ES2957853A1 - Complementary method of anaerobic treatment of slurry (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Complementary method of anaerobic treatment of slurry and whey, for an improved process that includes a previous phase (2) of collection, transfer, control, treatment and storage of slurry and whey that includes a discharge (9) of slurry and whey into the tank storage when the values of a sample are included in homogeneity limits, which includes a complementary stage after the discharge (9), of concentration (39) of the organic matter through the filtration and sterilization of an excess of nitrogenous water, which It is transferred to an additional tank, arranged next to the storage tank at least during the night hours and connected to it, thus concentrating the slurry and serum in the storage tank and accumulating a sterile liquid fertilizer in the additional tank. Finally, this method includes a final phase of equipment sterilization. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Complementary method of anaerobic treatment of slurry

Technical field of the invention

The present invention corresponds to the technical field of anaerobic treatment processes for slurry, especially those generated on farms and livestock farms.

Background of the Invention

On farms and, especially in livestock farms, large quantities of slurry are produced, made up of animal excrement, mixed with urine, water and other elements (straw, etc.), and its management entails a series of problems that make it neither economical or sustainable.

These manures are usually used as fertilizer for the land, however, this use as fertilizer entails serious environmental and economic problems, since if it is applied to the soil in excessive quantities, it can run down the slope and end up in streams, rivers, lakes... Or, with rain or irrigation water, it can filter through the subsoil and reach the aquifers. This is why the direct use of slurry as fertilizer is currently generally prohibited with some exceptions.

A solution to this problem is the processing of slurry in biogas plants, in which it is transformed into biogas and digestate, for use in energy generation and as fertilizer, respectively.

However, this process is economically viable only for large livestock farms, where the logistics cost per ton is very low and acceptable collection rates can be charged, but in rural areas where extensive and small-scale livestock farming predominates, despite being the most environmentally friendly livestock farming and the one that produces the highest quality products, these costs are unaffordable.

Small ranchers generally manage it by storing slurry in cesspools to spread it later on the field, often exceeding the permitted limits. This generates a degradation of soil quality, pollutes water, emits unpleasant odors that harm rural tourism and puts the health of farmers and livestock at risk.

As the volumes produced by these small livestock farms are more limited, they are forced to store them until they have a sufficient quantity so that the withdrawal costs are affordable. Thus, livestock farmers deposit slurry in open tanks in which an uncontrolled aerobic digestion process spontaneously begins, altering the quality of the waste for its gasification.

Since there is no control at source and given that each farm has different storage times, finally a mixture of very different products with different degrees of aerobic fermentation arrives at the biogas plant, which greatly complicates their exploitation. as well as being able to establish corrective measures in the livestock of origin.

Thus, the heterogeneity and variability of slurry in physical, chemical and biological characteristics makes the performance of anaerobic digestion inefficient, and this makes the composition and volume generated of the resulting biogas unstable and therefore of variable quality and generally , poor in methane. Likewise, impurities in the slurry cause frequent breakdowns in the gasification installations, and excess humidity generates excessive discharges in the plant.

All this leads to a loss of value of slurry as input in biogas plants, and the digestate produced has an unstable quality, so its commercial value also falls. With this, the cost of collecting the manure is not worth it and the biogas plants need to charge high amounts to remove it, with small livestock farmers being the most affected.

To solve this problem, the owner of this application has previously requested Spanish patent P202230325, which discloses an improved anaerobic treatment process for slurry, to carry out correct management of the same in its transformation into biogas and digestate.

The process disclosed in the aforementioned patent includes a phase of transport under controlled anaerobic conditions of said slurry to the biogas plant, and a previous phase of collection, transfer, control, treatment and storage of slurry, prior to the transportation phase.

Said previous phase of collection, treatment and storage of slurry comprises a watertight and thermally insulated storage tank, inside which certain anaerobic, thermal and biochemical conditions are guaranteed and which has a traveling position between two or more collection points according to a route. of locations, so that each farmer chooses the collection point closest to his facility and when the tank is there, he makes an appointment to unload the slurry there.

These slurries are transferred to the biogas plant when the filling volume of the storage tank reaches a certain pre-established volume (normally it will be something close to 80%) or when a pre-set maximum time interval has elapsed since the first discharge occurred in said storage tank. In this way, multiple trips to different farms to load small quantities of slurry are avoided. Furthermore, with this process a reduction in aerobic fermentation times and processes is achieved, so that the slurry that reaches the biogas plant is much more homogeneous and there is control of its chemical, physical and biological parameters. In addition, it is possible to trace the origin of the slurry, since each volume of slurry introduced into the tank is carried out after identifying the farmer who discharges it.

