EP2874956A1

EP2874956A1 - Anaerobic waste water treatment having sludge degassing and sludge feedback, and treatment plant

Info

Publication number: EP2874956A1
Application number: EP13734439.6A
Authority: EP
Inventors: Axel Gommel; Ronald Mulder
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2012-07-19
Filing date: 2013-07-09
Publication date: 2015-05-27
Also published as: DE102012212675A1; CN104470859A; WO2014012817A1

Abstract

The invention relates to a method and an associated plant for biological waste water cleaning by means of biological sludge (2) having anaerobic micro-organisms, wherein the biological sludge (2) is situated in a reactor tank (3), the waste water (1) is fed under the biological sludge (2), flows through the biological sludge (2) from bottom to top and is discharged above the biological sludge (2). A reduction in degradation performance is counteracted by degassing biological sludge (2) that is discharged together with the waste water (1) from the reactor tank (3) and at least partially feeding said biological sludge back into the reactor tank (3).

Description

ANAEROBIC WASTEWATER TREATMENT WITH SLIMMING GAS AND

MUD RECYCLING AND TREATMENT PLANT

The invention relates to a method for biological wastewater treatment by means of anaerobic microorganisms having biosludge, wherein the biosludge is located in a reactor vessel, the waste water is supplied below the biosludge, the biosludge flows through from bottom to top and is discharged above the biosludge. The invention also relates to plants for biological, anaerobic wastewater treatment comprising a reactor vessel containing anaerobic microorganisms containing biosludge and at least one inlet for the wastewater to be cleaned in the lower part and at least one overflow for discharging the wastewater and at least one separator for separation in the upper part of the biogas produced in the wastewater treatment of the purified wastewater, in particular for carrying out the method.

For wastewater treatment, a variety of mechanical, chemical and biological processes and corresponding reactors are known. In biological wastewater treatment, the wastewater to be treated with aerobic or anaerobic microorganisms is contacted, which contains the organic impurities contained in the wastewater in the case of aerobic microorganisms predominantly to carbon dioxide, biomass and water and in the case of anaerobic microorganisms mainly to carbon dioxide and methane and only reduce a small part to biomass.

In this case, the biological wastewater treatment methods are increasingly carried out recently with anaerobic microorganisms, because in the anaerobic wastewater treatment not with high energy consumption oxygen in the bioreactor must be introduced when cleaning energy-rich biogas is generated, which can subsequently be used to generate energy, and significantly lower amounts of surplus sludge are generated. Depending on the type and form of biomass used, the reactors for anaerobic wastewater treatment are divided into contact sludge reactors, UASB reactors, EGSB reactors, fixed bed reactors and fluidized bed reactors.

While the microorganisms in fixed bed reactors to stationary support materials and the microorganisms in fluidized bed reactors adhere to freely movable, small carrier material, the microorganisms are used in the UASB and EGSB reactors in the form of so-called pellets. Unlike UASB (upflow anaerobic sludge blanket) reactors, expanded granular sludge bed (EGSB) reactors are higher and have a much smaller footprint at the same volume.

In the case of the UASB and EGSB reactors, the wastewater or a mixture of wastewater to be purified and already purified wastewater from the outlet of the anaerobic reactor is fed to the reactor via an inlet in the lower reactor region and passed through a sludge bed containing microorganism pellets located above the feed.

When decomposing the organic compounds from the wastewater, the microorganisms form in particular methane and carbon dioxide-containing gas (which is also referred to as biogas), which partially accumulates in the form of small bubbles on the microorganism pellets and partly rises in the form of free gas bubbles in the reactor upwards. Due to the accumulated gas bubbles, the specific gravity of the pellets decreases, which is why the pellets in the reactor go up climb. In order to separate the biogas formed and the rising pellets from the water, separators are usually arranged in the middle and / or upper part of the reactor, under the ridge of which biogas accumulates, which forms a gas cushion, including a flotation layer of microorganism pellets and wastewater is located. Purified water freed of gas and microorganism pellets rises in the reactor and is withdrawn via overflows at the top of the reactor. Such processes and corresponding reactors are described, for example, in EP 0 170 332 A and in EP 1 071 636 B.

In high load reactors for anaerobic wastewater treatment usually two three-phase separators are used. These consist of stacked Gassammeihauben offset among which rising biogas bubbles and ascending granulated biosludge (pellets) collects. The gas is removed as already mentioned from the hoods. The granulated biomass either gives off its adhering gas and then sinks again to the bottom of the reactor or is passed as a gas / water / pellet mixture via a pipe system in a gas separation device on the reactor head. From there, the biosludge gets back into the process.

