WO2000034187A1

WO2000034187A1 - A method and a bio reactor for use in the purification of water, and a bio-element for use in this connection

Info

Publication number: WO2000034187A1
Application number: PCT/DK1999/000675
Authority: WO
Inventors: Knud Peter Brockdorff
Original assignee: Knud Peter Brockdorff
Priority date: 1998-12-04
Filing date: 1999-12-03
Publication date: 2000-06-15
Also published as: AU1549600A

Abstract

In a method for use in biological purification of waste water, the water is passed through at least one bioreactor containing bioelements on which microorganisms grow which can produce the desired conversion of the polluting substances in the waste water. In addtion to nitrification, the bioreactor is used for denitrification by periodically carrying out flushing of the bioelements with a fluid, preferably air or deoxidized water, for so short periods of time that the microorganisms do not suffer damage, but sufficient for the bioelements to be cleaned of dead biomaterial. Also disclosed is a system which, with various units, may be designed for concrete wishes, and moreover a bioelement is disclosed.

Description

A method and a bio reactor for use in the purification of water, and a bio-element for use in this connection.

The present invention relates to a method and bioreactors for use in biological purification of waste water, preferably for recirculating fish breeding systems- in that the water is passed through at least one container containing bioelements on which microorganisms grow which are capable of producing the desired conversion of the polluting substances in the waste water. The invention also relates to a bioelement.

Such methods and systems are well-documented in the pat- ent literature, cf. e.g. DE 35 04 037 Al , DE 29 36 826 A, EP 058 974 Al, EP 575 314 A, JP-A 62-61696. Also, WO 96/03351 discloses a highly efficient system for use in the nitrification of waste water, wherein bioelements are driven around in a container by means of an air lift and aeration at the sides of the container. Since the operation of the system constantly requires supply of a large amount of air/oxygen, it cannot be used for performing denitrification of the waste water for excellent reasons, since a denitrification is an anaerobic process, i.e. a process without the presence of oxygen.

It is now scientifically recognized that for the microorganisms to carry out an optimum conversion of the substances in the water it is important that dead microor- ganisms are gradually removed from the microfilm, so that this constantly appears with as active microorganisms as possible, i.e. a relatively thin microfilm. The problem of the existing denitrification systems is to keep these clean, since they become overgrown relatively rapidly.

The invention realizes that by denitrification flushing of the bioelements may be performed periodically with a fluid, preferably air or deoxidized water, for so short periods of time that the microorganisms do not suffer damage, but sufficient for the bioelements to be cleaned of dead biomaterial . How frequently the flushing is to be initiated and the duration of the operating time are determined on the basis of the concrete conditions, as it depends on the nature of the waste water, the variation in the polluting load of the water, the resistance of the microorganisms to oxygen, the concrete structure of the system, etc.

Expediently, a bioreactor is used, filled with discrete bioelements and with a fluid lift for performing the de- nitrification, said fluid lift being operated periodically for so short periods of time that the microorganisms do not suffer damage or noticeable damage, but sufficient for the bioelements to be cleaned of dead biomaterial. Such a bioreactor has the advantage that the discrete bioelements have a large to extremely large surface .

To increase the efficiency of some of the bioreactors by denitrification, it has been found expedient to create flow of the water in these so that the water passes the bioelements. This flow may be created by a circulating pump, where the water is discharged at the bottom of the reactor and is returned through an inlet at the top, or vice versa. Of course, the bioreactor may also be used for nitrification of waste water, in that the fluid lift is used as an air lift which is kept operated all the time or almost all the time.

Another useful structure of the bioreactor is characterized in that it comprises a preferably cylindrical container with a height h which is smaller than its diame- ter, or a height h which is greater than its diameter but smaller than about 2.5 metres, and that air nozzles are arranged at least along the outer wall of the container immediately above the bottom, preferably in the form of at least one pipe with nozzle holes and connected to a fluid source for creating a steady flow in the water. This bioreactor is unique in having low initial and operating costs, but is not as effective as a reactor with a fluid lift. However, the structure will be attractive in many cases .