All these aspects allow a reduction in the rates applied to livestock farmers.

However, as a result of the recent trials and tests carried out, the applicant has come to the conclusion that it is possible to improve this process even further, by acting on the concentration of the slurry. The tests carried out have shown that the livestock manure collected in the storage tanks has a low concentration of total solids, approximately 8%, and it is desirable to reach a minimum of 12%-15% to optimize the anaerobic digestion processes in biogas plants. This means that, in many cases, slurry is made up of nitrogenous water with a concentration of organic matter below its optimal levels for gasification in a biogas plant.

Therefore, the consequence of this is that large volumes of collected slurry are being transported, even knowing that a large part of it is not usable, given the low concentration of organic matter. In short, excess water is being transported.

In addition, there is another aspect to consider in the improved process initially proposed, since many ranchers are reluctant to discharge the volumes of slurry they generate in their livestock facilities, since they need it to fertilize the fields.

It is therefore necessary to apply certain changes or variations that allow these observed aspects of the practice to be solved.

Description of the invention

The complementary method of anaerobic treatment of slurry presented here is proposed with respect to an improved anaerobic treatment process in biogas and biomethane plants of slurry generated in livestock farms that includes a phase of transport under controlled anaerobic conditions of said slurry to the biogas plant and a previous phase of collection, transfer, control, treatment and storage of slurry.

This preliminary phase includes the following stages:

- Search or location by the farmer of the location of at least one first slurry collection point, where a watertight and mobile storage tank is temporarily located;

- Obtaining an appointment or confirming a pre-scheduled appointment to unload slurry at the first collection point located in the previous stage;

- Transport of a volume of slurry, carried out by the livestock user, to the first collection point at the place and time set in the appointment of the previous stage;

- Registration and identification of the livestock user at the first collection point;

- Connection of the means of transport used by the user farmer to the first collection and discharge point of a first determined portion of the volume of manure in the storage tank, during a first time interval;

- Automated sampling and analysis of chemical, physical and/or biological characteristics of the first portion of discharged slurry volume, in such a way that when these values are included within predetermined quality ranges, the following stages of the process are carried out and When these values do not meet the quality limits, the download is denied;

- Conservation of the slurry sample from each discharge for collection by the operator and subsequent reference and analysis in a specialized laboratory

- Discharge of the remaining portion of the volume of slurry transported to the first collection point;

- Collection or payment of the amount of the service by the rancher, and;

- Automated communication of the storage tank with a central server, notifying the quantitative and qualitative data of the discharge in real time;

Once the phase of collection, transfer, control, treatment and storage of slurry is completed, the phase of transporting the slurry to the biogas plant takes place, subsequent to said previous phase, which in turn includes the following stages executed by a operator:

- Movement of a tank vehicle to the storage tank to empty its contents under anaerobic conditions, when its filling volume reaches a preset value or when a preset maximum time interval has elapsed since the first discharge occurred in said storage tank. storage;

- Transfer of the removed volume of slurry with the tanker vehicle to a predetermined location.

Thus, based on this improved anaerobic treatment process, the complementary method of anaerobic slurry treatment proposed here includes a complementary stage, after the stage of discharging the volume of slurry into the storage tank, of concentration of the organic matter. in it, through an additional tank that is arranged next to the storage tank at least during the night hours and is connected to it, to transfer the excess nitrogenous water to the additional tank, forming a sterile fertilizer in it.

With the improved anaerobic slurry treatment process proposed here, a significant improvement in the state of the art is obtained.

This is because a process is achieved with which it is possible to obtain a concentrated slurry, which is what is transferred to the biogas plant in the initial phase and which is optimal for gasification. In this way, it is avoided to transport large volumes of slurry with a low concentration of solids, of which a small part can actually be used, after having to concentrate them.

By achieving a concentrated slurry prior to its transport to the biogas plant, a more efficient process is achieved and a significant increase in its performance, significantly reducing costs.

Furthermore, with the concentration of the manure, a surplus is obtained consisting of a volume of nitrogenous water that is suitable for use as a sterile fertilizer and, as said concentration is carried out at the collection points themselves, close to the livestock farms, farmers and ranchers can remove the fertilizer they require throughout the day.

