DE102019109328A1 - Process for treating wastewater in a sewage treatment plant, as well as sewage treatment plant - Google Patents

Abstract

The invention relates to a method for treating wastewater (A) in a sewage treatment plant (1) with a clarifier (1a), the wastewater (A) in the clarifier (1a) being treated biologically by nitrification of microorganisms (Msess, Msus), for this purpose, there is at least one carrier body (2) in the clarifier (1a), on which sessile biomass (Bsess) from sessile microorganisms (Msess) grows, the sessile microorganisms (Msess) the wastewater (A) with a sessile nitrification rate ( Nsess) biologically treat, wherein there is suspended biomass (Bsus) from suspended microorganisms (Msus) in the wastewater (A), wherein the suspended microorganisms (Msus) treat the wastewater (A) with a suspended nitrification rate (Nsus), and where a Part of the sessile biomass (Bsess) is sheared off in a controlled manner from the at least one support body (2) in order to reduce a layer thickness (D) of the sessile biomass (Bsess). According to the invention, it is provided that s the shearing of the sessile biomass (Bsess) from the at least one support body (2) as a function of the parameters (Xabl, Xzul, tTS, TS, SVI, Nsus, D) pertaining to the suspended nitrification rate (Nsus) takes place in such a way that the suspended Increased nitrification rate (Nsus) after shearing.

Description

The invention relates to a method for treating waste water in a sewage treatment plant according to the preamble of claim 1, as well as a sewage treatment plant.

Biologically cleaning wastewater treatment plants that work according to the IFAS process conventionally have a clarifier in which the wastewater is carried as activated sludge past carrier bodies, for example fixed beds (IFAS system). The carrier bodies have a large surface on which microorganisms from the activated sludge settle. The suspended and the sessile biomass feed on pollutants or nutrients in the wastewater and convert them, e.g. in the breakdown of ammonium through nitrification. The conversion processes of carbon degradation and nitrification require oxygen, which is introduced into the wastewater in the form of air bubbles via ventilation systems.

Because biomass adheres and grows on the carrier bodies, the sessile biomass can remain in the system longer than the suspended biomass. This gives slowly growing microorganisms better growth conditions than in the suspension. Nitrifying species usually grow more slowly than microorganisms that break down carbon. Hence the growth of nitrifying species in the sessile biomass is favored. This allows a sessile nitrification rate, i. the breakdown of pollutants by the sessile microorganisms, up to a certain layer thickness of the sessile biomass. Above a certain layer thickness, the lower layers of the sessile biomass cannot contribute to the nitrification, or only to a small extent, because they are less well supplied and no longer offer a target for the pollutants to attack. As a result, a constant increase or regrowth of the sessile biomass is no longer ensured. Therefore, in order to maintain a meaningful sessile sludge age, the sessile biomass has to be sheared off in certain periods of time.

Such shearing processes are exemplified in EP 0 201 924 A2 , WO 03/076350 A1 , EP 1 088 793 A1 and DE 22 35 470 A1 described, whereby the shearing takes place via mechanical shearing devices. A targeted further use of the sheared sessile biomass in the treatment process is not disclosed, so that shearing is only intended to influence the sessile nitrification rate, ie the waste water treatment by the sessile biomass located on the carrier body.

In the activated sludge process described above, not only the sessile microorganisms but also the suspended microorganisms contribute to the wastewater treatment. These are suspended or floating in the suspension and also treat the wastewater by nitrification, so that the overall nitrification rate of the sewage treatment plant is determined by the sessile nitrification rate described above and by a suspended nitrification rate. A specific adaptation or increase of the suspended nitrification rate to optimize the overall process is not known from the prior art. Rather, in the conventional activated sludge process with support bodies or IFAS systems, the aim is merely to increase the overall nitrification rate by optimally adding sessile biomass to the support bodies.

Starting from this, the object of the invention is to provide a method for treating wastewater in a sewage treatment plant, with which a high overall nitrification rate can be achieved in a simple manner by specifically increasing the nitrification performance in the suspension. The object of the invention is also to provide a sewage treatment plant for carrying out the method.

This object is achieved by a method according to claim 1 and a sewage treatment plant according to the further independent claim. The subclaims indicate preferred developments.

