WO2021074307A1

WO2021074307A1 - Wastewater treatment system

Info

Publication number: WO2021074307A1
Application number: PCT/EP2020/079066
Authority: WO
Inventors: Bert Gustafsson
Original assignee: Drain Fields Patents Ab
Priority date: 2019-10-18
Filing date: 2020-10-15
Publication date: 2021-04-22
Also published as: SE1951184A1; SE543681C2; CN112678951A

Abstract

A wastewater treatment system has a housing (21) 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) comprising carrier elements and 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 housing (21), and 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 chamber (5) in the system (1) when oxygen is supplied to the bioreactor (8).

Description

WASTEWATER TREATMENT SYSTEM

TECHNICAL FIELD

The present invention relates to a wastewater treatment system, a bioreactor and a method for the treatment of wastewater.

BACKGROUND

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

One known way of purifying wastewater biologically is to use a wastewater purifying plant. The wastewater flows into a sludge separator where sludge settles, and then flows into another part of the purifying plant, a bioreactor, where biological degradation of impurities takes place using microorganisms such as bacteria. In a final stage in this known purifying plant, the water flows into a third chamber for secondary sedimentation. A flocculating agent is added to the chamber and the precipitant can be removed from the wastewater.

In order to keep bacteria and other biodegrading microorganisms alive in the wastewater purifying plant, oxygen has to be supplied to create an aerobic environment for the microorganisms. Some sludge separators include an oxygen supply to form so called “ activated sludge ”, where oxygen stimulates the degradation of impurities. US20110132822A1 discloses an open-ended floating microbial bioreactor system provided with a bioreactor where oxygen is supplied. Further background art is disclosed in WO2014172791A1, SE512069C2, US20060180546A1, and US20030066790A1.

Even though the biological purification is widely used and a well-known method, a wastewater purifying plant as described above takes up a lot of space. The purification 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. SUMMARY

An 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 bioreactor supplied with oxygen and comprising apertures close to its top and bottom is placed within a sludge separator to save space and to create a wastewater purifying plant which comprises both an aerobic and an anaerobic environment. Air nozzles placed at the bottom of the bioreactor causes the water level within the bioreactor to rise such that it reaches apertures arranged close to the top of the bioreactor, causing wastewater to flow out from the bioreactor. Hence, the air nozzles placed at the bottom of the bioreactor causes the water within the bioreactor to flow upwards such that it reaches apertures arranged close to the top of the bioreactor, causing wastewater to flow out from the bioreactor. This in turn causes a water flow within the sludge separator. The air supplied from below inside the bioreactor and the water running out from the upper aperture of the bioreactor forces wastewater to be dragged in through the lower apertures in the bioreactor. This achieved circular flow, together with the possibility of creating an anaerobic environment in the sludge separator and an aerobic environment within the bioreactor, results in a very favourable conditions for efficient wastewater purification.

In a first aspect, there is provided a wastewater treatment system comprising a housing having an inlet configured to supply wastewater to the system, and an outlet configured to discharge treated wastewater from the system. Further, the system has a bioreactor comprising carrier elements, having at least one upper aperture and at least one lower aperture arranged below the upper aperture, and an oxygen supplying device configured to supply oxygen to the bioreactor. The bioreactor is arranged within the housing, and the upper and lower apertures are configured to receive and discharge wastewater, respectively, to provide circulation of wastewater between the bioreactor and a chamber in the housing when oxygen is supplied to the bioreactor. This is advantageous since the upper and lower apertures allow for the circulation of wastewater between the bioreactor and the housing and its associated chamber which provides efficient purification of the wastewater. Hence, wastewater can be cleansed biologically and quickly, without the need for chemicals or large purification plants. The circulation distributes the oxygen in the system, causing aerobic microorganisms present in the system to purify the wastewater.

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

In another embodiment, the housing comprises a sedimentation chamber. This is beneficial since wastewater which has been purified in the housing during circulation of the wastewater between the bioreactor and the chamber is transferred to the sedimentation chamber for a further sedimentation step, which cleanses the wastewater additionally.

In one embodiment, the system further comprises a first transferring device configured to transfer wastewater from the chamber or the bioreactor to the sedimentation chamber.

