SE543681C2

SE543681C2 - Waste water treatment system

Info

Publication number: SE543681C2
Application number: SE1951184A
Authority: SE
Inventors: Bert Gustafsson
Original assignee: Baga Water Tech Ab
Priority date: 2019-10-18
Filing date: 2019-10-18
Publication date: 2021-06-01
Also published as: WO2021074307A1; CN112678951A; SE1951184A1

Abstract

A method for the treatment of wastewater in a wastewater treatment system having a sludge separator (2) with an inlet (3), configured to supply wastewater to the system (1), and an outlet (4) configured to discharge treated wastewater from the system (1). The system (1) also has a bioreactor (8) provided with an upper aperture (9) and a lower aperture (10) arranged below the upper aperture (9). In addition, the system (1) has an oxygen supplying device (12) configured to supply oxygen to the bioreactor (8) which is arranged within the sludge separator (2). The upper and lower apertures (9, 10) are configured to discharge and receive wastewater, respectively to provide circulation of wastewater between the bioreactor (8) and the sludge separator (2) in the system (1) when oxygen is supplied to the bioreactor (8). The method comprises the steps of supplying wastewater to the system (1) through the inlet (3), supplying oxygen to the bioreactor (8) by means of the oxygen supplying device (12), such that the wastewater circulates in the system (1) between the bioreactor (8) and a primary chamber (5) through the upper and lower apertures (9, 10). Further, the method includes reducing the oxygen supply to the bioreactor (8), such that sludge is allowed to settle in the sludge separator (2) and in the bioreactor (8), and discharging the treated wastewater from the system (1) through the outlet (4).

Description

WASTEWATER TREATMENT SYSTEM TECHNICAL FIELD The present invention relates to a method for the treatment of Wastewater.

BACKGROUND Purifying Wastewater from polluting compounds, such as organic nutrients is ofgreat importance in order to avoid contamination of the environment. Non-purifiedsewage or Wastewater also imposes a large infection risk among humans and animals.

One known Way of purifying Wastewater biologically is to use a Wastewaterpurifying plant. The Wastewater ﬂows into a sludge separator where sludge settles, andthen flows into another part of the purifying plant, a bioreactor, Where biologicaldegradation of impurities takes place using microorganisms such as bacteria. In a finalstage in this known purifying plant, the Water ﬂows into a third chamber for secondarysedimentation. A ﬂocculating agent is added to the chamber and the precipitant can beremoved from the Wastewater.

In order to keep bacteria and other biodegrading microorganisms alive in theWastewater purifying plant, oxygen has to be supplied to create an aerobic environmentfor the microorganisms. Some sludge separators include an oxygen supply to form socalled “actívated sludgeﬂ where oxygen stimulates the degradation of impurities.US20l l0l32822Al discloses an open-ended ﬂoating microbial bioreactor systemprovided with a bioreactor where oxygen is supplied.

Even though the biological purification is Widely used and a Well-knownmethod, a Wastewater purifying plant as described above takes up a lot of space. Thepurification plant also generates a lot of sludge which has to be discarded. From the above it is understood that there is room for improvements in this technical field.

SUMMARYAn object of the present invention is to provide a concept which is improved over prior art and which solves or at least mitigates the problems discussed above. This object is achieved by the technique set forth in the appended independent claims,preferred embodiments being defined in the related dependent claims.

The present disclosure is - inter alia - based on the idea that a bioreactorsupplied with oxygen and comprising apertures close to its top and bottom is placedwithin a sludge separator to save space and to create a Wastewater purifying plant whichcomprises both an aerobic and an anaerobic environment. Air nozzles placed at thebottom of the bioreactor causes the water within the bioreactor to flow upwards suchthat it reaches apertures arranged close to the top of the bioreactor, causing Wastewaterto ﬂow out from the bioreactor. This in tum causes a water ﬂow within the sludgeseparator. The air supplied from below inside the bioreactor and the water running outfrom the upper aperture of the bioreactor forces wastewater to be dragged in through thelower apertures in the bioreactor. This achieved circular ﬂow, together with thepossibility of creating an anaerobic environment in the sludge separator and an aerobicenvironment within the bioreactor, results in a very favourable conditions for efficientwastewater purif1cation.

