The present invention relates to a system for reducing emission of nitrogen from animal manure containing ammonium. The present invention further relates to a method for reducing emission of nitrogen from animal manure containing ammonium.

Systems and methods for reducing emission of nitrogen from animal manure containing ammonium are known as such. A known example hereof is a so-called air washer which is generally in direct fluid connection with an interior space of a livestock accommodation.

Such an air washer “filters” ammonia from the air of the livestock accommodation, which has ended up in the air due to the ammonium-containing animal manure which is present in the livestock accommodation. The air washer consists of a filter pack comprising a porous carrier material through which the air from the livestock accommodation is guided. The pack of carrier material is moistened from the top with so-called washing water by means of sprinklers, and this washing water is recirculated with a pump and once again sprayed onto the filter pack from the top. In this way the air is brought into contact with the washing water, and the ammonia can dissolve in the washing water.

A drawback of the use of a prior art air washer is however that the air washer removes only the ammonia and particulate matter from animal accommodation air before the air leaves the accommodation. The reduction in nitrogen emission realized thereby generally leaves something to be desired.

It is therefore an object of the present invention to further reduce emission of nitrogen from animal manure containing ammonium.

According to a first aspect thereof, the present invention provides a system for reducing emission of nitrogen from animal manure containing ammonium, comprising a reservoir for collecting excreted animal manure therein, manure displacing means for removing the manure collected in the reservoir from the reservoir, a separator configured to separate a solid component of manure removed by the manure displacing means from a liquid component of the removed manure, and a device for removing nitrogen from the liquid component of the removed manure, comprising a reactor unit which is in fluid connection with the separator and which is configured to increase a free ammonia content in the liquid component of the removed manure separated by the separator in order to reduce the ammonium concentration in the liquid component of the removed manure. Using the system, the manure is treated, and not just the air in the livestock accommodation. In other words, actively reducing the ammonium content in the manure and capturing the ammonia released thereby prevents the manure present in the livestock accommodation from still causing a high nitrogen emission during further processing of the manure outside the livestock accommodation and/or when the livestock accommodation is opened. As a result, the ammonia emission, and thereby the nitrogen emission, decreases. Direct ammonia emission to the atmosphere and to the groundwater and surface water is hereby reduced.

It is particularly noted that the excreted manure is understood to mean all excreta of the animals in question, preferably cattle. The excreted manure thus comprises both urine and faeces. By collecting both urine and faeces and then removing therefrom the component suitable for having nitrogen removed therefrom using the device the fraction of the excreta which is subjected to the nitrogen removal is maximized, i.e. in any case substantially increased relative to systems which apply pre-separation of urine and faeces. Such systems have been specially designed to subject only urine to a nitrogen removal treatment, so that a liquid component of the excreted faeces is not treated and will thereby still emit nitrogen. Urine separators, for instance in the form of small openings, such as a very narrow gaps, in the floor of a livestock accommodation furthermore have the drawback that they can become blocked with solid excrement, i.e. faeces.

Due to such blockages, the desired pre-separation is on the one hand no longer (properly) possible and, on the other hand, the nitrogen emission by this nitrogen-containing excrement in the openings is not prevented. This therefore results in a sub-optimal reduction of the nitrogen emission from the animal manure containing ammonium.

In a preferred embodiment the device further comprises a manure water reservoir configured to collect therein the liquid component of the manure which has been treated by the reactor unit, so that the manure water reservoir maintains a low-ammonium liquid manure composition which is the product of the reduction of the ammonium concentration in the liquid component of the removed manure by the reactor unit, and the system further comprises transport means which are arranged between the manure water reservoir of the device and the reservoir and which are configured to transport the low-ammonium liquid manure composition situated in the manure water reservoir to a position outside the device to be able to utilize the low-ammonium liquid manure composition in order to further reduce the emission of nitrogen.

With the transport means the low-ammonium liquid manure composition situated in the manure water reservoir can be transported out of the device and then be used for fertilization of for instance agricultural land with the low-ammonium liquid manure composition. Since the composition is low in ammonium, the amount of nitrogen which is usually emitted to the atmosphere and to the ground and surface water by fertilization is drastically reduced. In a further preferred embodiment the transport means are configured to transport the low- ammonium liquid manure composition situated in the manure water reservoir to the reservoir and introduce it into the reservoir.

The manure present in the reservoir can hereby be diluted with the low-ammonium liquid manure composition, such that the concentration of ammonium in the manure present in the reservoir is reduced. As a result, the ammonia emission, and therefore the nitrogen emission from the manure present in the reservoir, decreases. Direct ammonia emission to the atmosphere and to the ground and surface water is also reduced hereby. Owing to the introduction of the low- ammonium liquid manure composition into the reservoir, the dilution will also provide for a reduction of the ammonia emission when the manure present in the reservoir is spread over the land.

