WO2007131522A2

WO2007131522A2 - Method and device for purification of wastewater

Info

Publication number: WO2007131522A2
Application number: PCT/EP2006/004548
Authority: WO
Inventors: Hans-Olof Thilander; Gunno Renman
Original assignee: BIOPTECH AB
Current assignee: BIOPTECH AB
Priority date: 2006-05-15
Filing date: 2006-05-15
Publication date: 2007-11-22
Anticipated expiration: 2008-11-15
Also published as: WO2007131522A3

Abstract

The present invention relates to purification of wastewater such that the content of sludge constituting sub millimetre particles can be reduced in the purified water. A method and an arrangement is provided comprising passing the wastewater through filtering means for filtering suspended material, whereby filtered water is obtained, passing the filtered water through a separating means adapted for separating oxygen consuming matter from the filtered water, whereby separated water is obtained, passing the separated water through a sorption unit for reducing the water phosphorous content, whereby phosphorous reduced water is obtained, characterized in that the method further comprises at least substantially separating sludge constituting sub millimetre particles from the filtered water prior to the step of separating the oxygen consuming matter from the filtered water, by passing the filtered water to straining means, thereby substantially reducing the sludge content of the obtained phosphorous reduced water.

Description

METHOD AND DEVICE FOR PURIFICATION OF WASTEWATER

TECHNICAL FIELD OF INVENTION

The present invention relates to treatment of water in general, and to a method and an arrangement for purifying wastewater in particular.

DESCRIPTION OF RELATED ART

There is a pronounced need for purifying wastewater around the world. Due to an increased urbanization in developing countries a need to purify wastewater has rapidly grown.

A common practise to purify waste or sewage water is to use principles of sedimentation and steps at which chemical reagents precipitate and degrade particulate and dissolved matter in wastewater.

Since the sedimentation process is a macroscopically relatively slow process, time is required for particle settling in sedimentation basins when such are being used for this purpose. The volume of the wastewater being purified is moreover proportional to the surface of the sedimentation basin and for that reason a large area is required to obtain a proportional amount of purified water by sedimentation.

In addition, the efficiency of the sedimentation process quickly decreases with increasing flow rate of the wastewater through the basin. Flowing causing turbulence of the particle containing water decreases the sedimentation rate and thus the efficiency of the sedimentation process.

For the reason that the sedimentation basins require a relatively large surface of slowly flowing water, water purification plants using sedimentation basins require considerable physical space. This may be a clear disadvantage in mountainous areas and in areas where the land is expensive or simply not easily available.

Further, when using sedimentation basins the settled sludge has to be collected by using some means. One example is using a drag-rake that is winched along the bottom of the sedimentation basin. At one end of the basin at which the sludge is collected by the drag- rake the settled sludge falls down into a cavity from which the sludge is pumped off. A drag- rake winched is typically slowly winched across the basin not to cause turbulence in the water. Using a drag-rake also means relying on moving parts that are subjected to tear and wear and which sooner or later will cause malfunction. Another disadvantage with outdoor sedimentation basins is that birds are attracted to them because of the biological material generally contained in the wastewater. The attraction of birds is a hygienic risk, which may involve contamination of the H5N1 , the subtype of influenza virus A, since birds can potentially carry the avian influenza.

Although no person has to date been infected directly from H5N1 carrying birds without close contact during prolonged duration.

It is however not desirable to use outdoor sedimentation basins for that reason.

The utilization of chemical processes in basins requires the addition of chemicals or chemical agents that obviously brings a cost and a step to control and monitor. Moreover it may be required to use aeration or add oxygen to the wastewater to maintain a high yield degradation product of the biochemical process.

Using sedimentation basins and/or chemical reaction steps are therefore not particularly preferable in many cases.

From EP 1 204 607 B1 it is known a method and an arrangement of purification of water. The method as described therein relies on using a three-compartment septic tank as a first sludge separator in a first step for separating the coarsest particles of sludge contained in wastewater that is discharged into the septic tank.

A three-compartment septic tank is a fairly standard product for sludge separation. This standard product is typically cylindrical in shape and can have a diameter of about 1 ,5-2,0 meter. Three-compartment septic tanks utilize the sedimentation process in each one of the three-compartments to gain water from which particles have settled. Settled material has hence to be emptied after usage typically about two times a year.

