Improvement of a facility and a sequential waste treatment process for organic matter with a view to its biological recovery, Energy and Matter

Abstract

The invention relates to an installation and a method for treating solid waste containing fermentable organic matter to produce gas; the installation comprises: - at least one compartment (4a-4F), including an internal volume (Vint) adapted to receive the waste to be treated, a waste inlet opening, and a liquid accumulation zone for the decomposition of the organic matter, - means for capturing (30, 30') a gas produced by the decomposition of the waste, and - liquid injection means adapted to introduce liquid into the internal volume of at least one compartment. The liquid injection means are configured to introduce into the compartment, at at least a predefined time, a volume (Vl) of liquid greater than a minimum volume Vmin of liquid sufficient to saturate the upper layers of the waste mass. Application to the methanation of solid waste. Abstract figure: Figure 1

Description

Title of the invention: Improvement of an installation and a sequential treatment process for waste containing organic matter for biological recovery, Energy and Matter technical field

[0001] The invention relates to a waste treatment installation and a method for implementing this installation.

[0002] The invention relates to the treatment and recovery of any solid, non-toxic waste containing organic matter. The main source of such waste is the collection of household waste and so-called plant waste or green waste, generated by agriculture or the maintenance of green spaces. State of the art

[0003] The invention aims more specifically to improve the installation and the treatment process which is the subject of patent DI = FR3038532. The installation described in DI is a solid waste methanization installation enabling the production of biogas; the latter constitutes a renewable energy with high energy potential since it contains a substantial fraction of methane and has a very favorable carbon balance.

[0004] Methanization results from the action of certain groups of interacting microbial microorganisms constituting a trophic network. Four successive phases are classically distinguished: hydrolysis, acidogenesis, acetogenesis and methanogenesis.

[0005] Complex organic matter is first hydrolyzed into simpler molecules by microorganisms. Thus, lipids, polysaccharides, proteins, and nucleic acids become monosaccharides, amino acids, fatty acids, and nitrogenous bases. This decomposition is carried out by extracellular enzymes. In a methanation process, the hydrolysis phase can become the rate-limiting phase because it is "too slow" in the case of compounds that are difficult or slow to hydrolyze, such as lignin, cellulose, starch, or fats. In the case of a mixture of solid waste, hydrolysis occurs at different rates depending on the bioaccessibility of the components of the organic matter being treated, whereas it occurs at a much faster and more homogeneous rate in homogeneous and more liquid media.

[0006] The substrates resulting from the hydrolysis phase are used during the acidogenesis phase by so-called acidogenic microbial species, which will produce alcohols and organic acids, as well as hydrogen (H2) and dioxide. carbon (CO2). This phase is 30 to 40 times faster than hydrolysis.

[0007] The next phase of acetogenesis allows the transformation of the various compounds produced during the acidogenesis phase into direct precursors of methane: acetate, carbon dioxide, and hydrogen. Two groups of acetogenic bacteria are distinguished: - Obligate hydrogen-producing acetogens (OHPAs) are strict anaerobes capable of producing acetate and H2 from reduced metabolites of acidogenesis, such as propionate and butyrate. The accumulation of hydrogen leads to the cessation of acetogenesis by OHPAs, necessitating the constant removal of the hydrogen produced. This removal can be achieved through the syntrophic association of these bacteria with hydrogen-loving microorganisms. - Non-syntrophic acetogenic bacteria, whose metabolism is primarily geared towards acetate production, thrive in environments rich in carbon dioxide. Homoacetogenic bacteria belong to this group; they utilize hydrogen and carbon dioxide to produce acetate. They do not appear to compete for hydrogen with hydrogenophilic methanogenic Archaea and are present in much lower quantities in anaerobic biotopes.

[0008] Finally, the methanogenesis phase is carried out by strict anaerobic microorganisms belonging to the Archaea. This final stage results in the production of methane. It is achieved via two possible pathways: one using hydrogen and carbon dioxide by so-called hydrogenotrophic species, and the other using acetate by acetophilic species (also called acetoclasts). Their growth rate is lower than that of acidogenic bacteria. CO2 + 4 H2 → CH4 + 2 H2O CH3COOH -> CH4 + CO2.

[0009] The present invention aims to improve the DI installation and process by optimizing the yield of biogas production, and more particularly by optimizing the execution of at least one of the phases of the methanization process. Description of the invention

[0010] The invention proposes a plant for treating solid waste containing fermentable organic matter to produce gas and recover the gas produced, plant comprising: - at least one compartment, each compartment comprising peripheral walls and a base together defining an internal volume (Vint) suitable for receiving waste to be treated, a waste inlet opening and a liquid accumulation zone originating at least in part from the decomposition of organic matter, - at least one cover suitable for covering and sealing at least one compartment in a gas- and liquid-tight manner, - means of capturing a gas originating at least in part from the decomposition of waste, and - suitable liquid injection means to bring liquid into the internal volume of at least one compartment.

[0011] The installation according to the invention is characterized in that the liquid injection means are configured to introduce into the internal volume of an active bioreactor compartment containing a mass of waste to be treated, at at least a predefined instant, a volume VI of liquid greater than a minimum volume Vmin of liquid suitable for saturating the upper layers of the mass of waste.

[0012] The invention also proposes a method for implementing the installation described above, a method comprising, for an active bioreactor compartment: - a step of filling the internal volume of the active bioreactor compartment with the waste to be treated in order to form a waste mass, - a covering step consisting of placing a gas- and liquid-tight cover (20) over the waste mass so as to make the active bioreactor compartment substantially airtight, - a stage of at least partial anaerobic digestion of fermentable organic matter from waste in order to produce a gas and a liquid, the gas being captured and the liquid being accumulated in the accumulation zone, and - a step of injecting liquid into the active bioreactor compartment.

[0013] The process according to the invention is characterized in that the liquid injection step consists of introducing a volume VI of liquid greater than a minimum volume Vmin of liquid suitable for saturating the upper layers of the waste mass.