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

In a second aspect, there is provided a bioreactor to be included in a housing of a wastewater treatment system. The bioreactor comprises carrier elements, at least one upper aperture and at least one lower aperture arranged below the upper aperture, wherein said bioreactor is associated with an oxygen supplying device and is configured to provide circulation of wastewater in the wastewater treatment system between the bioreactor and a chamber in the housing by receiving and discharging wastewater through the apertures when oxygen/air is supplied to the bioreactor. This is an advantageous bioreactor since it provides circulation of wastewater in any kind of wastewater treatment system. The circulation enhances the efficiency of biological purification of the wastewater.

In a third aspect, there is provided a method for the treatment of wastewater. The method comprises providing a wastewater treatment system, supplying wastewater 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 the chamber through the upper and lower apertures, reducing the oxygen supply to the bioreactor, whereby sludge is allowed to settle in the housing and in the bioreactor, and discharging the treated wastewater from the system through the outlet.

This method if efficient since the circulation between the bioreactor and the chamber stimulates the biological purification of the wastewater. The oxygen supply stimulates the degradation of organic substances polluting the wastewater. In addition, the reduction of oxygen provides a more anaerobic, preferably anoxic, environment, which assists the denitrification process of the purification. Hence, the method provides both an aerobic and anoxic environment in the wastewater treatment system. Thus, both aerobic and anoxic purification of the wastewater takes place resulting in cleansed wastewater.

In a fourth aspect, there is provided a wastewater treatment housing comprising a bioreactor accommodated therein. The housing has an inlet for wastewater supply and an outlet for discharge of wastewater treated by the bioreactor. Further, the bioreactor has wall opening means configured to direct a flow of wastewater to circulate partially within the bioreactor and partially within the housing.

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

In a fifth aspect, there is provided the use of a bioreactor being accommodated within a wastewater treatment system. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described in the following; references being 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 one embodiment;

Fig. 2b is a section illustrating of a wastewater treatment system according to another embodiment;

Fig. 2c is a section illustrating a wastewater treatment system according to yet another embodiment;

Fig. 2d is a section illustrating a wastewater treatment system according to another embodiment;

Fig. 2e is a section illustrating a wastewater treatment system according to yet 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, such as compounds comprising nitrogen, using microorganisms, e.g. bacteria.

In an aerobic environment, the supply of oxygen is abundant. So called “active biological sludge” is obtained when wastewater is led into an aerobic environment. The active sludge comprises bacteria and other microorganisms which degrade organic material in the sewage water. Chemically, nitrification is one of the major reactions that takes place. Nitrification is the biological oxidation of ammonia or ammonium (MFC) to nitrite followed by the oxidation of the nitrite to nitrate (NCh )_· Microorganisms form a thin layer of a bio film on a surface of a carrier element, such that the biological cleansing and the above mentioned chemical reactions may take place. In anoxic environments, where the oxygen levels are low, denitrification takes place. Denitrification is a microbially facilitated process where nitrate (NCb ) is reduced and produces molecular nitrogen (N2).

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

With reference to Fig. 1, a schematic wastewater treatment system 1 is shown. The wastewater treatment system 1 has a sludge separator 2 also referred to as a housing 2’, having an inlet 3, an outlet 4 and a chamber 5. The housing T further has a sedimentation chamber 6. A partition 7 separates the chamber 5 and the sedimentation chamber 6 from each other.

As shown in Fig. 1, a bioreactor 8 is housed within the chamber 5 of the housing 2’. The bioreactor 8 has upper apertures 9 and lower apertures 10. 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, which for instance may be a diffuser, a compressor or a pump. The air supplying device 12 can switch between an active state where air is supplied to the bioreactor 8 and a non-active state where no air is supplied to said bioreactor 8. The amount of oxygen/air may also be varied.

The housing T may be any other type of purification, separation and/or sedimentation vessel suitable for treatment of wastewater, which accommodates the bioreactor 8. Further, the wastewater purificati on/separation/ sedimentation housing T may form part of a larger wastewater treatment plant system (not shown).