Accordingly, it is provided in a method according to the preamble of claim 1 that the shearing or the detachment or removal of sessile biomass from the at least one support body, for example in the form of a suspended sludge flake, which thus merges into the suspension of the wastewater, depending on the parameters relating to or influencing the suspended nitrification rate are carried out in such a way that the suspended nitrification rate increases after shearing.

The overall nitrification rate is thus advantageously increased in that the suspended nitrification rate is increased in a targeted manner. This takes place in that sludge flakes with a high biomass age and high density of nitrifying microorganisms are detached from the sessile biomass on the carrier body and transferred into the suspension in a targeted manner. As a result, the originally sessile biomass, which has now passed into the suspension as suspended biomass, can act on the pollutants with a larger area of attack, since the sheared sludge flake now floats completely or with a three-dimensional interface in the suspension. In contrast, with sessile biomass, only a flat or two-dimensional interface on the support body. This means that the suspended nitrification rate can already be greatly increased.

Thus, in the treatment process according to the invention, the nature or the activity of the sheared sludge flakes are specifically controlled or adjusted in order to significantly influence the suspended nitrification rate that follows. This plays a subordinate role in the conventional activated sludge process with an IFAS system, since the shearing process usually only takes place to optimize the sessile nitrification rate, i.e. Subsequent processes in the suspension are not considered.

In contrast, the biological activity of the sessile biomass in the method according to the invention is given less importance than the biological activity of the sheared biomass or the suspended biomass. This can advantageously take place because the biological activity or the suspended nitrification rate of the suspended biomass in the process according to the invention has a very much higher proportion of the total nitrification rate than the sessile nitrification rate. The shearing process thus takes place largely on the basis of the suspended nitrification rate as well as an optimized growth of the sessile biomass on the carrier body, so that a transition into the suspension and a high biomass age of the sessile biomass can be permanently ensured. How the sessile nitrification rate develops plays a subordinate role, since it only makes up a very small proportion of the total nitrification rate.

The only side effect that can be achieved is that the shearing off exposes lower layers of the sessile biomass and these can also contribute to the treatment process. According to one embodiment, the sessile nitrification rate can also be used as an additional parameter in order to control the shearing.

Advantageously, the sheared sludge flakes are comparatively rich in nitrifying organisms and have a comparatively high density compared to the suspended biomass, which also floats or floats in the suspension in the form of suspended sludge flakes. As a result, it can be achieved that this sludge or the active suspended biomass can be concentrated better in the process than in conventional processes because of their good settling behavior, since this settles very quickly in the secondary clarification. This also allows the sludge age of the suspension and thus the suspended nitrification rate to be increased in a targeted and permanent manner. This means that it is also possible to react more quickly to peak loads, as the amount of active biomass in the process can be increased for a short time. In this way an optimum between the achievable sludge age and the required shearing can be achieved.

The shearing of the sessile biomass from the carrier bodies can preferably be controlled in a targeted manner by setting a certain intensity of air bubbles blown into the waste water, the air bubbles being provided by a ventilation system that supplies the microorganisms with oxygen. This can, for example, be a ventilation hose with holes through which air or oxygen can be pumped, which then passes through the holes into the waste water in the form of air bubbles. Thus, a device for shearing off the sessile biomass is advantageously used, which is already available and easy to activate and control. This means that further adjustments to the sewage treatment plant can be omitted.

It is therefore only necessary to ensure that the intensity of the air bubbles is adjusted at the appropriate point in time in such a way that the sessile biomass can detach and pass into the suspension as sheared sludge flakes in order to greatly increase the suspended nitrification rate therein as suspended biomass as described. This can be achieved, for example, by setting an intensity of the air bubbles that is at least in phases greater than the intensity that is usually set for supplying the microorganisms with oxygen via this ventilation system.

This can be done with a short pulse or over a longer period of time, the intensity preferably being set in a control loop as a function of the suspended nitrification rate and / or an inflow concentration of pollutants in the wastewater supplied. This enables a targeted response to the circumstances in the sewage treatment plant at the relevant point in time.

Alternatively or in addition, it can be provided that the shearing is achieved by a mechanical shearing device that mechanically detaches the sessile biomass from the at least one support body.

It is also preferably provided that the shearing of the sessile biomass from the at least one support body takes place at a time of shearing off over a shearing period, the time of shearing off and / or the time of shearing off depending on a layer thickness of the sessile biomass on the at least one support body and / or a TS- Content in the suspension and / or the determined sludge age Suspension and / or of inflow quantities and / or inflow concentrations and / or outflow concentrations and / or the suspended nitrification rate and / or a sludge volume index are selected for the targeted increase of the suspended nitrification rate. Other common control parameters can also be taken into account.

