TECHNICAL FIELD OF THE INVENTION

The present invention relates to a plant and a method suitable for use in zootechnical farming, of cattle, pigs and/or other farm animals, for the abatement of the nitrogen load of the relevant organic waste. STATE OF THE PRIOR ART

Zootechnical farming are often faced with the problem of a high percentage of nitrogen present in the organic waste of the livestock bred. The nitrogen component in waste, consisting mainly of NH ₄ and nitrates, is an onerous problem for farmers. Indeed, they are forced, with a substantial expenditure of money and time, to abate this component, in order to be able to spread the waste in the farmland.

Indeed, in the so called "Nitrates Directive", that is, in the EU Directive 91/676/EEC, the percentage of nitrogen compounds that is allowed to be present in the organic waste of animal origin is regulated, by determination of stringent limits, to enable the waste to be disposed of via its distribution in farmlands.

Techniques currently used for the abatement of the nitrogen load in waste are mainly: separation, nitro/de-nitro, stripping, flotation, and photocatalysis.

However, these methods have the disadvantage of being rather expensive, both in terms of implementation and of maintenance of the plant, as is the case in the stripping and photocatalysis techniques, and above all they do not provide for recycling of the nitrogen removed from the waste itself.

This latter aspect is an important advantage, also from an economic point of view, for the company itself. The nitrogen recovered from animal sewage can, in fact, be used, for example, as a fertilizer for organic farming.

Some types of biological purification of the nitrogen load of animal waste through the use of microalgae are described in the prior art.

However, the data reported in the literature only refer to laboratory experiments.

To the best knowledge of the inventors, to date no system has been provided which is capable of accomplishing this type of biological purification of waste and of being applied in a business context.

OBJECTS OF THE INVENTION One object of the present invention is to improve the state of the prior art.

Another object of the present invention is to provide a plant for the abatement of the nitrogen load of organic waste of zootechnical farms that is advantageous in economic terms.

A further object of the present invention is to provide a plant for the abatement of the nitrogen load of organic waste of zootechnical farms that is effective.

This task and these objects are achieved by the plant for the abatement of the nitrogen load of organic waste of zootechnical farms according to the appended claim 1.

Another object of the present invention is to provide a method for the abatement of the nitrogen load of organic waste of zootechnical farms that is advantageous in economic terms.

A further object of the present invention is to provide a method for the abatement of the nitrogen load of organic waste of zootechnical farms that is effective. This task and these objects are achieved by the method for the abatement of the nitrogen load of organic waste of zootechnical farms according to the appended claim 11. The dependent claims relate to preferred and advantageous embodiments of the invention. All the claims form an integral part of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages will be better understood by those skilled in the art from the following description and from the accompanying drawings, provided as non-limiting examples, wherein:

Figure 1 is a schematic view of a first embodiment of the plant for the abatement of the nitrogen load of organic waste of zootechnical farms according to the present invention; and

Figure 2 is a partial schematic view of a second embodiment of the plant for the abatement of the nitrogen load of organic waste of zootechnical livestock breeding farms according to the present invention

EMBODIMENTS OF THE INVENTION

With reference to Figure 1 , the present invention relates to a first embodiment of a plant for the abatement of the nitrogen load of organic waste of zootechnical farms, indicated in its entirety by 1.

The plant 1 exploits the presence of native microalgae for the abatement of the nitrogen load of organic waste of animal origin. These microalgae, in fact, are able to transform the nitrogen absorbed by the sewage into noble forms of nitrogen, such as protein, chlorophyll and other substances useful for the growth of the microalgae themselves. Once this nitrogen transformation has occurred, the collected microalgae can be used in various ways, also according to their final content. In particular, the microalgae can be used as (a) feed for fish farming; (b) fertilizer for organic farming; (c) a food supplement in animal feed, especially if rich in protein; (d) a source of molecules with high commercial value, such as carotenoid pigments, proteins, polysaccharides, fatty acids; (e) a source of oils for the production of biofuel; (f) additives in matrices to be subjected to biodigestion for biogas production.

