Field of the invention [0001] The invention relates to the organic matter digestion field. More particularly, the invention relates to a two-step process enabling the production of biogas from organic matter which is at least partly solid. The invention also relates to an apparatus for carrying out an organic matter digestion process according to the invention.

Prior art

[0002] The digestion of organic matter with a view to producing biogases is a process that has been used for many years. Thus, processes for methanization of organic matter, in liquid form or in solid form, in order to produce methane-rich biogas are used in order to convert these organic matters. Methanization is therefore a known process. Generally, methanization is a process which occurs in several phases. The first phase consists in degrading the organic matter. This phase takes place in the form of hydrolysis of the organic matter. The next phase is an acidogenesis phase, consisting of the formation of organic acids, in particular of volatile fatty acids. A third phase of acetogenesis consists in particular of the formation of acetates and of formic acid from in particular organic acids. Finally, the last phase of a conventional methanization process is the phase termed methanogenesis phase, converting at least a part of the acetates in particular to biogas, comprising in particular methane.

[0003] These various phases require different reaction conditions in order to comply with the reaction kinetics. Thus, the methanization process is commonly separated into two steps: a first step combines the hydrolysis phase and the acidogenesis phase; a second step combines the acetogenesis phase and the methanogenesis phase. During a two-step methanization, each of the steps is carried out in its own compartment (generally in two separate tanks). With this process, it is possible to manage the general kinetics of the methanization process by adjusting one of the kinetics of one of the steps in order to reduce the duration of the process, or to produce a larger amount of methane-rich biogas, or a biogas of greater quality.

[0004] Generally, the solid organic matter used in methanization processes is composed of a rapidly fermentable fraction and of a more recalcitrant fraction. During the hydrolysis step, the rapidly fermentable fraction moves rapidly into the water-soluble state, unlike the recalcitrant fraction, which requires a much longer period of time. The organic matter is, after the hydrolysis step, in two forms: a water-soluble form contained predominantly in the liquid phase and an insoluble form contained predominantly in the solid phase. For this reason, it is necessary to provide for a different treatment of the solid organic matter and of the liquid organic matter after the first hydrolysis step. Indeed, the solid organic matter requires a very variable hydrolysis time depending on the size of the organic matter and on the composition of this organic matter in terms of slowly degradable compounds, for instance lignin, cellulose or hemicellulose. This necessity therefore means that it is required to provide for apparatuses and processes which treat the solid organic matter and the liquid organic matter differently.

[0005] Processes which make it possible to modify the treatment time for one type of organic matter compared with another are known. For example, in document FR 2 920 761 , the residence time of the liquid organic matter in the first-step reaction tank is dissociated from the residence time of the solid matter in the first-step reaction tank by virtue of the presence of a step of separating the liquid phase and the solid phase after the first step, making it possible to increase the time spent by the solid matter in the first tank without necessarily impacting on the residence time of the liquid matter in this same tank, by virtue of a return of the separated solid phase to the first tank, and modulation of a stream of liquid organic matter between the second reaction space and the first reaction space.

[0006] However, such a process is not satisfactory when the solid organic matter has a relatively long degradation time, making it necessary to limit the provision of organic matter in the first tank, and thus to reduce the amount of biogas produced for a given period of time, or to considerably increase the size of the first tank in which in particular the hydrolysis phase takes place.

[0007] A process, and incidentally an apparatus for carrying out such a process, which makes it possible to have a better yield by optimizing the treatment times, is therefore lacking.

Summary of the invention

[0008] The invention is defined by the independent claims. The dependent claims define preferred embodiments of the invention.

[0009] According to the invention, a process for methanization of an organic matter which is at least partly solid is provided, comprising the steps of: introduction of said organic matter into a first reaction space,

hydrolysis of at least a part of the solid organic matter and acidogenesis of the organic matter within said first reaction space,

discharge of the organic matter from the first reaction space via a first extraction means,

introduction of at least a part of the organic matter discharged from the first reaction space into a second reaction space,

- acetogenesis and methanogenesis of the organic matter present within the second reaction space,

discharge of a first digestate from the second reaction space via a second extraction means,

characterized in that the step of discharge of the organic matter from the first reaction space is activated according to a degree of hydrolysis of the solid part of the organic matter introduced within said first reaction space,

and in that, after the discharge of organic matter from the first reaction space, no solid part of the organic matter extracted is reintroduced into said first reaction space.

[0010] By virtue of the method according to the invention, the residence time of the organic matter in the first reaction space is controlled according to a degree of hydrolysis, making it possible to adjust this residence time according to the intrinsic characteristics of the organic matter, while at the same time retaining a simple process. With such a process, the size of the reaction spaces may be relatively modest, according to the intrinsic characteristics of the solid organic matter, and to the volume of solid organic matter introduced into the first reaction space, without impacting on the yield of the subsequent reactions of a methanization process.

[0011] Another objective of the invention is to improve the treatment of the various types of organic matter present. This objective is achieved by separating the treatment of the solid organic matter and of the liquid organic matter after the first hydrolysis and acidogenesis step, in order to optimize the methanization process, and in particular the acetogenesis and methanogenesis steps, for each form of organic matter. Thus, preferably, in the methanization process according to the invention:

the step of discharge of the organic matter from the first reaction space is followed by a separation step in order to obtain a separated liquid organic matter and a separated solid organic matter,

said separation step being followed by introduction of the separated liquid organic matter into the second reaction space,

an acetogenesis and a methanogenesis of the separated liquid organic matter is carried out in the second reaction space,

- the separated solid organic matter is evacuated via an outlet for separated solid organic matter.