Inside the bioreactor 8, carrier elements 13 are present. The upper and lower apertures 9, 10 are smaller than the dimensions of the carrier elements 13, to avoid the carrier elements 13 from exiting the bioreactor 8. A dashed line indicates a maximum wastewater level Lmax. Four rounded arrows in Fig. 1 indicate circular water flow inside the system 1 when the air supplying device 12 is active. More detailed illustrations of a wastewater treatment system 1 are shown in Figs 2a and 2b. Wastewater treatment systems 1 according to other embodiments are shown in Figs 2c and 2d. The wastewater treatment system 1 includes the housing T provided with the inlet 3, the outlet 4 and the chamber 5. The housing T further has the sedimentation chamber 6. A first partition 7a and a second partition 7b (shown in Fig. 3 only) separate the chamber 5 and the sedimentation chamber 6 from each other. Both the chamber 5 and the sedimentation chamber 6 further comprises a lower portion 20, 21, respectively.

The housing T may have varying dimensions. For instance, the chamber 5 may hold approximately 4m³ of wastewater and the diameter of the housing T may be about 2m. A height of the housing T may be about 2.5m. The wastewater treatment system 1 disclosed herein may have varying dimensions and volumes. A line Lmax indicates a maximum wastewater level in Figs 2a and 2b. The minimum wastewater level is indicated by a dashed line Lmin.

The bioreactor 8 is arranged within the chamber 5 of the housing 2’, and has upper apertures 9 and lower apertures 10. The apertures 9, 10 may have different dimensions and shapes. In Figs 2a and 2b, the apertures 9, 10 are arranged in groups of five. The bioreactor 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 10 respectively which are spaced apart such that a circular flow of wastewater between the bioreactor 8 and the chamber 5 can be accomplished. The apertures 9, 10 may be arranged in any way such that a circulation between the bioreactor and the chamber 5 is achieved. Preferably, the lower apertures 10 are arranged close to a bottom area 11 of the bioreactor 8. However, in the lower portion 20 of the chamber 5 sludge may settle. Thus, the lower apertures 10 should be placed sufficiently high enough from the bottom area 11 such that clogging of the lower apertures 10 is prevented.

At a bottom area 11 of the bioreactor 8, the oxygen supplying device 12 is arranged. In Figs 2a- 2d, the oxygen supplying device 12 is in the form of air diffusers. However, the air supplying device 12 may be any type of device which may supply air/oxygen to the bioreactor 8, such as a compressor, a pump or an air diffusing tube. Just as the system 1 shown in Fig. 1, the bioreactor 8 in the wastewater treatment system 1 shown in Figs 2a-2d contains carrier elements 13 (not shown). The number of upper and lower apertures 9, 10 is optional. However, the dimensions of the upper apertures 9 and lower apertures 10 are designed in such a way that the carrier elements 13 cannot exit the bioreactor 8 through the upper and lower apertures 9, 10. An exemplary dimension of the diameter of the carrier elements 13 is about 25 mm, and an exemplary dimension of the diameter of the apertures 9, 10 is about 15-20 mm. The carrier elements 13 in Fig. 1 are made of a material floating in water. However, the carrier elements 13 may also be made of a non-floating material and be fixed inside the bioreactor 8.

The upper and lower apertures 9, 10 have a circular shape as shown in Figs 2a and 2b, or may for instance be present as a grid having openings with dimensions sufficiently small to prohibit the carrier elements 13 from exiting the bioreactor 8 (not shown). Such grid may for instance be of a rectangular shape and be arranged in the zone between the maximum wastewater level Lmax and the minimum wastewater level Lmin. A wastewater treatment system 1 comprising upper and lower apertures 9, 10 in the form of rectangular grids is shown in Fig. 2e. The rectangular grids are positioned around the bioreactor 8 arranged within the chamber 5 inside the housing 2’. Apart from the grid shaped upper and lower apertures 9, 10, the arrangement of the wastewater treatment system 1 shown in Fig. 2e may be as explained with reference to Figs l-2d.

The chamber 5 shown in Figs 2a and 2b is further provided with a first transferring device 14 (also referred to as a transferring device), configured to transfer wastewater from the chamber 5 to the sedimentation chamber 6. A pipeline 23 connects the chamber 5 to the sedimentation chamber 6. The first transferring device 14 may be a first pump. Alternatively, as shown in Figs 2c and 2d, the first transferring device 14 may be installed inside the bioreactor 8. In such case the first transferring device 14 will transfer wastewater from the bioreactor 8 to the sedimentation chamber 6. When the first transferring device 14 is arranged within the bioreactor 8, the carrier elements 13 will prevent the first transferring device 14 from becoming clogged with sludge. In addition, the wastewater pumped from the bioreactor 8 has most certainly been purified. In addition, a further or second transferring device 18, and a discharge device 19, are arranged in the sedimentation chamber 6 in Figs 2a-2d. The second transferring device 18 is a second pump and the discharge device 19 is a third pump. The second and third pump are herein also referred to as a sludge pump and a discharge pump respectively. Sedimented material will sink to the lower portion 21 of the sedimentation chamber 6. The second transferring device 18 is configured to transfer settled material, such precipitated agglomerated sludge, from the sedimentation chamber 6 back to the chamber 5.