However, it has been found that the mass of active biosludge can decrease relatively strongly, which has a correspondingly negative effect on the degradation capacity of the reactor. The object of the invention is therefore to counteract the reduction of the degradation efficiency of the reactor as efficiently as possible.

According to the invention, the object was achieved with regard to the method in that discharged together with the wastewater from the reactor vessel Bioschlamnn degassed and at least partially returned to the reactor vessel.

It was recognized that, despite the separators in the reactor vessel, biosludge with the treated effluent could escape, resulting in a corresponding reduction in the amount of biosludge and adversely affecting the performance of the reactor.

This is especially the case when the biosludge contains too much gas and therefore floats in the reactor.

Accordingly, the biosludge discharged with the waste water must be separated and degassed before it can be returned to the reactor vessel. The degassing of the biosludge can take place before or during the separation of the same.

It has proven to be advantageous if the discharged together with the wastewater biosludge is exposed to the shearing forces for degassing.

The shearing forces rupture layers which hinder the release of gas or even partially peeled off the biosludge.

However, the degassing of the biosludge can also be promoted if the biosludge discharged together with the wastewater is subjected to centrifugal forces for degassing. Shearing forces can also be generated by the centrifugal forces.

In any case, the shear or centrifugal forces should only be so great that, although the outer layers of the biosludge (pellets) are affected, but the pellets are not destroyed.

Gas obstruction is often due to gas bubbles within the pellets or under a skin or layer that forms around the pellets. These layers or skins can be formed by polymers contained in the wastewater or by the bacteria themselves.

The so degassed pellets can easily with components detached therefrom on suitable and well-known facilities, such as sieves, or the like. retained and returned, for example via a low-shear pump back into the reactor vessel.

The degassing and separation of the biosludge can be done by means of a hydrocyclone. For this purpose, the wastewater discharged from the reactor vessel is passed into the hydrocyclone and any resulting heavy particles are at least partially returned to the reactor vessel.

Hydrocyclones are well suited to concentrate heavy particles (biosludge) and light parts (wastewater) by centrifugal forces and to separate them separately via the outlet or the separator. To form the rotational flow within the hydrocyclone, the hydrostatic pressure at the outlet of the reactor vessel can be utilized.

This type of degassing and separation also has the advantage that flocculent biosludge, which is not normally desired in the reactor, is passed as a lightweight part with the wastewater.

To form sufficient centrifugal forces, the inner diameter of the hydrocyclone should be greater than 20 cm, preferably greater than 25 cm.

Alternatively, the separation of the biosludge can also be carried out with the aid of a sieve, through which the effluent discharged from the reactor vessel is passed. The shear forces created by the retention of the biosludge on the sieve can sometimes be sufficient for degassing. In this case, the resulting rejects can be at least partially recycled to the reactor vessel without further treatment. In most cases, however, larger forces are required for the degassing of the biosludge, which is why the screen should be part of a sorter, in particular a pressure sorter. In this case, a rotational flow is generated in the sorter on the inlet side of the screen via a rotor, which leads to the formation of appropriate centrifugal forces.

As a result, the wastewater passes through the screen, while the biosludge degassed due to the centrifugal and shear forces can be retained on the screen and returned to the reactor vessel. As a further alternative, the effluent from the reactor vessel wastewater for degassing the entrained biosludge can be passed through a centrifugal pump. Again, the rotational flow in the centrifugal pump leads to the formation of sufficiently high centrifugal forces without destroying the biosludge. The so degassed biosludge can then be separated in a subsequent treatment unit of the wastewater and at least partially recycled to the reactor vessel.

Advantageously, the following treatment unit for separating the biosludge can be formed by the sedimentation in which the biosludge settles. The invention will be explained in more detail below with reference to two exemplary embodiments.

In the attached drawing shows:

FIG. 1 shows a schematic cross section through a reactor vessel 3;

Figure 2: a partial plant scheme for wastewater treatment and

Figure 3: another system sub-scheme.

The bioreactor shown in Figure 1 comprises a reactor vessel 3, which is cylindrical in its middle and upper part and tapers in its lower part downwardly conically. In the lower part of the reactor, ie in the hopper, the inlet distribution system 4 for supplying the waste water 1 to be cleaned is housed.