Thus, a large number of parameters can be set which determine the suspended nitrification rate or from which a change in the suspended nitrification rate can be concluded and depending on which a shearing can take place in order to increase the suspended nitrification rate even further as a result. The biomass age of the sessile biomass and / or the sessile nitrification rate can also contribute to the selection of the shear time and the shear period, in particular to ensure regrowth of the sessile biomass or to optimize the treatment process.

The setting of the shearing time and / or the shearing period preferably takes place in a control loop as a function of the suspended nitrification rate as a control variable. Accordingly, the suspended nitrification rate is specifically adapted, in particular maximized, and readjusted within the possible limits as a function of the further parameters by the shearing.

Furthermore, a sewage treatment plant for the biological treatment of wastewater by nitrification, in particular according to a method according to the invention, is claimed, which has a control device which is designed to shear off the sessile biomass from the at least one support body by a corresponding device (ventilation system or mechanical shear device) Depending on the parameters relating to or influencing the suspended nitrification rate, the effect is that the suspended nitrification rate increases after shearing.

The at least one carrier body can preferably be designed as a fixed bed, preferably made of plastic or textile material, in order to enable the sessile biomass to grow as efficiently as possible.

• 1 eine schematische Ansicht einer Kläranlage.

The invention is explained in more detail below with reference to a drawing. It shows:

• 1 a schematic view of a sewage treatment plant.

In 1 is a sewage treatment plant 1 shown very schematically, with the sewage treatment plant 1 a clarifier 1a has, in the supplied wastewater A. (Activated sludge) that is in biological purification stages in the sewage treatment plant 1 is to be treated in a so-called activated sludge process. The clarifier 1a a clarification follows 1b at, being between the clarifier 1a and the clarification 1b an inlet and a return are arranged, via which the sludge can get in the respective direction. The biological cleaning takes place here on the basis of an IFAS system (Integrated Fixed-film Activated Sludge), in which in the clarifier 1a one or more support bodies 2 (Growth medium) each with large surfaces, preferably made of plastic or textile materials, are located, for example a fixed bed, or the like. On these support bodies 2 Sessile biomass settles during the treatment process Bsess from those in the sewage A. present microorganisms.

The sewage A. is therefore in the clarifier 1a on the carrier bodies 2 passed or are the carrier bodies 2 in the clarifier 1a completely submerged, with settled sessile microorganisms Msess in the sessile biomass Bsess from the pollutants S. in the sewage A. feed and thereby reproduce. This increases the sessile biomass Bsess sessile microorganisms, depending on the depth in the biofilm Msess which, depending on the depth, also contain different harmful substances in the sewage A. can reduce. The sessile microorganisms Msess ensure a certain cleaning effect in the wastewater A. eg by so-called nitrification with a certain sessile nitrification rate Nsess .

The sessile microorganisms Msess in the sessile biomass Bsess will continue to have a ventilation system 3 , for example a ventilation hose 3a with holes 3b , supplied with oxygen, since the nitrification has a high oxygen demand. Through the holes 3b can therefore air bubbles L. a certain intensity I. into the sewage A. are admitted, these also on the support bodies 2 be passed so that the sessile microorganisms Msess can be supplied with oxygen for the nitrification process. This can promote the growth of the sessile microorganisms. The ventilation system 3 can for example at the bottom of the clarifier 1a be arranged.

The growth of these sessile microorganisms Msess requires a high generation time, with the sessile nitrification rate Nsess with increasing biomass age Ba of sessile biomass Bsess initially increases as the density of sessile microorganisms Msess increases. At the same time, the sessile microorganisms settle and multiply Msess with increasing biomass age Ba but also an increasing layer thickness D. of sessile biomass Bsess , creating deeper layers on the carrier body 2 no longer adequately supplied and contribute to the treatment process through nitrification. Accordingly, the sessile biomass Bsess after a certain operating time of the sewage treatment plant 1 shear off or ablate in order to reduce the sessile nitrification rate Nsess to counteract. According to the invention, this shearing process is targeted for a further increase in the performance of the sewage treatment plant 1 is used as explained below.