In Figs 2b and 2d, the sedimentation chamber 6 comprises a cylindrical pipe 22. The pipeline 23 is connected between the first pump 14 and the pipe 22. The sedimentation chamber 6 shown in Figs 2b and 2d is further equipped with cleansing devices 15, 16, 17. The cleansing device 15 arranged within the pipe 22 is a hydrocyclone, the cleansing device 16 is a pipe sedimentation unit, and the cleansing device 17 is a filter unit, such as a sand filter.

The pipe sedimentation unit 16 is made of a matrix like web material covered with biofilm. Due to gravity, the biofilm on the pipe sedimentation unit 16 will eventually fall off, thus preventing clogging of the pipe sedimentation unit 16. The pipe sedimentation unit 16 includes several tube shaped units arranged vertically side by side. The tubes are made of grid shaped material with a rough surface. The pipe sedimentation unit 16 incorporates biological treatment as biofilm forms on the surface of the material. Filtration of the wastewater also occurs in the grid. Due to the vertical position of the tubes, excessive biofilm and filtrated particles can exit the pipes by gravity and settle at the bottom of the sedimentation chamber 6, thus preventing clogging of the pipe sedimentation unit 16. Wastewater will pass through the pipe sedimentation unit 16 in a substantially horizontal direction.

However, the use of device hydrocyclone 15 and a filter unit 17 is optional, and other types of cleansing devices may also be used in the system 1. The hydrocyclone 15, the pipe sedimentation unit 16, the filter 17 and the discharge device 19 are shown in dashed 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 housing 2’, the inlet 3, the outlet 4, the chamber 5 and the bioreactor 8 are seen from above. The oxygen supplying device 12 is arranged inside the bioreactor 8. The wastewater treatment system 1 further includes the sedimentation chamber 6 which is separated from the chamber 5 by the first partition 7a and the second partition 7b arranged adjacent to a discharge container 24 having an opening 25. The first 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 be explained more in detail with reference to the figures. The wastewater treatment systems 1 shown are filled with wastewater through the inlet 3. This is indicated by the arrow at the inlet 3 in Fig. 3.

Wastewater flows into the chamber 5 and the bioreactor 8. When the chamber 5 of the housing T is completely full, the wastewater reaches the maximum wastewater level Lmax, indicated by a horizontal line in Figs 1 and 2a-b. The wastewater treatment system 1 also has the lower minimum wastewater level Lmin, as seen in Figs 2a-b. The wastewater treatment system 1 has a buffering capacity between the two water levels Lmin and Lmax, such that the system 1 is efficient even when the water supply varies, and is arranged below the inlet 3 to avoid backflow of wastewater.

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

Also, when oxygen is supplied to the bioreactor 8 the water level inside the bioreactor 8 will rise towards the upper aperture(s) 9. Hence, when oxygen is supplied to the bioreactor 8 the water inside the bioreactor 8 will flow upwards towards the upper aperture(s) 9 and exit the bioreactor 8 through the upper aperture(s) 9. Thus, when the water level of wastewater has risen in level with or higher than the upper apertures 9, the wastewater will simultaneously exit the bioreactor 8 through the upper aperture(s) 9. Hence, the oxygen/air supply causes a circular flow of the wastewater within the system 1. Four rounded arrows shown in Fig. 1 indicate this circular water flow inside the system 1. The wastewater is sucked into the bioreactor 8 through the lower aperture(s) 10 and exists the bioreactor 8 through the upper aperture(s) 9. Hence, a recirculation of the wastewater between the chamber 5 and the bioreactor 8 occurs when the oxygen supplying device 12 is active. The oxygen supplying device 12 is arranged in the bottom area 11 of the bioreactor 8 in the figures of the present disclosure. However, the oxygen supplying device 12 may be arranged elsewhere in the bioreactor 8 causing a wastewater flow during air supply in other directions than that indicated by the arrows in Fig. 1.