In a further embodiment of the bioreactor, this is equipped with a stirrer having a trumpet-like configuration provided with carriers on the upper side for producing a steady vertical flow in the water in the reactor. The operating costs of such a stirrer are relatively modest. With the speed of rotation and the configuration of the rotor and its carriers, the water flow may be adjusted to the need concerned.

An alternative, likewise for denitrification, is a bioreactor with bioelements in the form of preferably replaceable blocks, e.g. of the make Exponet which is used for eel breeding. Exponet blocks consist of pipes made of plastics wires and have a surface of about 150 to 250 m /m . A scavenging air arrangement is provided at the bottom of the container for scavenging the blocks with a fluid. The arrangement may be formed by pipes with scavenging nozzles. Here, too, nitrification may be performed in that a further air arrangement is provided at the bottom of the container for continuous supply of air/oxygen to the container. This arrangement may consist of diffusers or a pipe with nozzles.

A system according to the invention for biological purification of waste water comprises one or more prefilters, a nitrification unit consisting of at least one container with an air lift and/or air nozzles, a denitrification unit likewise consisting of a container with an air lift/air nozzles, alternatively a unit with reverse osmosis. Additionally, the system may comprise a phosphorous precipitation unit and after this optionally an active carbon filter. Finally, the system may comprise a settling unit through which the dirty water may finally be passed. It may e.g. be a three-compartment system or another form of particle filtering unit for removal of large particles from the water.

A bioelement which according to the invention has a den- sity of about 1.1-1.5 and a surface which is larger, preferably two times larger, than the external surface of the base shape of the element.

The bioelements may be formed as a cylinder with an in- ternal framework and external ribs or as a cube with external ribs on at least two opposed side faces. The element may have many other shapes of course, but a shape suitable for making the elements by extrusion, preferably of plastics, is preferred. The bioelements expediently have a length which is between 0.2 and 3 times the transverse dimension of the element.

The invention will be described more fully below with reference to the system shown schematically in the drawing. In the drawing:

fig. 1 shows a cross-section through a reactor for a system according to the invention,

fig. 2 shows a cross-section through a reactor according to the invention,

fig. 3 shows a schematic perspective view of a reactor according to fig. 2, but with another air supply arrangement,

fig. 4 shows a cross-section through another embodiment of a reactor according to the invention,

fig. 5 shows a cross-section through a further embodiment of a reactor according to the invention,

fig. 6 shows a cross-section through a reactor like in fig. 1, but in a slightly different version,

fig. 7 shows a cross-section through a reactor with biobodies in the form of replaceable blocks, and

fig. 8 shows a diagram of a system according to the invention.

As will appear from fig. 1 of the drawing, the reactor comprises a cylindrical container 1 with a conical bottom 2. An inlet 3 for waste water is arranged at the top of the container. An outlet 4 for the purified waste water is arranged at the bottom or in the side wall at the bottom. The outlet is covered by a grating 5 to retain the bioelements in the container. The grating may be cleaned by flushing or scavenging with a fluid, such as air or water which is optionally deoxidized, by means of a device not shown in the drawing. A further inlet 6 for water for subsequent flushing of the system may be provided at the top of the container. A fluid lift 7 is arranged in the centre of the container, said fluid lift terminating a distance below the water surface, e.g. 20-50 cm, which has been found to be more effective and energy-saving in relation to a termination above the water surface. The side wall of the conical bottom 2 is relatively steep, so that the bioelements can slide down the wall at the bottom.

The container is filled about 40-80% with bioelements having a large surface, e.g. small cylinders of plastics with e.g. an internal framework and with a density of about 1.1-1.5.

With the combination of the steep side wall at the coni- cal bottom 2, causing the bioelements to slide down to the bottom, the fluid lift 7 and the light bioelements (e.g. 130-300 kg/m ) in spite of a density of about 1.1- 1.5 (e.g. 500,000-3,000,000 bioelements/ ³ or more) and a very large surface of the individual bioelements and

-3 2 3 per m (e.g. 500-3,000 m /m or more), the conditions are combined such that the desired degree of growth or fouling can easily be established. For denitrification, the reactors may be provided with a pressure pump 28 which may be adjustable. The pressure pump is connected via a valve arrangement 29 with nozzles at the lower end of the fluid lift 7 as well as with a pipe ring 30 with nozzles at the transition between the cylindrical and conical parts of the container. When starting the pressure pump, pressure water will be sent from the bottom of the reactor to the fluid lift and to the pipe ring. The biobodies will hereby be flushed clean with oxygen-poor water. The advantage over scavenging with air is that the biofilm does not suffer damage by being subjected to oxygen. The valve arrangement allows individual control of the water amount for the fluid lift and the pipe ring to provide optimum cleaning of the biobodies .

