WO2017080558A1

WO2017080558A1 - Plant, its use and method for acidifying animal manure

Info

Publication number: WO2017080558A1
Application number: PCT/DK2015/050347
Authority: WO
Inventors: Ken Hyldgaard
Original assignee: Jørgen Hyldgaard Staldservice A/S
Priority date: 2015-11-12
Filing date: 2015-11-12
Publication date: 2017-05-18

Abstract

Disclosed is a plant (1) for acidification of animal manure (5). The plant (1) comprises a process tank (2) provided with control means (10) for controlling one or more parameters of the animal manure (5), wherein the process tank (2) is also provided with supply means (6) for supply of nutrition (4) to the animal manure (5) in the process tank (2) to promote acid production in the animal manure (5). The plant (1) comprises also comprises conveying means (7) for conveying a quantity of animal manure (5) from a livestock stable (8) and to the process tank (2), and return means (9) for returning at least a portion of the acidified animal manure (5) from the process tank (2) to a livestock stable (8). A method for acidifying animal manure (5) is also disclosed.

Description

PLANT, ITS USE AND METHOD FOR ACIDIFYING ANIMAL MANURE

Field of the Invention

The present invention relates to a plant for acidifying animal manure by means of a process tank, a method for acidifying animal manure, and use of a plant.

Background of the Invention

In traditional livestock holdings, it is a known problem that animal manure - typically in the form of liquid manure - from livestock, such as cows and pigs, smells. It is also recognized that some of these obnoxious originates from ammonia emission from livestock manure.

Furthermore, ammonia emission has the drawback that the fertilizing effect of the livestock manure is reduced, and thus it is desirable that the ammonia emission from livestock manure is reduced to both reduce obnoxious smells in and from the livestock stable as well as to increase the fertilizing effect of the livestock manure.

Thus, from European patent EP2322025B1 it is known to acidify liquid manure by adding acid in order to reduce the ammonia emission from the liquid manure. But the acid is dangerous to use and cannot be use in organic farming.

Consequently, it is an object of the invention to provide an advantageous technique for acidifying animal manure. The invention

The invention relates to plant for acidification of animal manure. The plant comprises a process tank provided with control means for controlling one or more parameters of the animal manure, wherein the process tank is also provided with supply means for supply of nutrition to the animal manure in the process tank to promote acid production in the animal manure. The plant comprises also comprises conveying means for conveying a quantity of animal manure from a livestock stable and to the process tank, and return means for returning at least a portion of the acidified animal manure from the process tank to a livestock stable.

It is advantageous to add nutrition to the animal manure to promote acid production in the animal manure preferably by means of acid producing cultures naturally present in the animal manure, but e.g. also in acid producing cultures being added to the animal manure. However, the acid production of such cultures are dependent on many parameters - such as temperature, pH level, light, moisture level, availability of nutrition and other - and to better control one or more of these parameters it is advantageous to add the nutrition in a more controlled environment of a process tank comprising control means for controlling one or more parameters of the animal manure.

And providing the plant with conveying means and return means is advantageous in that it enables that the process tank may be arranged as a separate unit separate from the existing livestock equipment.

It should be noted that in this connection the term "animal manure" should be taken to mean any form of urine and/or faeces, either separately or mixed to liquid manure, and in this connection the term "livestock" primarily covers cows and pigs, but it is also conceivable to use the plant for acidifying animal manure from goats, sheep, horses, mink, chickens or other farm animals.

It should also be noted that in this connection the term "acidification" means that the pH level of the animal manure is lowered, i.e. that the animal manure is acidified. I.e. in most cases the animal manure is acidified from its normal pH level (typically above 7) to a pH level of between 5 and 6.

It should further be noted that in this connection the term "nutrition" means any kind of substance on which an organism can feed i.e. in this case any kind of carbohydrate containing substance or any kind of substance containing elements that can be modified to carbohydrates, so that it e.g. may promote growth in a lactic acid bacteria culture in the liquid manure.