Experiments conducted in the laboratory have shown that these microalgae are able to reduce the levels of nitrogen in organic waste by a percentage that is greater than 90%, with reference to the original nitrogen content in the waste itself.

The plant 1 of the present invention is a modular system, comprising at least three tanks 2, 3, 4 connected in series as described in detail hereinafter.

These at least three tanks 2, 3, 4 are connected to each other by means of a system of pipes 5 and are altimetrically staggered relative to one another.

In particular, the plant 1 shown in Figure 1 comprises a first tank 2, placed at a height above the ground H', configured to receive the organic waste 6 of animal origin coming from a zootechnical farm.

Animals bred in this zootechnical farm may be cattle or pigs or other animals suitable for this type of farming.

The organic waste 6 comprises a solid part and a liquid part.

The first tank 2 is fed with the organic waste 6 and fresh water, which is mixed with the waste itself via a mixing system, not represented in the figure, which for example may consist of a system of blades.

The mixing system renders the plant 1 of the invention suitable for the treatment of semisolid zootechnical waste, such as cattle dung, although it is also adaptable for the treatment of more liquid waste, such as pig dung.

The plant 1 shown in Figure 1 also comprises a first pipe 7 for transport and supply of fresh water, as indicated by the arrows 7'.

In the first tank 2, the solid part of the organic waste 6 settles, leaving its liquid part at the surface which, together with the fresh water, extracts the nitrogen component contained in the waste itself. Therefore, the liquid part of the waste contains the nitrogen component of the waste. In this first tank 2 the stages of dilution and mixing of the waste 6 with fresh water can be repeated several times until the extraction of all the extractable nitrogen from the solid part.

In the first tank 2 the ratio between the solid part and the liquid part should preferably be between 1 : 1 and 1 :2.

The plant 1 shown in Figure 1 also comprises a duct 8, connecting the first tank 2 with a second tank 3 placed at a height above the ground H". The second tank 3 is fed with the liquid part of the organic waste 6, transported to the second tank 3 from the first tank 2 by means of the duct 8. The second tank 3 is also supplied with fresh water via the pipe 7.

The duct 8 comprises a filter 9 at the input, which is able to prevent solid particles of the solid part of the waste 6 being accidentally transported to the second tank 3. The duct 8 also comprises gate means 10. The gate means 10 enable regulation of the flow from the first tank 2 to the second tank 3. The gate means 10 are located at a suitable position between the input and the output of the duct 8.

The height above the ground FT of the first tank 2 is greater than the height above the ground H" of the second tank 3: the latter is therefore positioned at a lower level with respect to the first tank 2. Therefore, the liquid portion of the waste is transported from the first tank 2 to the second tank 3, via the duct 8, by gravity and, in an orderly way, by the gate means 10. This way, the presence of pumps or other forced transport systems between one tank and the other is not necessary.

While the first tank 2 is essentially a mixing tank where extraction of nitrogen from organic waste 6 occurs, the second tank 3 is essentially a dilution tank.

In the second tank 3 the liquid part of the waste is left to remain for a predetermined time sufficient to allow sedimentation of the solid part of the waste. This way, the second tank 3 contains a solid part deposited on the bottom of the tank and a liquid part, essentially free from further solid residues.

The liquid part of the waste, separated from the solid part by sedimentation, is also sufficiently clear to allow the occurrence of the subsequent reactions necessary for the abatement of the nitrogen load as better described hereinafter.

The plant shown in Figure 1 also comprises a third tank 4 for culture, placed at a height above the ground FT".

The plant 1 also comprises a conduit 11, connecting the second tank 3 and the third tank 4.

The third tank 4 is fed via the conduit 11 with the liquid part of the waste coming from the second tank 3, after said liquid part has been sufficiently diluted in the second tank 3.

Similarly to the duct 8, the conduit 11 comprises a filter 9 at the input, able to prevent any solid particles of the waste 6 still present in the diluted liquid part coming from the second tank 3 being accidentally transported to the third tank 4.