[0014] The invention thus proposes to use suitable liquid injection means to introduce large quantities of liquid into the waste mass, sufficient to saturate the upper layers of the waste mass. Liquid saturation of the upper layers allows for optimized distribution of the liquid over the entire surface of the upper layers, followed by homogeneous wetting of the waste mass as the liquid flows down through it by gravity. Liquid saturation of the upper layers also prevents the formation of liquid flow paths within the mass, which would cause the liquid to sink too quickly by gravity to the bottom of the compartment and prevent diffusion of the liquid over the entire surface of the upper layers of the mass.Liquid saturation thus makes it possible to obtain a homogeneous humidity level in the upper layers and more generally in all layers of the massif, resulting in a similarly homogeneous advancement of methanation. as much as possible across the entire massif. Moreover, when carried out at the beginning of methanization, saturation injection accelerates the hydrolysis phase which takes place at generally more homogeneous rates although different depending on the bioaccessibility of the components of the solid organic matter treated. Brief description of the figures

[0015] The invention will be better understood, and other features and advantages of the invention will become apparent from the following description of examples of implementations of the invention. These examples are given by way of non-limiting example. The description is to be read in conjunction with the accompanying drawings in which: - [Fig. 1] [Fig. 1] is a perspective view illustrating an installation according to the invention, - [Fig.2] [Fig.2] is a top view of the installation of [Fig.1], - [Fig.3] [Fig.3] is a perspective view of a compartment of the installation in Figures 1 and 2 illustrating the gas capture means, - [Fig.3] [Fig.3] is a perspective view of a compartment of the installation shown in Figures 1 and 2, illustrating the gas capture means equipping said compartment. - [Fig.4] [Fig.4] is a perspective view of a compartment of the installation shown in Figures 1 and 2, illustrating the liquid circulation means equipping said compartment. - [Fig.5] [Fig.5] is a cross-sectional view of the compartment in Figures 3 and 4, along the VV line shown in [Fig.2], - [Fig.6] [Fig.6] is a perspective view of the compartment of [Fig.5], from a different angle than figures 3 and 4, with cuts along line VV, - [Fig.7] [Fig.7] is a schematic representation of the flow of liquids in an installation according to the invention.

[0016] The dimensions and more generally all the numerical values ​​in the description are for the most part orders of magnitude given for purely indicative purposes; they are not limiting the scope of the invention and are naturally to be adapted according to the embodiments and applications envisaged.

[0017] Figures 1 to 6 reproduce Figures 1 to 6 of patent D1, supplemented by elements specific to the present invention. The following numerical references are used in the drawings: 1. Common Functional Space 4A-4F compartments: 2 Base 1A-1F Walls of 1 3A-3F Radial walls 10 Bottom of a compartment 11 Outer part of the bottom Z Accumulation zone 12 Enclosure wall 14 Peripheral track 14' Peripheral track 15 Oblique ramp 16 Embankment 17 Sol 20 Coverage of catchment areas: 30, 30' Capture units 31.31' Main Tube 32, 32' Secondary Tubes 33 Collector 34. Pump for capturing liquid injection means: 40, 40' Injection Assemblies 41 Main tube 42 Secondary Tubes 44 injection pump 70 liquid distribution methods: liquid extraction methods: 43 Pumping unit 43', 43" Ends of 43 46 Extraction pump 45 purge storage areas 471, 472 buffer zones 473, 474 storage areas 48 mixing medium Twenty interior volume of a compartment VI volume of injected liquid Vlmin minimum value of VI injection time Timax maximum value of the injection time

[0018] Detailed description of embodiments of the invention

[0019] As stated previously, the installation and method according to the invention are intended to To treat solid waste containing fermentable organic matter. Solid waste includes, for example, household waste, agricultural by-products, and waste from the chemical or agri-food industries.

[0020] An installation according to the invention essentially comprises at least one compartment, at least one cover, means for capturing gas and means for injecting liquid.

[0021] In an improved version as shown in the figures, the installation according to the invention essentially comprises a centrally located common functional space 1 and several compartments extending radially from this common functional space. More precisely, the common functional space 1 is hollow and has a polygonal shape when viewed from above. It rests on a base 2, also polygonal, which has larger radial dimensions than the space itself. The number of sides of the functional space corresponds to the number of compartments in the installation. Each peripheral wall IA to 1F of the functional space, corresponding to one side thereof, forms a first lateral wall of a respective compartment. From each corner of the functional space, namely each intersection between two consecutive sides, a respective radial wall 3A to 3F extends outwards.Two consecutive radial walls 3A and 3B, 3B and 3C, ..., 3F and 3A, form two further lateral walls of a respective compartment. In addition to lateral walls, a compartment includes a bottom 10; the bottom 10 and the walls of a compartment together delimit, on the one hand, an internal volume Vint adapted to receive the waste to be treated and, on the other hand, a zone Z in which the liquid accumulates by gravity.

[0022] In its simplest form, an installation according to the invention comprises a single compartment. In the illustrated example, the installation according to the invention comprises six waste reception and treatment compartments, which are designated by the reference numerals 4A to 4F. However, a different number of compartments may be used, in particular between 4 and 6. An installation comprising several compartments is more efficient. Indeed, the compartments are used and operate at staggered intervals. Thus, as soon as one compartment is full, it is possible to fill a second compartment as waste is collected, without waiting for the previous compartment to be emptied after processing.This also allows liquid extracted from one compartment to be injected into another: on the one hand, this limits the storage time of a liquid, and on the other hand, it allows for a large quantity of liquid and / or a quantity of liquid with biochemical and / or bacterial properties appropriate to the needs of a compartment to be watered.

[0023] The cover 20 is adapted to selectively cover the interior volume of one or the other of the above compartments in a gas- and liquid-tight manner, depending on the progress of the waste treatment process. A cover is shown as an example on compartment 4E (full and covered) in Figures 1 and 2. The number of covers (at least one) for the installation depends on the number of compartments. Details on the selection of the number of compartments, the specific design and dimensions of the compartments, the number of covers, and the specific design and installation of a cover can be found in document D1, page 10, line 4 to page 14, line 14.