The circulation between the bioreactor 8 and the 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 the wastewater. The circulation causes the carrier elements 13 to swirl around within the bioreactor 8, resulting in that the wastewater comes into contact with biofilm present on the 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 size of the bioreactor 8, and the state of the wastewater. The more oxygen supplied, the more the water level within the bioreactor 8 will rise. The bioreactor 8 may be designed in such a way that the wastewater flows in an opposite direction as shown in Fig. For the purification of wastewater, the direction of the flow between the bioreactor 8 and the chamber 5 may be varied, as long as circulation between the bioreactor 8 and the chamber 5 is achieved.

The supply of oxygen to the bioreactor 8 results in a wastewater treatment system 1 having an aerobic environment during oxygen supply, and the system 1 being an essentially low oxygen anoxic environment when the air supplying device 12 is switched off. The aerobic environment provides suitable conditions for biological cleansing, e.g. nitrification, to occur. As mentioned above, efficient nitrification requires a high amount if oxygen.

The carrier elements 13 present in the bioreactor 8 are covered with microbial growth, a so called bio film. The bio film hosts aerobic microorganisms suitable for the degradation of contaminating particles. When the air supplying device 12 is active, wastewater which is pulled into the bioreactor 8 is purified by the microorganisms present in the bio film on the carrier elements 13. The circular flow facilitates cleansing of 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 5 hours, such as between 15 minutes and 4 hours, such as between 30 minutes and 3 hours, such as between 45 minutes and 120 minutes. Preferably, the oxygen supplying device 12 is active between 45 minutes and 90 minutes. The oxygen supplying time varies 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 the wastewater. A higher temperature of the wastewater results in a more efficient reduction of nitrogen.

The supply of oxygen should be sufficient to rise the water level inside the bioreactor 8 and to allow for aerobic biological purification 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 large surface area. The combination of a large surface area for hosting microorganisms together with the remaining system 1 results in a degree of nitrification up to 100%.

The anoxic environment provides suitable conditions for denitrification. As mentioned above, efficient denitrification requires a low oxygen environment. Hence, when the air supplying device 12 is switched off the system 1 transforms into a low oxygen environment. Denitrification also requires a carbon source. The carbon source in the wastewater treatment system 1 is the sludge itself, which comprises a large amount of carbon containing materials. The degree of denitrification in the system 1 is also sufficient, being approximately 50-80%, such as 60-70%.

After a period of time, the oxygen supply is reduced or stopped. Preferably, the oxygen supplying device 12 is switched off. The non-active state of the oxygen supplying device 12, or when the amount of oxygen supplied by the oxygen supplying device 12 is reduced, are referred to as a sedimentation period. When the oxygen supplying device 12 is switched off and/or when the oxygen supply is reduced, the water flow in the system 1 stops and the sludge is allowed to settle at the bottom portion 20 of the housing 2’. The sludge present in the bioreactor 8 will settle in the bottom area 11 of the bioreactor 8. The sedimentation period may for instance be between 2 minutes and 5 hours, such as between 5 minutes and 4 hours, such as between 7 minutes and 3 hours, preferably between 9 and 120 minutes, and most preferred about 10 to 60 minutes.

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

When the sludge has settled, the first pump 14 pumps treated wastewater into the sedimentation chamber 6. The wastewater is pumped from the chamber 5 or the bioreactor 8 through the pipeline 23 and to the sedimentation chamber 6. If the pipe 22 is present in the sedimentation chamber 6, the wastewater enters the pipe 22 horizontally, which causes the wastewater to swirl along an inner surface of the pipe 22. A baffle (not shown) stops the rotational swirl of the wastewater at a lower end of the pipe 22 before the wastewater exits at the bottom of the pipe 22. The bottom of the pipe 22 is open, such that the wastewater flows into the bottom 21 of the sedimentation chamber 6.

Wastewater present in the sedimentation chamber 6 passes through the pipe sedimentation unit 16 which is made of a permeable web like material also covered with microbial growth. Hence, the wastewater will be further purified by the microorganism present in said microbial growth.