In a first aspect, there is provided a method for the treatment of wastewater in awastewater treatment system. The wastewater treatment system comprises a sludgeseparator having an inlet conf1gured to supply wastewater to the system, and an outletconfigured to discharge treated wastewater from the system. Further, the system has abioreactor optionally comprising carrier elements, having at least one upper apertureand at least one lower aperture arranged below the upper aperture, and an oxygensupplying device configured to supply oxygen to the bioreactor. The bioreactor isarranged within the sludge separator, and the upper and lower apertures are conf1guredto discharge and receive wastewater, respectively, to provide circulation of wastewaterbetween the bioreactor and the sludge separator in the system when oxygen is suppliedto the bioreactor.

This is advantageous since the upper and lower apertures allow for thecirculation of wastewater between the bioreactor and the sludge separator whichprovides efficient purification of the wastewater. Hence, wastewater can be cleansed biologically and quickly, without the need for chemicals or large purif1cation plants.

The circulation distributes the oxygen in the system, causing aerobic microorganismspresent in the system to purify the Wastewater.

In one embodiment, the oxygen supplying device is arranged below the loweraperture. Preferably, the oxygen supplying device is arranged at a bottom area of thebioreactor. This is advantageous since the introduction of oxygen and/or air in thebottom area of the bioreactor assists the circulation of the wastewater. When the oxygensupplying device is turned on, it causes a suction force to suck wastewater from thesludge separator into the lower apertures of the bioreactor. Simultaneously the water inthe bioreactor will ﬂow upwards due to the oxygen supply and wastewater will exit thebioreactor through the upper apertures.

In another embodiment, the sludge separator comprises a primary chamber anda secondary chamber. This is beneficial since the secondary chamber may serve as asecondary sedimentation chamber. Wastewater which has been purified in the duringcirculation of the wastewater between the bioreactor and the primary chamber istransferred to the secondary chamber for a secondary sedimentation step, whichcleanses the wastewater additionally.

In one embodiment, the system further comprises a first transferring deviceconf1gured to transfer wastewater from the primary chamber to the secondary chamber.

In yet another embodiment, the carrier elements are configured to be coveredby microbial growth.

The bioreactor comprises carrier elements, at least one upper aperture and atleast one lower aperture arranged below the upper aperture, wherein said bioreactor is inﬂuid communication with an oxygen supplying device and is configured to providecirculation of wastewater in a wastewater treatment system between the bioreactor andthe system by receiving and discharging wastewater through the apertures when air issupplied to the bioreactor. This is an advantageous bioreactor since it providescirculation of wastewater in any kind of wastewater treatment system. The circulationenhances the efficiency of biological purification of the wastewater.

. The method comprises providing a wastewater treatment system, supplyingwastewater to the system through the inlet, supplying oxygen to the bioreactor by means of the oxygen supplying device, whereby the wastewater circulates in the system between the bioreactor and a primary Chamber through the upper and lower apertures,reducing the oxygen supply to the bioreactor, whereby sludge is allowed to settle in thesludge separator and in the bioreactor, and discharging the treated wastewater from thesystem through the outlet.

This method if efficient since the circulation between the bioreactor and thesludge separator stimulates the biological purification of the wastewater. The oxygensupply stimulates the degradation of organic substances polluting the wastewater. Inaddition, the reduction of oxygen provides a more anaerobic environment, which assiststhe denitrification process of the puriﬁcation. Hence, the method provides both anaerobic and anaerobic environment in the wastewater treatment system. Thus, bothaerobic and anaerobic purification of the wastewater takes place resulting in cleansedwastewater.