Since the three-compartment septic tank use settling and due to the design of the compartments, the purification capacity in terms of volume per time duration, such as litres per minute is limited, since the sedimentation process is negatively affected by the turbulence caused by the flowing of water through the three-compartment septic tank. A typical capacity for three-compartment septic tanks is 10 person equivalents, when being used in households.

If overloading a three-compartment septic tank overflow occurs, which may result in that wastewater passes through the septic tank without being purified. The idea behind EP 1 204 607 B1 is to provide a simply and inexpensive arrangement to install and run, and an arrangement that can produce a high degree of water treatment, at moderate water flows.

There is still a need to provide size efficient purification arrangement and a method thereof, where the method and arrangement are biologically considerate to the environment, even at considerably higher water flows.

SUMMARY OF THE INVENTION

The invention is therefore directed towards providing a purification method and an arrangement thereof for purifying wastewater in a biologically considerate manner avoiding excessive fertilization of the environment.

This is achieved by providing purifying in which sludge constituting sub millimetre particles can be separated from the wastewater in a controlled manner.

A first object of the present invention is to provide a method of purifying in which sludge constituting sub millimetre particles can be separated from the wastewater in a controlled manner.

According to a first aspect of this invention, this object is achieved by a method of purifying wastewater, comprising the steps passing the wastewater through filtering means for filtering suspended material, whereby filtered water is obtained, passing the filtered water through a separating means adapted for separating oxygen consuming matter from the filtered water, whereby separated water is obtained, passing the separated water through a sorption unit for reducing the water phosphorous content, whereby phosphorous reduced water is obtained, characterized in that the method further comprises at least substantially separating sludge constituting sub millimetre particles from the filtered water prior to the step of separating the oxygen consuming matter from the filtered water, by passing the filtered water to straining means, thereby substantially reducing the sludge content of the obtained phosphorous reduced water.

A second object of the present invention is to provide an arrangement for purifying in which sludge constituting sub millimetre particles a can be separated from the wastewater in a controlled manner.

According to a second aspect of this invention, this object is achieved by an arrangement for purification of wastewater, said arrangement comprising filtering means, through which in operation, the wastewater is passed, for filtering suspended solids whereby filtered water is obtained, separating means connected to the filtering means, wherein in operation the filtered water is passed through the separating means for separating oxygen consuming matter, whereby separated water is obtained, and a sorption unit connected to the separating means and adapted to contain sorbent material, wherein in operation, the separated water is passed through the contained sorbent material, for reducing the water phosphorous content, whereby phosphorous reduced water is obtained, characterized in that the arrangement further comprises straining means connected to the filtering means and to the separating means such that the filtered water in operation is passed through the straining means, which at least substantially separates sludge constituting sub millimetre particles from the filtered water, thereby reducing the sludge content of the obtained phosphorous reduced water.

The present invention brings the following advantages:

A clear advantage of the present invention is the knowledge of the size of particles being separated from the wastewater. This enables optimization of separating means dependent of the particle content of the water being purified. Presence of particles having a certain size may thus be taken in consideration such that particle purified water can be obtained with at a maintained high flow rate.

It is moreover an advantage that an arrangement according to the present invention is relatively small and at the same time has a high water purifying capacity in terms of flow, which makes the present invention economically competitive in relation to other technical solutions for purifying wastewater. The size of an arrangement of the present invention typically is of the order of about 100 square meters. This brings that the capacity in liters per minute per square meter land that is occupied by the arrangement is competitively high, which is an advantage that may be very valuable. Typical sizes of comparable arrangements for purification of wastewater are about 500 square meters.

The number of moving parts during operation is reduced to a minimum which provides a reliable purification process, decreasing the risk of malfunction of the purification process due to breakdown of movable parts.

The arrangement of the present invention is typically an installation that is positioned above ground, which provides easy access to different parts of the arrangement for monitoring purposes and possibly maintenance purposes. Moreover providing an above ground arrangement, moving of the entire arrangement of part thereof so that the arrangement may be rearranged at a different location, is facilitated.