In this way, it is possible to manage the slurry for transport to the biogas plants that is effective and profitable for all livestock farmers and, at the same time, they can continue to have a part of it as fertilizer, thus avoiding rejection that the delivery of slurry may generate in the face of the problem that running out of fertilizer for their fields could pose.

It is therefore a very effective process with which an increase in the performance of the biogas plant is achieved and at the same time a better use of the slurry, since a part is destined for the production of biogas and digestate and another part continues to be used. by the farmers themselves as fertilizer.

Brief description of the drawings

In order to help a better understanding of the characteristics of the invention, in accordance with a preferred example of its practical implementation, a series of drawings are provided as an integral part of said description where, with an illustrative and non-limiting nature, it has been represented the following:

Figure 1.- Shows a block diagram of a complementary method of anaerobic treatment of slurry, for a first preferred embodiment of the invention.

Figure 2.- Shows a block diagram of a complementary method of anaerobic treatment of slurry, for a second preferred embodiment of the invention.

Figure 3.- Shows a schematic view of an intermediate treatment center of an improved anaerobic slurry treatment process, for a second preferred embodiment of the invention.

Figure 4. - Shows a diagram of the storage tank assembly and the additional tank with the functionalities of the system, as well as a small graph indicating the location of one and the other during the day and night in an example of embodiment.

Detailed description of a preferred embodiment of the invention

In view of the figures provided, it can be seen how in a first preferred embodiment of the invention, the complementary method of anaerobic treatment of slurry that is proposed here, for an improved anaerobic treatment process in biogas and biomethane plants of slurry generated on livestock farms that includes a transport phase (1) of the slurry to the biogas plant and a previous phase (2) to said transport phase (1), of collection, transfer, control, treatment and storage of slurry.

The previous phase (2) of collection, transfer, control, treatment and storage of slurry comprises a first stage consisting of the search or location by the farmer of the location (3) of at least one first collection point of slurry, where A watertight and mobile storage tank is temporarily located. Once it is located, an appointment or confirmation of a pre-scheduled appointment (4) is obtained to unload slurry and the farmer transports (5) the volume of slurry to be removed to the first collection point at the place and time set in the appointment. from the previous stage.

In a subsequent stage, the registration and identification (6) of the livestock user is carried out at the first collection point, after which the means of transport used by the livestock farmer user are connected to the first collection point and a first portion (7) is unloaded. ) determined from the volume of slurry in the storage tank, during a first time interval. The automated sampling and analysis (8) of the chemical, physical and/or biological characteristics of the first portion of discharged slurry volume will then be carried out, in such a way that when these values are included (8.1) within predetermined quality ranges The following stages of the process are carried out and when these values do not meet (8.2) the quality limits, the discharge is denied (13), keeping in any case a slurry sample from each discharge for collection by the operator and subsequent reference. and analysis in a specialized laboratory.

Once it has been verified that the slurry meets the pre-established quality ranges, the remaining portion (9) of the slurry volume is unloaded and the collection or payment (10) of the amount of the service by the rancher and communication takes place. (11) Automated storage tank with a central server, reporting quantitative and qualitative data of the discharge in real time.

Furthermore, in this first preferred embodiment of the invention, the process comprises an additional stage of optimizing the quality (12) of the slurry contained in the storage tank, after the stage of unloading the remaining portion (9) into the same, where the storage tank includes reagent and enzyme dispensers and mixers thereof in the volume of slurry, to carry out said optimization.

The complementary method presented here includes a complementary stage, in the previous phase (2) after the discharge stage (9) of the volume of slurry in the storage tank. This complementary stage consists of the concentration (39) of the organic matter in the storage tank, through an additional tank that is arranged next to the storage tank at least during the night hours and is connected to it, for the transfer of excess water. nitrogen to the additional tank, forming a sterile liquid fertilizer.

To achieve the desired concentration, the excess nitrogen water is filtered and sterilized overnight and transferred to the additional tank, thus concentrating the slurry in the storage tank and accumulating a sterile liquid fertilizer in the additional tank.

To control the concentration of total solids, and ensure that a value between 12 and 15% is reached, a flowmeter and a weighing cell are used. Based on the filtration efficiency and the original solids content, it is possible to determine the volume of slurry that must be filtered to obtain the desired concentration.

The formula applied is the following:

Where:

T= Volume to transfer

C<s>= Original concentration

C<e>= Filtering efficiency

C<t>= Target concentration

V<i>= Original volume (at original concentration)

On the other hand, to control how much excess water we transfer to the additional tank, the solids content in the storage tank is controlled by measuring, for example, the value of the electrical conductivity, since there is a positive correlation between the electrical conductivity of the slurry and the dry matter content, the value of said correlation being 0.627.