The sludge separator comprises a housing and a bioreactor accommodatedtherein. The housing has an inlet for wastewater supply and an outlet for discharge ofwastewater treated by the bioreactor. Further, the bioreactor has wall opening meansconfigured to direct a ﬂow of wastewater to circulate partially within the bioreactor andpartially within the sludge separator housing.

In one embodiment, the sludge separator comprises means configured to direct the treated wastewater to and out of the discharge outlet.

BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments of the invention will be described in the following; referencesbeing made to the appended diagrammatic drawings which illustrate non-limiting examples of how the inventive concept can be reduced into practice.

Fig. l is a schematic illustration of a wastewater treatment system; Fig. 2a is a section illustrating a wastewater treatment system according to oneembodiment; Fig. 2b is a section illustrating of a wastewater treatment system according to another embodiment; and Fig. 3 shows the Wastewater treatment system of Fig. 2b in a slightly modified embodiment.

DETAILED DESCRIPTION To cleanse Wastewater, such as sewage water, biological processes may be used.Biological purification of Wastewater comprises degradation of organic substances, suchas compounds comprising nitrogen, using microorganisms, e. g. bacteria.

In an aerobic environment, the supply of oxygen is abundant. So called “activebiological sludge” is obtained when Wastewater is led into an aerobic environment. Theactive sludge comprises bacteria and other microorganisms which degrade organicmaterial in the sewage water. Chemically, nitrif1cation is one of the major reactions thattakes place. Nitrification is the biological oxidation of ammonia or ammonium (NHU)to nitrite followed by the oxidation of the nitrite to nitrate (NOí). Microorganisms forma thin layer of a bio film on a surface of a carrier element, such that the biologicalcleansing and the above mentioned chemical reactions may take place.

In anaerobic “anox” environments, where the oxygen levels are low,denitrif1cation takes place. Denitrification is a microbially facilitated process wherenitrate (N 03-) is reduced and produces molecular nitrogen (Nz).

Biological cleansing of wastewater commonly further comprises a step ofchemical precipitation, using a ﬂocculating agent to form precipitates in the wastewater.Such step is mainly performed to reduce phosphorous (P) and the biochemical oxygendemand (BOD) of the wastewater. BOD is the amount of dissolved oxygen demandedby aerobic biological organisms to break down organic material present in thewastewater at certain temperature over a specific time period.

With reference to Fig. l, a schematic wastewater treatment system l is shown.The wastewater treatment system l has a sludge separator 2 with a housing 2°, an inlet3, an outlet 4 and a primary chamber 5. The sludge separator 2 further has a secondarychamber 6. A partition 7 separates the primary chamber 5 and the secondary chamber 6from each other.

As shown in Fig. l, a bioreactor 8 is housed within the primary chamber 5 of the sludge separator 2. The bioreactor 8 has upper apertures 9 and lower apertures l0. At a bottom area 11 of the bioreactor 8, an oxygen supplying device 12 is arranged. Herein,the oxygen supplying device 12 is also referred to as an air supplying device 12, whichfor instance may be a diffuser, a compressor or a pump. The air supplying device 12 canswitch between an active state where air is supplied to the bioreactor 8 and a non-activestate where no air is supplied to said bioreactor 8. The amount of oxygen/air may alsobe varied.

Inside the bioreactor 8, carrier elements 13 are present. The upper and lowerapertures 9, 10 are smaller than the dimensions of the carrier elements 13, to avoid thecarrier elements 13 from exiting the bioreactor 8. A dashed line indicates a maximumwastewater level Lmax. Four rounded arrows in Fig. 1 indicate circular water ﬂow insidethe system 1 when the air supplying device 12 is active.