In the middle and upper reactor vessel 3 there are two separators 6. These separators 6 can each have multiple gas hoods or even multiple layers of gas hoods.

Above the upper separator 6 are processes each in the form of an overflow 5, via which the purified wastewater 1 is withdrawn from the reactor vessel 3.

On the reactor vessel 3, a gas separation device 14 is arranged, which is connected to the two separators 6 via the lines 13. In addition, a sink line 12 leads from the bottom of the gas separation device 14 into the lower part of the reactor vessel 3.

Furthermore, located in the lower part of the reactor vessel 3, namely in the lower part of the funnel, a sediment discharge 15, 15 solids or a suspension of solid and liquid from the reactor vessel 3 can be withdrawn through the sediment discharge and via the inlet 4 liquid to Rinsing the lower reactor vessel part can be introduced.

The feed distribution system 4 is formed by a plurality of inlets 4, which are arranged uniformly at the bottom of the reactor vessel 3, here the inner wall of the funnel and lead to the wastewater to be purified 1 in the reactor vessel 3.

A high number of controllable feed lines 4 makes it possible to adjust the distribution of the supplied waste water 1 at the bottom of the reactor vessel 3.

During operation of the reactor is to be cleaned via the feeds 4 1 in the Introduced reactor vessel 3, wherein there is an intimate mixing between the supplied wastewater 1 and the medium in the reactor, which consists of already partially purified wastewater 1, biosludge 2 (microorganism pellets) and small gas bubbles.

The introduced wastewater 1 flows slowly from the feeds 4 in the reactor vessel 3 upwards until it enters the microorganism-containing biosludge 2. The microorganisms contained in the biosludge 2 decompose the organic impurities contained in the waste water 1 mainly to methane and carbon dioxide gas. The generated gases produce gas bubbles, the larger of which detach from the biosludge 2 and bubble in the form of gas bubbles through the medium, whereas small gas bubbles remain attached to the biosludge 2 (pellets). Those pellets to which small gas bubbles adhere, and which therefore have a lower specific gravity than the other pellets and the water, rise in the reactor vessel 3 until they reach the lower separator 6.

The free gas bubbles catch in the gas hoods of the separator 6 and form a gas cushion.

The gas collected in the gas hoods as well as pellets and water from the flotation layer are optionally mixed with each other via a mixing chamber, not shown, and passed via line 13 into the gas separation device 14.

The water, the rising pellets and the gas bubbles, which have not already been separated in the lower separator 6, rise further in the reactor vessel 3 up to the upper separator 6.

Due to the decrease in the hydrostatic pressure between the lower and the upper separator 6 further small gas bubbles dissolve from the upper Separators emit microorganism pellets so that the specific gravity of the pellets increases again and the pellets sink downwards.

The remaining gas bubbles are collected in the upper separator 6 and fed via line 13 into the gas separation device 14.

The now purified wastewater 1 rises from the upper separator 6 further up until it is withdrawn through the overflows 5 from the reactor vessel 3 and discharged through a drain line.

In the gas separation device 14, the gas separates from the remaining water and the microorganism pellets, wherein the suspension of pellets and the waste water 1 is recirculated via the sink line 12 into the reactor vessel 3. In this case, the outlet opening of the sinking line 12 opens into the lower part of the reactor vessel 3, where the recycled suspension of pellets and waste water 1 with the, the reactor via the feeds 4 supplied wastewater 1 is mixed, after which the cycle begins again.

Via the sediment discharge 15, the calcareous sediment collecting at the top of the reactor vessel 3 can be withdrawn continuously or batchwise from the reactor as required.

Despite the separator 6 and the internal recirculation via the gas separation device 14, it happens that with the treated wastewater 1 and biosludge 2 is discharged from the reactor vessel 3.

As already stated, this is due to the gas which adheres in or to the biosludge 2, which can reduce the specific gravity of the biosludge 2 to below 1 kg / l and thus ensures the floating of the biosludge 2 in the reactor vessel 3. In order to counteract the associated reduction of biosludge 2 in the reactor vessel 3, therefore, there is a separation, degassing and jerking of discharged with the waste water 1 from the reactor vessel 3 biosludge 2. In the system of Figure 2, the waste water 1 of the reactor vessel 3 is in this a hydrocyclone 7 or a pressure sorter 8 out. In both devices, the waste water 1 rotates, resulting in the formation of centrifugal and shear forces. These forces cause the rupture or removal of layers of biosludge 2, which hinder the gas delivery.

