DE29620426U1 - Plant for material separation using membrane filtration - Google Patents

Description

Plant for material separation using membrane filtration

The invention relates to a system for material separation using membrane filtration, in particular for biological wastewater treatment. In principle, however, the system can also be used wherever a solid-liquid separation up to the separation of colloidal particles (> approx. 100 nm) or a liquid-liquid separation in the area of emulsions is to be achieved.

Description

In municipal and industrial wastewater treatment, three main processes or corresponding systems are used to separate filterable substances or sludge from the treated wastewater:
is - gravity dewatering by means of sedimentation (secondary clarifier or thickener),

flotation,

conventional surface and depth filtration (sand, gravel and multi-layer filters).

Secondary clarifiers and thickeners rely on substances that are easy to sediment. Suspended matter or small, difficult-to-sediment particles are often not captured and end up in the plant’s effluent, where they can lead to an increase in effluent parameters (filterable substances, COD, phosphorus, etc.). In addition, a lot of space is required to set up the plants; this is particularly true when expanding existing plants in urban areas.

Flotation generally leads to higher dry matter contents, but is only applicable when there are small differences in density between particles and wastewater.

Conventional filtration is in principle able to separate smaller particles, but if the solids content is too high it can lead to rapid blockage of the units. If the backwash intervals are too short, the economic viability of the filtration is called into question. In addition, it is not possible to retain very fine particles, which, due to their large specific surface area, can contain significant amounts of substances to be removed. Separation is always based on the principle that the filter becomes loaded and must be backwashed when the pressure loss is above what was previously considered to be economical.

Membrane processes are becoming increasingly important, particularly due to the cleaning performance required. However, the pressure loss across the membrane must be taken into account, so that only microfiltration processes can be operated economically with the volume flows that occur in wastewater treatment. The development of the modules has now progressed to the point that only small pressure differences need to be imposed in order to ensure a sufficient permeate flow (corresponds to the purified wastewater flow). This significantly reduces the required energy input. The problem with the use of membrane processes in wastewater areas with a relatively high solids content is the risk of rapid fouling, i.e. membrane blockage and thus premature termination of operation. To counteract this, the membranes are operated in crossflow, so that the growth of deposits can be avoided or at least greatly reduced.

Devices for activated sludge treatment and municipal wastewater treatment in which membrane processes are used are already known. EP 0 510 328 contains a device for activated sludge treatment, consisting of an activated sludge tank in which vertically arranged membrane modules are arranged at defined intervals.

are suspended from each other and over which the water flows upwards. This device enables, for example, the use of membranes in plate packages directly in the aeration tank of a municipal sewage treatment plant. If the tank was designed from the outset for the use of membranes, a secondary settling tank can be dispensed with entirely. The effluent is free of filterable substances as well as bacteria and most viruses. The disadvantage of this device is the time required to clean the membranes, which is necessary to prevent fouling. This results in a plant availability of around 83%.

&iacgr;&ogr; This is done by means of permeate return and the flow to the membrane that is also present during feeding. The permeate pressure is too low to ensure rapid, effective flushing. During feeding, there is no way to free the membranes of deposits. The plate packs are not sufficiently pressure-stable to withstand the high loads during sudden pressurized backflushing. Since the plates are arranged parallel to one another at relatively short distances, the pressure loss and thus the amount of energy required increases significantly with increasing plate height. Energy must be used to generate a vacuum on the suction side of the membranes.

The object of the invention is to improve the known solutions for material separation by means of membrane filtration and in particular to increase the plant availability.

According to the invention, this object is achieved by claim 1. Advantageous elaborations of the inventions are contained in the associated subclaims.

The present invention therefore comprises a system for material separation, by means of membrane filtration. This contains at least one of a variety of

number of individual filter membranes. The filter membranes are connected to one another by at least two plates with devices for draining the permeate at the membrane ends, e.g. by means of casting compounds, whereby the length of the filter membranes exceeds the distance between the plates. Within this frame construction, the filter membranes are combined in a horizontal arrangement to form a unit. Due to this inventive arrangement of the membranes, they are freely movable and are kept in motion by the flow of the medium to be treated. The treatment intervals can be adjusted by

“ the mobility of the membranes can be extended, since particles in the medium cannot settle in the pores of the membranes or are released again.