More detailed illustrations of a wastewater treatment system 1 are shown in Figs2a and 2b. The wastewater treatment system 1 includes the sludge separator 2 providedwith the inlet 3, the outlet 4 and the primary chamber 5. The sludge separator 2 furtherhas the secondary chamber 6. A first partition 7a and a second partition 7b (shown inFig. 3 only) separate the primary chamber 5 and the secondary chamber 6 from eachother. Both the primary chamber 5 and the secondary chamber 6 further comprises alower portion 20, 21, respectively.

The sludge separator 2 may have varying dimensions. For instance, the primarychamber 5 may hold approximately 4m3 of wastewater and the diameter of the sludgeseparator may be about 2m. A height of the sludge separator may be about 2.5m. Thewastewater treatment system 1 disclosed herein may have varying dimensions andvolumes. A line Lmax indicates a maximum wastewater level in Figs 2a and 2b. Theminimum wastewater level is indicated by a dashed line Lmin.

The bioreactor 8 is arranged within the sludge separator 2, and has upperapertures 9 and lower apertures 10. The apertures 9, 10 may have different dimensionsand shapes. In Figs 2a and 2b, the apertures 9, 10 are arranged in groups of five. Thebioreactor 8 has at least one upper aperture 9 and at least one lower aperture 10.Preferably, the bioreactor 8 has a plurality of upper apertures 9 and lower apertures 10respectively which are spaced apart such that a circular ﬂow of wastewater between the bioreactor 8 and the primary chamber 5 can be accomplished. The apertures 9, 10 may be arranged in any way such that a circulation between the bioreactor and the primaryChamber 5 is achieved. Preferably, the lower apertures 10 are arranged close to a bottomarea 11 of the bioreactor 8. However, in the lower portion 20 of the primary chamber 5sludge may settle. Thus, the lower apertures 10 should be placed sufficiently highenough from the bottom area 11 such that clogging of the lower apertures 10 isprevented.

At a bottom area 11 of the bioreactor 8, the oxygen supplying device 12 isarranged. In Figs 2a and 2b, the oxygen supplying device 12 is in the form of airdiffusers. However, the air supplying device 12 may be any type of device which maysupply air/oxygen to the bioreactor 8, such as a compressor, a pump or an air diffusingtube.

Just as the system 1 shown in Fig. 1, the bioreactor 8 in the wastewater treatmentsystem 1 shown in Fig. 2a and 2b contains carrier elements 13 (not shown). The numberof upper and lower apertures 9, 10 is optional. However, the dimensions of the upperapertures 9 and lower apertures 10 are designed in such a way that the carrier elements13 cannot exit the bioreactor through the upper and lower apertures 9, 10. An exemplarydimension of the diameter of the carrier elements 13 is about 25 mm, and an exemplarydimension of the diameter of the apertures 9, 10 is about 15-20 mm. The carrierelements 13 in Fig. 1 are made of a material ﬂoating in water. However, the carrierelements 13 may also be made of a non-ﬂoating material and be fixed inside thebioreactor 8.

The upper and lower apertures 9, 10 have a circular shape as shown in Figs 2aand 2b, or may for instance be present as a grid having openings with dimensionssuff1ciently small to prohibit the carrier elements 13 from exiting the bioreactor 8 (notshown). Such grid may for instance be of a rectangular shape and be arranged in thezone between the maximum wastewater level Lmax and the minimum wastewater levelLmin.

The primary chamber 5 shown in Figs 2a and 2b is further provided with a firsttransferring device 14, configured to transfer wastewater from the primary chamber 5 to the secondary chamber 6. A pipeline 23 connects the primary chamber 5 to the secondary Chamber 6. The first transferring device 14 may be a first pump.Altematively, the first transferring device 14 may be installed inside the bioreactor 8.

In addition, a further or second transferring device 18, and a discharge device19, are arranged in the secondary chamber 6 in Figs 2a and 2b. The second transferringdevice 18 is a second pump and the discharge device 19 is a third pump. The secondand third pump are herein also referred to as a sludge pump and a discharge pumprespectively. Sedimented material will sink to the lower portion 21 of the secondarychamber 6 of the sludge separator 2. The second transferring device 18 is configured totransfer settled material, such precipitated agglomerated sludge, from the secondarychamber 6 back to the primary chamber 5.