[0024] The capture means equipping the installation according to the invention make it possible to extract, from each compartment, the gas released by the waste during its treatment. These capture means are particularly visible in Figures 5 and 6, as well as in [Fig. 3] where the liquid injection means are not shown, for the sake of clarity.

[0025] The capture means include a collector 33, a capture pump 34 and, in each compartment, at least one capture tubular assembly 30, 30'.

[0026] A collection assembly 30, 30' comprises a main tube 31 extending radially and secondary tubes 32. These secondary tubes extend obliquely in the horizontal plane on either side of the aforementioned main tube 31. Advantageously, at least two similar tube assemblies 30, 30' are found (see [Fig. 5]), arranged one above the other within a compartment. The various tube assemblies, installed in the compartments of the system, open radially inwards into the common manifold 33, provided in the central common space (see in particular Figures 5 and 6). This manifold 33, which centralizes the gas flows, is associated with the pump 34, for example, a centrifugal pump.Advantageously, the collector 33 extends beyond the central common space 1 and terminates in an unshown power generation device, for example, a gas-fired engine (or turbine) driving an electric generator and advantageously operating in a combined cycle. Details on the practical implementation of the collection means can be found in document D1, page 10, line 4 to page 14, line 14. Further advantageously, the collection means are equipped with unshown devices for measuring the physicochemical parameters of the gas flows collected in each compartment. In particular, the volume of gas collected and / or the flow rate of gas collected, as well as the composition of the gas collected, including the proportion of methane (CH4) and / or hydrogen (H2) in the collected gas, can be determined for each compartment.These parameters are representative of the progress of waste digestion; they allow the phases of methanation to be identified in an active bioreactor compartment.

[0027] According to one embodiment, a pressure slightly lower than the pressure in the The compartment is maintained inside the tubular assembly(ies) 30, 30', so that the gases produced are drawn in by the capture means. This embodiment also has the advantage of limiting the risk of air entering the compartment during methanation.

[0028] In the example shown, the liquid injection means include, in particular, an injection element such as an injection pump 44 and, for each compartment, a tubular injection assembly 40 formed by a main tube 41 extending radially, and by secondary tubes 42 extending transversely on either side of this main tube 41, one end 41' of this main tube being connected to an outlet of the injection pump 44. Advantageously, in one compartment, there is a single tubular injection assembly 40, located above the tubular collection assemblies 30, 30'. This tubular injection assembly 40 is particularly visible in Figures 5 and 6, as well as in [Fig. 4], where the gas collection means are not shown, for the sake of clarity. Details on the concrete implementation of the means of capture can be found in document Dl, page 10 line 4 to page 14, line 14.Pump 44 is arranged to alternately supply liquid to the injection assembly 40 of either compartment.

[0029] According to the invention, the installation includes liquid injection means configured to introduce into the internal volume of an active bioreactor compartment containing a mass of waste to be treated, at at least a predefined instant, a volume VI of liquid greater than a minimum volume Vlmin of liquid suitable for saturating the upper layers of the mass of waste with liquid.

[0030] By saturating the upper layers with liquid, we ensure the most homogeneous possible percolation of liquids through the entire mass of waste, thus enabling efficient methanization.

[0031] To this end, in one embodiment, the volume Vlmin is determined by Vmin = S*H*M where - S and H are respectively a surface area and a height of the waste mass and - M is a macroporosity index of the waste mass. S and H are related to the compartment structure and the volume of waste within it. M is defined as the ratio of the void volume in the waste mass to the total volume of the waste mass, expressed as a percentage. M is correlated with the particle size distribution of the organic matter constituting the waste mass and is usually between 20% and 60% for fine and coarse particle sizes, respectively. M is determined, for example, from a measurement of the particle size distribution of the waste in the waste mass and a lookup table or nomogram.

[0032] In a practical example, the cross-section of the main tube 41 of an injection assembly, and the maximum flow rate of the pump 44, are chosen so as to be able to inject a large volume of liquid into the compartment, and more precisely a volume of liquid greater than Vmin. As an order of magnitude, for a compartment with a cross-section of approximately 130 m² to be modified and a height of approximately 6 m, Vmin is approximately 160 m³.

[0033] Preferably, the injected volume VI is injected in an injection time Ti less than a maximum injection time Timax determined by: Timax = [VI / (S*C)] * N where: - S is the surface area of ​​the waste mass. - parameter C is an index of the hydraulic conductivity of the waste mass, and - N is a parameter representing the expected efficiency of percolation of the injected liquid into the waste mass, N being greater than 1, preferably greater than 5 and ideally greater than 10.

[0034] In a practical embodiment, the section of the tube 41 and the pump 44 are chosen to be able to inject into the waste mass a volume of liquid greater than Vlmin in a liquid injection time Ti less than the maximum time Timax.

[0035] C is, for example, determined according to Darcy's law, a physical law that expresses the flow rate of an incompressible fluid filtering through a porous medium. The fluid flow between two points is determined by the hydraulic conductivity or the permeability coefficient of the substrate and by the fluid pressure gradient. The parameter C is usually expressed in m³ / h and varies from 0.1 to 2 depending on the nature of the waste mass (types of inputs, particle size, compaction, etc.).

[0036] N is a parameter representative of the conditions for efficient percolation of the injected liquid into the waste mass; N is greater than 1; N is preferably chosen to be greater than 5 for average efficiency and ideally greater than 10 to obtain very rapid accumulation of liquid in the mass. The parameter N is chosen by the plant operator, notably according to the waste to be treated, the desired duration of waste treatment, and the injection capacity of the installed liquid injection equipment. As an order of magnitude, for a compartment with a cross-sectional area S of approximately 130 m² and a height of approximately 6 m of waste with a hydraulic conductivity index C of 0.3, the maximum injection time of the volume Vlmin (calculated in the preceding paragraph) is 240 minutes, 48 ​​minutes, or 24 minutes respectively for a factor N equal to 1, 5, or 10.

[0037] In addition, the installation includes liquid distribution means 70 comprising liquid storage areas 47 and a mixing means 48 arranged to supply the injection means with a liquid mixture comprising liquid from at least one storage area.