One aspect of the invention is that the process tank further comprises a mixing unit.

To ensure an efficient acidification of all of the liquid manure in the process tank and to ensure that the nutrition is evenly distributed in the process tank, it is advantageous that the animal manure in the process tank is mixed. It should be noted that even though the mixing unit, the conveying means and the return means are mentioned as three separate units, this does not mean that they cannot be one and the same unit. E.g. in an embodiment the mixing unit could be arranged in such a way that the agitating movement both conveys (the conveying means) the animal manure from a stable and at the same time returns (the return means) the animal manure to a stable. Or the conveying means and the return means could be the same unit (e.g. the same pump) and the given function was merely defined by the direction of flow - and/or this unit could also be used as a mixing unit e.g. by forming a closed loop circulation of the animal manure through or in the process tank.

One aspect of the invention is that the mixing unit is a propel agitator.

A propeller agitator is particularly well-suited for mixing animal manure in a process tank as it quickly creates swirls and turbulence in the animal manure ensuring that the acid and nutrition evenly distributed in all of the animal manure.

One aspect of the invention is that the supply means comprises means for supply of liquid nutrition to the animal manure in the process tank. Liquids are easy to move e.g. by means of a pump and liquid nutrition is also easier to distribute evenly in animal manure. It is therefore advantageous to provide the process tank with means for supply of liquid nutrition to the animal manure. One aspect of the invention is that the supply means comprises means for supply of solid nutrition to the animal manure in the process tank.

Solid nutrition is often inexpensive and easy to store. It is therefore advantageous to provide the process tank with means for supply of solid nutrition to the animal manure.

One aspect of the invention is that the nutrition is chosen from a group consisting of: whey, molasses, ensilage, straw, beets, industrial sugar-containing by-products, waste food or milk.

Residual product such as whey, molasses and other contains a high percentage of carbohydrate and they are relatively inexpensive. It is therefore advantageous to chosen the nutrition from the above-mentioned group. One aspect of the invention is that the control means comprises temperature control means.

The temperature of the animal manure is a very important parameter in relation to how efficiency acid producing cultures - such as lactic acid bacteria - are at producing acid. It is therefore advantageous to provide the process tank with temperature control means.

One aspect of the invention is that the temperature control means comprises heating means for heating the animal manure in the process tank. The optimal temperature for acid producing cultures in animal manure is typically well above the surrounding temperature of an average livestock stable. It is therefore advantageous to make the temperature control means comprises heating means. One aspect of the invention is that the temperature control means comprises temperature detection means for detecting a temperature of the animal manure in the process tank.

If the animal manure becomes too hot or too cold the acid producing cultures will be damaged, destroyed or inefficient in producing acid and it is therefore advantageous to make the temperature control means comprises temperature detection means in that it hereby is possible to monitor the temperature of the manure and thereby control the temperature in accordance with the temperature. One aspect of the invention is that the acid is produced by lactic acid bacteria naturally occurring in the animal manure.

Acidifying the manure simply by means of lactic acid bacteria naturally occurring in the animal manure is advantageous in that it ensures a inexpensive and simple acidification process.

One aspect of the invention lactic acid bacteria is added to the animal manure.

If the natural growth of lactic acid bacteria in the manure is too slow it is advantageous to add additional lactic acid bacteria.

One aspect of the invention is that the control means comprises moisture control means. The water content of the animal manure can be an important parameter in relation to how efficiency acid producing cultures - such as lactic acid bacteria - are at producing acid. It is therefore advantageous to provide the process tank with moisture control means.

One aspect of the invention is that the moisture control means comprises moisture supply means for adding moisture to the animal manure in the process tank.

The optimal water content for acid producing cultures in animal manure can be above the water content of average animal manure. It is therefore advantageous to make the moisture control means comprises moisture supply means.