In this way, knowing the original dry matter content and the efficiency of the filtration, it is possible to calculate how much volume must be transferred to the additional tank to obtain a certain concentration in the storage tank. Other variables may be density or biochemical oxygen demand (BOD).

The additional tank is a device for receiving, modifying and distributing the filtered and pretreated volume of the liquid part of the slurry. It is very similar in structure to the storage tank, although its functions are different. The most relevant functionalities of said additional tank are:

• Admission of a volume of nitrogenous water

• Performing a second filtering and returning to primary

• Sterilization of a volume of nitrogenous water

• Modification of the biochemical characteristics of this volume, enriching it for fertilization

• Distribution of this volume of “fertilizer” by pumping to livestock farmers

The greatest value of this additional tank lies in the slurry upgrading ability to concentrate its organic matter and convert the excess into fertilizer that can be distributed on demand. The distribution of “fertilizer” volumes is done under reservation through the same portal that is used to make the download reservation.

The conversion of slurry into fertilizer is carried out by filtering and concentrating the solid matter of the slurry in the storage tank, sterilizing the filtered part during its transfer to the additional tank and modifying it by adding additional nutrients to the nitrogen that It already incorporates the filtered water.

Seasonality:

The demand for fertilizer has a very important seasonal component. The generation of manure, due to seasonal variations in stabling, as well. But they are not synchronized. This means that there are months in which there is an excess supply of fertilizer (winter) and others in which there is excess demand (spring-summer).

When there is an oversupply, the additional tank tends to fill up since farmers withdraw less volume of filtered water than is generated. In these cases, using a service tank, an additional operation is carried out consisting of emptying the additional tank and sending it for storage in a tank at the biogas plant. This is true in cases where, by weight, the contents of the additional tank exceed the transport quantity or if, together with the volume expected to be filtered that night, it exceeds the capacity of the additional tank. To do this, the additional tank also has a weight sensor and a communications system.

On the contrary, when there is excess demand, this service tank performs the additional operation of completing the filtered load of the additional tanks with the fertilizer stored in the biogas plant from the excess withdrawals from previous months.

Regardless of whether the distribution is carried out directly from the tank or stored seasonally, it is the slurry collection and pretreatment system that allows the generation of this fertilizer. By concentrating the slurry solid in the storage tank, the system allows the excess nitrogenous water of the slurry to be transformed into fertilizer with a minimum solid in the additional container and distributed from this to the ranchers and farmers in the area.

Fertilizer sterilization:

In the complementary stage in which the concentration of organic matter is carried out in the storage tank and the excess of nitrogenous water is transferred to the additional tank, the percentage of organic solids is reduced and, therefore, a large part of the bacterial load. in the contents of the additional tank.

If we assume that the separation efficiency is 70% in each phase and the original organic matter content of the slurry is 8%, in this case the final concentration after double filtering is the following:

8% x (1-70%) x (1-70%) = 0.72%

The sterilization of the filtered flow is carried out by UV radiation applied to the duct that transfers the filtrate to the additional container. It is a process that does not consume much energy and that eliminates the biological load that remains after filtering before transferring it to the additional container.

Fertilizer filtration and transfer

Concentration and transfer is done by pumping or injecting CO2 under pressure into the storage tank and connecting it to the additional tank through a membrane or filter.

The filtration system is installed inside each container or tank. Filtering is therefore carried out in two phases. A first phase in which the 8% slurry is filtered into the storage tank. Assuming a filtration efficiency of 70%, the filtered volume reduces the concentration of the solid to 2.4% of the total, which is stored in the chamber of the storage tank.

This volume is then transferred, by pumping or pneumatics, to a pre-chamber in the additional tank. In the additional tank, a second filtration is carried out to pass to its main chamber. In this phase, if we assume equal filtering efficiency, the concentration is reduced to 70%, leaving the final concentration at 0.72%. Finally, the residual volume of the main chamber of the additional tank, with a concentration of 2.4%, is pumped back to the storage tank.

There are, therefore, two connections between the storage and additional tanks, which flow in opposite directions. In the connections between tanks there are flowmeters to know the total filtered volume.