The conduit 11 comprises gate means 10, which enable the regulation of the flow from the second tank 3 to the third tank 4. The gate means 10 are positioned at a suitable position between the input and the output of the conduit 11.

The pipe system 5 therefore comprises the duct 8 and the conduit 11. The height above the ground H'" of the third tank 4 is less than the height above the ground H" of the second tank 3.

Therefore, the liquid part of the waste is transported from the second tank 3 to the third tank 4, via the conduit 11, by gravity and, in an orderly way, by the gate means 10.

The third tank 4 further comprises a suspension culture of one or more native strains of microalgae. The term "suspension culture of one or more native strains of microalgae" means a culture in a liquid medium of one or more strains of microalgae previously isolated in the laboratory from the specific waste that will subsequently be treated in the plant 1 of the invention. Microalgae are in fact naturally present in the waste from zootechnical farms. These are usually single-celled green algae, generally belonging to the Chlorophyta division, especially to the genus Chlorella, Scenedesmus or allied genera. These native microalgae, naturally present in the waste, are isolated from the waste itself in the laboratory, in order to prepare monocultures of these microalgae. The isolation protocol, produced in the laboratory, consists in carrying out known and increasing dilutions of the waste and in the use of the liquid portion of the diluted waste, separated from the solid portion by sedimentation, as selective means of isolation and growth of the microalgae according to conventional microbiological protocols.

The use of native strains of microalgae makes it advantageously possible to achieve an effective abatement of the nitrogen load contained in the decanted liquid portion of the organic waste 6. The native algal strains are actually already adapted to survive and multiply in the specific waste to be treated, unlike collected strains. The laboratory isolation of the native strain (or native strains) also allows determination of the dilution level of the waste that is permissive for the growth of the strain itself (or strains themselves). The prior isolation of the native algal strain or strains in the laboratory therefore not only allows the use of the strain or strains with the best ability to grow in the waste subjected to the treatment of nitrogen abatement, but also to determine the optimal final dilution which must be reached through gradual dilutions of the waste, previously described, from the tank 2 to the tank 4. Furthermore, the use of native microalgae offers security from an environmental point of view, since accidental dispersal of the organisms into the environment does not pose any danger to the environment itself. Microalgae in the presence of fresh water and nitrates/ammonium grow exponentially accumulating nitrogen in its organic form in their biomass. This way, the nitrogen is sequestered from the aqueous environment of the liquid part of the organic waste 6 present in the third tank 4. The nitrogen sequestration may reach a percentage of 98% with respect to its original amount.

The third tank 4 has predefined structural dimensions. Preferably, the third tank 4 has a depth of between 50 cm and 60 cm. This way, adequate illumination is ensured to the entire thickness of the liquid part contained therein, so as to allow efficient photosynthesis of the microalgae on which their growth depends.

The third tank 4 is therefore the culture tank of the microalgae.

The third tank 4 of the plant shown in Figure 1 also comprises a separation system of the microalgae from the purified liquid resulting after the abatement of the nitrogen percentage of the liquid part by means of said microalgae. This separation system comprises a filtration system 12 and a pumping system 13.

The filtration system 12 comprises a filter 12' movable between a raised position and a lowered position and preferably removable for the collection of the microalgae. This filter 12' is movable and separating and with respect to the pumping system 13.

The pumping system 13 comprises a pump 13'. The pump 13' is preferably housed in casing 13". Thanks to the pumping system 13 an output stream of purified liquid is created from the tank 4 towards the duct 17. The purified liquid flows freely through the filtration system 12, while the microalgae are retained on the surface of the removable filter 12'. Parallel to the movable filter that is preferably 12', and in proximity of the casing 13" of the pumping system 13, the third tank 4 comprises a movable and preferably removable flood gate 15 whose function is explained hereinafter. The filtration system 12 represents an example of the filtration technologies available and usable in the plant 1 of the invention, and is therefore replaceable with alternative systems, if required.

Microalgae are collected by filtration when the waste and/or the liquid part of the waste in the tank 4 are purified from the nitrogen load.