By retaining substances that cannot penetrate the filter membranes, concentration is increased. Filtration occurs as a result of a transmembrane pressure difference from the outside to the inside and the permeate is drained off via the plates mentioned. The horizontal arrangement of the membranes and the flow of the medium to be treated onto the membranes from below counteracts system fouling and achieves a significant reduction or prevention of deposits on the membranes.

According to a further feature of the invention, the filter membranes are designed as tubular or capillary membranes and have a pressure stability both from the inside to the outside and from the outside to the inside. Such filter membranes can be subjected to high pressures without any problem.

2β. The specific membrane surface of these membranes is more than twice as high as that of plate membranes, for example. The membranes used have a symmetrical structure and are characterized by very low transmembrane pressure differences with high cleaning performance and high permeate flows. The symmetrical structure allows operation in both filter directions with the same membrane. Abrasions on the membrane do not lead to

to destroy the active filter layer, which can significantly extend the service life of the membranes.

If the free mobility of the membranes is not sufficient to protect the pores of the membranes from clogging by particles that are too fine in the medium, a further feature of the invention provides means that impart vibrations (e.g. eccentric, ultrasound) to the frame of the unit, which are then transmitted to the membranes. This measure counteracts system fouling and enables either longer flushing intervals or a higher solids content in the treatment tank. In this case, the supply and discharge pipes are designed as hose lines so that the vibrations are not transmitted to the piping.

The membranes can be backwashed with permeate when the pressure difference increases. To achieve good cleaning performance within a short time, a significantly higher pressure is applied than during filter operation. Backwashing is preferably carried out via the permeate line. For flushing, the drain line is closed using a shut-off valve and the flushing water line is opened. Tubular membranes are sufficiently pressure-stable and do not need to be provided with an additional support layer. The membranes can be cleaned unit by unit, so that continuous filter operation is guaranteed across the remaining units. As already mentioned, the horizontally arranged membranes are flowed onto from below by the medium to be treated. Depending on the operating mode, the flow is either through rising air bubbles (aeration device), which are used to aerate the medium (e.g. in aerobic wastewater treatment) or, in the case of other separation tasks, through appropriate agitators and/or liquid distributors, which cause a flow to the membranes to minimize the formation of a covering layer on the membrane and are arranged below the membrane units.

To ensure easy assembly and disassembly of the units, the units and permeate lines are connected to each other via quick couplings. For the same reasons, this piping is preferably made with pressure-resistant hose lines. The hoses must be designed to withstand both overpressure and underpressure in order to ensure filtration and backwashing via one line.

According to a further feature of the invention, the membranes are arranged from bottom to top to reduce pressure losses so that the distances between the individual filter membranes within the unit

&iacgr;&ogr; from bottom to top.

The required pressure difference can be achieved by applying a negative pressure on the permeate side or by applying positive pressure on the side of the medium to be treated.
The transmembrane pressure difference is generated by applying overpressure on the concentrate or waste water side by pressurizing the container containing the filter membrane unit, whereby in the case of biological treatment either the feed pump is designed as a pressure booster pump (anaerobic) or the gassing with pressure holding valves in the exhaust air line is used to generate the overpressure (aerobic).

A particularly preferred feature of the invention includes that the water column of a high biology is used to generate the transmembrane pressure difference, wherein the membrane unit is either arranged directly in the container biology or is housed in a separate container which is connected to the high biology.

A special embodiment of the invention includes that at least one unit is arranged in a treatment tank for wastewater purification by means of suspensions. The brackets are designed so that the units can be removed for cleaning with little effort. The units are easy to dismantle in order to remove individual membranes.