[0012] In order to at least partially solve the problems present in the prior art, a process for treatment of organic matter which is at least partly solid is thus provided, in which at least one phase of the process is modulated independently for the solid organic matter and for the liquid organic matter after the first hydrolysis and acidogenesis step, while at the same time retaining a satisfactory yield of other steps of the process and without needing to have reaction spaces of disproportionate size.

[0013] According to this preferred embodiment, the liquid organic matter is separated from the solid organic matter after the first hydrolysis and acidogenesis step, and the conditions for the subsequent treatment of the separated liquid organic matter can be determined according to the nature of the separated liquid organic matter, without having to take into account the limitations that the presence of solid organic matter might bring, making it possible to have an optimized treatment time for the separated liquid organic matter by independently modulating the residence time of the separated liquid organic matter within the second reaction space.

[0014] More preferably, the process according to the invention also comprises the following steps:

the step of evacuation of the separated solid organic matter is followed by the introduction of said separated solid organic matter into a third reaction space,

- a hydrolysis, an acidogenesis, an acetogenesis and a methanogenesis of the separated solid organic matter are carried out in the third reaction space, a second digestate is discharged from the third reaction space via a third extraction means.

According to this preferential embodiment, the separated solid organic matter is treated, and the steps for treatment of the separated solid organic matter and of the separated liquid organic matter are carried out in two different spaces, making it possible to obtain a better yield for each of the types of organic matter, independently of one another. Thus, each of the residence times of the separated solid organic matter and of the separated liquid organic matter can be defined independently of one another.

[0015] In an even more preferred embodiment, the process according to the invention comprises a step in which the discharge of the digestate from a reaction space is activated according to a degree of abatement of a separated organic matter present in said reaction space.

Indeed, according to this embodiment, the digestate discharge steps are more successfully controlled according to the yield desired by the user of the process, making it possible to adjust the process to the logistical and/or material needs according to the size of the equipment within which the process is carried out, and to the nature and the amount of organic matter that the user wishes to treat.

[0016] The invention also relates to a methanization apparatus which makes it possible to carry out a method according to the invention. Brief description of the figures

[0017] These aspects and also other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, reference being made to the drawings of the figures, in which: shows schematically a methanization apparatus (50) according to one embodiment of the invention.

shows schematically a methanization apparatus (50) according to one preferred embodiment of the invention.

shows schematically a methanization apparatus (50) according to one even more preferred embodiment of the invention.

shows schematically a methanization apparatus (50) according to one even more preferred embodiment of the invention.

shows schematically a methanization apparatus (50) according to one even more preferred embodiment of the invention.

The drawings of the figures are neither to scale nor in proportion. Generally, similar elements are denoted by similar references in the figures.

Detailed description of embodiments of the invention

[0018] The process for methanization of an organic matter which is at least partly solid according to the invention comprises the steps of:

- introduction of said organic matter into a first reaction space,

hydrolysis of at least a part of the solid organic matter and acidogenesis of the organic matter within said first reaction space,

discharge of the organic matter from the first reaction space via a first extraction means,

- introduction of at least a part of the organic matter discharged from the first reaction space into a second reaction space,

acetogenesis and methanogenesis of the organic matter present within the second reaction space, discharge of a first digestate from the second reaction space via a second extraction means,

characterized in that the step of discharge of the organic matter from the first reaction space is activated according to a degree of hydrolysis of the solid part of the organic matter introduced within said first reaction space,

and in that, after the discharge of organic matter from the first reaction space, no solid part of the organic matter extracted is introduced into said first reaction space.

[0019] The organic matter comprises a biodegradable organic matter and a residual, or non-biodegradable, organic matter. It is understood that, throughout the process, the organic matter consists of biodegradable organic matter and of non-biodegradable organic matter, said non-biodegradable organic matter constituting the majority of the organic matter exiting the process, in the form of a digestate. The organic matter is at least partly solid, which means that it can be in the form of a mixture between a solid organic matter and a liquid organic matter, or in the form of a solid organic matter only. For example, the organic matter introduced can be in the form of waste from the food-processing industry, such as vegetable or fruit residues for example, which may be supplemented with liquids, for instance washing water from the food- processing industry, pressing juices, blood, milk, or any liquid loaded with organic matter.

[0020] The first reaction space may be a treatment tank or a reactor in which the organic matter undergoes at least one hydrolysis and one acidogenesis so as to convert at least a part of the organic matter into organic acids.

[0021] The discharge of organic matter from the first reaction space is a step during which at least one part of the organic matter present in the first reaction space is discharged from this space. The first extraction means may be any means for discharging the organic matter, such as an overflow means, a valve having at least one open position allowing organic matter to pass through and one closed position preventing organic matter from passing through, a means for suctioning the organic matter, such as a pump, a means for discharge of the organic matter by gravity, or a length of piping comprising a valve with an open position and a closed position.