[0038] Advantageously, in the liquid mixture, a proportion of liquid from each storage area (47 b 472, 473, 474) can be a function of parameters of the gas previously captured in the active bioreactor compartment and representative of an advancement of treatment in the active bioreactor compartment and / or a function of parameters of the liquid previously extracted from the active bioreactor compartment and representative of an average biochemical state of the waste mass contained in the active bioreactor compartment.

[0039] The liquid thus injected into the active bioreactor compartment is best adapted to the progress of the ongoing methanation and / or improves the average biochemical state of the waste mass for efficient methanization.

[0040] The distribution means 70 also include liquid extraction means 43, 46 arranged to extract liquid in the accumulation zone Z of at least one compartment and to bring the extracted liquid into a buffer storage zone of the distribution means.

[0041] The extraction means thus make it possible to transfer all or part of the liquid produced in a compartment during the digestion of organic matter from the waste, from the bottom of the compartment where this liquid accumulates by gravity, to a storage area.

[0042] The extraction means in the example shown include an extraction pump 46 and, for each compartment, a pumping element 43.

[0043] The pumping element 43 in the example shown has a tubular shape and extends over substantially the entire height of the common space 1. A first end 43' of the pumping element opens near the bottom of the compartment in the accumulation zone, passing through the bottom of the separating wall IA, and a second end 43" of the pumping element is connected to an inlet of the extraction pump 46. The extraction means may also include drainage tubes (not shown) installed at the bottom of the compartment in the accumulation zone and connected to the first end 43' of the pumping element.

[0044] The pumping unit 43 is advantageously equipped with means (not shown) for measuring at least one parameter of the liquid present in each compartment. The liquid parameters that can be measured or determined include, in particular, the volume of liquid flowing into the accumulation zone, the composition of the liquid, the percentage of organic matter suspended in the liquid, the pH of the liquid, etc. These parameters provide information on the average biochemical state of the waste mass at the time of measurement.

[0045] By way of example, the pumping element 43 shown in the figures is positioned vertically and is equipped with a gauge adapted to measure the height of liquid in a tube. Apart from the liquid extraction phases, the liquid in the element 43 The pumping unit is at the same altitude as the liquid in the associated accumulation zone. Since the accumulation zone Z has a perfectly defined geometry, the liquid height in the tubular pumping unit allows the volume of liquid present in the accumulation zone to be determined, and from this, the humidity level inside the compartment to be deduced. For example, a high-level sensor and a low-level sensor can be placed in the pumping unit 43 or in the accumulation zone inside the compartment to constantly maintain the accumulated liquid volume within a given range, corresponding to a target humidity range in the compartment.

[0046] As another example, it is possible to provide for placing, in the pumping unit 43 or in the accumulation zone or at the level of the pump 46, a device for taking a sample of liquid and to provide for a device for analyzing the composition of the liquid sample by spectroscopy.

[0047] The extraction pump 46 is adapted to extract liquid from the accumulation zone Z of a compartment and convey the extracted liquid to a buffer zone. In the example shown, a single pump 46 is used to extract the liquid from all compartments sequentially. Alternatively, one pump per compartment may be provided.

[0048] According to one embodiment (represented [Fig.5], 6), the storage means comprise a single buffer storage area and the liquid extracted from all the compartments is stored in said buffer area.

[0049] Alternatively ([Fig. 7]), the distribution means comprise at least two buffer storage zones (47b 472), and the extraction means are arranged to convey liquid extracted from one compartment to one or the other of the buffer storage zones depending on at least one biochemical parameter of the extracted liquid. The pH of the liquid is a parameter that may be taken into account for the choice of the storage zone.

[0050] The buffer zone(s) allow for the temporary storage of liquid extracted from one or more compartments, so that a quantity of liquid is available when liquid injection is planned to control the installation, as will be explained in more detail later. Since the duration of a methanation cycle is on the order of several weeks, the storage of the extracted liquid can last from a few days to a few weeks, depending on the liquid requirements in the compartments. The buffer storage zone(s) (47b 472) are, for example, concrete silos or large-capacity stainless steel tanks, on the order of several tens of cubic meters, for example, between 10 and 100 m³.

[0051] The buffer zone(s) (47b 472) also allow the liquids extracted from several compartments to be pooled, when the installation has several compartments, from This allows for the availability of the largest possible quantity of liquid in advance, enabling a significant injection of liquid into a compartment to saturate the upper layers of the waste mass present in the behavior. Finally, the presence of several buffer zones allows for the storage of extracted liquids with varying physicochemical or bacteriological parameters, which can then be injected into a compartment at the appropriate time, depending on the current digestion phase and their specific physicochemical or bacteriological characteristics.

[0052] For example, liquids extracted from a compartment in the hydrolysis or acidogenesis phase having a pH of around 5 to 7 can be stored in a first buffer zone 47 j, and liquids extracted from a compartment in the methanogenesis phase having a pH greater than 7 can be stored in a second buffer zone 472. They can thus be used later in a compartment, depending on their pH, to restore the biochemical balance of a compartment according to its specific needs to promote the methanation phase concerned.

[0053] The collection means may also include at least one drain valve 45 at the pump 46 or one drain valve per compartment. The drain valve 45 allows some of the liquid to be removed from a compartment. In particular, liquid may be drained if the overall quantity of liquid in the accumulation zone is too large and cannot be stored entirely, or to protect the pump in case of excessive viscosity of the liquids extracted from a compartment.

[0054] It is also possible to purge part of the liquid if its parameters cannot be easily corrected, as will be explained in more detail later. The purge device is preferably used when it is not appropriate to store the liquid in a buffer zone, for example, when the liquid parameters are unsuitable or when the buffer zone(s) are full.

[0055] In the installation according to the invention, the storage means may also include at least one storage area for a liquid adjuvant (473, 474).