•I ·· 2201GM*.

to be able to exchange them. The units are arranged in the middle of a treatment tank, whereby the distance between the edge of the tank and the unit must be large enough to develop a pronounced circulation flow. The medium flows upwards in the units and downwards again at the sides. Over the entire length of the tank, enough units are installed directly next to one another so that they are flush with the front sides of the tank. The side walls of the units also border directly on one another and form a continuous wall so that the medium flowing up cannot be pushed out to the side. In wide treatment tanks, it is also possible to arrange several rows of units parallel to one another; the medium to be treated moves downwards between the rows.

The use of this system directly in an aerobic activated sludge tank biology to separate the clear effluent by microfiltration results in the following advantages:

In the case of partial flow treatment in existing sewage treatment plants, the secondary clarifier is hydraulically relieved,

Sewage treatment plant extensions can be carried out in a very space-saving manner due to the saving of new secondary clarifiers, - filterable substances are completely retained; operating fluctuations and associated variations in the settleability of the solids do not occur,

the solids content in the aeration tank can be increased; this results in a higher turnover rate, the tank volume can be kept smaller,

Contaminants adsorbed on filterable substances are no longer discharged via the clear effluent.

As already mentioned, according to a further preferred feature of the invention, it is possible for at least one unit within a container of a container biology capable of being pressurized for biological

2201GJVL

Wastewater treatment is arranged. In this case, the filling level is chosen so high that the overpressure for operating the microfiltration membrane is generated solely by the geodetic height difference between the filling level and the upper edge of the membrane units. The gassing or the agitator must be designed accordingly to ensure the flow. The permeate line must be converted to the extended extraction. In this variant, the membrane units can also be installed in a separate container according to a further feature of the invention, which is connected to the container biology via an inlet and outlet line. The flow speed generated when pumping over serves to flow the membranes. In addition, an agitator can be installed below the units to further increase the flow speed. For inspection, the connecting lines are locked and the membrane unit can be removed after opening the container. This arrangement has the advantage that the unit does not have to be lifted out of the high container. In addition, a relatively complicated routing of the permeate line through the container wall is not necessary.

The invention will be explained in more detail below using an example embodiment. The figure shows

Figures: schematic structure and operating principle of a filter membrane unit,

5 Figure 2: Filtration with negative pressure,

Figure 3: Return operation when working with negative pressure,

Figure 4: Overpressure operation during aerobic treatment,

Figure 5: Overpressure operation in anaerobic treatment,

Figure 6: schematic structure of a high biology, where the membrane

bran unit is housed in a separate container,

Figure 7: schematic structure of a high biology, where the membrane unit is arranged directly in the container biology,

Figure 8: schematic arrangement of the membrane unit in an activated sludge tank for wastewater filtration

Figure 9: schematic representation of the arrangement of the membrane unit in a floc separation plant after precipitation (29) / flocculation (30)

Figure 0: schematic representation of the arrangement of the membrane unit in a system for separating emulsions of all kinds that do not tend to stick to the membranes, e.g. for separating oils (33) from emulsions

Figure 1: schematic representation of the arrangement of the membrane unit in a system for the separation of suspended solids in drinking water production, from groundwater and surface water before drinking water treatment (31)

Figure 2: schematic representation of the arrangement of the membrane unit in a system for reducing the number of germs (34) (disinfection) in the effluent of municipal sewage treatment plants (35).

Municipal wastewater is characterized by relatively low pollutant concentrations:

NH ₄ -N TKN CSB BSB ₅ Phosphate Filterable substances

40 - 60 mg/l 50 - 70 mg/l 400 - 900 mg/l 200 - 400 mg/l 8th - 15 mg/l 200 - 500 mg/l

&iacgr;&ogr;

Fig. 2 shows the system according to the invention.

The reactor (1), in which the activated sludge is located, is fed with the waste water to be cleaned by means of a feed pump (2) or by gravity (3). The reactor (1) can be designed as an open or closed container or as a concrete basin. It can be installed above ground or sunk into the ground. In the reactor (1), the membrane unit (3) already described in Fig. 1 is installed by means of suitable suspensions above the aeration devices (4) in such a way that an airlift flow is induced through the horizontally arranged membranes (5) of a membrane unit (3).