[0022] The second reaction space may be any space enabling an acetogenesis and a methanogenesis of the organic matter present within the second space to be carried out so as to convert the organic matter present at least partly into biogas. The biogas produced during the methanogenesis can be evacuated via a dedicated means, such as an outlet for biogas via a pipe made of stainless steel, made of high density polyethylene (HDPE) or any other material suitable for the transporting of biogas.

[0023] A digestate is the product which is the residue of the methanization and is composed mainly of non-biodegradable organic matter, of water and of minerals. The digestate may, however, comprise a portion of biodegradable organic matter, either in a negligible amount when a degree of abatement of the organic matter is close to 100%, or in a greater amount when the degree of abatement of the organic matter is relatively far from 100%. The discharge of the digestate from the second reaction space can be carried out by any extraction means which makes it possible to discharge the organic matter present within said space, such as an overflow means, a valve having at least one open position which enables the organic matter to pass through and one closed position which prevents the organic matter from passing through, a means for suctioning the organic matter, such as a pump, a means for discharge of the organic matter by gravity, or a length of piping comprising a valve with an open position and a closed position. The second extraction means may be any means which makes it possible to discharge a digestate, such as an overflow means, a valve having at least one open position which enables the digestate to pass through and one closed position which prevents the digestate from passing through, a means for suctioning the digestate, such as a pump, a means for discharge of the digestate by gravity, or a length of piping comprising a valve with an open position and a closed position.

[0024] The step of discharge of the organic matter from the first space is activated according to a degree of hydrolysis of the solid part of the organic matter introduced within said space. This degree of hydrolysis of the solid part of the organic matter is defined as being a ratio between, on the one hand, the difference between the amount of organic matter present in soluble form after hydrolysis of the solid organic matter and the amount of soluble organic matter present in the organic matter before hydrolysis of the solid organic matter (for example before its introduction into the first reaction space), and, on the other hand, the amount of organic matter present in all of the organic matter before hydrolysis of the solid organic matter (for example before its introduction into the first reaction space). This degree of hydrolysis can, for example, be determined by the following formula:

COD final soluble ^OD initial soluble

COD total

With COD expressed, for example, in milligrams of oxygen per liter.

COD is the Chemical Oxygen Demand. It can be determined according to the method described in standard ISO 6060:1989 for liquid organic matter. To measure the COD _to tai, the solid organic matter is ground beforehand in order to obtain fragments of a maximum size of about one millimeter, weighed and diluted with demineralized water before assaying according to standard ISO 6060:1989.

The Chemical Oxygen Demand (COD) makes it possible to assess the concentration of organic matters dissolved, in suspension in the water, or present in the solid organic matter, through the amount of oxygen required for the total chemical oxidation thereof.

[0025] The degree of hydrolysis can, for example, be determined from chemical tests carried out by a user or by an automated system. The CODinitiai soluble is the COD of the soluble organic matter before the beginning of the hydrolysis step (for example before its introduction into the first reaction space). The COD _to tai is the sum of the CODjnmai soluble and of the COD of the insoluble organic matter before its introduction into the first reaction space. The CODfinai soluble is the COD of the soluble organic matter after discharge thereof from the first reaction space. Thus, the COD _ini tiai soluble and the COD _to tai of the organic matter introduced into the first reaction space can be determined before the beginning of the hydrolysis step (for example before the introduction of this organic matter into the first reaction space). Samples are then taken by a user or controlled by means of control present either within the discharge of organic matter from the first reaction space, or by virtue of a means for taking a sample of the organic matter present in the first reaction space (such as a tap, for example) in order to determine the CODf _ina i soluble, until the degree of hydrolysis desired by the user is obtained. When the desired degree of hydrolysis is achieved, the user or an automated system activates the first extraction means in order to enable the discharge of the organic matter present within the first reaction space.

[0026] The discharge step is activated according to this degree of hydrolysis of the solid organic matter present within the first reaction space. The degree of hydrolysis of the solid organic matter therefore determines the moment at which the first extraction means will be activated. The determination of the degree of hydrolysis required for activating the first extraction means is dependent on the nature of the solid organic matter introduced into the first space. A solid organic matter which is slow to degrade occupies the first space for a long period of time. Thus, if a large amount of solid organic material which is slow to be degraded is to be treated, the degree of hydrolysis activating the step of discharge of the organic matter from the first reaction space may be quite low, so as to reduce the residence time of the organic matter in the first reaction space, while at the same time hydrolyzing a sufficient part of the organic matter in order to have a satisfactory overall yield of the methanization reaction. For example, if 60% of the solid organic matter is hydrolyzed in 5 days, but the rest of the solid organic matter is hydrolyzed in 25 days, the degree of hydrolysis required for activating the first extraction means may be defined at 60%. On the other hand, for a solid organic matter which degrades rapidly (for instance salad vegetable residues), complete hydrolysis of the organic matter is faster (about two days), and therefore the degree of hydrolysis required for activating the first extraction means can be defined at 80%, more preferentially at 90%, or indeed even more preferentially at 100%. Of course, the determination of the degree of hydrolysis required for activating the first extraction means may also be dependent on the size of the first reaction space according to the volume of organic matter to be treated. If the first reaction space has a relatively small volume compared with the volume of organic matter to be treated, the degree of hydrolysis required for activating the first extraction means may be defined at a relatively low threshold, and conversely, if the first reaction space has a relatively large volume compared with the volume of organic matter to be treated, the degree of hydrolysis required for activating the first extraction means may be defined at a relatively high threshold.