In summary, the emission by the system is reduced in four complementary ways: by (i) removing the solid component of the manure, (ii) reducing the ammonium concentration in the liquid component of the manure, (iii) diluting the manure present in the reservoir with the low- ammonium liquid manure composition, such that the ammonium concentration of the manure in the reservoir is reduced, and (iv) fertilizing agricultural land with the diluted (i.e. low-ammonium) manure composition present in the reservoir, or directly with the low-ammonium liquid manure composition from the manure water reservoir.

The reservoir preferably comprises a manure pit arranged under a floor of a livestock accommodation and/or a manure silo which is arranged optionally adjacently of the animal accommodation.

The reservoir is however not limited thereto. The reservoir can also comprise a manure silo which is arranged optionally adjacently of the animal accommodation and/or another collecting and/or storing means suitable for this purpose. It is important to note that the manure in the reservoir is diluted with a liquid component of the manure which was already present in the reservoir and has become low in ammonium through application of the method according to the invention.

In a preferred embodiment the reactor unit comprises a reactor housing with an inner space closed off from the atmosphere, and means arranged in the inner space of the reactor housing for the purpose of increasing a free ammonia content in a liquid component of the manure, and the device further comprises an air washer unit comprising an air washer housing with an inner space closed off from the atmosphere, and means arranged in the inner space of the air washer housing for the purpose of capturing ammonia from the air present in the inner space of the air washer housing, wherein the inner space of the reactor housing and the inner space of the air washer housing are in mutual fluid connection via a first air conduit and a second air conduit separated from the first air conduit, and wherein the device comprises air displacing means, wherein the air displacing means are configured to generate an airflow between the inner space of the reactor housing and the inner space of the air washer housing, such that air flows via the first air conduit from the inner space of the reactor housing to the inner space of the air washer housing and flows via the second air conduit from the inner space of the air washer housing to the inner space of the reactor housing.

With the reactor unit the liquid component of the manure is treated such that an equilibrium in the equilibrium reaction:

NH ₄ ⁺ + OH <=> NH ₃ + H ₂ O shifts such that ammonia is released from the thin fraction containing ammonium. The released ammonia is then displaced via the first air conduit to the inner space of the air washer housing using the air displacing means. The means provided therein capture the ammonia from the air in a manner such that the equilibrium in the above stated equilibrium reaction shifts back the other way. The airflow generated using the air displacing means then displaces the “washed” air, i.e. the air which was treated in the air washer housing and from which ammonia was removed, via the second air conduit back to the inner space of the reactor housing. Using the device, the manure is therefore treated, and not just the air in the livestock accommodation. In other words, actively reducing the ammonium content in the manure in an enclosed space and capturing the ammonia released thereby prevents the manure present in the livestock accommodation from /still causing a high nitrogen emission during further processing of the manure outside the livestock accommodation and/or when the livestock accommodation is opened. As a result, the ammonia emission, and thereby the nitrogen emission, decreases. Direct ammonia emission to the atmosphere and to the ground and surface water is hereby reduced.

As stated, the device is connected to a separator. The separator is configured to separate a liquid component of the manure from a solid component of the manure before the liquid component of the manure is treated by the device. The solid component can additionally be stored in an enclosed space before being applied to land to be worked. A particular advantage thereof is that the nitrogen emission in the livestock accommodation is thereby reduced further, since the solid component of the manure excreted in the livestock accommodation has been removed from the livestock accommodation. The effect of reduced nitrogen emission is then twofold. On the one hand, the ammonium content in the liquid component of the manure is reduced without ammonia being emitted to the outside air thereby. On the other hand, the solid component of the manure is stored in a storage space separate from the livestock accommodation.

In a preferred embodiment the means for increasing a free ammonia content in the liquid component of the manure comprise at least one of means for increasing the pH value of the liquid component of the manure, means for increasing an ammonium concentration in the liquid component of the manure and means for increasing a temperature of the liquid component of the manure. Although the ammonium content in the liquid component of the manure is reduced with each of the means, the means for increasing the pH value of the liquid component of the manure have the particular advantage that no heat energy is supplied to the liquid component of the manure by the device, making the device energy-efficient.

The means for increasing the pH value of the liquid component of the manure can comprise means for adding a base to the liquid component of the manure.

The base can comprise at least one of calcium hydroxide, sodium hydroxide and potassium hydroxide.

The means for adding a base can comprise a base pump.

In a preferred embodiment the reactor unit further comprises an area-increasing element configured to increase an exposure surface of the liquid component of the manure, which is exposed to the air of the airflow generated by the air displacing means, by guiding the liquid component of the manure through the area-increasing element.

The area-increasing element can comprise a porous element through which the liquid component of the manure is guided.

The area-increasing element can further be in connection with the means for increasing the free ammonia content in the liquid component of the manure, such that the liquid component of the manure which is guided through the area-increasing element is subjected to the treatment by the means for increasing the free ammonia content.