When the wastewater reaches the opening 25, it will flow into the discharge container 24 and exit through the outlet 4 by gravity flow. Alternatively, the wastewater is 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 before exiting the housing T through the outlet 4.

Preferably, a flocculating agent is added to the sedimentation chamber 6, or to the pipeline 23 connecting the chamber 5 to the sedimentation chamber 6, to cause the remaining sludge and phosphorous to precipitate. Optionally, the flocculating agent is added to the hydrocyclone 15. The precipitated sludge then sinks to the bottom portion 21 of the sedimentation chamber 6. At predetermined time intervals, such as once each day, the sludge pump 18 pumps the settled sludge from the bottom portion 21 of the sedimentation chamber 6 back to the bottom portion 20 of the chamber 5, as indicated by an arrow in Fig. 3. This provides additional carbon containing sludge to the denitrification process, making the denitrification in the chamber 5 even more efficient. In addition, more sludge is consumed by the processes (e.g. a biological or chemical process) in the system 1, reducing the amount of sludge present in the wastewater.

The treated wastewater leaves the discharge container 24 through the outlet 4, as indicated by the arrow in Fig. 3. The wastewater is either discharged using the discharge pump 19, or the wastewater flows out from the outlet 4 by gravity. Since the outlet 4 is arranged below the inlet 3 (shown in Figs 2a and 2b and indicated by the height “H”), the wastewater can automatically exit the housing T through the outlet 4 by gravity flow. However, the inlet 3 and the outlet 4 may be arranged at the same level in the housing 2’. The discharge device 19 may then pump wastewater out through the outlet 4.

All together, the wastewater treatment system 1 provides both an aerobic and an anoxic environment, and a circular water flow which together for advantageous conditions for efficient wastewater cleansing. The degree of mineralisation of the sludge in the chamber 5 is high, which is beneficial for the microorganisms in the bioreactor 8. In addition, due to the mineralisation, the amount of sludge in the system 1 is decreased. Efficient biological purification in the bioreactor 8 is advantageous for the denitrification in the chamber 5. The bioreactor 8 and the housing T recirculate the wastewater between themselves, and the recirculation is achieved through the oxygen supply in the bioreactor. Hence, the system 1 provides an efficient wastewater treatment process.

Finally, it should be mentioned that the inventive concept is not limited to the embodiments described herein, and many modifications are feasible within the scope of the appended claims. Various features disclosed herein and related to various embodiments may be combined depending on specific purposes to be achieved. For instance, the bioreactor may be arranged in the centre of the housing (as shown in Fig.

3) or it may be arranged eccentrically in the chamber of the housing (as shown in Figs l-2b). The wastewater treatment system may be of another kind than illustrated herein. Different pumps, oxygen supplying devices and chambers may be combined with each other, and the bioreactor disclosed herein may be arranged in any type of waste water treatment system where it is advantageous to provide circulation between the bioreactor and another part of said wastewater treatment system. Furthermore, the oxygen supplying device may be in different positions of the bioreactor than shown in the figures. The oxygen supplying device is associated with the bioreactor such that circulation is achieved between the bioreactor and an associated chamber in a wastewater treatment system.

Claims

1. A wastewater treatment system comprising: a housing having an inlet configured to supply wastewater to the system, and an outlet configured to discharge treated wastewater from the system; a bioreactor having at least one upper aperture and at least one lower aperture arranged below the upper aperture; and a device configured to supply oxygen to the bioreactor; wherein the bioreactor is arranged within the housing, and wherein the upper and lower apertures are configured to discharge and receive wastewater, respectively, to provide circulation of wastewater between the bioreactor and a chamber in the housing when oxygen is supplied to the bioreactor.

2. The system according to claim 1, wherein the oxygen supplying device is arranged below the lower aperture, preferably at a bottom area of the bioreactor.

3. The system according to claim 1 or 2, wherein the housing further comprises a sedimentation chamber.

4. The system according to claim 3, further comprising a transferring device configured to transfer wastewater from the chamber or the bioreactor to the sedimentation chamber.

5. The system according to claim 4, wherein the transferring device comprises a pump.

6. The system according to any one of the preceding claims, wherein the bioreactor comprises carrier elements, preferably configured to be covered by microbial growth.

7. The system according to claim 6, wherein the upper and lower apertures have a width smaller than a width of the carrier elements.