As another biologically active component of the sewage treatment plant 1 are located in the clarifier 1a also suspended microorganisms Msus that are in the suspension, ie the sludge-like sewage A. , also apart from the carrier body 2 float or float, for example as suspended sludge flakes Fsus or suspended biomass Bsus . These suspended microorganisms too Msus are from the air bubbles L. the ventilation system 3 supplied with oxygen in order to be able to contribute to the treatment process through nitrification. The suspended microorganisms Msus carry with a certain suspended nitrification rate Nsus also for the breakdown of pollutants S. in the sewage A. at. An overall rate of nitrification Nges the sewage treatment plant 1 is thus in particular due to the suspended nitrification rate Nsus and the sessile nitrification rate Nsess certainly. The suspended biomass Bsus or the suspended sludge flakes Fsus have a lower biomass age Ba than the sessile biomass Bsess .

Compared to conventional sewage treatment plants 1 is used in the wastewater treatment process according to the invention A. the overall rate of nitrification Nges increased by the fact that a controlled removal or shearing of sessile biomass Bsess from the carrier bodies 2 takes place and this sheared biomass in the form of sheared sludge flakes Fshear into the sewage A. or passes into the suspension and also ensures nitrification in this. This means that the sheared-off sludge flakes carry Fshear as active suspended biomass Bsus also for the suspended nitrification rate Nsus at.

When shearing, the sessile becomes biomass Bsess with a two-dimensional interface on the carrier body 2 a suspended biomass Bsus with a three-dimensional or fully circumferential interface in the suspension. This can reduce the number of pollutants S. in the suspension or the wastewater A. by nitrification reacting microorganisms are significantly increased, as the sheared sludge flakes Fshear for the pollutants S. offer a very large target. The sheared flakes of mud Fshear If the shear rate is set appropriately, they also have a higher biomass age Ba versus the suspended sludge flakes Fsus with the suspended microorganisms Msus , as the sheared mud flakes Fshear from the sessile biomass Bsess on the carrier body 2 come. Thus, the density of nitrifying microorganisms in the sheared sludge flake is also Fshear high, so this for a large increase in the suspended nitrification rate Nsus can worry.

Furthermore, each sheared sludge flake has Fshear a comparatively high density compared to the suspended sludge flakes that were present from the start Fsus in the suspension, so that the sheared sludge flakes Fshear better in the follow-up 1b or in the case of SBR processes in the clarifier 1a can settle. This allows the active suspended biomass Bsus can be kept more easily in the process, which also results in mud age tTS the suspension, ie a mean residence time or residence time of the microorganisms Msus , Msess increased in suspension. This allows higher concentrations of active suspended biomass Bsus than in conventional methods. This can reduce the suspended nitrification rate Nsus and thus also the overall nitrification rate Nges can be increased significantly.

At the same time, the remaining part of the unsheared sessile biomass can Bsess on the carrier body 2 , then with a two-dimensional interface, continue to the sessile nitrification rate Nsess contribute. The shearing creates deeper layers of the sessile biomass Bsess exposed and regained direct contact with the nutrients and oxygen in the wastewater A. . This can also reduce the sessile nitrification rate Nsess can be increased. At the same time, the sessile biomass can continue to grow Bsess be ensured.

In conventional IFAS processes, no particular importance is attached to the shearing process, ie the overall nitrification rate Nges is only very uncontrolled and arbitrary, if at all, from the sheared sludge flakes Fshear influenced. The sheared sludge flakes play a role in the control and optimization of the treatment process Fshear thus so far only a subordinate role, while they are sheared off in a controlled manner according to this invention and are thus specifically provided for nitrification in the suspension and thus through targeted control to increase the nitrification performance of the sewage treatment plant 1 contribute.

The detachment or shearing off of the sessile biomass is achieved Bsess from the carrier body 2 for example through a targeted control of the under the carrier bodies 2 arranged ventilation system 3 , for example the ventilation hose 3a with the holes 3b . In doing so, the air bubbles L. coming out of the holes 3b emerge at a certain point in time t for a shear period German specifically with a very high intensity compared to normal operation I. blown out and therefore with high intensity I. on the carrier bodies 2 passed by. The air bubbles L. reach with high intensity I. against the sessile biomass Bsess and thereby cause the outer layers to peel off, in the form of sheared sludge flakes Fshear pass into the suspension as described above. Mechanical shearing devices can also be used 5 can be used targeted via the sessile biomass Bsess can be guided to remove or detach the upper layers in a targeted manner.