One aspect of the invention is that the moisture control means comprises moisture detection means for detecting a moisture level of the animal manure in the process tank. If the animal manure becomes too moist or too dry the acid producing cultures could be damaged, destroyed or inefficient in producing acid and it is therefore advantageous to make the moisture control means comprises moisture detection means in that it hereby is possible to monitor the moisture level of the manure and thereby control the moisture level in accordance with the temperature.

One aspect of the invention is that the process tank is substantially enclosed in a thermal insulating layer.

To ensure a controlled environment inside the process tank it is advantageous that the possibility of thermal interaction with the surroundings is limited. It is therefore advantageous to enclose the process tank in a thermal insulating layer.

It should be noted that by the term "thermal insulation layer" is to be understood any means capable of significantly lowering thermal conductivity between the inside of the process tank and the outside. Such thermal insulation layer include any kind of material having a low thermal conductivity i.e. typically below 0.5 watts per meter kelvin (W m-1 K-l) such as mineral wool or foam, ceramic insulation tiles, glass foam or other.

One aspect of the invention is that the plant further comprises culture supply means for adding an acid-producing microbiological culture to the animal manure in the process tank.

If the natural growth of acid-producing microbiological culture in the manure is too slow it is advantageous to add additional acid-producing microbiological culture to the manure in the process tank.

One aspect of the invention is that the process tank is substantially sealed from the surroundings. Substantially sealing the process tank from the surroundings is advantageous in that it hereby is possible to create a more controlled environment inside the process tank.

One aspect of the invention is that the process tank comprises venting means for aligning a pressure inside the process tank with an outside pressure.

The natural decomposition processes and other processes in the manure can produce gas emission which could generate a dangerous overpressure inside the tank. It is therefore advantageous to let the process tank comprises venting means for aligning a pressure inside the process tank with an outside pressure.

One aspect of the invention is that the process tank comprises a pH sensor for detecting a pH level of the animal manure in the process tank.

The animal manure inside the process tank should in most cases not be returned to the livestock stable until the manure is acidified to a pre-determined pH level and it is therefore advantageous to make the process tank comprises a pH sensor. One aspect of the invention is that the process tank comprises cleaning means for cleaning the pH sensor. If the pH sensor is not cleaned between manure batches residual acidified manure on the pH sensors can influence the measurements of the new batch of manure and it is therefore advantageous to clean the sensor between manure batches.

One aspect of the invention is that said plant further comprises drainage means for draining at least a portion of the acidified animal manure from said process tank and on to a storage tank.

The conveyance of acidified animal manure to the storage tank ensures that the ammonia emission from the storage tank is reduced and that the fertilizing effect of the animal manure is increased.

The invention also relates to a method for acidifying animal manure, wherein the method comprises the following steps:

• conveying animal manure from a livestock stable to a process tank,

• adding nutrition to the animal manure in the process tank to promote acid production by an acid-producing microbiological culture in the animal manure,

• controlling one or more parameters of the animal manure to further promote acid production by the acid-producing microbiological culture in the animal manure, and

• returning at least a portion of the acidified animal manure to a livestock stable.

Adding nutrition and controlling parameters of the animal manure is advantageous in that it ensures a fast and efficient acidification of the animal manure simply by means of an acid-producing microbiological culture in the animal manure. And doing this in a dedicated process tank is advantageous in that it enables better control of the parameters of the animal manure, thus further ensuring fast and efficient acidification of the animal manure. One aspect of the invention is that the method further comprises the step of agitating the animal manure at least during parts of the acidification process.

Agitating the animal manure in the process tank is advantageous in that it will ensure fast and even distribution of the added nutrition and an even acidification level of the manure.

One aspect of the invention is that the nutrition is not added to the animal manure in the process tank until one or more parameters of the animal manure are above a predefined level or within a predefined range.

It is advantageous to not add nutrition until e.g. a specific temperature of the manure has been reached, a specific amount of the manure is in the process tank or other in that a more efficient acidification process hereby is achieved. One aspect of the invention is that the acidified animal manure is not returned to the livestock stable until a pH value of the animal manure in the process tank is below a predefined level.

