: Antonio Giangrasso; Andreas Skupin
Original assignee: Pfleiderer Water Systems Gmbh
Priority date: 2005-04-22
Filing date: 2006-04-24
Publication date: 2006-10-26
Also published as: DE102005018886A1; EP1877155A1

Abstract

Processes and devices are disclosed for separating solids from liquids, in particular for use in the last water treatment stage in sewage clarification plants. The claimed processes and devices are characterised, in particular, by the use of cartridge filters designed as surface filters and whose surface is bathed in gas bubbles during their operation. The present invention is characterised by the advantages that a large liquid throughput is achieved in a small ground area, and that no movable parts are used, which leads to low equipment outlay and energy consumption.

Description

Apparatus and method for separating solids and liquids

Technical area

The present invention relates to apparatus and methods for separating solids from liquids, especially for use as the final stage of water treatment in sewage treatment plants.

State of the art

In sewage treatment plants, sand filters are often used as the final stage of water treatment. These filters usually consist of a sand-filled concrete basin, through which the water is carried. Sand filters have the disadvantage of relatively slow filtration. Moreover, sand filters have a very high floor space requirement in terms of throughput. Sand filters are described, for example, in Chapter 8.4 of Stieß, "Mechanical Process Engineering 2", Springer Verlag, 1st edition 1994.

An alternative to the above-mentioned sand filters are the plate filters. These filters are characterized by a water basin in which a plurality of plate-shaped filters are attached to a horizontal axis. The plate-shaped filters rotate along the horizontal axis in the water, so as to achieve a falling of the accumulating on the surface of the filter plates filter cake. This measure increases the service life of the filter, ie the period of time until the same by adhering Filter cake is clogged to such an extent that it must be cleaned by establishing a counter flow of water.

However, plate filters have the disadvantage that the rotation requires an increased expenditure on equipment, as well as an increased energy consumption.

The object of the invention is therefore to provide devices and methods for the separation of solids from liquids, which allow to achieve a large liquid flow rate on a small floor area, and which have no moving parts and therefore awarded by a low expenditure on equipment and low energy consumption are.

Summary of the invention

The object underlying the present invention is achieved by the devices of claims 1 and 7 and by the method according to claim 10. Preferred embodiments of the present invention are described in the subclaims.

Description of the figures

FIG. 1a schematically illustrates the structure of a filter unit containing a filter module with three candle filters and a gas supply device.

FIG. 1 b schematically illustrates the filter module shown in FIG. 1 a in plan view.

Figure 2 shows schematically the flow of water treatment in a sewage treatment plant. Detailed description of the invention

In the context of this patent application, the term "candle filter" refers to all filter elements which have at least one porous surface suitable for filtration, which are designed such that an internal volume is separated from the external environment by the candle filter such that both volumes are only through the pores in the area suitable for filtration.

Preferably, the internal volume is separated from the environment only by the area suitable for filtration. Particularly preferred is an elongated shape with a circular cross-section. However, other cross sections such as e.g. oval or square cross sections.

It is also preferred that the area suitable for filtration be substantially vertical. This has the advantage that gas bubbles can smoothly sweep the surface as they rise through the solids-containing liquid. However, other shapes are also suitable, such as, for example, conical filter candles which have a larger diameter in the upper region than in the lower region.

It is further preferred that the candle filter is arranged substantially vertically. This in turn has the advantage that the gas bubbles can rise undisturbed along the surface of the candle filter and not move away from it. Smaller inclinations of less than 15 °, preferably less than 10 °, to the vertical are however acceptable.

The candle filter should be a surface filter. Surface filters are characterized in that the particles to be separated do not penetrate into the interior of the filter, but deposit on its surface. Such surface filters are described, for example, in chapter 7.3.2 by Stieß, "Mechanical Process Engineering 2", Springer Verlag, 1st edition 1994 described.

The material of the candle filter is not specified, provided that the filter is inert in the liquid to be filtered. Preferred for use in sewage treatment plants are plastic materials as described in DE 102 18 073. This concerns in particular the pore size distribution, starting materials and

Method according to paragraphs [0006] to [0012] of DE 102 18 073.