The shearing takes place here as a function of certain parameters, with a control device for this purpose 4th is provided that the ventilation system 3 and, if necessary, the mechanical cutting device 5 specifically controls for shearing. This is the control device 4th with sensors 6th connected in a signal-conducting manner, which can provide parameters relevant to the treatment process. About the sensors 6th can the control device 4th for example the layer thickness D. of sessile biomass Bsess determine and / or a dry matter content TS (Dry matter content of the activated sludge) in the suspension and / or the sludge age tTS the suspension and / or a feed concentration Xzul of pollutants S. in wastewater A. and / or an effluent concentration Xabl of pollutants S. in treated wastewater A. and / or the suspended nitrification rate Nsus and / or the sessile nitrification rate Nsess and / or a sludge volume index SVI , ie a measure of the settling ability of a sludge-water mixture.

Accordingly, a controlled shear can be for a short or long shear period German be effected if at a certain shear point t certain parameters indicate that, for example, due to higher inflow concentrations Xzul or increased runoff concentrations Xabl , a higher degradation rate or overall nitrification rate Nges is required, or that, for example, the overall nitrification rate due to lower temperatures Nges falls, so that an increase in the overall nitrification rate Nges by providing more sheared sludge flakes Fshear , ie by a targeted increase in the suspended nitrification rate Nsus , is required. The shear period German and the shear time t can be fixed or, preferably, variable. It can be provided, for example, that the control device 4th continuously checks the parameters in a control loop and then the shear time t and the shear period German specifies. This can reduce the rate of nitrification in suspension Nsus can be set specifically in a control loop.

Preferably, the shearing also takes place on the basis of the biomass age Ba of sessile biomass Bsess and / or the sessile nitrification rate Nsess . This ensures that the sessile biomass Bsess can constantly regrow, ie it is not sheared off too much, as this is responsible for increasing the suspended nitrification rate Nsus is necessary according to the method of the invention. The sessile nitrification rate can also be seen as a side effect Nsess Increase, as deeper layers of the sessile biomass are sheared off Bsess be exposed.

List of reference symbols

1

Sewage treatment plant

1 a

Clarifier

1b

After clarification

2

Carrier body

3

Ventilation system

3a

Ventilation hose

3b

Holes in the ventilation tube

4th

Control device

5

mechanical cutting device

6th

sensor

A.

sewage

Ba

Biomass age

Bsess

sessile biomass

Bsus

suspended biomass

D.

Layer thickness

German

Shear period

Fsus

suspended sludge flake

Fshear

sheared flake of mud

I.

intensity

L.

Air bubbles

Msess

sessile microorganisms

Msus

suspended microorganisms

Nges

Total nitrification rate

Nsess

sessile nitrification rate

Nsus

suspended nitrification rate

S.

Pollutant

tTS

Mud age

t

Shear time

TS

TS content

SVI

Sludge volume index

Xabl

Effluent concentration

Xzul

Feed concentration

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0201924 A2 [0004]
• WO 03/076350 A1 [0004]
• EP 1088793 A1 [0004]
• DE 2235470 A1 [0004]

Claims (13)