According to the present invention not all the manure in the stables are acidified. Only a portion is removed from e.g. the slurry channel of a stable, acidified in the process tank and then returned to the stable with a significantly lower pH value. Thus, according to the present invention a portion of the animal manure is used for acidifying all the other animal manure in the livestock stable and it is therefore advantageous to not returned the manure portion in the process tank until the pH value of the animal manure in the process tank is below a predefined level. One aspect of the invention is that the acidified animal manure is returned to the same livestock stable from which the animal manure was originally obtained.

Returning the acidified animal manure to the same livestock stable from which the animal manure was originally obtained is advantageous in that this makes it easier to control the acidification level in the stable more precisely and it reduces the risk of spreading infection and diseases.

One aspect of the invention is that the method is a method further comprises the step of cleaning one or more sensors used for controlling the one or more parameters of the animal manure.

Cleaning the pH sensor between manure batches is advantageous in that it ensures more precise pH readings.

One aspect of the invention is that the method is a method for acidifying animal manure in a plant according to any of the previously mentioned plants.

Hereby I achieved an advantageous embodiment of the invention.

The invention further relates to use of a plant according to any of the previously mentioned plants for acidifying animal manure from cows, pigs and/or mink.

In relation to cow, pig and mink farming ammonia emission is a significant problem and it is therefore particularly advantageous to use a plant according to the present invention in relation with cow, pig or mink farming.

Figures

The invention will be explained further herein below with reference to the figures in which: Fig. 1 shows a top view of an example of an acidification plant for e.g. a pig farm, and

Fig. 2 shows a top view of an example of an acidification plant for e.g. a cattle farm,

Fig. 3 shows a cross-sectional side view of an embodiment of a process tank.

Detailed description

Figure 1 shows a top view of an example of an acidification plant 1 for e.g. a pig farm.

In the example shown, the livestock stable 8 is divided into three independent stable sections 16, but in another embodiment of the invention the stable 8 might consist of one, two, four or more individual stable sections 16, or the acidification plant 1 might be connected to more than one livestock stable 8, such as two, three or more individual stables 8 each comprising one or more individual stable sections 16.

In the example shown, the animal manure is conveyed from one stable section 16 in the stable 8 to the process tank 2 by means of pipes from the stable 8 to a technical reservoir 26. A pump (not shown) positioned in the technical reservoir 26 acts as conveying means 7 to pump manure through pipes from the technical reservoir 26 to the process tank 2. When a desired level of animal manure has been conveyed to the process tank 2, the conveyance is stopped by stopping the pump 7 and/or by redirecting one or more valves.

In the process tank nutrition from the nutrition reservoir 17 is added to the animal manure in the process tank 2 during agitation by the mixing unit 3. The quantity of nutrition added to the animal manure can be determined based on a pH measurement of the animal manure in the process tank 2 or a preceding measurement of the pH value for the animal manure in the stable 8/stable section 16 from which said quantity of animal manure is obtained. However, in a preferred embodiment a fixed initial portion of nutrition is added to a given amount of animal manure - e.g. based on empirical studies. Further nutrition may be added during the acidification process - either fixed amounts or based on pH level measurements. Alternatively, the quantity of nutrition needed to run an efficient acidification process can be determined in another way.

The quantity of animal manure conveyed from the stable 8 and into the process tank 2 may be determined by one or more level sensors in the process tank 2 or in the stable 8 or in another way.

After the acidification of the animal manure in the process tank 2 by lowering the pH value of the animal manure, at least a portion of the acidified animal manure in the process tank 2 is returned to the stable 8 by return means 9 in the form of pipes from the process tank 2 to a technical reservoir 26. A pump (not shown) positioned in the technical reservoir 26 and pipes from the technical reservoir 26 and back to the stable 8 ensures that the acidified manure is transported all the way back into the stable 8. The acidified quantity of animal manure will typically be returned to the same stable 8 and/or stable section 16 from which it came, but it is also conceivable that the acidified quantity can be returned to one or more other stables 8 and/or to one or more other stable sections 16 in the same stable 8.