8. The system according to any one of claims 3 to 7, further comprising a further transferring device configured to transfer sedimented material from the sedimentation chamber back to the chamber.

9. The system according to claim 8, wherein said further transferring device comprises a pump.

10. The system according to any one of the preceding claims, further comprising a device configured to discharge treated wastewater from the housing through the outlet.

11. The system according to claim 10, wherein the discharge device comprises a pump.

12. The system according to any one of claims 3 to 11, further comprising at least one cleansing device arranged in the sedimentation chamber.

13. The system according to claim 12, wherein said at least one cleansing device comprises a hydrocyclone and/or a pipe sedimentation unit and/or a filter unit, wherein preferably the filter unit is a sand filter.

14. The system according to any one of the claims 6-13, wherein the carrier elements comprise a water floating material.

15. The system according to any one of the claims 6-14, wherein the carrier elements are fixed to an inner surface of the bioreactor.

16. A bioreactor to be included in a housing of a wastewater treatment system, said bioreactor comprising carrier elements, at least one upper aperture and at least one lower aperture arranged below the upper aperture, wherein said bioreactor is associated with an oxygen supplying device and configured to provide circulation of wastewater between the bioreactor and a chamber in the housing by receiving and discharging wastewater through the apertures when oxygen is supplied to the bioreactor.

17. The bioreactor according to claim 16, wherein the lower aperture is configured to receive wastewater when air is supplied to the bioreactor, and the upper aperture is configured to discharge wastewater when air is supplied to the bioreactor.

18. The bioreactor according to claim 16 or 17, wherein said upper and lower apertures have a width smaller than a width of the carrier elements.

19. A method for the treatment of wastewater, comprising the steps of:

- providing a wastewater treatment system according to any one of claims 1 to

15;

- supplying wastewater 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 the chamber through the upper and lower apertures;

- reducing the oxygen supply to the bioreactor, whereby sludge is allowed to settle in the housing and in the bioreactor; and

- discharging the treated wastewater from the system through the outlet.

20. The method according to claim 19, wherein the sludge is allowed to settle in the housing and in the bioreactor for approximately between 2 minutes and 5 hours, preferably between 5 minutes and 4 hours, preferably between 7 minutes and 3 hours, preferably between 9 and 120 minutes, and most preferred between about 10 to 60 minutes.

21. The method according to claim 19 or 20, wherein after the step of reducing said oxygen supply and before discharging the treated wastewater from the system through the outlet, the method further comprises transferring wastewater from the chamber or the bioreactor to a sedimentation chamber in the housing by means of a transferring device, and allowing sludge to settle in the sedimentation chamber.

22. The method according to claim 21, wherein the method further comprises a step where wastewater present in the sedimentation chamber passes through a pipe sedimentation unit.

23. The method according to claim 21 or 22, further comprising a step of adding a flocculating agent to the sedimentation chamber or to the pipe.

24. The method according to any one of claims 21 to 23, further comprising transferring sludge from the sedimentation chamber to the chamber, using a second transferring device.

25. The method according to any one of the claims 19 to 24, wherein the step of supplying oxygen to the bioreactor is performed between 5 minutes and 5 hours, such as between 15 minutes and 4 hours, such as between 30 minutes and 3 hours, such as between 45 and 120 minutes, preferably the step is performed between 45 and 90 minutes.

26. The method according to any one of the claims 19 to 25, wherein the wastewater is discharged using a discharge device, which preferably comprises a pump.

27. A wastewater treatment housing comprising a bioreactor accommodated therein, said housing having an inlet for wastewater supply and an outlet for discharge of wastewater treated by the bioreactor, said bioreactor having wall opening means configured to direct a flow of wastewater to circulate partially within the bioreactor and partially within the housing.

28. The housing according to claim 27, further comprising a device configured to direct said treated wastewater to and out of said discharge outlet.

29. The housing according to claim 27 or 28, wherein said wall opening means comprise at least two spaced openings through a wall section of the bioreactor, said flow of wastewater circulating between these two spaced openings within the bioreactor.

30. The housing according to claim 29, wherein said wall opening means comprise two pairs of spaced openings through opposite wall sections of the bioreactor, said pairs of spaced openings being configured to provide two circulating flows of wastewater within the bioreactor.

31. Use of a bioreactor according to any one of claims 16 to 18, said bioreactor being accommodated within a wastewater treatment system.