In a preferred embodiment the device further comprises a manure spraying conduit which is configured to arrange the liquid component of the manure on an upper surface of the area- increasing element, such that the liquid component of the manure moves through the area- increasing element under the influence of the force of gravity.

In a preferred embodiment the device further comprises a manure reservoir which is arranged under the area-increasing element in order to collect and/or store the liquid component of the manure which has been guided through the area-increasing element so that a liquid manure composition situated in the manure reservoir is low in ammonium.

The means for increasing a free ammonia content in a liquid component of the manure and the area-increasing element are preferably configured such that the ammonium concentration is reduced by at least 50%.

The device more preferably also comprises a pump for recirculating the liquid composition situated in the manure reservoir through the area-increasing element by pumping the liquid composition to the upper side of the area-increasing element in order to guide the liquid composition through the area-increasing element. If it is established that the ammonium content in the liquid composition has been insufficiently reduced, i.e. by less than 50%, the collected composition is pumped upward using the pump and once again guided from an upper side of the device through the area-increasing element, where the liquid composition is subjected to the treatment by the means for increasing the free ammonia content. This is done until the ammonium content in the liquid manure composition has been reduced by at least 50%.

In a preferred embodiment an opening of the first air conduit debouching into the inner space of the reactor housing is arranged on a first side of the inner space of the reactor housing and an opening of the second air conduit debouching into the inner space of the reactor housing is arranged on a second side of the inner space of the reactor housing, wherein the first side and the second side of the inner space of the reactor housing lie substantially opposite each other.

The area-increasing element can be arranged between the first side and the second side of the inner space of the reactor housing.

In a preferred embodiment the means for capturing ammonia comprise a filter element through which the air present in the inner space of the air washer housing is guided, and a washing water spraying conduit configured to arrange washing water on an upper surface of the filter element, such that the washing water moves through the filter element under the influence of the force of gravity.

The washing water can comprise water with acid and/or water with bacteria.

The acid can comprise nitric acid and/or sulphuric acid.

In a preferred embodiment the filter element comprises plastic elements provided with irregular holes.

In a preferred embodiment the device further comprises a washing water reservoir which is arranged under the filter element in order to collect and/or store the washing water which has been guided through the filter element so that water situated in the washing water reservoir is high in ammonium.

In a preferred embodiment an opening of the second air conduit debouching into the inner space of the air washer housing is arranged on a first side of the inner space of the air washer housing and an opening of the first air conduit debouching into the inner space of the air washer housing is arranged on a second side of the inner space of the air washer housing, wherein the first side and the second side of the inner space of the air washer housing lie substantially opposite each other.

The filter element can be arranged between the first side and the second side of the inner space of the air washer housing. According to a second aspect, the present invention provides a method for reducing emission of nitrogen from animal manure containing ammonium, comprising of collecting excreted animal manure in a reservoir, separating at least a part of the manure collected in the reservoir into a solid component and a liquid component, actively reducing an ammonium content in the liquid component of the manure in an enclosed space so that a low-ammonium liquid manure composition results, and applying the low-ammonium liquid manure composition to further reduce nitrogen emission.

Using the method, the manure is treated, and not just the air in the livestock accommodation. In other words, actively reducing the ammonium content in the manure and capturing the ammonia released thereby prevents the manure present in the livestock accommodation from still causing a high nitrogen emission during further processing of the manure outside the livestock accommodation and/or when the livestock accommodation is opened. As a result, the ammonia emission, and thereby the nitrogen emission, decreases. Direct ammonia emission to the atmosphere and to the ground and surface water is hereby reduced.

It is particularly noted that the excreted manure is understood to mean all excreta of the animals in question, preferably cattle. The excreted manure thus comprises both urine and faeces. By collecting both urine and faeces and then removing therefrom the component suitable for having nitrogen removed therefrom using the device the fraction of the excreta which is subjected to the nitrogen removal is maximized, i.e. in any case substantially increased relative to methods which apply pre-separation between urine and faeces. Such methods have been specially designed to subject only urine to a nitrogen removal treatment, so that a liquid component of the excreted faeces is not treated, and thereby still emits nitrogen. Urine separators, for instance in the form of small openings, such as a very narrow gaps, in the floor of a livestock accommodation furthermore have the drawback that they can become blocked with solid excrement, i.e. faeces. Due to such blockages, the desired pre-separation is on the one hand no longer (properly) possible and, on the other hand, the nitrogen emission by this nitrogen-containing excrement in the openings is not prevented. This therefore results in a sub-optimal reduction of the nitrogen emission from the animal manure containing ammonium.

By applying the low-ammonium manure composition the emission of nitrogen can be reduced further. The low-ammonium liquid manure composition can for instance be applied to fertilize agricultural land with the low-ammonium liquid manure composition. Since the composition is low-ammonium, the amount of nitrogen which is usually emitted to the atmosphere and to the ground and surface water by fertilization is drastically reduced.