Fertilizer enrichment:

In other preferred embodiments of the invention, the method comprises a phase of adding nutrients in the amount obtained of sterile fertilizer, which in this case are made up of phosphorus and potassium. This nutrient addition phase is carried out in the additional tank, after the complementary stage, when the total volume and concentration of solids are known. At this time you can correctly dose the amounts of nutrients necessary to obtain the desired concentration.

This phase is carried out automatically in the additional tank, according to its programming and the volumes and parameters of nitrogenous water stored inside.

In other preferred embodiments, it takes place in the biogas plant and is subsequently transferred to the additional tank.

Operating procedure

An example of the operating procedure is shown schematically in Figure 4. First thing in the morning, the storage tank is disconnected and taken to the next collection point, leaving the additional tank in the previous position for ranchers and farmers to remove (after identification in the system and debiting the account, if available). ) the liquid and sterilized fertilizer they require throughout the day. At the end of the day, the additional tank is transported next to the storage tank again and connected to it so that the concentration process can be carried out again at night.

In this first preferred embodiment of the invention, the improved process comprises two or more collection points distributed in a first area of action.

In this way, the storage tank has a traveling position between said collection points according to a location route for them, where after the change in position of the storage tank, the additional tank remains in its previous position until the end. of the day, for its transfer to the new position of the storage tank for connection to it during the night hours.

As shown in Figure 1, in this first preferred embodiment of the invention, after the concentration (39) of the organic matter in the storage tank, the method comprises a consumption phase (40) of the sterile liquid fertilizer by part of at least one rancher, after identification of the same and corresponding payment (46), which includes the withdrawal of a part of the volume contained in the additional tank during daylight hours.

For its part, the transport phase (1) of the slurry to the biogas plant includes a stage of moving a tanker vehicle (14) to the storage tank for emptying its contents under anaerobic conditions, when its volume filling reaches a preset value or when a preset maximum time interval has elapsed since the first discharge occurred in said storage tank and a transfer (15) of the removed volume of slurry with the tank vehicle to a predetermined location.

In this first preferred embodiment of the invention, the initial phase (1) presents a subsequent stage of movement (8) of the volume of slurry contained in a storage tank by means of a tanker vehicle, to the biogas plant.

In a second preferred embodiment of the invention, shown in Figure 2, it may occur that the initial transport phase (1), after the stage of moving a tank vehicle (14) to the storage tank, Once the volume to be transferred by the tank vehicle has been collected, instead of being transferred directly to the biogas plant, a stage (16) is carried out that includes a first transfer step (17) of the volumes collected from two or more first collection points to an Intermediate Treatment Center (25) which, as shown in Figure 3, includes at least one watertight reception tank (26) that guarantees the maintenance of anaerobic conditions. Furthermore, this second embodiment comprises an additional stage of unloading (18) of the tanker trucks into said reception tank (26) followed by sampling and analysis (19) of the chemical, physical and/or biological characteristics of the discharged volume. of purines.

As represented in Figures 2 and 3, in this second preferred embodiment of the invention, if the values obtained in sampling and analysis are included (19.1) in predetermined homogeneity and/or quality limits, the process followed comprises also a derivation (20) of the volume of slurry to a sealed process tank (27), to carry out pretreatment processes similar to those described in the first embodiment, but on a larger scale, as well as a first displacement (21). ) of the volume stored in the process tank (27) to a delivery tank (28) and, a second movement (22) from the same to the biogas plant (25) by means of one or more tank vehicles.

In the case in which the values obtained from sampling and analysis do not meet (19.2) limits of homogeneity and/or quality, the process includes a derivation (23) of the volume of slurry from the reception tank (26) to a tank waste (30), for its removal or transfer to a treatment plant (29) or controlled landfill.

As shown in Figure 3, each intermediate treatment center (25) covers several areas of action that are served by a traveling storage tank at its collection points. They also present a maintenance area (31) for the tanker truck fleet, where the vehicles and tanks in their area of operation are repaired and maintained, and an operation booth (32) where the process is monitored and operated, the operation and routes of service vehicles.

Addition of serums

Both in the first embodiment and in the second, as can be seen in Figures 1 and 2, the present method may also include a phase of adding whey (42) from small cheese factories close to the slurry collection point. This addition of whey can be concurrent or alternative to that of slurry.

The whey from the cheese factories are added to the slurry storage tank, after discharging (9) into said storage tank, the remaining portion of the slurry volume. The treatment of these serums is similar to that of manure.