[0056] A first type of liquid adjuvant is, for example, a liquid containing inocula, typically consisting of pre-selected bacterial colonies; the inocula allow for the rapid seeding of the waste mass to promote or accelerate one of the phases (hydrolysis, acidogenesis, acetogenesis, methanogenesis) of the anaerobic digestion stage or the transition between two phases of anaerobic digestion. For example, a liquid adjuvant containing bacteria that promote the hydrolysis of organic matter is stored in a storage area 473. In general, the liquid is highly concentrated in inocula so that a small quantity of liquid is sufficient for the installation; the storage area 473 of liquid containing inocula can thus consist, for example, of cylinders capable of holding a few liters or tens of liters of liquid and arranged to be able to be emptied into the reinjection network of liquids from a given compartment in a regular and controlled manner, for example by Venturi effect.

[0057] A second type of liquid additive is, for example, a liquid containing suspended organic matter (called the "organic load" of the liquid) that can be methanized. Typically, liquid additives contain an organic load ranging from 5% to 20% by volume, which is in the form of particles ranging in size from 0 mm (corresponding to dissolved particles of immeasurable size because they are too small) to 13 mm (for the largest dimension of three-dimensional particles). Liquid additives are, for example, liquid waste (also called "liquid digestate") from other facilities or food biowaste, collected in the form of a "slurry" and which can be temporarily stored, for example, in storage area 474 of the facility.Liquid additives, which are easily hydrolyzable, are used, for example, to initiate the hydrolysis phase of methanation, as will be explained in more detail later. In a preferred embodiment, the liquid waste is injected into a compartment upon arrival at the plant or shortly thereafter, so that the storage area 474 can be, for example, a tanker truck or containers dedicated to liquid waste, immobilized for a period of a few hours to a few days, the time required for transferring the liquid waste into a specific compartment. Typically, the liquid waste is transferred into a compartment undergoing hydrolysis via the liquid injection means.

[0058] Finally, as stated previously, the installation according to the invention also comprises, for each compartment: - means of measuring parameters of the gas captured in said compartment, in particular parameters representative of the progress of digestion, - means of measuring parameters of the liquid extracted from said compartment and representative of the biochemical state of the mass of waste in said compartment. And the installation is advantageously complemented by means of controlling the means of liquid distribution according to the parameters of the progress of digestion and / or the biochemical parameters representative of the biochemical state of the waste mass.

[0059] Figure 7 schematically illustrates the possible liquid flow movements between the different components of an installation according to the invention, the liquid flow movements being carried out by the distribution means. The extraction means are controlled to extract (flow 60A-60F) the liquid from a compartment 4A-4F as it is produced, in quantities appropriate to maintain the biochemical state of the waste mass most suitable for the phase (hydrolysis, acidogenesis, acetogenesis or methanogenesis) of the ongoing digestion. The extraction means are also controlled to store (flows 65 x 652) the extracted liquid in a suitable storage zone 47x, 472 or to discharge the extracted liquid via the purge device 45. The mixing means are controlled to supply (flows 50A-50F) to the injection means the liquid from (flows 66b 662, 663, 664) one or more of the storage zones 47b 472 of extracted liquid, optionally supplemented with a liquid additive stored in zones 473, 474 and / or optionally supplemented with water, depending on the liquid composition required to optimize the efficiency of the ongoing digestion phase or prepare the next decomposition phase.

[0060] The method of implementing the installation according to the invention will now be described below.

[0061] In a conventional manner, the method for implementing an installation as described above comprises, for an active bioreactor compartment: - a step of filling the internal volume of the active bioreactor compartment with the waste to be treated in order to form a waste mass, - a covering step consisting of placing a gas- and liquid-tight cover (20) over the waste mass so as to make the active bioreactor compartment substantially airtight, - a stage of at least partial anaerobic digestion of fermentable organic matter from waste in order to produce a gas and a liquid, the gas being captured and the liquid being accumulated in the accumulation zone, and - a step of injecting liquid into the active bioreactor compartment.

[0062] The compartment is filled conventionally using any suitable mechanical means that allow loading from the top. Emptying is carried out using the same means, possibly supplemented by the use of construction equipment fitted with buckets that can enter the compartment via the ramp provided for this purpose. Prior to filling, the waste may be crushed and / or mixed to obtain waste with a homogeneous particle size.

[0063] Controlling the system involves optimizing the physicochemical and bacteriological parameters within a compartment where the anaerobic digestion stage is taking place, so that this stage is as complete and rapid as possible. Since the digestion stage is carried out by bacteria, and moreover, bacteria of different types depending on the successive phases of the anaerobic digestion stage, controlling the system involves optimizing the physicochemical and bacteriological parameters within the compartment to ensure good development of the bacterial colonies necessary for the completion of the current phase of the digestion stage. In the context of the invention, this optimization is achieved in particular by optimizing the injection of liquid in the compartment as the digestion stage progresses.

[0064] The process according to the invention thus aims to control the operating conditions within the active bioreactor compartment during the anaerobic digestion phase, so as to advantageously have the following in the active bioreactor compartment: - a temperature between 25°C and 65°C, and preferably between 45°C and 55°C; - a humidity level between 20% and 80%, and preferably between 40% and 60%; - a pH between 5 and 9, and preferably between 5 and 6.5 during the hydrolysis and acidogenesis phases, and a pH greater than 7 during the methanogenesis phase. Advantageously, the invention implements this anaerobic digestion step in such a way as to allow the expression of at least 70%, and preferably at least 90%, of the methanogenic potential of the degradable organic matter present in the waste. This anaerobic digestion step typically lasts between 1 and 10 months in a compartment, and preferably between 2 and 3 months.

[0065] The process according to the invention can be implemented in an installation comprising a single compartment, as described below. Advantageously, however, it is implemented in an installation comprising several compartments (at least two); if so, the process is implemented compartment by compartment, at staggered times, as the waste is collected and the compartments are sequentially filled. For example, in an installation with 8 bioreactor compartments operating on a 12-week treatment cycle, including filling and emptying, the treatment start-up stagger between two bioreactor compartments is ideally 1.5 weeks.

[0066] In a multi-compartment installation, liquids extracted from one compartment can advantageously be used in another compartment to accelerate the rate of liquid injections into the other compartment, thereby speeding up digestion in said other compartment and simultaneously reducing the storage time of the extracted liquid. Furthermore, storing liquids extracted from several compartments in the same storage area provides a significant quantity of liquid for implementing the essential step of the invention described below.