The step of applying the low-ammonium liquid manure composition to further reduce emission of nitrogen therefore preferably comprises of spreading the low-ammonium liquid manure composition over agricultural land in order to fertilize the agricultural land thereby. In an alternative or further preferred embodiment the step of applying the low-ammonium liquid manure composition to further reduce emission of nitrogen comprises of introducing the low-ammonium liquid manure composition into the reservoir.

The manure present in the reservoir is thereby diluted with the low-ammonium liquid manure composition, such that the concentration of ammonium in the manure present in the reservoir is reduced. As a result, the ammonia emission, and therefore the nitrogen emission from the manure present in the reservoir, decreases. Direct ammonia emission to the atmosphere and to the ground and surface water is also reduced hereby. Owing to the introduction of the low- ammonium liquid manure composition into the reservoir, the dilution also provides for a reduction of the ammonia emission when the manure present in the reservoir is spread over the land.

By applying the method the emission of nitrogen is reduced in four complementary ways: by (i) removing the solid component of the manure, (ii) reducing the ammonium concentration in the liquid component of the manure, (iii) diluting the manure present in the reservoir with the low- ammonium liquid manure composition, such that the ammonium concentration of the manure in the reservoir is reduced, and (iv) fertilizing agricultural land with the diluted (i.e. low-ammonium) manure composition present in the reservoir or directly with the low-ammonium liquid manure composition from the manure water reservoir.

The reservoir preferably comprises a manure pit arranged under a floor of a livestock accommodation. The reservoir is however not limited thereto. The reservoir can also comprise a manure silo and/or other collecting and/or storing means suitable for this purpose which is situated optionally adjacently of the livestock accommodation. It is important to note that the manure in the reservoir is diluted with a liquid component of the manure which was already present in the reservoir and has become low in ammonium through application of the method according to the invention.

The ammonium concentration in the liquid component of the manure is preferably reduced by at least 50% by application of the method. More preferably, the ammonium concentration in the liquid component of the manure is reduced by 50-80% using the device. Although the reduction of the ammonium content by more than 80% has the advantage that the treated manure causes even less nitrogen emission, it has the drawback that realizing such a reduction takes so much time and/or energy that it is not very efficient.

Alternatively, the manure present in the reservoir can be diluted with a different liquid, such as water. Dilution with the low-ammonium liquid manure composition however has the particular advantage that the collecting capacity of the reservoir, such as a manure pit arranged under a floor of a livestock accommodation or a manure silo which is arranged optionally adjacently of the livestock accommodation, is largely preserved, since no liquid is added, but only a part of the manure already present in the reservoir is introduced into the reservoir after being treated by application of the method.

In a preferred embodiment the method further comprises of removing said component of the manure collected in the reservoir from the reservoir before the separation.

In a preferred embodiment the step of removing said component of the manure collected in the reservoir from the reservoir comprises of suctioning said component of the manure collected in the reservoir from the reservoir.

In a preferred embodiment the method further comprises of removing the solid component of the manure and, preferably, storing the removed solid component of the manure in a storage unit closed off from the atmosphere after the separation.

In a preferred embodiment the reservoir is located under a floor of a livestock accommodation and the method further comprises of limiting an area section of the floor which is soiled by the excreted manure and/or of removing the excreted manure from the floor.

The step of limiting the area section of a floor which is soiled by the excreted manure is preferably realized by an inclining upper surface of the floor and/or the absence of urine slots in the floor. An inclining upper surface ensures that manure, particularly a liquid component thereof, does not remain on the upper surface. Urine slots, i.e. small openings, such as very narrow gaps, in the floor of a livestock accommodation can become blocked by solid excrement, i.e. faeces. Due to such blockages, the nitrogen emission by this ammonium-containing excrement in the openings is not prevented. This therefore results in a sub-optimal reduction of the nitrogen emission from the animal manure containing ammonium. Dispensing with urine slots therefore contributes to a further reduction of the nitrogen emission by animal manure containing ammonium.

In a preferred embodiment the step of removing the excreted manure from the floor comprises of removing the excreted manure from the floor using a manure scraper and/or a manure robot and/or of spraying the floor with a low-ammonia liquid.

In a preferred embodiment the step of actively reducing an ammonium content in the liquid component of the manure comprises of actively increasing a free ammonia content in the liquid component of the manure and of separating ammonia released from the liquid component of the manure from the liquid component of the manure, comprising of discharging ammonia released from the liquid component of the manure, such that the released ammonia is not emitted and a low- ammonium liquid manure composition is obtained.