In Fig. 2b, the secondary chamber 6 comprises a cylindrical pipe 22. Thepipeline 23 is connected between the first pump 14 and the pipe 22. The secondarychamber 6 shown in Fig. 2b is further equipped with cleansing devices 15, 16, 17. Thecleansing device 15 arranged within the pipe 22 is a hydrocyclone, the cleansing device16 is a pipe sedimentation unit, and the cleansing device 17 is a filter unit, such as asand filter. The pipe sedimentation unit 16 is made of a matrix like web materialcovered with biofilm. Due to gravity, the biofilm on the pipe sedimentation unit 16 willeventually fall off, thus preventing clogging of the pipe sedimentation unit 16.However, the use of device hydrocyclone 15 and a filter unit 17 is optional, and othertypes of cleansing devices may also be used in the system 1. The hydrocyclone 15, thepipe sedimentation unit 16, the filter 17 and the discharge device 19 are shown indashed lines to indicate their optional presence.

Fig. 3 shows the wastewater treatment system 1 of Fig. 2b as seen from above.In Fig. 3, the sludge separator 2, the inlet 3, the outlet 4, the primary chamber 5 and thebioreactor 8 are seen from above. The oxygen supplying device 12 is arranged insidethe bioreactor 8. The sludge separator 2 further includes the secondary chamber 6 whichis separated from the primary chamber 5 by the first partition 7a and the secondpartition 7b arranged adjacent to a discharge container 24 having an opening 25. Thefirst pump 14, the sludge pump 18 and the discharge device 19 are also seen in Fig. 3, as well as the cleansing devices 15, 16, 17.

The function and operation of the Wastewater treatment system 1 will now beexplained more in detail with reference to the figures. The Wastewater treatmentsystems 1 shown are filled with wastewater through the inlet 3. This is indicated by thearrow at the inlet 3 in Fig. 3.

Wastewater ﬂows into the sludge separator 2 and f1lls the primary chamber 5and the bioreactor 8. When the sludge separator 2 is completely full, the wastewaterreaches the maximum wastewater level Lmax, indicated by a horizontal line in Figs 1 and2a-b. The wastewater treatment system 1 also has the lower minimum wastewater levelLmin, as seen in Figs 2a-b. The wastewater treatment system 1 has a buffering capacitybetween the two water levels Lmin and Lmax, such that the system 1 is efficient evenwhen the water supply varies, and is arranged below the inlet 3 to avoid backflow ofwastewater.

When the wastewater treatment system 1 has been filled with wastewater, theoxygen supplying device 12 is activated, and supplies oxygen to the bioreactor 8. Theoxygen or air supplied by the oxygen supplying device 12 generates a suction forcedirected from the primary chamber 5 towards the inside of the bioreactor 8. The suctionforce thus pulls wastewater into the bioreactor 8 through the lower aperture(s) 10.

Also, when oxygen is supplied to the bioreactor 8 the water inside the bioreactor8 will flow upwards towards the upper aperture(s) 9 and exit the bioreactor 8 throughthe upper aperture(s) 9. Hence, the oxygen/ air supply causes a circular ﬂow of thewastewater within the system 1. Four rounded arrows shown in Fig. 1 indicate thiscircular water ﬂow inside the system 1. The wastewater is sucked into the bioreactor 8through the lower aperture(s) 10 and exists the bioreactor 8 through the upperaperture(s) 9. Hence, a recirculation of the wastewater between the primary chamber 5and the bioreactor 8 occurs when the oxygen supplying device 12 is active. The oxygensupplying device 12 is arranged in the bottom area 11 of the bioreactor 8 in the figuresof the present disclosure. However, the oxygen supplying device 12 may be arrangedelsewhere in the bioreactor 8 causing a wastewater ﬂow during air supply in otherdirections than that indicated by the arrows in Fig. 1.