Further, the reactor may be provided with an adjustable circulating pump 32, by means of which the water content of the reactor may be caused to circulate, thereby in- creasing the capacity of the reactor, since the water circulates past the bioelements that are retained in the reactor tank.

For nitrification, the reactor is equipped with a blower 31 for the supply of air to the fluid lift 7 and the pipe ring 30 via the valve arrangement 29.

The throughput time in the reactor depends on the nitrate content of the water and added carbon amount, but is typically of the order of 20/30 minutes to 3 hours.

An alternative embodiment of a reactor is shown in fig. 2. The container shown is cylindrical with a height h which is smaller than its diameter. Two concentric pipes 10 connected with an air supply source are arranged along the outer walls 8 of the container immediately above the bottom 9. The pipes are formed with nozzle holes or air nozzles 11 which create a steady flow in the water, while aerating it. If relatively to the impurity present in the water no sufficient aeration of the bacterial culture takes place, the pipes 10 have associated therewith an additional set of pipes 12 with air diffusers 13 with the overall purpose of supplying oxygen to the water. The container includes a great concentration of biobodies 14 in the form of small plastics elements on which a biofilm can grow.

It will be appreciated that the air supply to the con- tainer may take place in various ways. Fig. 3 of the drawing thus shows a configuration with air nozzles 15 integrated in the bottom of the container, which is shown to be transparent here. Below the bottom, there may e.g. be a distributing chamber for the air.

Whether air is to be added through one, two or more concentric pipes, and where in the bottom these are to be placed, is decided by tests according to the size of the individual container. The same applies to a possible ad- ditional air supply through air diffusers.

In the reactor shown in fig. 4 of the drawing, the height h of the reactor is greater than its diameter, but smaller than about 2.5 metres. The air supply here takes place with air nozzles 16 arranged in the container wall at the bottom.

For reasons of strength, flow and cleaning, a cylindrical container is the most attractive one, but, of course, this does not exclude other geometrical shapes e.g. with a square, rectangular or oval cross-section.

An embodiment of the reactors shown in figs. 2-4 with circulation of the contents is shown in fig. 5. It is noted that the following description relates to a denitrification reactor. The motion in the reactor is produced with a specially configured rotor 33 which has a trumpet-like shape whose upper side is provided with arc- shaped carriers 34. The rotor is driven by a small electric motor 35 on the end of a shaft 36 which extends above the water level in the reactor . The rotor runs at a speed which allows the cleaning effect of the biobodies to be controlled. For this purpose, the number of revolu- tions of the rotor may be controlled by an inverter 37 connected to the electric motor. In the embodiment shown here, rotation of the rotor will bring about a flow in the height of the reactor which goes down at the rotor shaft and up outwards toward the external wall, which is caused by the special shape of the rotor. To support the upward movement of the water, the inner side of the reactor may be provided with guide plates which guide the water upwards. In addition, a ring pipe 38 with nozzles may be arranged somewhat above the bottom at the side wall. This ring pipe is connected with a pressure pump 39 which sucks in oxygen-poor water at the reactor bottom. The water flow sent out through the nozzles promotes the flow generated by the rotor, which can particularly be an advantage in case of high reactors. However, the efficiency will not be as good as with a reactor with a fluid lift. The reactor may have a flat or, as indicated, a conical bottom and be filled with biobodies with a density below 1.0. It will be appreciated that the reactor may also be used as a nitrification reactor, but then the necessary amount of oxygen must be added to the bacterial culture. Air may be supplied from a blower 40 through a hollow rotor shaft, so that the air gets out on the underside of the rotor and is thrown from the periphery thereof out into the water. The air supply from the rotor is configured so that it sends very fine air bubbles out into the water. Fine air bubbles promote the oxygen uptake in the water and thereby makes it easier to supply the microorganisms with the necessary amount of oxygen. In addition, if necessary, the reactor may be provided with pure oxygen. At the same time, air may be supplied to the nozzle ring 38 with the primary purpose of driving the water flow up- wards . These air bubbles are larger than the air bubbles from the rotor, but secondarily they will also contribute to aerating the water. It will be appreciated that the pressure pump is not operative in this situation. To optimize the conversion in the reactor, the addition of air may fundamentally be controlled on the basis of the necessary oxygen content in the water, just as mutual adjustment between the air supply to the rotor and the nozzle ring may be carried out.