The mean pore size on the outside of the candle filter should preferably be 3 to 5 times or less the average particle size of the particles in the liquid to be filtered. When used in wastewater filtration and in particular in the last stage of sewage treatment plants, preference is given to using filters whose mean pore size on the outside is 1 to 500 μm, more preferably 10 to 250 μm, and particularly preferably 30 to 200 μm.

The size of the candle filter is not fixed. Candle filters of circular cross section with a diameter of 4 to 15 cm, preferably 6 to 10 cm, and a length of 40 to 200 cm, preferably 50 to 150 cm, have proved to be advantageous.

The task of the gas delivery device is to generate a constant flow of gas bubbles which sweeps along the outer surfaces of the candle filters.

In the operating state, the gas supply device is connected to a gas supply line. Preferably, this is a supply of air.

The gas supply device is hollow inside and comprises one or more openings through which the gas into the liquid flows. Preferably, the gas supply device is equipped with a plurality of openings. In particular, it is preferred that each cartridge filter is assigned a separate gas supply device. In the most preferred variant these are separate

Gas supply devices formed along the respective outer surfaces of the candle filter. In the case of candle filters with a round cross-section, this means that the gas supply devices are preferably designed and arranged in a ring shape with a small spacing around the respective outer surfaces of the candle filters (or below the same). These rings are preferably provided at regular intervals with openings. This allows a uniform and effective supply of gas bubbles to the outer surfaces of the candle filter.

The material of the gas supply device is not specified if it is inert to the gas and to the liquid to be filtered. Preferred materials are polyethylene, polypropylene, polyvinyl chloride and stainless steel.

The filter module according to the invention comprises one or more of the candle filters described above, and one or more gas supply devices, as explained above, on.

It is preferred that the filter module according to the invention has at least three, more preferably three to ten cartridge filters.

The relative arrangement of the candle filter to each other is not specified. In order to ensure a favorable lengthening of the gas bubbles on the outer surface of the candle filter with equally good soil or space utilization, it is preferred, however, that the candle filters are arranged parallel to each other vertically. The candle filters can be arranged annularly (in plan view). However, also suitable is an arrangement in rows or at regular intervals in a raster grid. Other arrangements are also possible, but on the one hand on the best possible soil or space utilization should be sought. On the other hand, the design requirements with regard to suitable and cost-effective liquid discharges (as well as gas feeds) should be taken into account.

An attachment of the candle filter is provided via the liquid lines. If necessary, the cartridge filters can be connected to each other in the upper area to prevent vibrations. This is particularly advantageous for long candle filters.

A connection of the candle filter with the liquid line is possible via suitable screw or plug connections. Alternatively, it is possible with filter modules with multiple candle filters and advantageous to connect them with each other via a loop. This loop may in turn be equipped with suitable connections for connection to the liquid drainage.

In principle, it is conceivable to equip each filter module with a single gas supply device, even if the filter module has more than one candle filter. However, it is preferred if each cartridge filter is assigned its own gas supply device. It is likewise preferred if the gas supply device is arranged in the region of the foot of the relevant candle filter, ideally the gas outlet openings are arranged annularly around the outer surface of the foot of the candle filter, so that a uniform supply of gas bubbles to the entire surface of the candle filter can be ensured , However, other arrangements are also possible as far as the function of the escaping gas bubbles (ie the detachment of adhering filter cake by local convection) is ensured to a substantially considerable extent.

The purpose of the gas delivery device is to release a stream of gas bubbles which sweeps along the outer surface of the candle filter (s) so as to cause local convection of the liquid near the filter surface, causing the surface cake to fall or peel off should at least facilitate.

The gas supply device may be attached either to the candle filters, to the liquid lines or to the gas supply lines. This is not specified. An alternative variant is characterized by an attachment of the gas supply devices to the above-mentioned ring lines.

A connection of the gas supply with the gas or the gas lines is possible via all common screw, plug or other types of connections that are used for the connection of gas lines.