From the process tank 2, it is also possible that at least a portion of the acidified animal manure is conveyed to a storage tank 15, either directly from the process tank 2 as shown in Figure 1 or via the technical reservoir 26 from which a branch pipe can convey at least a portion of the acidified animal manure to the storage tank 15.

In the example shown, the conveying means 7 comprise a pump positioned in a dedicated technical reservoir 26, but in another embodiment of the invention the pump could be positioned in the process tank 2, in the stable 8 or somewhere else, or the conveying means 7 could simply be the pipes themselves conveying the animal manure from the stable 8 and to the process tank 2 wherein said pipes were arranged with a downward gradient so that gravity would drive the animal manure to the process tank 2.

Similarly, the return means 9 in the example shown also comprise a pump positioned in a dedicated technical reservoir 26, but in another embodiment of the invention the return pump could be positioned in the process tank 2, in the stable 8 or somewhere else, or the return means 9 could simply be the pipes themselves returning the animal manure from the process tank 2 and to the stable 8, wherein the pipes were arranged with a downward gradient so that gravity would drive the animal manure from the process tank 2 back to the stable 8.

As mentioned above, in the example shown the plant 1 comprises both a pump for conveying the animal manure to the process tank 2 and a pump for returning the animal manure to the stable 8, but in another embodiment of the invention, the same pump could perform both tasks and the pump could also be a part of the drainage means if the pump was also used for pumping acidified animal manure to the storage tank 15. If the pump has several purposes, the technical reservoir 26 will probably also comprise one or more valves to direct the animal manure in the desired direction.

In the example shown, the technical reservoir 26 is shaped as a well buried in the ground outside the stable 8 in which pump, valves and any other equipment are placed at the bottom of said well, but in another embodiment of the invention, the technical reservoir 26 could have the shape of a separate casing above the ground, or the technical reservoir 26 could be an integrated part of the stable 8 or the process tank 2. Alternatively, the technical reservoir 26 could also be divided into one or more separate technical reservoirs 18 with e.g. valves arranged in a reservoir 18 and the pump or pumps arranged in another reservoir 18. In the example shown, the acidification plant 1 furthermore comprises a nutrition reservoir 17 in the shape of a closed tank in which the nutrition can be stored until it is to be added to the animal manure in the process tank 2. In this case, the nutrition reservoir 17 is connected to the process tank 2 by supply means 6 which in this case comprise pipes and a pump capable of pumping the nutrition from the nutrition reservoir 17 and into the animal manure in the process tank 2. In another embodiment of the invention, the nutrition could also be conveyed from the nutrition reservoir 17 and into the process tank solely by means of gravity by positioning the nutrition reservoir 17 above the process tank 2.

In this embodiment of the invention, it is also possible to convey at least a portion of the animal manure from the process tank 2 and into a storage tank 15 such that the quantity of animal manure 5 circulating in the annular duct 25 remains within a fixed minimum and maximum quantity even though more manure is constantly added by the livestock in the stable 8.

Figure 2 shows a top view of an example of an acidification plant 1 for e.g. a cattle farm. Cattle farms in particular - but also other livestock farms - are characterized in that the stables 8 or stable sections comprise an annular duct 25 - also known as a slurry channel - in which the animal manure 5 can circulate.

In this embodiment of the invention, a process tank 2 is connected to this annular duct 25 so that the process tank 2 is arranged outside the stable 8. However, in another embodiment the process tank 2 could be arranged inside the stable 8 or even inside the annular duct 25.

In this embodiment of the invention, the plant 1 is provided with conveying means 7 arranged to pump manure 5 into the process tank and return means 9 for pumping the acidified manure back into the stable 8. However, in another embodiment the conveying means 7 and the return means 9 could be the same unit.