The step of actively increasing a free ammonia content in the liquid component of the manure preferably comprises at least one of the following steps: increasing the pH value of the liquid component of the manure, increasing the ammonium concentration in the liquid component of the manure and increasing a temperature of the liquid component of the manure. The step of increasing the pH value of the liquid component of the manure preferably comprises of adding a base to the liquid component of the manure, wherein the base comprises at least one of calcium hydroxide, sodium hydroxide and potassium hydroxide.

In a preferred embodiment the step of discharging ammonia released from the liquid component of the manure comprises of increasing the exposure surface of the liquid component of the manure which is exposed to the surrounding air and of capturing the released ammonia.

The step of capturing the released ammonia preferably comprises of bringing the released ammonia into contact with washing water, wherein the washing water comprises nitric acid and/or sulphuric acid.

In a preferred embodiment the step of actively reducing the ammonium content in the liquid component of the manure comprises of reducing the ammonium content in the liquid component of the manure until the ammonium content in the liquid component of the manure has decreased by at least 50%. The step of actively reducing the ammonium content in the liquid component of the manure preferably comprises of reducing the ammonium content in the liquid component of the manure until the ammonium content in the liquid component of the manure has decreased by 50-80%.

In a preferred embodiment of the method use is made of the system according to the present invention, particularly according to any one of the embodiments described above.

The present invention will be further elucidated with reference to the following figures, which show preferred embodiments of the device and the method according to the present invention and are not intended to limit the scope of protection of the invention in any way, wherein: figure 1 is a schematic perspective view of a preferred embodiment of the system according to the present invention; figure 2 is a perspective view of a preferred embodiment of the device for removing nitrogen of the system according to the present invention; figure 3 is a top view of the preferred embodiment shown in figure 2; figure 4 is a front view of the preferred embodiment shown in figure 2; figure 5 is a side view of the preferred embodiment shown in figure 2; figure 6 is a front view of a cross-section of the preferred embodiment shown in figures 2-5 along the cross-sectional line A- A shown in figure 3; figure 7 is a side view of a cross-section of the preferred embodiment shown in figures

2-5 along the cross-sectional line B-B shown in figure 3; figure 8 is a flow diagram of a preferred embodiment of the method according to the present invention; figure 9 is a flow diagram of a further preferred embodiment of the method according to the present invention; figure 10 is a flow diagram of a preferred embodiment of one of the method steps of the method shown in figure 8 and figure 9.

In a preferred embodiment of a system 2 according to the present invention, as shown in figure 1 , a device 1 for removing nitrogen from thin fraction containing ammonium is connected to a manure pit 42 arranged under a floor 41 of a livestock accommodation 40. Connected to manure pit 42 are means 43 for removing the manure present therein and for transporting removed manure to a separator 44. The separator 44 is configured to separate a solid component of the removed manure from a liquid component of the removed manure. The solid component, in other words the thick fraction, is then transported from the separator via a transport conduit 45 to a storage reservoir 46 for storage therein. The liquid component, in other words the thin fraction, is then transported by means of a transport conduit 47 to a reactor unit 10 of device 1. The thin fraction is there guided through the filter pack of reactor unit 10, whereby the ammonium concentration in the thin fraction is reduced and the ammonia content in the air in a reactor housing 11 of reactor unit 10 is increased. The ammonia-rich air is then guided to an air washer unit 20, where the ammonia reacts with the washing water. The ammonium-rich washing water is collected in a washing water reservoir 26 of air washer unit 20 and can then be transported via a conduit 49 to a silo for storage. This liquid fraction contains ammonium sulphate or ammonium nitrate and can be used as fertilizer or for the production of fertilizer.

The thin fraction guided through the filter pack of reactor unit 10 is collected in a manure reservoir 16 so that a low-ammonium liquid manure composition is situated in this manure reservoir 16. The manure reservoir 16 is then connected via a conduit 48 to manure pit 42 so that the low-ammonium liquid manure composition can be transported to the manure pit 42. In this way the manure present in manure pit 42 can be diluted with low-ammonium liquid manure composition, this contributing to a drastic reduction of the nitrogen emission from manure pit 42. The effect thereof is twofold. On the one hand, the nitrogen emission is reduced by the removal of the thick fraction and the reduction of the ammonium concentration in the thin fraction. On the other hand, the nitrogen emission is further reduced by the introduction of the low-ammonium thin fraction into manure pit 42, whereby the manure present in manure pit 42 is diluted such that the ammonium concentration of the overall quantity of manure present in manure pit 42 is reduced.

The device 1 thus consists of a reactor unit 10 and an air washer unit 20. Reference is made to figures 2-7. Reactor unit 10 and air washer unit 20 consist respectively of a reactor housing 11 and an air washer housing 21, these each having an inner space 12, 22 which is closed off to the outside air. Situated in the inner space 12 of reactor housing 11 is a porous element 13 comprising a column of filter material manufactured from plastic, also referred to as structured packing, with a contact surface of 100 m ² per cubic metre of filter material. The column has a height of a maximum of 2.7 m and a thickness of a maximum of 0.9 m. Further situated in the inner space 12 of reactor housing 11 is a spraying conduit 14 for arranging a quantity of a liquid component of excreted animal manure, also referred to as the thin fraction, on porous element 13 from above. This thin fraction is obtained by means of a separator whereby a liquid component of the excreted animal manure can be separated from a solid component of the excreted animal manure. The solid component is also referred to as the thick fraction.