The features of the filtration 12 and pumping 13 systems depend on: 1) the volume of the output liquid, 2) volumetric features of the native microalgae selected for the present invention, 3) the need to re-circulate the purified liquid.

In particular, the third tank 4 comprises a step 14 for the containment of possible sediment, and the filter 12', removable for the collection of microalgae, is positioned between the step 14 and the pump 13'. The flood gate 15 is parallel to the filter 12' and is movable between a raised position and a lowered position and is preferably removable for the collection of the microalgae. In the lowered position, the flood gate 15 is able to block the flow of liquid during the collection of the microalgae. The stages, in detail, are as follows: (a) the flood gate 15 is raised and the filter 12' is lowered; this way, thanks to the pumping system 13, the purified liquid flows out of the tank 4 towards the duct 17; (b) the microalgae adhere to the filter equipped with pores of a smaller diameter than the cells; (c) the flood gate 15 is lowered; (d) the filter 12' is raised and removed, along with the adherent microalgae for their collection .

As the flood gate 15 is lowered, the flow of liquid is momentarily blocked, to allow collection of the algae. The pump 13' retrieves the purified liquid filtered by the filter 12' and pumps it, recirculating it by means of second pipes 17.

In the complex the third tank 4 is fed with water coming from the first pipe 7, the liquid part of the waste coming from the second tank 3, and also from the recirculation (purified liquid) through the second pipe 17.

The first tank 2 and the second tank 3 can also be fed with purified liquid coming from the second pipe 17.

This way the clarity of the liquid part, in which the microalgae is grown, is regulated, along with the percentage of water present in the at least one tank 2, 3, 4.

The flow in the second pipe 17 is regulated by at least one gate means 10.

Through the pump 13' it is possible to temporally separate the emptying stage of the third tank 4 from the re-introduction stage. That is to say, the purified liquid from tank 4 passes through the duct 17 to a temporary containment (emptying) tank 18. There is a re- introduction of liquid from the second tank 3 to the third tank 4 through the conduit 11. In parallel the re-introduction of liquid from the first tank 2 to the second tank 3 can occur through the duct 8. From the containment tank 18 via the pipe 17 the purified liquid is used to dilute the liquid contained in the tanks 4, 3 and 2.

This occurs thanks to the presence, along the second pipe 17, of the temporary containment tank 18 of the purified liquid.

Figure 2 illustrates a second embodiment of the plant according to the present invention, and is provided for illustrative purposes. In this embodiment, the plant consists-of a system of three tanks 2 (2a-c), one tank 3 and seven tanks 4 (4a-g), which are filled in a discrete manner. In particular, each tank is periodically filled and emptied in accordance with staying times evaluated in preliminary laboratory tests, so that, overall, the whole plant may operate continuously. In the example, for cattle waste, the staying time in each of the tanks 2a-c for the extraction of nitrogen and phosphorus is estimated at 3 days; the dilution in tank 3 requires one day; the purification in each of the tanks 4a-g is estimated at 7 days. For simplicity, in Figure 2 downstream processes of the tanks 4a-g already illustrated with reference to Figure 1 are not represented. Moreover Figure 2 is not intended to represent the actual scale of the tanks.

As an example of operation, on the first day tank 2a is filled with the waste and the extraction water, on the second tank 2b, on the third tank 2c. On the fourth day, the liquid is recovered from tank 2a for the dilution and sedimentation stage in tank 3. On the fifth day the liquid of tank 3 passes to tank 4a for the dilution and purification carried out by native microalgae in seven days. This way, tank 3 is again available on the fifth day to receive the liquid content of tank 2b. On the sixth day the diluted content in tank 3 is poured into tank 4b for the purification by microalgae, making tank 3 free again to receive the content of tank 2c. The repetition of the filling sequence continues until the filling of all tanks 4. After filling the last tank 4g, tank 4a is emptied and is ready to receive new liquid from tank 3 for purification.

The present invention further relates to a method for the abatement of the nitrogen load of organic waste from zootechnical farming, which exploits the efficacy of native strains of microalgae for the abatement of the nitrogen load in the waste.