1. Slurry and whey can be mixed directly in the storage tank, not being necessary to carry out any coordination or temporal control between discharges of one product and the other. Nor is it necessary to have a minimum volume or a certain proportion between both products. The amounts of slurry or whey are simply added on demand and the storage tank identifies the user and in the authorization process defines what type of material (whey or slurry) is going to be discharged. The tank vehicle, after unloading the raw material into the storage tank, “knows” the composition of the mixture it carries and at the time of transfer to the biogas plant or the intermediate treatment center (25) the reception and composition of this is recorded. Upon receipt, the plant adjusts the amount of co-substrate depending on the content of the mixture it receives.

2. On the other hand, it is important to note that there is no type of interference between the process of adding serum and the removal of excess nitrogen water to the additional tank. The filtering process is carried out on the mixture of whey and slurry. The tank “knows” the solids content when discharging and adjusts the filtration based on this value.

3. The additional step of optimizing the quality (12) of the slurry contained in the storage tank, by adding reagents and enzymes, takes place after the discharge of all users of the day (discharge serum or slurry), and preferably after the filtering process is completed, so as not to increase the matter content in the storage tank.

It has been proven that the addition of these serums considerably improves the quality of slurry as raw material. The slurry carbonates much better with a whey mixture, which has a high content of organic matter. Furthermore, as the system allows the quantities and parameters to be recorded when loading, whether slurry or whey, the mixture can be known and, where appropriate, the process in the biogas plant can be adjusted.

Of course, by adding whey from small cheese factories to the storage tank, not only is the quality of the slurry being improved, but it is also solving another very important environmental problem, which is related to the treatment and disposal of these whey. which are highly polluting and represent a very relevant environmental management problem for small cheese factories.

Equipment sterilization

In both the first and second embodiments, the sterilization, by UV radiation or ozone, of the equipment in contact with the farmers' tanks is contemplated.

The objective is, although the possibility is remote, to minimize the risk of spread of communicable diseases through feces among livestock and cheese factories that use the system's equipment.

The sterilization of this equipment is carried out automatically through devices installed in the container, once the user concludes the operation of the system.

Claims (1)

1 - Complementary method of anaerobic treatment of slurry, for an improved anaerobic treatment process in biogas and biomethane plants of slurry generated on livestock farms that includes a transport phase (1) of slurry to the biogas plant and a previous phase ( 2) prior to said initial phase (1), of collection, transfer, control, treatment and storage of slurry in a sealed storage tank with anaerobic conditions inside, which includes a discharge (9) of slurry into the storage tank when the values of a sampling are included in limits of homogeneity, characterized in that it includes a complementary stage in the previous phase (2), after the discharge (9) of the volume of slurry in the storage tank, of concentration (39) of the organic matter in it, through the filtration and sterilization of an excess of nitrogenous water, which is transferred to an additional tank, which is arranged next to the storage tank at least during the night hours and is connected to it, thus concentrating the slurry in the storage tank and a sterile liquid fertilizer accumulating in the additional tank. 2- Method according to claim 1, wherein the concentration and transfer of excess nitrogenous water is carried out by pumping or injecting CO<2>under pressure into the storage tank and connecting it to the secondary one through a membrane/filter. 3- Method according to any of the previous claims, wherein the improved process comprises two or more collection points distributed in a first area of action, and the storage tank has a traveling position between said collection points according to a route of locations for the same, where after the change in position of the storage tank, the additional tank remains in its previous position until the end of the day, for its transfer to the new position of the storage tank for connection to it during the night hours. 4- Method according to any of the previous claims, which comprises a phase of consumption (40) of the sterile liquid fertilizer by at least one rancher, after identification thereof and corresponding payment (46), which includes the withdrawal of a part of the volume contained in the additional tank during daylight hours. 5- Method according to any of the previous claims, which comprises a phase of adding whey (42) from cheese factories close to the slurry collection point, in the slurry storage tank, either alternatively to the discharge of slurry or together with it. . 6- Method, according to any of the previous claims, comprising a phase of adding nutrients in the amount of sterile fertilizer obtained. 7- Method, according to claim 6, wherein the nutrient addition phase is carried out in the additional tank, after the complementary stage. 8- Method, according to claim 7, wherein the nutrient addition phase is carried out in the biogas plant and is subsequently transferred to the additional tank. 9- Method, according to any of claims 6 to 8, where the nutrients are formed by phosphorus and/or potassium. 10- Method, according to any of the previous claims, comprising a sterilization phase of the equipment at the end of the operation of the equipment.