[0027] The process according to the invention comprises no step of reintroduction of the solid organic matter within the first reaction space after this solid organic matter has been extracted from the first reaction space. Thus, following the discharge of the organic matter from the first reaction space, the amount of organic matter available for carrying out the subsequent methanization steps is known, making it possible to adjust the parameters of these reactions in order to obtain a higher yield. A residence time of the organic matter in the second reaction space is therefore determined independently of the prior steps of the methanization process. Thus, the process according to the invention makes it possible to have a first reaction space of smaller size, which is more robust and of which the amount of organic material available after discharge from the first reaction space for the subsequent steps of the methanization is known and the process is controlled according to the needs of the user, each step of the process being independent, thus enabling the optimization and/or the modulation of each of these steps.

[0028] According to one preferred embodiment, the process according to the invention comprises the following steps:

- the step of discharge of the organic matter from the first reaction space is followed by a separation step in order to obtain a separated liquid organic matter and a separated solid organic matter,

- said separation step being followed by introduction of the separated liquid organic matter into the second reaction space,

- an acetogenesis and a methanogenesis of the separated liquid organic matter is carried out in the second reaction space, - the separated solid organic matter is evacuated via an outlet for separated solid organic matter.

[0029] According to this preferred embodiment of the invention, a step of separation of the liquid organic matter and of the solid organic matter is present following the discharge of organic matter from the first reaction space. The separation can be carried out according to any known method. For example, the separation can be carried out by centrifugation, filtration, using an Archimedes screw press, a sieve, using a membrane, by distillation or by evaporation. It is understood that, depending on the separation means used, it is possible for the phase separation between the solid organic matter and the liquid organic matter not to be perfect, resulting in the presence of a small amount of solid organic matter within the separated liquid organic matter and, conversely, in the presence of a small amount of liquid organic matter within the separated solid organic matter. The separated solid organic matter can be defined as any solid organic matter of which the size or the density is greater than the limit of separation of the separation means. Thus, if the separation means is a sieve, the separated solid organic matter is considered to be all the organic matter which was not able to pass through the sieve.

[0030] After separation of the two forms of organic matter, the separated liquid organic matter is introduced into the second reaction space, whereas the separated solid organic matter is not introduced into this same space. This makes it possible to treat the separated liquid organic matter under optimum reaction conditions, which would not be possible if solid organic matter was present. Thus, the conditions for reactions taking place within the second reaction space (acetogenesis and methanogenesis) are defined according to the intrinsic properties of the separated liquid organic matter only.

[0031] According to this embodiment, the separated solid organic matter is not treated, and is evacuated via an outlet located after the separation means. This process will be favored when the organic matter introduced into the first reaction space comprises a rapidly hydrolyzable solid organic matter, signifying that the separated solid organic matter then comprises only a relatively negligible portion of solid organic matter which is hydrolyzable and therefore advantageous in the context of a methanization process, or that the degree of hydrolysis determining the activation of the discharge of organic matter from the first reaction space is a high degree of hydrolysis (such as 70%, more preferentially 80%, or indeed even more preferentially 90%, and even more preferentially 100%), the organic matter discharged from the reaction space then no longer exhibiting hydrolyzable solid organic matter in an amount sufficient for the presence of a supplementary reaction space to be useful.

[0032] According to an even more preferred embodiment, the process according to the invention is characterized in that the step of discharge of the first digestate from the second reaction space is activated according to a degree of abatement of the separated liquid organic matter within the second reaction space.

[0033] The expression "degree of abatement of a separated liquid organic matter" should be understood to mean the ratio between, on the one hand, the difference between the amount of separated liquid organic matter entering the second reaction space and the amount of organic matter leaving the same second reaction space present in the digestate, and, on the other hand, the amount of separated liquid organic matter entering the second reaction space. Thus, the activation of the discharge of the digestate occurs only when the amount of liquid organic matter reaches a predetermined threshold. This threshold may correspond to a threshold where the organic matter which can result in the formation of a biogas becomes negligible (for example owing to a low concentration), or of little interest in terms of reaction kinetics.

The degree of abatement of the separated liquid organic matter can, for example, be calculated with the following formula:

Amount COD entering - Amount COD digestate

Degree of abatement COD liquid

Amount COD entering

The amount COD is expressed, for example, in milligrams of oxygen. The amount of COD _en t _e rin _g can be determined by assaying thereof within the separated liquid organic matter before its entry into the second reaction space by the method described in standard ISO 6060:1989. The amount of COD _d ig _esta t _e can be determined by assaying thereof within a sample of digestate discharged from the second reaction space or by assaying thereof within the second reaction space by the method described in standard ISO 6060:1989.

[0034] According to one preferential embodiment, the methanization process according to the invention is characterized in that:

the step of evacuation of the separated solid organic matter is followed by the introduction of said separated solid organic matter into a third reaction space,

a hydrolysis, an acidogenesis, an acetogenesis and a methanogenesis of the separated solid organic matter are carried out in the third reaction space, a second digestate is discharged from the third reaction space via a third extraction means.