The filter unit according to the invention represents the complete and functional unit. This unit comprises at least one filter module. However, two or more filter modules are preferred, which in turn may be clustered. This may be advantageous, for example, since such a modular design with clustered filter modules allows the cleaning or regeneration of individual modules during operation by countercurrent, without the operation of the other filter modules would have to be interrupted.

The number of filter modules present in the filter unit depends on the need for filter capacity. Under the From the point of view of favorable soil or space use, it is advantageous if the filter modules are arranged at regular intervals, which are chosen as narrow as possible, without the individual filter modules interfere with each other during operation and so that maintenance of the individual filter modules is guaranteed ,

The container has the task to record the liquid to be filtered as well as the or the filter modules. Consequently, the container must be inert and dense to the liquid to be filtered. He is of course equipped with a liquid inlet, and an outlet for filter sludge. Furthermore, the liquid and gas line (s) are provided, which in turn can also be guided through suitable openings in the wall of the container.

With regard to the shape and dimensioning of the container, there are no specific requirements, apart from the fact that the internal volume must be sufficiently large to accommodate the desired number of filter modules can. However, it is expedient that the container is dimensioned so that the liquid level can be well above the upper ends of the candle filter. Such a high liquid level has the advantage that a hydrostatic pressure (so-called "water column") is built up, which leads to an increased liquid throughput. Preference is given to a liquid level of 1 m to 5 m above the upper ends of the candle filters. Such a construction allows filtration solely by the hydrostatic pressure, which is built up by the gravity of the liquid to be filtered. The use of pumps and in particular of suction pumps is therefore not required. Therefore, preferred embodiments of the present invention are characterized by the absence of pumps of any kind, and particularly suction pumps. The process according to the invention for the separation of solids is described below.

In principle, the method according to the invention is not restricted to a specific field of application, and it can be used for any liquid containing any solid particles. A preferred field of application is the use for the filtration of water as a final stage in the treatment of water by treatment plants, ie after the secondary treatment (25) in Figure 2. However, other applications are conceivable, the inventive method is particularly advantageous if a filtration at low pressures and with low power consumption is desired.

When used as the last filtration stage in sewage treatment plants, of course, water is the liquid to be filtered and it is separated as solids in particular sewage sludge in low concentration and sand.

However, the method of the invention is not limited to use with this liquid and these solids. Rather, the inventive method for any liquids and any solids can be used. In this case, it is only necessary to select suitable inert materials for the constituents of the filter unit according to the invention, and to adapt the average pore width of the surface filter to the average solid particle size.

As a gas offers due to the low cost and general availability in particular air. However, other gases may also be beneficial under certain conditions. For example, the use of nitrogen gas lends itself to when the liquid to be filtered or the solids contained therein are sensitive to oxygen. In a filter module with 7 candle filters of a length of 0.75 m and a diameter of 72 mm, a liquid flow rate of 1 m ^ / h to 40 m ^ / h can be achieved, preferably a gas amount of 0.5 to 10 m ^ / h is released from the gas supply devices.

The liquid flow rate can be controlled by specifying the filling level of the container, it should be noted that with increasing degree of clogging of the filter modules, the liquid flow rate decreases. When the liquid flow rate falls below a predetermined limit, it is desirable to reverse the flow of liquid briefly so as to blast off the adhered filter cake from the outer surface of the candle filter. For this purpose, a suitable connected to the liquid lines pump is advantageous.

The function and operation of the filter unit according to the invention will be explained below with reference to FIGS. 1a and 1b.

FIG. 1a shows a filter unit according to the invention in a side view. Via the liquid feed (2), the liquid passes into the container (3), in which a filter module (4) is located. The liquid level is indicated by reference numeral (5). In the liquid is the filter module (4) with (in this case) three candle filters (6). The liquid penetrates through the surface filters of the candle filter and is guided in its interior via a ring line (7) and a liquid line (8) from the filter unit. Outside the container (3), the liquid line (8) is connected to a pump (9) which allows the candle filters to be regenerated by backwashing. The pump is followed by a drain (10). Near the bottom of the container, a further opening (11) is provided which can be used as sludge discharge. Not shown, but practically useful, it is inclined to the bottom of the container for mud discharge form, as this significantly facilitates the sludge discharge.