The circulation between the bioreactor 8 and the primary chamber 5 stimulates the aerobic purification in the system 1. Recirculation of the wastewater in and out of the bioreactor 8 assists efficient degradation of organic pollutions present in theWastewater. The circulation causes the carrier elements 13 to swirl around within thebioreactor 8, resulting in that the Wastewater comes into contact with biofilm present onthe carrier elements.

A preferred oxygen supply is for instance 3-15 m3/h, such as 5-10 m3/h.However, the amount of oxygen needed depends on a variety of factors, such as the sizeof the bioreactor 8, and the state of the Wastewater. The bioreactor 8 may be designed insuch a way that the Wastewater ﬂows in an opposite direction as shown in Fig. For thepurification of Wastewater, the direction of the ﬂow between the bioreactor 8 and theprimary chamber 5 may be varied, as long as circulation between the bioreactor 8 andthe primary chamber 5 is achieved.

The supply of oxygen to the bioreactor 8 results in a Wastewater treatmentsystem 1 having an aerobic environment during oxygen supply, and the system 1 beingan essentially low oxygen anaerobic “anox” environment When the air supplying device12 is switched off The aerobic environment provides suitable conditions for biologicalcleansing, e. g. nitrif1cation, to occur. As mentioned above, efficient nitrif1cation requiresa high amount if oxygen.

The carrier elements 13 present in the bioreactor 8 are covered With microbialgrowth, a so called bio film. The bio film hosts aerobic microorganisms suitable for thedegradation of contaminating particles. When the air supplying device 12 is active,Wastewater which is pulled into the bioreactor 8 is purif1ed by the microorganismspresent in the bio film on the carrier elements 13. The circular ﬂow facilitates cleansingof the Wastewater efficiently due to the occurring recirculation in the system 1.

The oxygen supplying device 12 is active for instance between 5 minutes and 5hours, such as between 15 minutes and 4 hours, such as between 30 minutes and 3hours, such as between 45 minutes and 120 minutes. Preferably, the oxygen supplyingdevice 12 is active between 45 minutes and 90 minutes. The oxygen supplying timevaries depending on for instance the size of the system, the amount of oxygen supplied(m3/h), the condition of the Wastewater and its BOD and the temperature of theWastewater. A higher temperature of the Wastewater results in a more efficient reduction of nitrogen. ll The supply of oxygen should be suff1cient to allow for aerobic biologicalpurif1cation of the Wastewater.

Preferably, the carrier elements 13 are shaped as small cogwheels (not shown).The cogwheeled shape provides a large surface area for the growth of a bio film.However, the carrier elements 13 may have any irregular shape or shape providing largesurface area. The combination of a large surface area for hosting microorganismstogether with the remaining system 1 results in a degree of nitrification up to 100%.

The anaerobic environment provides suitable conditions for denitrif1cation. Asmentioned above, efficient denitrification requires a low oxygen environment. Hence,when the air supplying device 12 is switched off the system 1 transforrns into a lowoxygen environment. Denitrification also requires a carbon source. The carbon source inthe wastewater treatment system 1 is the sludge itself, which comprises a large amountof carbon containing materials. The degree of denitrif1cation in the system 1 is alsosuff1cient, being approximately 50-80%, such as 60-70%.

After a period of time, the oxygen supply is reduced or stopped. Preferably, theoxygen supplying device 12 is switched off. The non-active state of the oxygensupplying device 12, or when the amount of oxygen supplied by the oxygen supplyingdevice 12 is reduced, are referred to as a sedimentation period. When the oxygensupplying device 12 is switched off and/or when the oxygen supply is reduced, thewater ﬂow in the system 1 stops and the sludge is allowed to settle at the bottom portion20 of the sludge separator 2. The sludge present in the bioreactor 8 will settle in thebottom area 11 of the bioreactor 8. The sedimentation period may for instance bebetween 2 minutes and 5 hours, such as between 5 minutes and 4 hours, such asbetween 7 minutes and 3 hours, preferably between 9 and 120 minutes, and mostpreferred about 10 to 60 minutes.