Providing a purification arrangement without relying on sedimentation basins, animals such as birds and other species do not risk being entrapped in such sedimentation basins, which else could lead to a hygienic risk to the environment surrounding an arrangement or purification plant according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail in relation to the enclosed drawings, in which:

fig. 1 presents a flow chart of a method of purification of wastewater according to one embodiment of the present invention, and fig. 2 schematically shows an arrangement for purification of wastewater according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The underlying idea of the present invention is thus to provide an efficient purification method that can be implemented in a small sized arrangement for purification, for enabling controlling the content of the sludge constituting sub millimetre particles in water being purified using the present invention.

The biological consideration is exemplified by maintaining the sludge content the purified water at a controlled and significantly reduced level, as compared with prior art techniques.

With reference to figs. 1 and 2, presenting a flow chart of a method of purification of wastewater according to one embodiment of the present invention and schematically showing an arrangement for purification of wastewater according to one embodiment of the present invention, respectively, the present invention will be explained in more detail.

According to one embodiment the method starts by step 102, receiving wastewater to be purified. In this embodiment wastewater may comprise run-off water.

According to an alternative embodiment of the present invention the wastewater may comprise industrial wastewater.

According to yet an alternative embodiment of the present invention the wastewater may comprise domestic wastewater.

The wastewater may also comprise any combination of three types of wastewater mentioned above.

The wastewater to be purified may initially be discharged through a pipe or a channel or the like. The method of purification of wastewater according to one embodiment of the present invention starts by the step of receiving wastewater to be purified in step 102, for example from the wastewater being discharged.

Having received the wastewater to be processed in step 102, filtering suspended solids from the wastewater obtaining filtered water, in step 104 is followed. This step, step 104, may be performed by passing the wastewater through a filtering means 202. Among all examples of filtering means 202 that may be used can be mentioned a grating filter 202 have a filter mesh of the order of 1 mm. Other filter mesh sizes may also be used, such as 2 mm. However, since this wastewater treatment step is the first step of the method of purifying wastewater of the present invention, a relatively coarse filter mesh is preferably used to avoid a too rapid filter congestion.

Having obtained filtered wastewater from the filtering means from step 104, sludge constituting sub millimetre particles are separated from the filtered wastewater in step 106.

According to one embodiment of the present invention this step is achieved by passing filtered wastewater through straining means 204. Said straining means 204 typically comprises a filter mesh, through which the filtrate is passed when using the straining means 204 in operation for treating wastewater. According to one embodiment of the present invention the filter mesh is comprised in a microstrainer. According to this embodiment it is thus the filter mesh within the microstrainer that separates the sludge constituting sub millimetre particles from the separation treated wastewater.

According to one embodiment the filter mesh has a certain mesh size, which when being used in the present invention separates particles being larger than this mesh size.

According to one embodiment of the present invention the step 106 separating sludge constituting sub millimetre particles from the filtered wastewater is also achieved by passing the wastewater through a second straining means 206, subsequent to passing the filtered wastewater trough the first straining means 204.

Similar to the first straining means 204, the second straining means 206 comprises a filter mesh which may be comprised in a microstrainer according to one embodiment of the present invention. The filter mesh moreover has a filter mesh size in analogy with the filter mesh size of the filter mesh of the straining means 204.

According to one embodiment of the present invention, the filtered wastewater obtained from the filtering means 202, is thus passed through two straining means of which the first straining means 204 has a first filter mesh size and the second straining means 206 has a second filter mesh size. According to one embodiment of the present invention, the first and second mesh size may each be between 1 micrometer and 250 micrometer.

According to one preferred embodiment of the present invention the first filter mesh size is larger than the second filter mesh size.

According to a more preferred embodiment of the present invention the first filter mesh size is within the interval 41 micrometer to 150 micrometer and the second mesh filter size is within the interval 10 micrometer to 40 micrometer.

According to yet another embodiment of the present invention other intervals of the first and second filter mesh sizes may be realized such as the first filter mesh size being within the interval 55 micrometer to 110 micrometer, and the second filter mesh size being within the interval 15 micrometer to 30 micrometer.

Subsequent to the step of separating sludge constituting sub millimetre particles from the filtered wastewater, the step of separating oxygen consuming matter from the particle separated water follows in step 108, according to one embodiment of the method of the present invention.

Since oxygen consuming matter is separated from the water that is passing through the separating means the oxygen that is consumed by matter remaining in the separated water is decreased. Hence, the biological oxygen demand (BOD), is decreased in this step. One specific measure of BOD is BOD₇, which is a measure determined over a time period of seven consecutive days.