In this embodiment the acidification plant 1 are physically located at different locations - although these are close to each other - in that the acidification plant 1 are formed as an integrated part of the cattle farm. However, in another embodiment the acidification plant 1 could be formed as a single independent unit e.g. arranged to be subsequently installed at existing farms - such as at existing organic livestock farms. I.e. in such an embodiment the acidification plant 1 could e.g. be arranged in a standard ISO container - making it easy the transport and install - or the acidification plant 1 could in another way be formed as a self-containing unit or at least a compact unit just needing power and an pipes connected to the stable to be acidified. In this embodiment the operation of the plant 1 is controlled by control means 10 arranged as part of the plant 1 in the form of a PLC (Programmable Logic Controller), but in another embodiment the control means 10 could instead or also comprise a PC, hard wired circuits or other kinds of hardware and/or software suitable for controlling and operating an automated or semi-automated process.

In this embodiment the plant 1 also comprises a stable pH level sensor 28 arranged to detect the general pH level of the animal manure 5 in the stable 8. In an embodiment the operation of the plant 1 could be in response to reading from this sensor 28 in that e.g. the operation of the plant 1 is not started until the pH level of the manure 5 in the stable 8 is above a predefined level and/or the operation of the plant 1 is continued until the pH level of the manure 5 in the stable 8 is under a predefined level.

Figure 3 shows a cross-sectional side view of an embodiment of a process tank 2. In the example shown, the animal manure 5 is conveyed to a process tank 2 via conveying means 7 conveying the animal manure 5 into the top of the process tank 2. The conveying means 7 convey the animal manure 5 into the process tank 2 until a level sensor 27 detects that a given level has been reached. However in another embodiment the conveying means 7 could be controlled by a timer so that when the conveying means 7 had operated for a given time period the manure 5 would have reached a desired level. Or the amount of manure 5 in the tank 2 could be detected by means of a flow detector or other means.

In this embodiment of the invention, the process tank 2 is provided with supply means 6 in the form of an upper pipe arranged for conveying the substantially liquid nutrition 4 into an upper part of the process tank 2 and a lower pipe arranged for conveying the substantially solid nutrition 4 into a lower part of the process tank 2. However, in another embodiment the supply means 6 could be formed differently in the process tank 2 and/or the arranged differently in the process tank 2. Or in another embodiment the process tank 2 would only comprise a single supply means 6 arranged for supplying solid nutrition, liquid nutrition or both.

In this embodiment the process tank 2 is also provided with venting means 22 to ensure that the pressure inside the tank 2 is not substantially different from the pressure outside the tank 2.

In this embodiment the process tank 2 is also provided with moisture supply means 19 in the form of a pipe arranged for suppling water to the content of the tank 2 and the tank 2 is provided with moisture detection means 19 for detecting the water content level of the manure 5 in the tank 2. However, in a preferred embodiment of the invention the moisture supply means 19 or particularly the moisture detection means 19 would not be present in the process tank 2.

In this embodiment the tank 2 is also provided with a pH sensor 23 arranged to detect a pH level of the manure in the tank 2. Cleaning means 24 is provided to clean the pH 23 sensor between manure batches. In this embodiment the process tank 2 is provided with a thermal insulation layer 20 in the form of a layer of mineral wool substantially enclosing the tank 2 to significantly reduce the thermal conductivity between the inside of the process tank 2 and the outside.

In this embodiment the process tank 2 is also provided with culture supply means 21 enabling that additional acid producing cultures many be added to the manure e.g. if the acidification process runs slow or cannot be initiated by the nutrition. However, most manure 5 inherently contains a sufficient amount of acid producing microbiologic cultures - such as lactic acid bacteria - and in a preferred embodiment of the invention the culture supply means 21 could be omitted.

In this embodiment the process tank 2 is also provided with temperature control means 11 comprising heating means 12 arranged to heat the manure 5 in the tank 2. Given that the tank is thermally insulated the heating means could operate based on empiric studies of the manure's temperature but in this embodiment the heating means 12 is operated in response to measurements of temperature detection means 13 so that the temperature of the manure 5 is maintained above a specific predefined level to better promote acid production of the acid producing microbiologic cultures in the manure 5.