The carrier elements 13 in Fig. 1 are made from a ﬂoating material. Hence, whenthe water ﬂow stops or decreases, the carrier elements 13 will ﬂoat on the water surfaceinside the bioreactor 8.

When the sludge has settled, the first pump 14 pumps treated wastewater into thesecondary chamber 6. The wastewater is pumped from the primary chamber 5 through the pipeline 23 and to the secondary chamber 6. If the pipe 22 is present in the 12 secondary Chamber 6, the Wastewater enters the pipe 22 horizontally, which causes theWastewater to swirl along an inner surface of the pipe 22. The bottom of the pipe 22 isopen, such that the Wastewater flows into the bottom 21 of the secondary chamber 6.

Wastewater present in the secondary chamber 6 rises through the pipesedimentation unit 16 Which is made of a perrneable Web like material also covered Withmicrobial growth. Hence, the Wastewater Will be further purified by the microorganismpresent in said microbial growth.

When the Wastewater reaches the opening 25, it Will ﬂow into the dischargecontainer 24 and exit through the outlet 4 by gravity ﬂow. Altematively, the Wastewateris pumped out from the discharge container 24 by the discharge pump 19. Optionally,the Wastewater is also filtered through the sand filter unit 17 shown in Fig. 2b beforeexiting the sludge separator 2 through the outlet 4.

Preferably, a ﬂocculating agent is added to the secondary chamber 6, or to thepipeline 23 connecting the primary chamber 5 to the secondary chamber 6, to cause theremaining sludge and phosphorous to precipitate. Optionally, the ﬂocculating agent isadded to the hydrocyclone 15. The precipitated sludge then sinks to the bottom portion21 of the secondary chamber 6.

At predeterrnined time intervals, such as once each day, the sludge pump 18pumps the settled sludge from the bottom portion 21 of the secondary chamber 6 backto the bottom portion 20 of the primary chamber 5, as indicated by an arrow in Fig. 3.This provides additional carbon containing sludge to the denitrification process, makingthe denitrification in the primary chamber 5 even more efficient. In addition, moresludge is consumed by the chemical processes in the system 1, reducing the amount ofsludge present in the Wastewater.

The treated Wastewater leaves the discharge container 24 of the sludge separator2 through the outlet 4, as indicated by the arrow in Fig. 3. The Wastewater is eitherdischarged using the discharge pump 19, or the Wastewater ﬂows out from the outlet 4by gravity. Since the outlet 4 is arranged below the inlet 3 (shown in Figs 2a and 2b andindicated by the height “H”), the Wastewater can automatically exit the sludge separator 2 through the outlet 4 by gravity ﬂow. However, the inlet 3 and the outlet 4 may be 13 arranged at the same level in the sludge separator 2. The discharge device 19 may thenpump Wastewater out through the outlet 4.

All together, the Wastewater treatrnent system 1 provides both an aerobic and ananaerobic environment, and a circular Water ﬂow Which together for advantageousconditions for efficient Wastewater Cleansing. The degree of mineralisation of the sludgein the primary chamber 5 is high, Which is beneficial for the microorganisms in thebioreactor 8. In addition, due to the mineralisation, the amount of sludge in the system 1is decreased. Efficient biological purification in the bioreactor 8 is advantageous for thedenitrification in the primary chamber 5. The bioreactor 8 and the sludge separator 2recirculate the Wastewater between themselves, and the recirculation is achievedthrough the oxygen supply in the bioreactor. Hence, the system 1 provides an efficientWastewater treatment process.