In a preferred embodiment, the method of the invention is implemented by means of the plant 1 previously described. In another preferred embodiment, the method according to the present invention comprises a stage of introducing organic waste 6 of animal origin containing nitrogen from zootechnical farming, comprising a solid part and a liquid part, into the first tank 2.

One stage of the method comprises supplying fresh water to the first tank 2, preferably via a first pipe 7, and mixing the organic waste 6 with fresh water.

In the first tank 2, the solid part of the waste 6 is allowed to settle, - leaving its liquid part at the surface.

The fresh water introduced into the first tank 2 and the liquid part of the waste 6 extract the nitrogen component of the waste itself.

It is possible to repeat the stage of providing fresh water and mixing the organic waste with fresh water several times until extractable nitrogen is completely extracted from the solid part. The percentage of extracted/extractable nitrogen from the solid part can be determined using routine laboratory analysis.

The method according to the present invention also comprises a stage of transporting the liquid part of the waste from the first tank 2 to the second tank 3, preferably through a duct 8.

The liquid part of the waste from the first tank 2 is then diluted with fresh water, which is fed into the second tank 3 preferably through the first pipe 7, to a variable extent depending on the type of the waste itself.

The liquid part of the waste is left to remain in the second tank 3 for the time necessary for the sedimentation of any further solid residues, with the attainment of a liquid essentially free from solid residues. Once the liquid part essentially free from solid residues has been sufficiently diluted in the second tank 3, it is then fed into the third tank 4 preferably by means of a conduit 1 1.

The third tank 4 comprises a culture of one or more native strains of microalgae as previously defined.

These native strains of microalgae facilitate the abatement of the nitrogen load contained in the liquid part of the organic waste 6, sequestering the nitrogen from the aqueous medium. The method according to the present invention may further comprise an optional separating stage, in the third tank 4, of the microalgae from the liquid part of the organic waste 6 by means of filtration of the suspension contained in the third tank 4 through a filtration system 12, comprising a movable and preferably removable filter 12' for the collection of microalgae, thereby obtaining a purified liquid. Thereafter, the purified liquid can be removed from the third tank 4 through pumping, via a pumping system 13 which comprises a pump 13' preferably housed in a casing 13".

The method according to the present invention comprises the possibility of replacing the filtration system 12 with other filtration systems suitable for the purpose of algae collection.

The pumping stage, which is also optional, allows the recovery of the purified liquid filtered by the filter 12' and its re-circulation by means of the second pipe 17.

The method according to the present invention may also comprise a further optional stage of re-introducing the purified liquid, via the second pipe 17, into the tanks 2, 3, 4, thereby ensuring the saving of fresh water coming from the first pipe 7. Through the pump 13' it is possible to temporally separate the emptying stage of the third tank 4 from the re-introduction stage. This occurs thanks to a stage of temporarily containing the purified water, along the second pipe 17, through a temporary containment system 18. This stage is also optional. To verify the features of the algal inoculum and its growth, it is possible to carry out nephelometric (turbidity) analyses of the suspension contained in the third tank 4.

According to the amount of waste to be treated, as well as the space available for the implementation of such a plant in the company, the presented invention will consist of modules of varying sizes, which may be appropriately multiplied in series or parallel, respecting the fundamental features of the present invention. It may also be noted that the at least one tank 2, 3, 4 comprises a liquid part comprising both the purified liquid resulting from the filtering and pumping of the third tank 4, and fresh water coming from normal aqueduct ducts or other origin. The plant and the method according to the present invention are economically advantageous also because they envisage a recycling system that compensates for the need to use high volumes of water for the cultivation of microalgae.

The solid fraction of the waste, remaining after the treatment, can be used according to usual agronomic practices of spreading or introduced into a biodigester for the production of biogas.

The microalgae are left in the tank 4 for example until the complete or essentially complete abatement of the nitrogen load of the organic waste 6.

The invention conceived as such is susceptible to numerous modifications and variations, all within the scope of the inventive concept.

Moreover, all the details are replaceable by other technically equivalent elements, without departing from the scope of protection of the following claims.