By arranging the thin fraction on top of porous element 13 by means of spraying conduit 14 the thin fraction seeps through the porous element 13 which, owing to its large contact surface of 100 m ² per cubic metre, considerably increases the contact surface or exposure surface of the thin fraction with which the thin fraction is exposed to the air present in the inner space 12 of reactor housing 11. At the same time, a base is added to the porous material of porous element 13 in order to increase the pFl value of the thin fraction. In this way the equilibrium in the equilibrium reaction:

NH ₄ ⁺ + OH <=> NH ₃ + H ₂ O shifts such that ammonia is released from the thin fraction containing ammonium. Situated under porous element 13 is a manure reservoir 16 for collecting the thin fraction which has been guided through porous element 13 and which has acquired a lower ammonium concentration due to the addition of the base. Low-ammonium thin fraction is therefore situated in this manure reservoir 16. The ammonium concentration is preferably reduced by at least 50%. If the ammonium content has been reduced insufficiently, i.e. by less than 50%, the collected thin fraction is pumped upward and once again guided from an upper side of the device through porous element 13, to which the base is supplied. This is done until the ammonium content has been reduced by at least 50%.

The ammonia released by the base ends up in the air situated in porous element 13 and is transported via an outgoing conduit 32 between the inner space 12 of reactor housing 11 and the inner space 22 of air washer housing 21 to the inner space 22 of air washer housing 21 using a fan 31. Fan 31 is configured and arranged such that an airflow is created in the inner space 12 of reactor housing 11, which airflow runs from a first long inner side 17 of reactor housing 11, via porous element 13 to a second long side 18 of reactor housing 11, where the outgoing conduit 32 is in connection with the inner space 12 of reactor housing 11. As an alternative to or in addition to the addition of a base to the thin fraction in porous element 13, the thin fraction can likewise be treated with heat so that a temperature of the thin fraction increases. In this way ammonia is likewise released from the thin fraction containing ammonium. The addition of a base to the thin fraction in order to reduce the ammonium content however has the advantage that the energy consumption of device 1 is low because no heat need be supplied to the thin fraction.

By increasing the pH value or the temperature of the thin fraction the ammonium, and therefore the nitrogen, in the thin fraction is therefore converted into ammonia, which passes into the gaseous phase, in the reactor unit 10, also referred to as the evaporator unit. The air in the inner space 12 of reactor housing 11 is then transported via outgoing conduit 32 to air washer unit 20, also referred to as air washer for short. In air washer unit 20 the ammonia present in the air reacts with an acid, such as sulphuric acid or nitric acid, into respectively liquid ammonium sulphate or ammonium nitrate. These substances can be used or sold as fertilizer, and can be stored in a silo (not shown) placed near the air washer unit. This fertilizer can of course be applied for own use, or be sold.

The ammonia-rich air coming from reactor housing 11 is then guided through a chemical washer 23 in the inner space 22 of the air washer housing 21 of air washer unit 20 in order to there capture the ammonia. For this purpose chemical washer 23 is constructed from a column of filter material manufactured from plastic, also referred to as structured packing or filter pack, with a contact surface of 100 m ² effective metres of filter material and a height of a maximum of 2.7 m and a thickness of a maximum of 0.9 m. The capacity of the filter pack is a maximum of 6522 m ³ of air per hour per square metre of approach flow area. For the purpose of filtering the ammonia from the air so-called washing water, comprising water with an acid or water with bacteria, is introduced into the filter pack on the upper side of the filter pack by means of a spraying conduit 24 and guided through the filter pack. In this way the equilibrium in the equilibrium reaction:

NH ₄ ⁺ + OH <=> NH ₃ + H ₂ O shifts such that ammonia from the ammonia-rich air is captured in the washing water, and the washing water therefore becomes ammonium-containing. Situated under the filter pack of the air washer unit is a washing water reservoir 26 for collecting the washing water which has been guided through filter material of the structure and which has acquired an increased ammonium concentration due to the passage of the ammonia-rich air. Ammonium-rich water with acid, particularly liquid ammonium sulphate or ammonium nitrate, is thus situated in this washing water reservoir 26. Fan 31 then causes the low-ammonia air, i.e. filtered air, coming from the filter pack of the chemical washer 23 of air washer unit 20 to flow via a return conduit 33 to the inner space 12 of reactor housing 11 of reactor unit 10, which air enters this inner space 12 on a side of the porous element/the filter pack of reactor unit 10 which lies opposite the side of the porous element/the filter pack of reactor unit 10 facing toward the outflow opening of outgoing conduit 32. Outgoing conduit 32 further comprises between reactor unit 10 and air washer unit 20 a draw-off point 34 for drawing off air from the airflow in outgoing conduit 32 between reactor unit 10 and air washer unit 20 in the direction of air washer unit 20.