While in the hydrocyclone 7 it comes by the centrifugal forces to a division into heavy (biosludge 2) and light parts (wastewater 1), the separation of these takes place at the sorter 8 by means of sieve.

The use of a hydrocyclone 7 offers the advantage that the admission pressure of the wastewater 1 can be used for generating the flow in the hydrocyclone 7. In order to generate the required forces, the inner diameter of the hydrocyclone 7 should be greater than 20 cm.

The sorter 8, the centrifugal and shear forces are generated by a rotor, which is present on the inlet side of the most cylindrical screen. While the wastewater 1 passes through the sieve together with flocculent biosludge 2, the active biosludge 2 is retained on the sieve and can be cleared away from it by the rotor.

In both cases, the degassing takes place simultaneously with the separation of the biosludge 2 from the effluent. 1 While the wastewater 1 can be further treated, the biosludge 2 is optionally returned via a low-shear pump 1 1 in the reactor vessel 3.

In contrast, in FIG. 3, the waste water 1 is conducted out of the reactor vessel 3 through a centrifugal pump 9. Again, centrifugal forces are generated by rotation, which facilitate or allow the degassing of the biosludge 2. However, the separation of the Bioschlannnns 2 takes place only in a following treatment unit 10 here in the form of sedimentation.

In this treatment unit 10, the degassed and thus relatively heavy biosludge 2 settles on the ground and can be returned from there by means of low-shear pump 1 1 to the reactor vessel 3.

Claims

claims

1 . Method for biological wastewater treatment by means of anaerobic microorganisms having biosludge (2), wherein the biosludge (2) is in a reactor vessel (3), the waste water (1) is supplied below the biosludge (2), the biosludge (2) from below flows through above and above the biosludge (2) is discharged, characterized in that together with the waste water (1) from the reactor vessel (3) discharged biosludge (2) is degassed and at least partially returned to the reactor vessel (3).

2. The method according to claim 1, characterized in that the together with the waste water (1) discharged biosludge (2) is exposed to the shearing forces for degassing.

3. The method according to claim 1 or 2, characterized in that the

together with the waste water (1) discharged biosludge (2) for degassing centrifugal forces is exposed.

4. plant for biological, anaerobic wastewater treatment comprising a

Reactor container (3) containing anaerobic microorganisms biosludge (2) and in the lower part at least one inlet (4) for the wastewater to be purified (1) and in the upper part at least one overflow (5) for discharging the waste water (1) and at least one separator (6) for separating at least the biogas produced during the wastewater treatment from the treated wastewater (1), in particular for carrying out the method according to one of the preceding claims, characterized in that the effluent (1) discharged from the reactor vessel (3) ) into a hydrocyclone (7) directed and thereby incurred heavy parts are at least partially returned to the reactor vessel (3).

5. Plant according to claim 4, characterized in that the inner diameter of the hydrocyclone (7) is greater than 20 cm, preferably greater than 25 cm.

6. plant for biological, anaerobic wastewater treatment comprising a

Reactor container (3) containing anaerobic microorganisms biosludge (2) and in the lower part at least one inlet (4) for the wastewater to be purified (1) and in the upper part at least one overflow (5) for discharging the waste water (1) and at least one separator (6) for separating at least the biogas produced during the wastewater treatment of the purified wastewater (1), in particular for carrying out the method according to one of claims 1 to 3, characterized in that the effluent discharged from the reactor vessel (3) (1) passed through a sieve and resulting rejects are at least partially returned to the reactor vessel (3).

7. Plant according to claim 6, characterized in that the sieve is part of a

Sorter (8), in which on the inlet side of the screen via a rotor, a rotational flow is generated.

8. Plant for biological, anaerobic wastewater treatment comprising a

Reactor container (3) containing anaerobic microorganisms biosludge (2) and in the lower part at least one inlet (4) for the wastewater to be purified (1) and in the upper part at least one overflow (5) for discharging the waste water (1) and at least one separator (6) for separating at least the biogas produced during the wastewater treatment of the purified wastewater (1), in particular for carrying out the method according to one of claims 1 to 3, characterized in that the from the

Reactor vessel (3) discharged wastewater (1) for degassing the entrained biosludge (2) by a centrifugal pump (9) and the degassed biosludge (2) in a subsequent treatment unit (10) of the wastewater (1) and at least partially deposited in the reactor vessel (3) is returned.

9. Plant according to claim 8, characterized in that the following

Treatment unit (10) for separating the biosludge (2) is formed by the sedimentation.