[0035] According to this preferred embodiment of the invention, the step of separation of the liquid organic matter and of the solid organic matter is followed by the introduction of the separated solid organic matter within a third reaction space. This introduction step can be carried out by means of a valve, of an overflow, of a pump or of any other means of transfer connecting the outlet for separated solid organic matter, of the separation means, to the third reaction space.

[0036] The separated solid organic matter is inserted into the third reaction space, whereas the separated liquid organic matter is not introduced into this same space. This makes it possible to treat the separated solid organic matter under optimum reaction conditions, which would not be possible if liquid organic matter was present. Thus, the conditions for reactions taking place within the third reaction space are defined according to the intrinsic properties of the separated solid organic matter only. It should be noted that all of the methanization steps can take place within this third reaction space. Thus, the hydrolysis, acidogenesis, acetogenesis and methanogenesis steps can take place in this third reaction space. [0037] According to this embodiment, the separated solid organic matter is also treated. This process will be favored when the organic matter introduced into the first reaction space comprises a slowly hydrolyzable solid organic matter and/or when the degree of hydrolysis determined for activating the discharge of organic matter from the first reaction space is relatively low, signifying that the separated solid organic matter comprises a substantial portion of solid organic matter which is hydrolyzable and therefore advantageous in the context of a methanization process with a view to the production of a biogas.

[0038] According this embodiment, preferentially, the step of discharge of the second digestate from the third reaction space is activated according to a degree of abatement of the separated solid organic matter within the third reaction space.

[0039] The expression "degree of abatement of the separated solid organic matter" should be understood to mean the ratio between, on the one hand, the difference between the amount of separated solid organic matter entering the third reaction space and the amount of organic matter exiting the third reaction space present in the digestate, and, on the other hand, the amount of separated solid organic matter entering the third reaction space. Thus, the activation of the discharge of the digestate is carried out only when the amount of solid organic matter reaches a predetermined threshold. This threshold may correspond to a threshold where the organic matter which can result in the formation of a biogas becomes negligible (for example owing to a low concentration), or of little interest in terms of reaction kinetics.

The degree of abatement of the separated solid organic matter can, for example, be calculated according to the following formula:

Amount COD _en , - Amount COD . , ,

Degree of abatement COD ... =

Amount COD _entemig

With amount COD expressed in milligrams of oxygen. The amount COD _en t _e rin _g can be determined by assaying thereof within the separated solid organic matter before its entry into the third reaction space by the method described in standard ISO 6060:1989, the solid organic matter being ground beforehand, weighed and diluted. The amount of COD _d i _g estat _e can be determined by assaying thereof within a sample of digestate discharged from the third reaction space, or by assaying thereof within the third reaction space, the assaying being carried out on the liquid digestate, and the solid digestate if it is present, by the method described in standard ISO 6060:1989 for the liquid digestate and for the solid digestate if it is present, the solid digestate being ground beforehand, weighed and diluted before assaying.

[0040] Still preferentially, the process according to this embodiment can be carried out in such a way that the step of discharge of the first digestate from the second reaction space and the step of discharge of the second digestate from the third reaction space are activated independently of one another.

[0041] According to this embodiment, the means of discharge of the digestate from a second and from a third reaction space are activated independently of one another, preferentially according to each of the degrees of abatement of the organic matter present within each of the reaction spaces, in order to have a process which is more efficient within each of the reaction spaces while having residence times of the liquid organic matter and of the solid organic matter which are independent of one another, and defined according to the intrinsic qualities of each of the forms of organic matter, and to the efficiency or to the yield desired by the user.

[0042] According to one preferred embodiment, any one of the processes already described may comprise a step in which at least a part of the separated liquid organic matter present within the second reaction space is introduced into the first reaction space.

[0043] In this embodiment, the step of introduction of separated liquid organic matter present in the second reaction space, into the first reaction space, can be carried out by virtue of a valve followed by a length of piping connecting the two reaction spaces. This introduction can be controlled by a control means which allows the optional introduction of liquid organic matter. It is understood that the volume of the liquid organic matter thus transferred can be determined, and that the COD of this liquid organic matter transferred can be determined in order to take it into account during the determination of a degree of abatement of the separated liquid organic matter within the second reaction space and so as to take it into account during the determination of the degree of hydrolysis within the first reaction space, in order to retain optimum reaction conditions within each of the reaction spaces. The determination of the COD present within a stream of organic matter can be determined according to standard ISO 6060:1989. This step can be carried out when the organic matter present in the first reaction space exhibits volatile fatty acid concentrations which are too high, or when the organic matter within this first reaction space essentially consists of solid matter and/or when the content of this first reaction space is difficult to stir and/or to homogenize as it is.

[0044] According to this preferred embodiment, it is possible for the introduction of said separated liquid organic matter into the first reaction space to be controlled in order to maintain, within the first reaction space, a volatile fatty acid concentration below a threshold. This threshold can, for example, be chosen as being a threshold above which the acidogenesis reaction is inhibited. This inhibition can be determined by chemical assays known to those skilled in the art.

[0045] Maintaining the volatile fatty acid concentration below a predetermined threshold makes it possible to maintain acidogenesis kinetics which are satisfactory in the context of a methanization process.