Both the reactor unit 10 and the air washer unit 20 have on their front side a control area 19, 29 for controlling respectively the reactor unit 10 or evaporator unit and the air washer unit 20. Device 1 also comprises a central processor (not shown) where data of air washer unit 20 are recorded, as well as the measurement data of measurements of the added base and the measurement data of measurements of the pH value of the filter pack of both reactor unit 10 and air washer unit 20. The pH value of low-ammonia thin fraction discharged from reactor unit 10, which must not have a pH value higher than 8, is also tracked.

Device 1 thus makes it possible to drastically reduce the ammonium concentration in animal manure without ammonia being emitted to the outside air, so that an ammonia emission and therefore nitrogen emission from the animal manure can be drastically reduced.

Two manure compositions therefore remain after processing of the manure, i.e. a solid manure composition, the thick fraction, with a high concentration of organic substance and a liquid manure composition, the thin fraction, with a low concentration of ammonium. In addition, an acid liquid fraction also remains, which can be used for the production of fertilizer. Because reducing the ammonium content in the thin fraction takes place in enclosed spaces, no emission of ammonia occurs.

In summary, the thick fraction with the high concentration of organic substance can be stored and be spread on own land and/or be sold. The acid liquid fraction which remains as a result of the “washing” of the ammonia-rich air in the device, comprising ammonium nitrate or ammonium sulphate, can be used for the production of fertilizer.

The low-ammonium/low -nitrogen thin fraction can also be spread on own land, or be utilized for a further reduction of the nitrogen emission. This will be described hereinbelow.

With the method according to the present invention the nitrogen emission from a manure pit of a livestock accommodation and/or a manure silo is reduced by reducing the ammonia emission from the manure present in the manure pit and/or the manure silo. This ammonia emission can be reduced by a factor of 4 with the method according to the present invention. Referring to the flow diagram as shown in figure 8, the manure is for this purpose collected (S 101 a) in a reservoir, such as a manure pit and/or the manure silo, removed and transported to a separator, where a solid component of the manure, also referred to as the thick fraction, is separated (S102) from a liquid component of the manure, also referred to as the thin fraction. The thick fraction comprises a great deal of organic substance and can be stored and then be spread (SI 04) on own land or be sold. The thin fraction is processed further. In particular, the ammonium content in the thin fraction is actively reduced (SI 03) in an enclosed space of a device suitable and intended for this purpose. The low-ammonium thin fraction obtained with this device is then fed out by the device and guided back into the reservoir so as to be introduced into the reservoir (SlOlb). In this way the manure present in the manure pit and/or the manure silo is diluted with the low-ammonium thin fraction, i.e. a low-ammonium liquid manure composition. This dilution of the manure present in the manure pit and/or the manure silo ensures that the ammonium concentration of the overall quantity of manure present in the manure pit and/or the manure silo is drastically reduced. As a result, the amount of free ammonia in the manure is drastically reduced, whereby the emission of nitrogen from the manure pit and/or the manure silo can be significantly reduced, i.e. by a factor of 4. The effect is twofold. On the one hand, the nitrogen emission is reduced by the removal of the thick fraction and the reduction of the ammonium concentration in the thin fraction. On the other hand, the nitrogen emission is further reduced by the introduction of the low- ammonium thin fraction into the manure pit and/or the manure silo, whereby the manure present in the manure pit and/or the manure silo is diluted such that the ammonium concentration of the overall quantity of manure located in the manure pit and/or the manure silo is reduced.

After processing of the manure according to the method two manure compositions therefore remain, i.e. a solid manure composition, the thick fraction, with a high concentration of organic substance and a liquid manure composition, the thin fraction, with a low concentration of ammonium. In addition, a third fraction remains as a result of the method step of actively reducing the ammonium content in the thin fraction. Reference is made to the flow diagram as shown in figure 9. When the ammonium content in the thin fraction is actively reduced (S103) using the device, ammonia is released, which ends up in the air in the enclosed space of the device in the gaseous phase. This ammonia is then removed from the air using a filter element and acidic washing water, with which the ammonia reacts into an acidic liquid containing ammonium. This acidic liquid fraction can be used for the production of fertilizer (S105). Because actively reducing the ammonium content in the thin fraction (S103) takes place in an enclosed space, no emission of ammonia occurs.