A gas line (12) provides the gas supply device (13) with the required gas.

FIG. 1 b shows the filter unit (1) in a plan view. The inlet (2) can be seen on the left, in the center of the barrel-shaped container (3) a filter module (4) is arranged, the three candle filters (6), a ring line (7 ), and a gas supply device (13). Finally, a liquid line (8) can be seen on the right side.

FIG. 2 schematically illustrates the sequence of the individual purification stages in a conventional sewage treatment plant. The wastewater is transported via a screw lifting installation (20) to a mechanical pretreatment stage, which includes, inter alia, screening (21) of the wastewater to be clarified. After the pre-treatment (22), the biological treatment of the waste water follows, which comprises the step of denitrification (23) as well as the step of nitrification (24). In the subsequent stage of secondary clarification (25) sludge is separated from the clarified water and fed to the wastewater at the beginning of the biological treatment. The clarified water can now be introduced in principle into a river or the sea. Often, however, at this point still a sand filter (not shown in Figure 2) downstream, which is advantageously replaced according to the present invention against one or more of the filter units according to the following claim 7. Reference numerals (28) and (29) represent the recycling of mud and water. Reference numeral (30) refers to a stirring device.

Claims

claims

1. Filter module comprising

one or more candle filters, which are arranged in the case of a plurality of candle filters substantially parallel to each other, wherein the candle filters are designed as surface filters, and wherein the candle filters are closed at the upper end and connectable to liquid lines at the lower end; such as

one or more gas supply devices, each comprising one or more nozzles suitable for the delivery of gas, wherein the devices are arranged in the vicinity of the lower end of the candle filters and can be connected to gas lines.

2. Filter module according to claim 1, wherein the filter module comprises at least three, preferably three to ten candle filters.

3. Filter module according to one or more of claims 1 or

2, wherein the candle filter are fastened in each case at the lower end on a common ring line, wherein the ring line in turn can be connected to a liquid line.

4. Filter module according to one or more of claims 1 to

3, wherein the candle filter have a circular cross-section.

5. Filter module according to one or more of claims 1 to

4, wherein the candle filters are provided with pores whose average pore size at the outer surface is lower than at the inner surface.

6. Filter module according to one or more of claims 1 to 5, wherein each candle filter is associated with a gas supply device so that it is in the region of the lower end of the candle filter.

7. Filter unit comprising

one or more of the filter modules according to one or more of claims 1 to 6, wherein each of the candle filters of each of the filter modules is connected to a liquid line, and wherein each of the gas supply devices of each of the filter modules is connected to a gas line for supplying gas;

one or more containers for holding liquid, each having at least one liquid inlet, wherein in the containers at least one of the filter modules is arranged, and wherein the containers are provided at the bottom or in the vicinity of the bottom with an outlet opening for filter sludge.

8. Filter unit according to claim 7, wherein each filter module is connected to a separate backflushing device.

9. Filter unit according to one or more of claims 7 or 8, wherein in each case a liquid line is connected to each of the filter modules, so that each of the candle filter of a filter module is conductively connected to the same liquid line.

10. A process for separating solids from liquids, comprising

the provision of at least one candle filter in a liquid containing solids, so that the liquid, but not the solids, passes from the outside into the interior of the candle filter, and simultaneously passing gas through one or more gas supply devices into the area around the outer surfaces of the one or more candle filters.

11. The method according to claim 10, wherein the candle filter and gas supply device (s) form parts of a filter unit according to one or more of claims 7 to 9.

12. The method according to one or more of claims 10 or 11, wherein the liquid is water.

13. The method according to claim 12, wherein water, which comes from the secondary clarification stage of sewage treatment plants, is used.

14. The method according to one or more of claims 10 to 13, wherein the retained by the candle filter solids accumulate at the bottom of the container and are removed at periodic intervals.

15. The method according to one or more of claims 10 to 13, wherein the retained by the candle filter solids accumulate at the bottom of the container and are removed continuously.

16. The method according to one or more of claims 10 to 15, wherein the gas is air.