Method for treating wastewater (A) in a sewage treatment plant (1) with a clarifier (1a), wherein the wastewater (A) in the clarifier (1a) of microorganisms (Msess, Msus) is biologically treated by nitrification, in which case the clarifier (1a) is at least one carrier body (2) on which sessile biomass (Bsess) from sessile microorganisms (Msess) grows, the sessile microorganisms (Msess) biologically treating the wastewater (A) with a sessile nitrification rate (Nsess) , wherein there is suspended biomass (Bsus) from suspended microorganisms (Msus) in the wastewater (A), wherein the suspended microorganisms (Msus) treat the wastewater (A) with a suspended nitrification rate (Nsus), and where part of the sessile biomass (Bsess) is sheared from the at least one carrier body (2) to reduce a layer thickness (D) of the sessile biomass (Bsess), characterized in that the shearing off of the sessile biomass (Bsess) of the at least one support body (2) depending on the parameters (Xabl, Xzul, tTS, TS, SVI, Nsus, D) pertaining to the suspended nitrification rate (Nsus) takes place in such a way that the suspended nitrification rate (Nsus) increases after shearing . Procedure according to Claim 1 , characterized in that the shearing of the sessile biomass (Bsess) from the at least one support body (2) continues to depend on the layer thickness (D) and / or a biomass age (Ba) of the sessile biomass (Bsess) and / or the sessile nitrification rate ( Nsess) takes place to ensure that the sessile biomass (Bsess) is washed on the at least one support body (2). Procedure according to Claim 1 or 2 , characterized in that the shearing is achieved by setting an intensity (I) of air bubbles (L) blown into the wastewater (A), the air bubbles (L) being supplied by a ventilation system (3) that supplies the microorganisms (Msus, Msess) with oxygen ) to be provided. Procedure according to Claim 3 , characterized in that the set intensity (I) for shearing the sessile biomass (Bsess) from the at least one support body (2) can be at least in phases greater than the intensity (I) for supplying the microorganisms (Msus, Msess) with oxygen. Procedure according to Claim 3 or 4th , characterized in that the intensity (I) is set in a control loop as a function of a feed concentration (Xzul) and / or the suspended nitrification rate (Nsus). Method according to one of the preceding claims, characterized in that the shearing is achieved by a mechanical shearing device (5) which mechanically detaches the sessile biomass (Bsess) from the at least one support body (2). Method according to one of the preceding claims, characterized in that the sessile biomass (Bsess) is sheared from the at least one support body (2) at a shear time (t) over a shear period (dt), the shear time (t) and / or the shearing period (dt) as a function of a layer thickness (D) of the sessile biomass (Bsess) on the at least one support body (2) and / or an inflow concentration (Xzul) and / or an outflow concentration (Xabl) and / or a TS content ( TS) in the suspension and / or a sludge age (tTS) of the suspension and / or the suspended nitrification rate (Nsus) and / or a sludge volume index (SVI) can be selected for the targeted increase of the suspended nitrification rate (Nsus). Procedure according to Claim 7 , characterized in that the shearing time (t) and / or the shearing period (dt) are selected as a function of a biomass age (Ba) of the sessile biomass (Bsess) and / or the sessile nitrification rate (Nsess). Procedure according to Claim 7 or 8th , characterized in that the shearing time (t) and / or the shearing period (dt) are set in a control loop as a function of the suspended nitrification rate (Nsus) and / or other common control parameters. Sewage treatment plant (1) for the biological treatment of wastewater (A) by nitrification, in particular according to a method according to one of the preceding claims, with a clarifier (1a) and at least one carrier body (2) arranged in the clarifier (1a) on which each sessile Biomass (Bsess) from sessile microorganisms (Msess) can grow, for the biological treatment of the wastewater (A) with a sessile nitrification rate (Nsess), with suspended biomass (Bsus) from suspended microorganisms (Msus) in the wastewater (A) biological treatment of the wastewater (A) with a suspended nitrification rate (Nsus), the sewage treatment plant (1) furthermore having a device (5) for removing part of the sessile biomass (Bsess) from the at least one carrier body (2) in order to reduce a layer thickness (D) the sessile biomass (Bsess), characterized in that the Sewage treatment plant (1) has a control device (4) which is designed to shear off the sessile biomass (Bsess) from the at least one support body (2) by the device (3, 5) as a function of parameters relating to the suspended nitrification rate (Nsus) (Xabl, Xzul, tTS, TS, SVI, Nsus, D) in such a way that the suspended nitrification rate (Nsus) is increased after shearing. Sewage treatment plant (1) Claim 10 , characterized in that the device for removing part of the sessile biomass (Bsess) from the at least one carrier body (2) is formed by a ventilation system (3; 3a), the air bubbles (L) in the waste water (A) with such Intensity (I) can produce that the sessile biomass (Bsess) can detach from the at least one carrier body (2) and pass into the wastewater (A) as suspended sludge flakes (Fshear), the aeration system (3; 3a) the microorganisms (Msus, Msess) can simultaneously supply oxygen in the clarifier (1a) if the sessile biomass (Bsess) is not sheared off. Sewage treatment plant (1) Claim 10 or 11 , characterized in that the device for removing part of the sessile biomass (Bsess) from the at least one carrier body (2) is designed as a mechanical shearing device (5). Sewage treatment plant (1) after one of the Claims 10 to 12 , characterized in that the at least one support body (2) is designed as a fixed bed, preferably made of plastic or textile material.

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