The method step of actively reducing the ammonium concentration in the thin fraction (SI 03) will be further elucidated with reference to the flow diagram shown in figure 10, which shows a preferred embodiment of said method step. The ammonium content in the thin fraction can be reduced by adding (SI 06) a base, such as calcium hydroxide, sodium hydroxide or potassium hydroxide, to the thin fraction. This increases the pH value of the thin fraction, whereby the equilibrium in the equilibrium reaction:

NH ₄ ⁺ + OH <=> NH ₃ + H ₂ O shifts such that ammonia is released from the thin fraction containing ammonium.

This results in a reduction of the ammonium concentration in the thin fraction. The extent of the reduction is determined by the quantity of base added to the thin fraction. In the method step shown in figure 10 a quantity of base is added to the thin fraction such that the ammonium content in the thin fraction is reduced by at least 50%, before it is deemed low-ammonium and can be introduced into the manure pit and/or the manure silo. Adding a base is for instance done by having the thin fraction seep downward through a porous element from an upper side of the device, wherein the base is supplied to the porous element and the thin fraction. At the bottom of the porous element is situated a receptacle for collecting the fraction which has seeped through the porous element, in which a sensor is preferably situated for measuring the ammonium content. If the ammonium content has been insufficiently reduced, i.e. by less than 50%, the collected thin fraction is pumped up and once again guided through the porous element, to which the base is added (S106), from an upper side of the device. This recirculation and addition of the base (S106) takes place until the ammonium content has been reduced by at least 50%.

By adding the base to the thin fraction (S106) ammonia is released, which ends up in the air in the enclosed space of the device. This ammonia can then be removed from the air by “washing” the air (S 107) using an air washer. This air washer comprises a filter element which contains washing water and through which the ammonia-rich air is guided. The washing water comprises water with an acid, whereby the equilibrium in the equilibrium reaction:

NH ₄ ⁺ + OH <=> NH ₃ + H ₂ O shifts such that ammonia is captured from the ammonia-rich air in the water. Depending on the acid used, which can for instance be nitric acid or sulphuric acid, a liquid fraction results comprising for instance liquid ammonium nitrate or ammonium sulphate, respectively. This substance can be stored in a silo placed near the device and be used as fertilizer.

The yield of the ammonium removal in the device depends on the amount of base added to the thin fraction. Typically, said device can process a quantity of thin fraction corresponding to a yearly quantity of manure excretion of about 300 to 350 cows, wherein the reduction of the ammonium content, i.e. of the substances causing nitrogen emission, amounts to 50 to 80%. Because no heat is used in the shown preferred embodiment for increasing the free ammonia content in the thin fraction, the energy consumption of the device suitable and intended therefor is low. It is noted for the sake of clarity that, due to the fact that the method step of actively reducing the ammonia content in the thin fraction (S103) takes place in an enclosed space, no nitrogen emission to the outside air occurs during said method step.

With the method as shown in figures 8-10 the surface area of the nitrogen-emitting surface of the manure present in the manure pit and/or the manure silo is reduced in two ways. Firstly, a reduction of said surface area takes place by separating and removing (SI 02 and SI 04) the solid fraction from the manure pit and/or the manure silo. Secondly, said surface area is reduced by the introduction of the low-ammonium liquid manure composition (SlOlb), i.e. the low-ammonium thin fraction, into the manure pit and/or the manure silo, whereby the manure present in the manure pit and/or the manure silo is diluted such that the ammonium concentration thereof is reduced.

In addition to removing the thick fraction and diluting the manure present in the manure pit and/or the manure silo with the low-ammonium thin fraction a number of additional measures can be taken. The surface area of the nitrogen-emitting surface of the floor of the livestock accommodation situated above the manure pit can thus be reduced by designing the floor such that as much of the manure excreted by the cattle present in the livestock accommodation as possible finds its way into the manure pit. The floor can thus have slots through which the manure falls into the manure pit. Such a floor provided with slots can result in a reduction of about 20% of the surface area of the nitrogen-emitting surface of the floor relative to a completely closed floor.

Urine can also be discharged quickly here. Manure can also be prevented from sticking to the floor with a tapering distance between floor beams of the floor. In addition, a reduction in surface area of the nitrogen-emitting surface of the floor is obtained by dispensing with urine slots in the floor, which may become blocked, causing urine to remain on the floor.

Alternatively or additionally to the above stated measures, the surface area of the nitrogen- emitting surface of the floor of the livestock accommodation can be reduced by frequently removing the manure present on the floor using a manure scraper or manure robot, or by means of spraying the floor with a low-ammonia liquid. The manure scraper and/or the manure robot is then preferably provided here from a material manufactured from plastic, preferably elastically deformable, so that the floor can be cleaned properly. The manure scraper and/or the manure robot also comprises a time switch which can be set in order to ensure the cleaning frequency of the floor of the livestock accommodation required for the reduction in nitrogen emission.

The present invention is not limited to the shown embodiments but also extends to other embodiments falling within the scope of protection of the appended claims.