In this embodiment of the invention, the process tank 2 is provided with a mixing unit 3 in the form of a propeller agitator driven by an electric motor; but in another embodiment of the invention, the propeller agitator could be driven by another means or the mixing unit 3 could be constructed as a whisk, mixing paddles, nozzles creating high velocity circulation in the animal manure, a unit for shaking or rotating the entire process tank 2 or it could be any other unit suitable for ensuring that the nutrition 4 is quickly and efficiently distributed in the animal manure 5. When the nutrition 4 has been thoroughly mixed with the animal manure 5, the acidified animal manure 5 can be returned to a livestock stable 8 by the return means 9 which in this case is a pump arranged in a separate outlet pipe. However, in another embodiment the return means 9 could be a submerged pump placed at the bottom of the process tank 2. At least a portion of the acidified animal manure 5 is pumped out of the process tank 2 and into a stable 8 by means of the return means 9. The return means 9 could possibly also be used to convey a portion of the animal manure 5 into a storage tank, or the process tank 2 could be provided with a separate pump for this purpose. The acidified animal manure 5 could also be returned to the stable 8 by reversing the pumping direction of the conveying means 7 or by doing something completely different.

Normal operation of the plant 1 would be as follows: First animal manure 5 is conveyed into the process tank 2 by means of the conveying means 7 until a desired level is reached. In an embodiment the manure could be pre-heated before nutrition was added but in this embodiment nutrition is added immediately after the manure 5 is placed in the tank 2. During this or shortly after the mixing unit 3 will ensure that the nutrition 4 is substantially evenly distributed in the manure 5. The temperature detection means 13 will monitor the temperature of the manure and via the heating means 12 ensure that the temperature of the manure is maintained above a predefined level to ensure better conditions for the acid-producing culture in the manure 5. Further nutrition could be added during the acidification process e.g. in response to pH level readings. After a certain amount of time the acid-producing cultures will have consumed nutrition and in response produced acid which will lower the pH level of the manure 5. When the pH sensor 23 detects that the pH level of the manure is under a predefined level - such as 5, 4.5 or 4 - the return means is activated to convey the acidified manure back to the stable 8 to acidify the rest of the manure in the stable 8. In an embodiment the conveying means could be activated in response to a reading of the pH level of the manure in the stable 8. Once the tank 2 is empty cleaning means 24 will clean the pH sensor 23 and/or other sensors in the tank 2. In the foregoing, the invention is described in relation to specific embodiments of acidification plants 1, process tanks 2, stables 8 etc. as shown in the drawings, but it is readily understood by a person skilled in the art that the invention can be varied in numerous ways within the scope of the appended claims.

List

1. Plant for acidifying animal manure 2. Process tank

j. Mixing unit

4. Nutrition

5. Animal manure

6. Supply means

7. Conveying means

8. Livestock stable

9. Return means

10. Control means

11. Temperature control means 12. Heating means

13. Temperature detection means 14. Moisture control means

15. Storage tank

16. Stable section

17. Nutrition reservoir

18. Moisture supply means

19. Moisture detection means 20. Thermal insulating layer

21. Culture supply means

22. Venting means

23. pH sensor

24. Cleaning means

25. Annular duct

26. Technical reservoir

27. Level sensor

28. Stable pH level sensor

Claims

1. A plant (1) for acidification of animal manure (5) wherein said plant (1) comprises a process tank (2) provided with control means (10) for controlling one or more parameters of said animal manure (5), wherein said process tank (2) is also provided with supply means (6) for supply of nutrition (4) to said animal manure (5) in said process tank (2) to promote acid production in said animal manure (5), conveying means (7) for conveying a quantity of animal manure (5) from a livestock stable (8) and to said process tank (2), and return means (9) for returning at least a portion of the acidified animal manure (5) from said process tank (2) to a livestock stable (8).