γ is (see also Fig. 1). The formation of a covering layer is minimized by the airlift flow and the air bubbles passing through the membranes (5). If necessary, the flow over the membranes can be increased by stirring elements (6) or a circulation pump (7) with a liquid distributor (8). The membrane units (3) are arranged in a row, i.e. with the front sides of the

The permeate-removing plates (9) are installed one behind the other above the aeration elements (4), so that a loop flow (11) is formed between the permeate-removing plates (9) and the reactor walls (10). The transmembrane pressure difference required to separate the purified water from the activated sludge is generated by a negative pressure on the permeate side using a vacuum pump (12). The purified water leaves the reactor (1) via the permeate line (13). Fig. 3 shows a detailed drawing of the permeate discharge. Driven by the negative pressure generated inside the membranes (5) using a vacuum pump, the purified water flows from the outside through the membrane-active layer into the interior of the membrane tubes or capillaries (5) and is discharged via the end plates (9) of the membrane unit (3) and the permeate line (13) through the open valve (14). The valve (16) is closed during the filtration phase. Membranes with pore sizes of 0.1 - 0.5 pm are used so that the activated sludge (bacteria size approx. 1 pm) is retained and remains in the reactor. This safe retention of the activated sludge means that biomass concentrations of 20 - 40 g/l can be set in the reactor, which can be increased by

Factor 5-15 higher than in conventional activated sludge plants with secondary clarification. As described above, this results in a corresponding increase in the space-time yield or corresponding volume savings, furthermore, germs and viruses are also retained, which means that the purified water can be discharged into bathing water without further disinfection.

The vacuum pump (12) that removes the permeate generates a negative pressure of 0.3 - 0.5 bar depending on the operating state of the membranes and the required discharge volumes. The particles that are retained during filtration

The thickness of the covering layer forming on the membranes (5) is minimized by the flow described above, but creates a filter resistance corresponding to its thickness and consistency. To remove the covering layer, membrane backwashing is initiated periodically (see Fig. 4). To do this, the vacuum pump (12) is switched off and the permeate valve (14) is closed. The backwash valve (16) is then opened and the backwash pump (17) is used to force filtrate through the membranes for a few seconds against the filter direction. The resulting puncture rinses the membrane surface clean. For backwashing, overpressures of 1-3 bar are set as required. The backwash frequency of the membrane elements (3) depends on the respective application and mode of operation, whereby each individual membrane element (3) can be backwashed separately. The membrane elements (3) can be removed individually for inspections and for intensive cleaning.
The air required for aerobic biological decomposition processes is added to the reactor via aeration devices (4). The exhaust air leaves the reactor via the exhaust air nozzle (18).

The excess sludge produced during biological wastewater treatment is drained off via a nozzle (19) by opening the sludge drain valve (20) depending on the desired biomass concentration in the reactor.

In the reactor described in Fig. 2, the wastewater constituents COD and BOD ₅ are biologically oxidized. The suspended matter (filterable substances) is completely retained. About 40% of the phosphate is eliminated biologically, i.e. by incorporation into the resulting biomass. Increased biological phosphorus elimination can be achieved by installing an anaerobic stage (not shown). With additional simultaneous chemical precipitation, the required phosphate discharge limits can be safely complied with. The ammonium is oxidized to nitrate with high space-time yields. For the biological denitrification of the nitrate, an anoxic bioreactor (not shown) based on the principle of upstream denitrification is located upstream of the reactor described above (Fig. 2). The discharge values that can be achieved with the patented system are:

NH ₄ -N NO ₃ -N COD BOD ₅ Phosphate Suspense

< 1 mg/l 5 mg/l

45 mg/l 10 mg/l

< 1 mg/l 0 mg/l

Figures 5, 6, 7 and 8 show further embodiments of the device according to the patent.

Fig. 5 shows a bio-reactor (1) in which the membrane elements (3) are installed above the aeration elements (4). In this application, the differential water column (19) is used to generate the transmembrane pressure difference required for filtration. A vacuum pump is not required here. The overpressure effective for filtration results directly from the difference in height between the water level of the bioreactor and the permeate discharge pipe.