Step 108 of separating oxygen consuming matter from the particle separated water may be implemented by passing the water to be treated through a polyethylene filter having a pore size of about 125 micrometer, in which filter oxygen consuming particles are adsorbed and thus separated from the water flow.

According to an alternative embodiment the separating means may be implemented by using other means than the polyethylene filter as mentioned above.

Separating oxygen consuming matter and thereby lowering the BOD can be considered to be a biological process, since oxygen consuming matter typically being biological matter is accumulated in the separating means.

By passing water through the separating means 208 in step 108, separated water is obtained. It should be emphasized that this separated water that is obtained in step 108, was treated in step 106 such that the content of sludge constituting sub millimetre particles was significantly lowered. For this reason there is practically insignificant amount of fouling in the wastewater after treatment in step 108.

After having separated oxygen consuming matter from the particle separated filtered water obtaining separated water, follows the step reducing the phosphorous content of the separated water in step 110. By performing this step phosphorous reduced water is obtained.

This step may be implemented by passing water to be treated, here the separated water, water , through a sorption unit containing a sorbent material which reduces the phosphorous content of the water passed through.

The sorbent material may be the rock Opoka or the processed form thereof, Polonite®, or other natural sorbent material having phosphorous content reducing capacities. Passing water through a sorbent material phosphorous is thus removed from the water and accumulated in the sorbent material.

Apart from the phosphorous reducing or removing capacity, sorbent materials such as Opoka and Polonite®, and the like often show other advantageous properties, such as a property to reduce nitrogen of the water being passed through the material.

Heavy metals may also be reduced by the sorbent material.

According to an alternative embodiment of the present invention, the sorption unit for reducing of the phosphorous content may contain a reactive filter material for reducing the water phosphorous content.

After prolonged usage of a sorbent material in a sorption unit according to the present invention the sorption capacity reduces and eventually reaches a stage at which the sorbent material preferably is exchanged with unused sorbent material in order to guarantee a at least a minimum phosphorous reducing capacity.

The phosphorous absorbed material can with preference be used as a fertilizer in agriculture directly or even immediately after being used in the present invention.

It should be noted that the step of separating sludge constituting sub millimetre particles from the filtered water significantly prolongs the lifetime of the sorbent material before it had better be exchanged with new unused sorbent material to guarantee a minimum phosphorous reducing capacity. In case straining means according to the present invention is not used the capacity of the sorbent material is rapidly decreased by sub millimetre particles that are accumulated within the sorbent material. This is thus clearly disadvantageous and has to be circumvented.

The inclusion of the straining means in the present invention is thus serving multiple purposes of which one is to minimize fouling in water to be passed to a recipient, and the other to prolong the lifetime of the sorbent material being used.

Having performed the step of reducing the phosphorous content of the separated water in step 110, the step of forwarding the sludge reduced phosphorous reduced water to a recipient, step 112, according to one embodiment of the present invention.

The recipient may typically be a lake, the sea, a river or the like.

It is worth to point out that fouling in the sludge reduced phosphorous reduced water that may be passed to the recipient, is minimized by using the method of purifying wastewater according to the present invention. Since fouling is minimized this invention provides a purification arrangement and a method thereof, where the method and arrangement are biologically considerate to the environment, even at considerably higher water flows.

The typical capacity of an implementation of the arrangement of the present invention is a capacity exceeding 500 person equivalents, which is a significant capacity for a small sized movable arrangement for purifying of wastewater.

The described present invention thus carries the following advantages:

It is moreover an advantage that an arrangement according to the present invention is relatively small and at the same time has a high water purifying capacity in terms of flow, which makes the present invention economically competitive in relation to other technical solutions for purifying wastewater. The size of an arrangement of the present invention typically is of the order of about 100 square meters. This brings that the capacity in liters per minute per square meter land that is occupied by the arrangement is competitively high, which is an advantage that may be very valuable. Typical sizes of comparable arrangements for purification of wastewater are about 500 square meters. The number of moving parts during operation is reduced to a minimum which provides a reliable purification process, decreasing the risk of malfunction of the purification process due to breakdown of movable parts.

The arrangement of the present invention is typically an installation that is positioned above ground, which provides easy access to different parts of the arrangement for monitoring purposes and possibly maintenance purposes. Moreover providing an arrangement above ground level, moving of the entire arrangement of part thereof so that the arrangement may be rearranged at a different location, is facilitated.