Fig. 6 of the drawing shows a structure similar to the one in fig. 1, but filled with biobodies 17 having a density below 1.0 which are disposed as a floating mass below the water level. The degree of filling may be between 45% and preferably up to about 75%. Depending on the height and base face of the reactor, the fluid lift 7 may optionally be omitted, so that use is made solely of the nozzles 11 in the pipe 11 at the container wall. Outlet as well as inlet may be arranged in the container bottom, alternatively the water may be fed to the reactor at the top. The reactor may alternatively be used as a fine particle filter. When the water is passed through the mass of biobodies which stand still when used as a fine particle filter, the biobodies retain the particles. To clean the filter, the fluid lift/nozzle ring 10 may be activated briefly, whereby the retained material is released and removed e.g. by exchanging the water or by precipitation in the reactor. In preference to scavenging with air, the reactor may accommodate a separate flushing system, e.g. based on flushing with water, optionally deoxidized or oxygen-poor water.

In the same manner as with the reactor illustrated in fig. 1, the reactor shown in fig. 6 may be provided with a pressure pump for flushing with oxygen-poor water, just as the reactor may be equipped with a circulating pump for circulation of its content of water and biobodies. For use as a denitrification reactor, deoxidized/oxygen- poor water is used as a fluid, and for use as a nitrifi- cation reactor the fluid lift and optionally also the pipe ring are kept in constant operation with addition of air. For reactors which are not too high, the fluid lift may be omitted of course, and instead only one or more nozzle rings are used.

As illustrated in fig. 7, an alternative to the previously mentioned reactors is a bioreactor, likewise for denitrification, with bioelements in the form of preferably replaceable blocks 41, e.g. of the make Exponet, which are used in eel breeding. The Exponet blocks, which rest on gratings or girders, consist of pipes made of plastics wire and have a surface of about 150 to 250 m 2/m . A flushing arrangement 42 is provided at the bottom of the container for flushing of the blocks with a fluid. The arrangement may be formed by pipes with flushing nozzles. Like in the other reactors, a circulating pump 43 for circulating the content of water may be used here too to increase the efficiency. Here, too, nitrifi- cation may be carried out by passing air through the flushing arrangement, or by arranging a separate aeration arrangement at the bottom of the container for continuous supply of air/oxygen to the container. This arrangement may consist of diffusers or a pipe with nozzles.

A further aspect of the invention is that the reactors described above may also be used for a nitrification (with partial denitrification) when air is added uninterruptedly. Alternatively, the efficiency may be increased by adding pure oxygen, if a sufficient amount of oxygen is not fed through the addition of air. In the reactors in which stirring takes place, current surface removal of old bacteria will take place - but not as efficiently as in the system according to WO 96/00351, but nevertheless with a very good effect. There is every reason to believe that a partial denitrification will take place in this process, depending on the configuration of the bioelement used.

The first time a new system is started, it takes max. 3 to 4 weeks under usual conditions . After flushing with normal oxygen-containing water, under normal conditions it takes from a few hours to a few days before the system works again. In the denitrification, carbon must perhaps be added currently, e.g. ethanol, methanol or carbon material separated in a prefilter, cf. the following, if sufficient carbon is not present in the water fed. Fig. 8 of the drawing shows a complete system for purification of waste water, preferably for recirculating fish breeding systems . The system comprises one or more nitrification units 18, e.g. according to WO 96/03351 or cf. the foregoing, and thereafter a denitrification unit 19, cf. the foregoing. The process proceeds as follows: ammonium — nitrate -> free nitrogen. In case of great loads of BOD in the water there may be several nitrification reactors in series, typically two, where in the first re- actor preferably only BOD is degraded because of the great load. In the second reactor, in which the water is freed of large amounts of BOD, a subsequent degradation of nitrogen compounds takes place.