(13) (e.g. 10m &xgr; 1bar). Fig. 6 shows a variant of the application from Fig. 5

in which the membrane elements (3) are housed in a separate container (21) that is connected to the high biology via a circulation line (22) with a circulation pump (7). The flow to the membranes (5) of the membrane elements (3) is realized with the circulation flow through a liquid distribution system (8), possibly supported by stirring elements (6). The advantage of this variant is the better accessibility of the membrane units (3) for inspection and intensive cleaning of the membranes. For this purpose, the separate container (21) is separated from the high biology (1) by the valves (23) and (24). After removing a cover, the membrane elements can be removed (not shown). The operation and function otherwise corresponds to the above statements.

Fig. 7 shows the application of the patented device in existing aeration plants. The membrane unit (3) is arranged in an existing aeration tank above the aeration elements (4) in a removable manner using suitable suspensions (25), whereby the distance between the tank edge (28) and the permeate-discharging end plate (9) is large enough to form a loop flow (11). This application enables a relief of overloaded aeration and secondary clarification tanks. By removing purified water from the aeration tanks using membrane units (3), the hydraulic load on the secondary clarification tank is significantly reduced. By safely retaining the biomass, the biomass concentration in the aeration tank can be increased, thereby achieving a significant increase in the performance of the aeration plant.

5 Fig. 8 shows a variant of the application from Fig. 2 in which the required transmembrane pressure difference is not generated by a vacuum pump, but by applying overpressure on the concentrate side. The overpressure is generated during aerobic operation of the system by gassing with pressure-maintaining valves (26) in the exhaust air line (27).

The applications of the patented plant for aerobic biological wastewater treatment listed so far can also be used for anaerobic wastewater treatment.

2203 SM

water purification by using agitators and/or circulation pumps with liquid distributors to direct the flow of liquid to the membranes instead of the aeration devices. Another possibility is the recirculation of digester gas and introduction via gas distributors below the membrane units (3) (not shown).

Figures 9,10,11,12 show non-biological applications of the patented device for different material separation tasks.

Claims (12)

Protection claims 1. Plant for material separation by means of membrane filtration, which contains at least one unit comprising a plurality of individual filter membranes, characterized in that the filter membranes are connected to one another by at least two plates at the membrane ends, which have devices for discharging the permeate, the length of the filter membranes exceeding the &iacgr;&ogr; distance between the plates and the filter membranes are combined in a horizontal arrangement within this frame construction to form a unit. 2. Plant according to claim 1, characterized in that the filter membranes are designed as tubular or capillary membranes and have pressure stability in every possible filter direction. 3. Installation according to one of the above claims, characterized in that Means are provided which impart vibrations to the frame of the unit which are transmitted to the membranes. 4. Installation according to one of the above claims, characterized in that at least one closure valve is provided which enables backwashing of the filter membranes via the permeate line. 5. Plant according to at least one of the above claims, characterized indicates that the distances between the individual filter membranes within the unit decrease from bottom to top. 6. System according to at least one of the above claims, characterized in that at least one unit is removably arranged in a treatment tank for waste water purification by means of suspensions, whereby the distance between the edge of the tank and the unit is large enough to develop a circulating flow. 7. System according to at least one of the above claims, characterized in that &iacgr;&ogr; at least one unit is arranged within a pressurizable container of a container biology for biological wastewater treatment. 8. Plant according to claim 7, characterized in that In anaerobic operation of the system, the feed pump is designed as a pressure booster pump. 9. Plant according to claim 7, characterized in that When the system is operated aerobic, gassing with a pressure-maintaining valve in the exhaust air line is used to generate overpressure. 10. Plant according to claim 7, characterized in that the water column of a high biologic in which at least one unit is arranged causes the overpressure. 11. Plant according to claim 10 ₁ , characterized in that the unit is arranged in a separate container that is connected to the water column of a high biology. 12. Installation according to at least one of the above claims, characterized in that agitators and/or gassing devices and/or liquid distributors are arranged below the units.