[0046] According to one preferential or alternative embodiment, it is possible for the methanization process to comprise a step in which at least a part of the separated liquid organic matter is introduced into the first reaction space before its introduction into the second reaction space.

[0047] This step can be carried out, for example, using a valve followed by a length of piping connecting an outlet for separated liquid organic matter, of the separation means, to the first reaction space.

[0048] According to this preferential or alternative embodiment, the introduction of the separated liquid organic matter into the first reaction space before its introduction into the second reaction space is controlled in order to maintain a pH, for example, below 5.5 within the first reaction space. [0049] This introduction of separated liquid organic matter to the first reaction space can be controlled by any means, for instance a programmed means of regulation with instructions, these instructions being adjustable according to the pH within the first reaction space, the instructions optionally allowing the passage of a more or less large stream of liquid organic matter according to the pH within the first reaction space. The testing of the pH within the first reaction space can be carried out by any known means, such as the use of a pH meter located within the first reaction space. It is also possible to test the pH of the separated liquid organic matter concomitantly, in order to determine the volume of separated liquid organic matter to be transferred according to the pH of the separated liquid organic matter and to the pH of the organic matter present within the first reaction space, to the volume of the first reaction space and/or to the amount of organic matter present in the first reaction space, and thus to modify the instructions of the regulation means. It is understood that the volume of the liquid organic matter thus transferred can be determined, and that the COD of this liquid organic matter transferred can be determined in order to take it into account during the determination of the degree of hydrolysis within the first reaction space, in order to retain optimum reaction conditions of this first space.

[0050] In one preferred embodiment, the methanization process also comprises a step in which at least a part of the separated liquid organic matter present within the second reaction space is introduced into the third reaction space.

[0051] This step can be carried out when the separated solid organic matter present in the third reaction space does not exhibit sufficient viscosity qualities for it to be stirrable within the third reaction space, for example when the organic matter within this third reaction space essentially consists of solid organic matter which is very large in size or particularly solid (for instance ligneous residues). Thus, it is possible to stir the content of the third reaction space if required. The introduction of separated liquid organic matter from the second reaction space to the third reaction space can be carried out by virtue of a valve followed by a length of piping connecting these two reaction spaces, or any equivalent means. This valve can, as required, be controlled by a control or regulation means, and the introduction of separated liquid organic matter can depend on various parameters, for example the viscosity of the content of the third reaction space, or the amount of dry matter of the content of the third reaction space. The control or regulation means can comprise instructions, these instructions being adjustable according to these parameters. It is understood that the volume of the liquid organic matter thus transferred can be determined, and that the COD of this liquid organic matter transferred can be determined in order to take it into account during the determination of the degrees of abatement within each of the reaction spaces.

[0052] The invention also relates to a methanization apparatus (50) in order to carry out at least one process according to the invention as described above.

[0053] As illustrated in fig. 1 , the invention also relates to a methanization apparatus (50) for methanization of organic matter which is at least partly solid, said apparatus comprising:

- a first reaction space (1 ) designed for carrying out therein a hydrolysis and also an acidogenesis of the organic matter and comprising a first inlet for organic matter (10) and also a first outlet for organic matter (12),

- a second reaction space (2) designed for carrying out therein an acetogenesis and also a methanogenesis of organic matter and comprising a second inlet for organic matter (20) and also a second outlet for a digestate (21 ),

- first controllable extraction means (1 1 ) designed for extracting organic matter from the first space via the first outlet (12) and for transferring this organic matter to the second inlet (20),

characterized in that said apparatus also comprises:

- first measuring means (60) for measuring a degree of hydrolysis of the solid part of the solid organic matter contained in the first space (1 ),

- a first controller (70) having a first measuring inlet (71 ) connected to the first measuring means and a first control outlet (72) connected to the first extraction means, said first controller (70) being configured for controlling an activation of the first extraction means according to a degree of hydrolysis provided by the first measuring means (60), and in that no means for returning solid organic matter originating from the first reaction space (1 ) to said first reaction space (1 ) is present.

[0054] The first reaction space (1 ) may be any space enabling an organic matter which is at least partly solid to at least partly undergo a hydrolysis and an acidogenesis. This first reaction space may, for example, be a hydrolysis tank.

[0055] A first inlet for organic matter (10) may be any means for introducing an organic matter which is at least partly solid into the first reaction space (1 ), for instance an opening, a hatch, an Archimedes screw system, or a valve. A first outlet for organic matter (12) may be any means for discharging the organic matter in solid or liquid form from the first reaction space (1 ), for instance a valve continued by a length of piping, or a hatch.

[0056] A second reaction space (2) may be any space enabling an organic matter to at least partly undergo an acetogenesis reaction and a methanogenesis reaction for the purpose of producing a biogas, and in particular methane. The second reaction space (2) may also comprise an outlet devoted to the biogas produced, which is, for example, in the form of a pipe made of stainless steel or of high density polyethylene (HDPE).

[0057] A second inlet for organic matter (20) may be any means for introducing an organic matter into the second reaction space (2), for instance an opening, a hatch, an Archimedes screw system, a length of piping, or a valve. A first outlet for a digestate (21 ) may be any means for discharging the digestate from the second reaction space (2), for example a valve continued by a length of piping, or a hatch.