2. A plant (1) according to claim 1, wherein said process tank (2) further comprises a mixing unit (3).

3. A plant (1) according to claim 2, wherein said mixing unit (3) is a propel agitator.

4. A plant (1) according to one or more of the preceding claims, wherein said supply means (6) comprises means for supply of liquid nutrition (4) to said animal manure (5) in said process tank (2).

5. A plant (1) according to one or more of the preceding claims, wherein said supply means (6) comprises means for supply of solid nutrition (4) to said animal manure (5) in said process tank (2).

6. A plant (1) according to one or more of the preceding claims, wherein said nutrition (4) is chosen from a group consisting of: whey, molasses, ensilage, straw, beets, industrial sugar-containing by-products, waste food or milk.

7. A plant (1) according to one or more of the preceding claims, wherein said control means (10) comprises temperature control means (11).

8. A plant (1) according to claim 7, wherein said temperature control means (11) comprises heating means (12) for heating said animal manure (5) in said process tank

(2).

9. A plant (1) according to claim 7 or 8, wherein said temperature control means (11) comprises temperature detection means (13) for detecting a temperature of said animal manure (5) in said process tank (2).

10. A plant (1) according to one or more of the preceding claims, wherein said control means (10) comprises moisture control means (14).

11. A plant (1) according to claim 10, wherein said moisture control means (14) comprises moisture supply means (18) for adding moisture to said animal manure (5) in said process tank (2).

12. A plant (1) according to claim 10 or 11, wherein said moisture control means comprises moisture detection means (19) for detecting a moisture level of said animal manure (5) in said process tank (2).

13. A plant (1) according to one or more of the preceding claims, wherein said process tank (2) is substantially enclosed in a thermal insulating layer (20).

14. A plant (1) according to one or more of the preceding claims, wherein said plant (1) further comprise culture supply means (21) for adding an acid-producing microbiological culture to said animal manure (5) in said process tank (2).

15. A plant (1) according to one or more of the preceding claims, wherein said process tank (2) is substantially sealed from the surroundings.

16. A plant (1) according to one or more of the preceding claims, wherein said process tank (2) comprises venting means (22) for aligning a pressure inside said process tank (2) with an outside pressure.

17. A plant (1) according to one or more of the preceding claims, wherein said control means (10) comprises a pH sensor (23) for detecting a pH level of said animal manure (5) in said process tank (2).

18. A plant (1) according to claim 17, wherein said process tank (2) comprises cleaning means (24) for cleaning said pH sensor (23).

19. A method for acidifying animal manure (5), wherein said method comprises the following steps:

• conveying animal manure (5) from a livestock stable (8) to a process tank (2),

• adding nutrition (4) to said animal manure (5) in said process tank (2) to promote acid production by an acid-producing microbiological culture in said animal manure (5),

• controlling one or more parameters of said animal manure (5) to further promote acid production by said acid-producing microbiological culture in said animal manure (5), and

• returning at least a portion of the acidified animal manure (5) to a livestock stable (8).

20. A method according to claim 19, wherein said method further comprises the step of agitating said animal manure (5) at least during parts of said acidification process.

21. A method according to claim 19 or 10, wherein said nutrition (4) is not added to said animal manure (5) in said process tank (2) until one or more parameters of said animal manure (5) is above a predefined level or within a predefined range.

22. A method according to one or more of claims 19-21, wherein said acidified animal manure (5) is not returned to said livestock stable (8) until a pH value of said animal manure (5) in said process tank (2) is below a predefined level.

23. A method according to one or more of claims 19-22, wherein said acidified animal manure (5) is returned to the same livestock stable (8) from which said animal manure (5) was originally obtained.

24. A method according to one or more of claims 19-23, wherein said method is a method further comprises the step of cleaning one or more sensors (13, 19, 23) used for controlling said one or more parameters of said animal manure (5).

25. A method according to one or more of claims 19-24, wherein said method is a method for acidifying animal manure (5) in a plant (1) according to any of claim 1-

18.

26. Use of a plant (1) according to any of claim 1-18 for acidifying animal manure (5) from cows, pigs and/or mink.