When the system according to the invention is used for denitrification, the air lift/air nozzles are operated at regular intervals depending on the load of the system. In systems with reactors with the special stirrer, this, however, is in operation all the time at a speed depend- ing on the pollution load. Methanol addition or addition of other carbon, which takes place from a reactor 20, is regulated in relation to the nitrate content of the waste water and with the speed of the water flowing through.

As will appear from fig. 8, the water in a main stream H from the fish breeding system arrives from the left in the drawing, usually at a prefilter 21, preferably a drum or band filter, in which about 60 to 70% of the biologically degradable material (BOD) can be removed. This car- bon material, cf . 44, may be used as a carbon addition to the denitrification reactors. The main stream H is passed further on to the nitrification reactor 18, from which a substream D is passed directly or through a drum filter to the denitrification reactor 19, from which the puri- fied water is passed to a phosphorous precipitation unit 22 for separation of phosphorous. From there, if so required, the water may be passed through an active carbon filter 23 for cleaning the water of particles.

Finally, the system may comprise a UV or ozone unit for killing bacteria or vira that might be present in the water. The UV or ozone unit may be placed arbitrarily in the system where it is most expedient.

In case of minor loads or where expedient for other reasons, a reverse osmosis unit 24 may be inserted instead of the denitrification reactor. The purified water from the reverse osmosis unit may be passed to phosphorous precipitation, as described above.

The main stream H from the nitrification reactor 18 may be returned directly to the fish breeding system in certain cases, or where fish particularly sensitive to dead biomaterial are involved, the main stream may be returned through a drum or band filter 25 before the main stream is passed back to the fish.

The dirty water stream from the prefilter 21 may be con- veyed together with the dirty water stream from the filter 25 and further on optionally to another drum or band filter 26 in which a further cleaning of BOD and other material takes place. The partially clean water from the last filter may be passed back to the main stream, while the dirty water stream with the filtered BOD material may be passed to a sedimentation system 27 (e.g. a three-compartment system) for precipitation of the BOD material and other material. In a "technologically green solution", precipitation of organic material and phosphorous precipitation take place in a three-compartment system. The precipitated material is passed through a band filter or other filtering unit and is used as a fertilizer optionally after storage in a storage unit, which may par- ticularly be a possibility in the cold season.

The "clean" water is returned to the system, expediently upstream of one of the filters. This "technologically green solution" is very compact and is water-saving, e.g. there are just 3-4 m sludge liquor/day per 100,000 kg production of fish.

Where sufficient space is available, a "natural green solution" with plants may be used, e.g. the plant le na in a three-compartment system. Here, a natural nitrification as well as a denitrification will take place. Here, too, the water, which is discharged from the three-compartment system, may be returned to the system upstream of a filter, after an optional phosphorous precipitation. Another possibility is to use the water for watering greenhouses or plants. The sludge may also be used as a fertilizer, as described above.

For degassing the water, typically for removal of C02 , an aeration unit, e.g. in the form of a trickling filter, may be inserted between the prefilter 21 and the nitrification reactor 18 and/or after this.

An interesting aspect of the described process (in addi- tion to the very large surface and also hole opening which facilitates effective flushing) is that the bioelements are very light in spite of the density of about 1.1-1.5. Hereby, very little energy is required for flushing these. Another useful bioelement is a sand grain-like element e.g. with a density of 0.8 to 1.5 which is so large that the outlet grating may be established without it getting clogged. In this case, the outlet may be moved to the inclined side wall at the bottom.

It will be appreciated that the various system units mentioned in the preamble to the description, the example as well as the claims may be arranged arbitrarily to achieve the desired result. In its simplest form, the system may consist of a prefilter 21 and a nitrification unit 18 as well as optionally a phosphorous precipitation unit 22 and an active carbon filter 23. After the nitrification unit, a denitrification unit 19 or a reverse osmosis unit 24 may be inserted. In all cases, a three-compartment system 27, described previously as a "technically" or "natural" green solution, may be inserted, as needed. The system thus appears as a modular system, in which the in- dividual units may be combined according to the need concerned. It will moreover be appreciated that the present invention may find general use for the purification of waste water and is not restricted to water culture systems. Examples of other fields of use include waste water from households, fish industries, hospitals, etc.