[0067] The process according to the invention is in fact characterized in that the liquid injection step consists of introducing a volume VI of liquid greater than a minimum volume Vmin of liquid suitable for saturating the upper layers of the waste mass.

[0068] The introduction of a large volume of liquid capable of saturating the upper layers of the waste mass makes it possible to obtain a more homogeneous humidity level over the whole mass, facilitating the more homogeneous digestion of the waste mass.

[0069] The first liquid injection step is preferably carried out between the step of The introduction of liquid allows the hydrolysis phase to begin immediately after the compartment is covered. Furthermore, introducing a large quantity of liquid homogenizes the hydrolysis phase throughout the bulk, accelerates it, and shortens the phase during which no gas is produced.

[0070] Other liquid injection steps can be carried out subsequently during the anaerobic digestion step. The timing of such steps, as well as the quantity and quality of the liquid injected at each time, may depend on the progress of the anaerobic digestion reaction, the physicochemical parameters of the captured gas and / or the physicochemical parameters of the extracted liquid, as will be explained in more detail later.

[0071] The liquid injected into the waste mass may originate from a source external to the installation according to the invention. Advantageously, the injected liquid originates at least partially from the installation itself.

[0072] For this purpose, the process according to the invention may include a step of extracting at least a part of the liquid from the accumulation zone, the extracted liquid being brought into a storage zone 47b 472. The liquid extraction step is carried out during the digestion step.

[0073] During the digestion stage, the liquid extraction stage can be performed once or several times. The extraction stage can be performed at predefined time intervals, for example, from 1 to 40 times per week, depending on the treatment stage in which the compartment concerned is located. Alternatively, the extraction stage can be performed based on the liquid saturation level of the compartment. This saturation level can, for example, be determined indirectly by the system's control means or directly from a measurement of the liquid level in the pumping unit 43 as mentioned above.

[0074] In practice, the physico-chemical parameters of the extracted liquid, as well as the variety and quantity of the major bacteria in the extracted liquid, evolve as the anaerobic digestion reaction progresses, and in particular according to the phases of the digestion stage: hydrolysis, acidogenesis, acetogenesis and methanogenesis.

[0075] In order to make the best use of the properties of the collected liquid, during the anaerobic digestion step, the extracted liquid can be brought into a first storage zone 47 j or a second storage zone 472 depending on at least one biochemical parameter of the extracted liquid.

[0076] In one embodiment, the biochemical parameter taken into account is the pH of the extracted liquid, the pH of the extracted liquid being measured, for example, in the pumping element 43; the extracted liquid is in this case brought into the first zone of storage 47 days or in the second storage zone 472 depending on whether a pH value of said extracted liquid is lower or higher than a neutral pH value (pH 7) for the process.

[0077] To control the progress of the anaerobic digestion step, the process according to the invention also includes, carried out in parallel with the digestion step: - a monitoring step of at least one parameter of the accumulated liquid and / or at least one parameter of the gas captured in the active bioreactor compartment and, - if at least one parameter reaches a predefined alert value associated with said at least one parameter, a liquid injection step or a gas injection step into the active bioreactor compartment is carried out.

[0078] The monitoring step consists of acquiring parameters of the accumulated liquid and / or parameters of the gas captured in the compartment, and comparing the acquired parameters to expected parameters representative of optimal digestion; the acquired gas parameters are compared to expected parameters relating to optimally efficient digestion, and the acquired liquid parameters are compared to expected parameters representative of a biochemical state in accordance with the growth and activity of the bacterial colonies required to optimize the efficiency of the phase of the ongoing digestion step and / or to prepare in advance the next step.

[0079] Some parameters are acquired directly through measurements, such as the pH of the liquid or the gas flow rate. Other parameters are determined immediately from measurements and structural characteristics of the installation. For example, the volume of the accumulated liquid or the humidity level in the compartment is obtained from a measurement of the liquid height in the pumping unit 43 and the shape and dimensions of the accumulation zone; the volume of extracted gas is determined from the continuously measured captured gas flow rate and the cross-section of the main capture tubes 31, etc. Still other parameters require analyses that cannot be performed in real time and are carried out at predefined intervals, for example, hourly, daily, monthly, etc.The level of organic matter in the liquid is determined, for example, by mass spectrometry; the nature of the bacterial colonies present in the liquid is determined, for example, by culturing a sample of the liquid in a Petri dish and analyzing it.

[0080] The monitoring stage is ideally carried out throughout the anaerobic digestion stage; some parameters are measured or determined in real time, others at predefined time intervals. Sampling and analysis are, for example, performed hourly or twice an hour. These can be carried out by automated systems located within the installation or in the immediate vicinity of the installation.

[0081] In one example, during the monitoring step, a height of the liquid in the The active bioreactor compartment is measured, and if its level is below a low alert level, the liquid injection step into the active bioreactor compartment is repeated. A liquid level below the low alert level may indicate insufficient liquid saturation in the waste mass, preventing the proper development of the bacterial colonies necessary for digestion.

[0082] In another example, during the monitoring step, a parameter of the captured gas representative of the progress of the anaerobic digestion step is monitored, and during the repetition of the liquid injection step, the composition of the injected liquid is adjusted according to at least one parameter of the captured gas. For example, at any given time, the amount of methane CH4 and the amount of oxygen O2 present in the captured biogas provides information on the progress of the reaction in the anaerobic digestion step: the absence of CH4 and / or the presence of O2 in the captured gas indicates digestion at the stage of hydrolysis, acidogenesis, or acetogenesis; the presence of CH4 and / or the absence of O2 indicates digestion at the stage of methanogenesis; and so on.

[0083] The expected parameters for the accumulated liquid or the captured heap can be determined from average values ​​of measurements taken during previous implementations of the process, or from charts from the literature.