Finally, it should be mentioned that the inventive concept is not limited to theembodiments described herein, and many modifications are feasible Within the scope ofthe appended claims. Various features disclosed herein and related to variousembodiments may be combined depending on speciﬁc purposes to be achieved. Forinstance, the bioreactor may be arranged in the centre of the sludge separator (as shownin Fig. 3) or it may be arranged eccentrically in the sludge separator (as shown in Figs1-2b). The sludge separator may be of another kind than illustrated herein. Differentpumps, oxygen supplying devices and sludge separators may be combined With eachother, and the bioreactor disclosed herein may be arranged in any type of Waste Watertreatment system Where it is advantageous to provide circulation between the bioreactorand another part of said Wastewater treatment system. Furthermore, the oxygensupplying device may be in different positions of the bioreactor than shown in thefigures. The oxygen supplying device is associated With the bioreactor such thatcirculation is achieved between the bioreactor and an associated chamber in a Wastewater treatment system.

Claims

1. A method for the treatment of Wastewater in a Wastewater treatment system(1) Which comprises a sludge separator (2) having an inlet (3) conf1gured to supplyWastewater to the systern (1), and an outlet (4) configured to discharge treatedWastewater from the system (1); a bioreactor (8) having at least one upper aperture (9)and at least one lower aperture (10) arranged below the upper aperture (9); and a device(12) configured to supply oxygen to the bioreactor (8); wherein the bioreactor (8) isarranged Within the sludge separator (2); and wherein the upper and lower apertures (9,10) are configured to discharge and receive Wastewater, respectively to providecirculation of Wastewater between the bioreactor (8) and the sludge separator (2) in thesystem (1) When oxygen is supplied to the bioreactor (8); said method comprising thesteps of: - supplying Wastewater to the system (1) through the inlet (3); - supplying oxygen to the bioreactor (8) by means of the oxygen supplyingdevice (12), Whereby the Wastewater circulates in the system (1) between the bioreactor(8) and a primary chamber (5) through the upper and lower apertures (9, 10); - reducing the oxygen supply to the bioreactor (8), Whereby sludge is allowedto settle in the sludge separator (2) and in the bioreactor (8); and - discharging the treated Wastewater from the system (1) through the outlet (4).

2. The method according to claim 1, wherein the sludge is allowed to settle inthe sludge separator (2) and in the bioreactor (8) for approximately between 2 minutesand 5 hours, preferably between 5 minutes and 4 hours, preferably between 7 minutesand 3 hours, preferably between 9 and 120 minutes, and most preferred between about 10 to 60 minutes.

3. The method according to claim 1 or 2, wherein after the step of reducingsaid oxygen supply and before discharging the treated Wastewater from the system (1) through the outlet (4), the method ﬁlrther comprises transferring Wastewater from a primary Chamber (5) to a secondary Chamber (6) in the s1udge separator (2) by means of a transferring device (14), and allowing the s1udge to sett1e in the secondary chamber (6)-

4. The method according to c1aim 3, further comprising a step of adding a ﬂocculating agent to the secondary chamber (6) or to a ji ,e1i1if: '(235 conrtectiitxg the tvrítnzirx» chatnïyer (53 to the secondary chat/idéer (of).

5. The method according to any one of c1aims 2 to 4, further comprisingtransferring sludge from the secondary chamber (6) to the primary chamber (5), using a second transferring device (18).

6. The method according to any one of the c1aims 1 to 5, wherein the step ofsupp1ying oxygen to the bioreactor is performed between 5 minutes and 5 hours, such asbetween 15 minutes and 4 hours, such as between 30 minutes and 3 hours, such asbetween 45 and 120 minutes, preferab1y the step is performed between 45 and 90 minutes .

7. The method according to any one of the c1aims 1 to 6, wherein thewastewater is discharged using a discharge device (19), preferab1y the discharge device (19) comprises a pump.