The system may be provided with a computer-based control, alarm and monitoring system which controls water pressure, oxygen addition, etc. to the individual fish ba- sins, bioreactors for nitrification as well as pH and nitrate and ozone content in the water and controls the methanol addition to the denitrification reactor. In case of failure of the system, an automatic alarm is given, and it may be read on the monitor of the computer system where the error occurs. In addition, all data are logged continuously.

Claims

P a t e n t C l a i m s :

1. A method for use in biological purification of waste water by passing the water through at least one bioreactor containing bioelements , on which microorganisms grow which are capable of producing the desired conversion of the polluting substances in the waste water, c h a r a c t e r i z e d in that by denitrification flushing of the bioelements is performed periodically with a fluid, preferably air or deoxidized water, for so short periods of time that the microorganisms do not suffer damage, but sufficient for the bioelements to be cleaned of dead bio- material .

2. A method according to claim 1, c h a r a c t e r i z e d by using a bioreactor filled with discrete bioelements and with a fluid lift for performing the deni- trification, said fluid lift being operated periodically for so short periods of time that the microorganisms do not suffer damage, but sufficient for the bioelements to be cleaned of dead biomaterial .

3. A method according to claim 2, c h a r a c t e r - i z e d in that the fluid lift of the bioreactor is an air lift which is driven continuously for performing a nitrification .

4. A method according to claim 1, c h a r a c t e r - i z e d by using a reactor having a preferably cylindrical container with a height h which is smaller than its diameter, or a height h which is greater than its diameter but smaller than about 2.5 metres, and that air nozzles are arranged at least along the outer wall (8) of the container immediately above the bottom (9), preferably in the form of at least one pipe (10) with nozzle holes and connected to a fluid source for creating a steady flow in the water.

5. A method according to claim 1 or 4 , c h a r a c t e r i z e d by using a reactor equipped with a stirrer having a trumpet-like shape provided with carriers on the upper side for producing a steady vertical flow in the water in the reactor.

6. A method according to claim 1, c h a r a c t e r i z e d by using for the denitrification a bioreactor with bioelements in the form of preferably replaceable blocks, e.g. of the make Exponet, said container being arranged with a scavenging air arrangement at the bottom for scavenging the blocks, said scavenging air being applied periodically for so short periods of time that the microorganisms do not suffer damage, but sufficient for the bioblock to be cleaned of dead biomaterial .

7. A method according to claim 4, c h a r a c t e r i z e d in that air/oxygen may continuously be added to the container through a further air arrangement at the bottom of the container for performing a nitrification.

8. A method according to claim 1, c h a r a c t e r i z e d by using a bioreactor with biobodies with a density below 1.0 and with a degree of filling above about 45% and preferably up to about 80% as a particle filter, said reactor being cleaning by flushing with a fluid at given intervals and for given periods of time depending on the load.

9. A system for biological purification of waste water, c h a r a c t e r i z e d in that it optionally comprises a prefilter, a nitrification unit consisting of one or more containers with an air scavenging arrange- ment, e.g. an air lift, for bioelements in the container, a denitrification unit likewise consisting of a container with bioelements and with fluid addition, preferably an air lift as well as optionally also a precipitation unit or other form of particle filtering unit and optionally finally a unit with reverse osmosis as an alternative to the denitrification unit.

10. A bioelement, c h a r a c t e r i z e d by a density of about 1.1-1.5 and a surface which is larger, preferably twice the external surface of the base shape of the element.

11. A bioelement according to claim 10 in the form of cylinders with an internal framework and external ribs .

12. A bioelement according to claim 10 in the form of cubes with external ribs on at least two opposite side faces .

13. A bioelement according to claim 10, 11 or 12, c h a r a c t e r i z e d in that it has a length which is between 0.2 to 3 times the transverse dimension of the element .