[0084] Alternatively, the process according to the invention may advantageously include an initialization step during which the expected theoretical results of the anaerobic digestion step are determined. These results are obtained, for example, by the following steps: - The waste is analyzed before being placed in a compartment; the analysis makes it possible to identify the main biochemical components in the waste to be treated (such as cellulose, hemicellulose, sugars, proteins, lipids, etc.), and to determine the relative mass of each component identified in the waste to be treated, then - For each biochemical component, its characteristic parameters for anaerobic digestion are determined, for example from nomograms; the characteristic parameters include, in particular: * the theoretical quantity of CH4 (called "methanogenic potential", or BMP) that can be expected to be obtained during the anaerobic digestion of the identified biochemical component; this theoretical quantity of CH4 is usually expressed in liters per kg of dry matter * the rate of degradation under anaerobic conditions (called the kinetic factor or k factor) of the identified biochemical component; this rate of degradation is usually expressed as a percentage of degradation per day and finally - the results are determined, for example, by a weighted average calculation expected from the anaerobic digestion stage of the waste present in the compartment; said expected results are for example represented in the form of a theoretical degassing curve, showing the volume of CH4 produced at any time during the duration of the anaerobic digestion between tO (time of triggering the hydrolysis phase by the first injection of liquid) and tO + D (D being the expected duration of the anaerobic digestion)

[0085] The expected theoretical degassing curve allows for optimal control of the digestion stage, the control consisting of bringing the actual curve as close as possible to the theoretical curve.

[0086] The liquid introduced during a liquid injection step is preferably liquid extracted from at least one compartment of the installation and stored in the buffer storage area(s) 47b 472 of the installation. If the quantity of liquid extracted and stored is not sufficient to carry out a liquid injection step at a given time and / or if the physicochemical parameters of the extracted and stored liquid are not in accordance with the physicochemical parameters of the liquid to be injected at a given time, it is possible to inject, in addition to or instead of the extracted and stored liquid, one or more liquid adjuvants which may be a liquid containing targeted inocula, or a liquid containing suspended organic matter, as described above, or even water.

[0087] Thus, during a liquid injection step into the active bioreactor compartment, the injected liquid comprises liquid extracted from at least one compartment of the installation and / or a liquid additive. From a practical standpoint, within the installation, based on the liquids contained in the installation's storage means and the parameters measured for the extracted liquid or captured gas, the distribution means supply the injection means with a liquid mixture comprising liquid extracted from at least one compartment of the installation and / or a liquid additive, according to an appropriate composition.

[0088] Also, during the monitoring step, the concentration of dihydrogen (H2) in the captured gas is measured, and if this concentration is below a low alert value, a step involving the injection of dihydrogen into the compartment is carried out. The presence of H2 promotes the growth of hydrogen-loving bacteria at the end of acidogenesis and the beginning of acetogenesis. The addition of hydrogen allows for the establishment of a balance between the types of bacteria present in the compartment to optimize the transition from one phase to the other.

[0089] At the end of the anaerobic digestion step, the process may further include a step of injecting air into the active bioreactor compartment, a step carried out at the end of the anaerobic digestion step and triggering an aerobic fermentation step inside the compartment. Thus, at the end of the anaerobic digestion step, the Aerobic digestion (or composting) can be carried out directly in the active bioreactor compartment, without the need to empty the compartment and spread the residual waste on an adjacent spreading area.

[0090] Ideally, air injection is coordinated with the removal of the cover 20 and can be continued during all or part of the aerobic fermentation (composting) stage in order to accelerate its completion. The cover can be removed completely or partially; it can also be removed gradually to control the release of fumes and any potential odor nuisances. The aerobic digestion stage typically lasts between 1 and 6 weeks, preferably between 2 and 3 weeks.

[0091] Advantageously, during the air injection step, the air is injected via means previously used for liquid extraction (pumping member 43, extraction pump 46, drainage tube) and / or via means 30, 30' previously used for gas capture.

[0092] Thus, air injection does not require any additional means. Alternatively, the means 40, 40' previously used for injecting the liquid can be removed. At the end of the aerobic digestion stage, the compartment is emptied, notably using the mechanical means employed for the initial filling of the compartment, supplemented by the use of construction equipment that can enter the compartment via the access ramp provided for this purpose.

[0093] By way of example, in an installation used continuously, comprising 10 compartments filled one after the other, taking into account the time (from a few weeks to a few months) required to carry out each step, we can have: - a compartment being filled, - a compartment in the phase of hydrolysis followed by acidogenesis (pH substantially acidic), - a compartment in the acidogenesis phase (substantially neutral pH), - five compartments in the methanogenesis phase (pH approximately alkaline), - one compartment undergoing aerobic digestion, and - a compartment being emptied which, once emptied, can be refilled.

[0094] According to another aspect of the invention, the composition of the mass of waste stored inside the compartment can be optimized to optimize the performance of the anaerobic digestion step.

[0095] First, before filling the compartment, the waste to be treated can be ground up so as to have waste with a homogeneous particle size suitable for the desired duration of the process.

[0096] Also, to form the waste mass during the filling stage, are introduced into the compartment of elongated structural solids having a width or diameter of 1 to 10 cm, a length equal to 5 to 10 times the width or diameter and always greater than 10 cm, the said fraction of structural waste constituting at least 10% and preferably at least 30% by volume of the waste mixture. Ideally, to form the waste mass during the filling stage, an alternation of layers of structural materials and layers of methanogenic organic materials are introduced into the compartment.

[0097] Structuring solid materials, by virtue of their shape, dimensions, and rigidity, limit the compaction of the waste mass during compartment filling. Furthermore, since these structural materials contain a high proportion of lignic or lignocellulosic carbon compounds, their decomposition under anaerobic conditions is limited, even negligible, during the digestion stage. This limits the compaction of the waste mass during digestion, thus preserving its homogeneous character throughout the anaerobic digestion process. Structuring materials therefore facilitate the digestion stage. The mixture of structural organic materials and methanogenic organic materials optimizes the efficiency (in terms of the quantity of methane produced and the duration) of the digestion stage.