Providing a purification arrangement without relying on sedimentation basins, animals such as birds and other species do not risk being entrapped in such sedimentation basins, which else could lead to a hygienic risk to the environment surrounding an arrangement or purification plant according to the present invention.

It is emphasized that this invention can be varied in many ways, of which the alternative embodiments above only are examples of a few. These different embodiments are hence non-limiting examples. The scope of the present invention, however, is only limited by the subsequently following claims.

According to another embodiment of the present invention, a single microstrainer as one example of straining means is being used in the flow of filtered water from the filtering means to the separating means. According to this embodiment the filter mesh size of this single microstrainer is within the interval 10 micrometre and 100 micrometre.

According to another preferred embodiment of the present invention the filter mesh size of such a single mictrostrainer as being used as straining means, is 80 micrometre.

Claims

1. Method of purifying wastewater, comprising the steps: passing the wastewater through filtering means for filtering suspended material, whereby filtered water is obtained, passing the filtered water through a separating means adapted for separating oxygen consuming matter from the filtered water, whereby separated water is obtained, passing the separated water through a sorption unit for reducing the water phosphorous content, whereby phosphorous reduced water is obtained,

characterized in

that the method further comprises at least substantially separating sludge constituting sub millimetre particles from the filtered water prior to the step of separating the oxygen consuming matter from the filtered water, by passing the filtered water to straining means, thereby substantially reducing the sludge content of the obtained phosphorous reduced water.

2. Method of claim 1 , further comprising the step of forwarding the sludge content reduced phosphorous reduced water to a recipient.

3. Method of claim 1 or 2, wherein the step of substantially separating sub millimetre particles comprises separating particles larger than a first size from the filtered water.

4. Method of claim 3, wherein the first size is within the interval 1 micrometer to 250 micrometer.

5. Method of claim 4, wherein the first size is within the interval 10 micrometer to 100 micrometer.

6. Method according to claim 3 or 4, wherein the step of substantially separating sub millimetre particles comprises separating particles larger than a second size from the filtered water, wherein the second size is smaller than the first size.

7. Method of claim 6, wherein the second size is within the interval 1 micrometer to 250 micrometer.

8. Method of claim 7, wherein the first size is within the interval 41 micrometer to 150 micrometer and the second size is within the interval 10 micrometer to 40 micrometer.

9. Arrangement for purification of wastewater, said arrangement comprising:

filtering means, through which in operation, the wastewater is passed, for filtering suspended solids whereby filtered water is obtained, separating means connected to the filtering means, wherein in operation the filtered water is passed trough the separating means for separating oxygen consuming matter, whereby separated water is obtained, and a sorption unit connected to the separating means and adapted to contain sorbent material, wherein in operation, the separated water is passed through the contained sorbent material, for reducing the water phosphorous content, whereby phosphorous reduced water is obtained,

characterized in that the arrangement further comprises straining means connected to the filtering means and to the separating means such that the filtered water in operation is passed through the straining means, which at least substantially separates sludge constituting sub millimetre particles from the filtered water, thereby reducing the sludge content of the obtained phosphorous reduced water.

10. Arrangement of claim 9, wherein the straining means comprises a first filter mesh being adapted to separate sub millimetre particles larger than a first size.

1 1. Arrangement of claim 10, wherein the straining means further comprises a second filter mesh being adapted to separate sub millimetre particles larger than a second size, wherein the second size is smaller than the first size.

12. Arrangement of claim 11 , wherein the first filter mesh and the second filter mesh are provided in series such that the separated water from the first mesh filter is passed to the inlet of the second mesh filter.

13. Arrangement of claim 11 -12, wherein the first and second size are within the interval 1 micrometer to 250 micrometer.

14. Arrangement of any one of claim 11-13, in which the first size is larger than the second size.

15. Arrangement of any one of claim 11-14, wherein the first size is within the interval 41 micrometer to 150 micrometer and the second size is within the interval 10 micrometer to 40 micrometer.

16. Arrangement of any one of claim 10-15, wherein the first filter mesh is comprised in a first microstrainer.

17. Arrangement of any one of claim 11 -16, wherein the second filter mesh is comprised in a second microstrainer.