[0058] First controllable extraction means (1 1 ) may be a motorized worm screw, a pump or a solenoid valve.

[0059] First measuring means (60) for measuring a degree of hydrolysis of the solid organic matter contained in the first space may be a device for assaying the organic matter present in the liquid organic matter and in the solid organic matter present in the first reaction space (1 ). Advantageously, these first measuring means may be a COD meter.

[0060] A first controller (70) may, for example, be a microprocessor or a computer, a first measuring inlet (71 ) of which is connected to the first measuring means (60) for example by virtue of a communication cable connected via one of its ends to the first measuring means (60) and via another end to an incoming port of the first controller (70). The first controller (70) also has a first control outlet (72), for example an outgoing port, and a communication cable connects this outgoing port to the first controllable extraction means (1 1 ). Preferentially, the first controller (70) is configured for activating the first controllable extraction means (1 1 ) when the degree of hydrolysis of the solid organic matter present in the first reaction space (1 ) reaches a defined threshold of hydrolysis of the solid organic matter.

[0061] According to one preferred embodiment illustrated in figure 2, the methanization apparatus (50) also comprises a separation means (13) capable of separating an entering organic matter into a separated liquid organic matter and a separated solid organic matter, said separation means (13) being inserted between the first extraction means (1 1 ) and the second inlet (20), said entering organic matter originating from the first controllable extraction means (1 1 ), said separated liquid organic matter feeding the second inlet (20), and said separated solid organic matter being directed to an outlet for separated solid organic matter (14).

[0062] A separation means (13) may be any means for separating a mixed liquid organic matter and solid organic matter in order to separately obtain a separated liquid organic matter and a separated solid organic matter. A separation means (13) may, for example, be a centrifuge, a screw press, an overflow separator, a sieve, a filter, or a means for separation by settling out or by sedimentation.

[0063] The outlet for separated solid organic matter (14) may be any means for discharging the solid organic matter from the separation means (13), for example a length of piping or a hatch.

[0064] According to an even more preferred embodiment illustrated in figure 3, the methanization apparatus (50) also comprises:

- second controllable extraction means (22) designed for extracting the digestate from the second space via the second outlet (21 ),

- second measuring means (80) for measuring a degree of abatement of the separated liquid organic matter contained in the second space (2), - a second controller (90) having a second measuring inlet (91 ) connected to the second measuring means (80) and a second control outlet (92) connected to the second extraction means (22), said second controller (90) being configured for controlling an activation of the second extraction means (22) according to a degree of abatement provided by the second measuring means (80).

[0065] The second controllable measuring means (22) may be a motorized worm screw, a pump or a solenoid valve. The second measuring means (80) for measuring a degree of abatement of the separated liquid organic matter may be a device for assaying the organic matter present in the second reaction space (2). Advantageously, these second measuring means may be a COD meter coupled to a device for measuring the weight and/or the volume of the organic matter introduced into the second reaction space (2).

[0066] A second controller (90) may, for example, be a microprocessor or a computer, a second measuring inlet (91 ) of which is connected to the second measuring means (80) for example by virtue of a communication cable connected by one of its ends to the second measuring means (80) and via another end to an incoming port of the second controller (90). The second controller (90) also has a second control outlet (92), for example an outgoing port, and a communication cable connects this outgoing port to the second controllable extraction means (22). Preferentially, the second controller (90) is configured for activating the second controllable extraction means (22) when the degree of abatement of the separated liquid organic matter present in the second reaction space (2) reaches a defined degree of abatement of the separated liquid organic matter.

[0067] According to one even more preferred embodiment illustrated in figure 4, the methanization apparatus (50) also comprises:

- a third reaction space (3) designed for carrying out therein a hydrolysis, an acidogenesis, an acetogenesis and also a methanogenesis of separated solid organic matter and comprising a third inlet for organic matter (24) and also a second outlet for a digestate (31 ), said third inlet for organic matter (24) being connected to the outlet for separated solid organic matter (14), said separated solid organic matter originating from said outlet for separated solid organic matter (14), said separated solid organic matter feeding the third reaction space (3),

- third controllable extraction means (32) designed for extracting the digestate from the third space (3) via the second outlet for a digestate (31 ),

- third measuring means (83) for measuring a degree of abatement of the separated solid organic matter contained in the third space (3),

- a third controller (93) having a third measuring inlet (94) connected to the third measuring means (83) and a third control outlet (95) connected to the third controllable extraction means (32), said third controller (93) being configured for controlling an activation of the third extraction means (32) according to a degree of abatement provided by the third measuring means (83).

[0068] The third reaction space (3) may be any space enabling a solid organic matter to at least partly undergo hydrolysis, acidogenesis, acetogenesis and methanogenesis reactions, for instance a continuous-flow stirred-tank digester (CSTR) or a dry digester (garage or barn system type). The third reaction space (3) may also comprise an outlet devoted to the biogas produced, which is, for example, in the form of a pipe made of stainless steel or of HDPE. This outlet for biogas can be connected to the outlet for biogas present on the second reaction space (2). The second outlet for a digestate (31 ) may be any means for discharging the digestate from the third reaction space (3), for example a valve continued by a length of piping, or a hatch. The third inlet for organic matter (24) may be any means for introducing the separated solid organic matter originating from the separation means (13) via the outlet for separated organic matter (14), for instance an opening, a hatch or a length of piping.