Claims

Claims

1. Installation for treating solid waste containing fermentable organic matter to produce gas and recover the gas produced, installation comprising: - at least one compartment (4a-4F), each compartment comprising peripheral walls (1A-1F, 3A-3F) and a bottom (10) together defining an interior volume (Vint) adapted to receive waste to be treated, a waste inlet opening and a liquid accumulation zone originating at least in part from the decomposition of the organic matter, - at least one cover (20) adapted to cover and close at least one compartment in a gas- and liquid-tight manner, - means (30, 30', 33, 34) for capturing a gas originating at least in part from the decomposition of the waste, and - liquid injection means (40, 40', 44) adapted to bring liquid into the interior volume of at least one compartment,installation characterized in that the liquid injection means are configured to introduce into the interior volume of an active bioreactor compartment containing a mass of waste to be treated, at at least one predefined instant, a volume (VI) of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the mass of waste with liquid.,

2. Installation according to claim 1 in which the minimum volume Vmin is determined by Vmin = S*H*M where - S and H are respectively a surface area and a height of the waste mass and - M is a macroporosity index of the waste mass.

3. Installation according to one of claims 1 or 2 in which the liquid injection means are configured to inject the volume (VI) of liquid during a liquid injection time (Ti) less than a maximum injection time (Timax) determined by Timax = [V1 / (S*C)]*N where: - S is the surface area of ​​the waste mass, - C is a hydraulic conductivity index of the waste mass, and - N is a parameter representative of an expected efficiency of a percolation of the liquid injected into the waste mass, N being greater than 1, preferably greater than 5 and ideally greater than 10.

4. Installation according to one of the preceding claims also comprising liquid distribution means (70) comprising liquid storage zones (47 b 472, 473, 474) and a mixing means arranged to supply the injection means with a liquid mixture comprising liquid coming from at least one storage zone.

5. Installation according to the preceding claim in which the mixing means is configured to provide the liquid mixture comprising a proportion of liquid originating from each storage zone (47 b 472, 473, 474) as a function of parameters of the gas previously captured in the active bioreactor compartment and representative of a progress of the treatment in the active bioreactor compartment and / or as a function of parameters of the liquid previously extracted from the active bioreactor compartment and representative of an average biochemical state of the mass of waste contained in the active bioreactor compartment.

6. Installation according to the preceding claim, in which the distribution means (70) also comprise liquid extraction means (43, 46) arranged to extract liquid in the accumulation zone (Z) of at least one compartment and to bring the extracted liquid into a buffer storage zone of the distribution means.

7. Installation according to the preceding claim, in which the distribution means (70) comprise at least two buffer storage zones (47b 472) and in which the extraction means are arranged to bring extracted liquid to one or other of the buffer storage zones as a function of at least one biochemical parameter of the extracted liquid.

8. Installation according to one of the preceding claims in which storage means also comprise at least one storage zone for a liquid adjuvant (473, 474).

9. Method for implementing a waste treatment plant containing fermentable organic matter to produce gas and recover the gas produced, said plant being in accordance with one of the preceding claims and comprising at least one compartment (4A-4F), the or each compartment comprising peripheral walls (1A-1F, 3A-3F) and a bottom (10) together defining an interior volume (Vint) adapted to receive waste to be treated, a waste inlet opening and an accumulation zone (Z) of liquid originating at least in part from a decomposition of the matter organic waste, said method comprising, for an active bioreactor compartment: - a step of filling the interior volume of the active bioreactor compartment with the waste to be treated so as to form a mass of waste, - a covering step consisting of placing a gas- and liquid-tight cover (20) above the mass of waste so as to make the active bioreactor compartment substantially watertight, - a step of at least partial anaerobic digestion of the fermentable organic matter of the waste so as to produce a gas and a liquid, the gas being captured and the liquid being accumulated in the accumulation zone, and - a step of injecting liquid into the active bioreactor compartment, method characterized in that the liquid injection step consists of introducing a volume (VI) of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the mass of waste with liquid.

10. The method of claim 9 wherein the liquid injection step is performed before the anaerobic digestion step.

11. Method according to one of claims 9 to 10 also comprising during the digestion step, a step of extracting at least part of the liquid from the accumulation zone, the extracted liquid being brought into a storage zone (47b 472).

12. The method of claim 11 wherein, during the anaerobic digestion step, the extracted liquid is brought into a first storage zone (47 J or a second storage zone (472) depending on at least one biochemical parameter of the extracted liquid.

13. Method according to one of claims 9 to 12 also comprising, in parallel with the digestion step: - a step of monitoring at least one parameter of the accumulated liquid and / or at least one parameter of the gas captured in the active bioreactor compartment and, - if at least one parameter reaches a predefined alert value associated with said at least one parameter, a step of injecting liquid or a step of injecting gas into the active bioreactor compartment is carried out.

14. The method of claim 13 wherein, during the step of monitoring, a height of the liquid in the active bioreactor compartment is measured and, if said height is lower than a low alert height, the step of injecting liquid into the active bioreactor compartment is repeated.

15. Method according to claim 14 in which: - during the monitoring step, a parameter of the captured gas representative of a progress of the digestion step is monitored, and - during the repetition of the liquid injection step, a composition of the injected liquid is adjusted according to the at least one parameter of the captured gas.

16. Method according to one of claims 9 to 15 wherein, during the liquid injection step, the injected liquid comprises liquid extracted from at least one compartment of the installation and / or a liquid adjuvant.

17. Method according to one of claims 13 to 16 in which, during the monitoring step, a di-hydrogen (H2) level in the captured gas is measured and, if said di-hydrogen level is lower than a low alert value, a step of injecting di-hydrogen into the compartment is carried out.

18. Method according to one of claims 9 to 17 also comprising a step of injecting air into the compartment, a step carried out at the end of the anaerobic digestion step and triggering an aerobic fermentation step inside the compartment.

19. A method according to claim 18 wherein, during the air injection step, the air is injected via means previously used for liquid extraction and / or via means previously used for gas capture.

20. Method according to one of claims 9 to 19 in which, to form the mass of waste during the filling step, structuring solid materials of elongated shape having a width or diameter of 1 to 10 cm, a length equal to 5 to 10 times the width or diameter and greater than 10 cm are introduced into the compartment, the said fraction of structuring waste constituting at least 10% and preferably at least 30% by volume of the waste mixture.

21. Method according to claim 20 in which, to form the mass of waste during the filling step, alternating layers of structuring materials and layers of methanogenic organic matter.

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