[0069] The third controllable extraction means (32) may be a motorized worm screw, a pump or a solenoid valve. The third measuring means (83) for measuring a degree of abatement of the separated solid organic matter may be a device for assaying the organic matter present in the third reaction space (3). Advantageously, these third measuring means may be a COD meter coupled to a device for measuring the weight of the organic matter introduced into the third reaction space (3).

[0070] A third controller (93) may, for example, be a microprocessor or a computer, a third measuring inlet (94) of which is connected to the third measuring means (83), for example by virtue of a communication cable connected via one of its ends to the third measuring means (83) and via another end to an incoming port of the third controller (93). The third controller (93) also has a third control outlet (95), for example an outgoing port, and a communication cable connects this outgoing port to the third controllable extraction means (32). Preferentially, the third controller (93) is configured for activating the third controllable extraction means (32) when the degree of abatement of the separated solid organic matter present in the third reaction space (3) reaches a defined degree of abatement of the separated solid organic matter.

[0071] According to any one of the embodiments of a methanization apparatus described, the second reaction space (2) is a reactor which accepts a load greater than or equal to 5 kg VM/m ³ .d.

[0072] A reactor which accepts a load greater than or equal to 5 kg VM/m ³ .d may, for example, be a fixed bed methanizer described in patent application EP 2 207 873, or any other methanizer for liquid corresponding to this criterion (for instance an "Upflow Anaerobic Sludge Blanket" (UASB) methanizer or an "Expanded Granule Sludge Blanket" (EGSB) methanizer). The term "load" should be understood to mean the amount of volatile matter (VM) introduced per unit of volume of the second reaction space and per day. The volatile matter is defined as the biodegradable matter present within the second reaction space.

[0073] According to one preferred embodiment illustrated in figure 5, the methanization apparatus (50) comprises a first introduction means (41 ) for introducing the separated liquid organic matter present within the second reaction space (2) into the first reaction space (1 ).

[0074] The first introduction means (41 ) may be any means for connecting the second reaction space (2) to the first reaction space (1 ), while at the same time enabling a stream of liquid organic matter to be directed from the second reaction space (2) to the first reaction space (1 ). This first introduction means (41 ) may, for example, be a valve followed by a length of piping. This first introduction means (41 ) may comprise controllable pumping means designed for extracting the liquid organic matter from the second reaction space (2) and introducing the liquid organic matter into the first reaction space (1 ).

[0075] According to one preferred embodiment illustrated in figure 5, the methanization apparatus (50) comprises a second introduction means (43) for introducing the liquid organic matter which has been separated, before its introduction into the second reaction space (2), into the first reaction space (1 ).

[0076] The second introduction means (43) may be any means for introducing liquid organic matter which has been separated, but not introduced into the second reaction space (2), into the first reaction space (1 ), for instance a length of piping connected via one of its ends to the methanization apparatus (50) between the separation means (13) and the second inlet (20), and via another end to the first reaction space (1 ). This second introduction means (43) may comprise controllable pumping means designed for extracting the liquid organic matter after separation and introducing it into the first reaction space

(1 )-

[0077] According to an even more preferred embodiment illustrated in figure 5, the methanization apparatus (50) comprises a third introduction means (45) for introducing the separated liquid organic matter present within the second reaction space (2) into the third reaction space (3).

[0078] The third introduction means (45) may be any means for connecting the second reaction space (2) and the third reaction space (3), while at the same time enabling a stream of liquid organic matter to be directed from the second reaction space (2) to the third reaction space (3). This means may, for example, be a valve followed by a length of piping optionally comprising a pump. This third introduction means (45) may comprise controllable pumping means designed for extracting the separated liquid organic matter present within the second reaction space (2) and introducing it into the third reaction space (3).

[0079] According to one preferred embodiment illustrated in figure 5, the methanization apparatus (50) comprises a first introduction means (41 ) for introducing the separated liquid organic matter present within the second reaction space (2) into the first reaction space (1 ), a second introduction means (43) for introducing the separated liquid organic matter into the first reaction space and a third introduction means (45) for introducing the separated liquid organic matter present within the second reaction space (2) into the third reaction space (3).

[0080] The present invention has been described in relation to specific embodiments, which have a purely illustrative value and should not be considered to be limiting. Generally, it will appear to be obvious to those skilled in the art that the present invention is not limited to the examples illustrated and/or described above. The presence of reference numbers in the drawings cannot be considered to be limiting, including when these numbers are indicated in the claims.

The use of the verbs "comprise", "include", "contain", or any other variant, and also conjugations thereof, cannot in any way exclude the presence of elements other than those mentioned.

The use of the indefinite article "a" or of the definite article "the" for introducing an element does not exclude the presence of a plurality of these elements.

[0081] The invention can also be described as follows: the invention relates to a two-step process for methanization of organic matter in which the parameters of each of the steps are controlled independently of one another in order to obtain a satisfactory overall reaction yield according to the nature of the organic matter used in the methanization process. The invention also relates to an apparatus for carrying out the process according to the invention.