FR3139578A1 - Improvement of an installation and a process for the sequential treatment of waste containing organic materials with a view to their biological recovery, Energy and Material - Google Patents

Abstract

The invention relates to an installation and a method for treating solid waste containing fermentable organic materials to produce gas; the installation comprises: - at least one compartment (4a-4F), comprising an interior volume (Vint) adapted to receive waste to be treated, a waste intake opening and a liquid accumulation zone from decomposition organic materials, - means (30, 30') for capturing a gas coming from the decomposition of waste, and - liquid injection means adapted to bring liquid into the interior volume of at least one compartment . The liquid injection means are configured to introduce into the compartment, at at least a predefined instant, a volume (Vl) of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass. Application to solid waste methanization. Abstract Figure: Figure 1

Description

Improvement of an installation and a process for the sequential treatment of waste containing organic materials with a view to their biological recovery, Energy and Material

The invention relates to a waste treatment installation as well as a method of implementing this installation.

The invention aims at the treatment and recovery of any solid, non-toxic waste containing organic materials. The main source of such waste is the collection of household waste and waste known as plant waste or green waste, generated by agriculture or the maintenance of green spaces.

State of the art

The invention aims more precisely to improve the installation and the treatment process covered by patent D1 = FR3038532. The installation described in D1 is a solid waste methanization installation allowing the production of biogas; the latter constitutes a renewable energy whose energy potential is high since it contains a substantial fraction of methane and whose carbon footprint is very favorable.

Anaerobic digestion results from the action of certain groups of interacting microbial microorganisms constituting a food web. We classically distinguish four successive phases: hydrolysis, acidogenesis, acetogenesis and methanogenesis.

Complex organic matter is first hydrolyzed into simple molecules by microorganisms. Thus, lipids, polysaccharides, proteins and nucleic acids become monosaccharides, amino acids, fatty acids and nitrogen bases. This decomposition is carried out by exocellular enzymes. In a methanization process, the hydrolysis phase can become the 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 takes place at different speeds depending on the bioaccessibility of the components of the treated organic matter, whereas it takes place at a much faster and much more homogeneous speed in the media. homogeneous and more liquid.

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 carbon dioxide ( CO2). This phase is 30 to 40 times faster than hydrolysis.

The following phase of acetogenesis allows the transformation of the various compounds resulting from the acidogenesis phase into direct precursors of methane: acetate, carbon dioxide and hydrogen. There are two groups of acetogenic bacteria:
- Obligate hydrogen producing bacteria, strictly anaerobic, also called OHPA (“Obligate Hydrogen Producing Acetogens”). They are capable of producing acetate and H2 from reduced metabolites resulting from acidogenesis such as propionate and butyrate. The accumulation of hydrogen leads to the cessation of acetogenesis by OHPA bacteria. This implies the need for constant elimination of the hydrogen produced. This elimination can be achieved through the syntrophic association of these bacteria with hydrogenophilic microorganisms.
- Non-syntrophic acetogenic bacteria whose metabolism is mainly oriented towards the production of acetate. They thrive in environments rich in carbon dioxide. “Homoacetogenic” bacteria are part of this group, they use hydrogen and carbon dioxide to produce acetate. They do not seem to compete for hydrogen with hydrogenophilic methanogenic Archaea and are present in much lower quantities in anaerobic biotopes.

Finally, the methanogenesis phase is carried out by strict anaerobic microorganisms which belong to the Archaea domain. This last step results in the production of methane. It is carried out by two possible routes: one from hydrogen and carbon dioxide by so-called hydrogenotrophic species, and the other from acetate by acetophilic species (also called acetoclasts). Their growth rate is lower than that of acid-forming bacteria.
CO2 + 4 H2 → CH4 + 2 H2O
CH3COOH → CH4 + CO2.

The present invention aims to improve the installation and the process of D1 by optimizing the yield of biogas production, and more particularly by optimizing the implementation of at least one of the phases of the methanization process.

Description of the invention

The invention proposes an installation for processing solid waste containing fermentable organic materials to produce gas and recover the gas produced, installation comprising:
- at least one compartment, each compartment comprising peripheral walls and a bottom together defining an interior volume (Vint) adapted to receive waste to be treated, a waste admission opening and a liquid accumulation zone coming from at least in part of the decomposition of organic matter,
- at least one cover suitable for covering and closing at least one compartment in a gas- and liquid-tight manner,
- means for capturing a gas coming at least partly from the decomposition of waste, and
- liquid injection means adapted to bring liquid into the interior volume of at least one compartment.

The installation according to the invention is 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 a predefined instant, a volume Vl of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass.

The invention also proposes a method of implementing the installation described above, a 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 waste mass so as to make the active bioreactor compartment substantially waterproof,
- a step of at least partial anaerobic digestion of the fermentable organic materials 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 liquid injection step into the active bioreactor compartment.

The method according to the invention is characterized in that the liquid injection step consists of introducing a volume Vl of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass.

The invention thus proposes to use liquid injection means adapted to introduce into the waste mass large quantities of liquid, sufficient to saturate the upper layers of the waste mass with liquid. The liquid saturation of the upper layers allows an optimized distribution of the liquid over the entire surface of the upper layers then a homogeneous humidification of the waste mass when the liquid descends by gravity into the mass. Liquid saturation of the upper layers also prevents the formation in the mass of liquid flow paths carrying the liquid too quickly by gravity towards the bottom of the compartment and preventing the 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, leading to progress of methanization as homogeneous as possible over the entire massif. In addition, when carried out at the start of methanization, saturation injection accelerates the hydrolysis phase which takes place at generally more homogeneous speeds although different depending on the bioaccessibility of the components of the solid organic matter treated.

Brief description of the figures

The invention will be better understood, and other characteristics and advantages of the invention will appear in light of the following description of examples of implementations of the invention. These examples are given without limitation. The description should be read in relation to the appended drawings in which:
- there is a perspective view illustrating an installation according to the invention,
- there is a top view of the installation of the ,
- there is a perspective view of a compartment of the installation of Figures 1 and 2 illustrating the gas capture means,
- there is a perspective view of a compartment of the installation of Figures 1 and 2 illustrating the gas capture means equipping said compartment,
- there is a perspective view of a compartment of the installation of Figures 1 and 2 illustrating the liquid circulation means equipping said compartment,
- there is a sectional view of the compartment of Figures 3 and 4, along the line VV shown ,
- there is a perspective view of the compartment of the , at an angle different from Figures 3 and 4, with cuts along line VV,
- there is a schematic representation of the circulation of liquid flows in an installation according to the invention.

The dimensions and more broadly all the numerical values in the description are for the most part orders of magnitude given for purely indicative purposes; they do not limit the scope of the invention and are naturally to be adapted according to the embodiments and the applications envisaged.

Figures 1 to 6 repeat Figures 1 to 6 of the D1 patent, supplemented by elements specific to the present invention. The following reference numbers 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 Exterior part of the bottom
Z Accumulation zone
12 Enclosure wall
14 Perimeter track
14' Perimeter track
15 Oblique ramp
16 Embankment
17 Floor
20 Cover
means of capture:
30, 30' Catchment assemblies
31, 31' Main tube
32, 32' Secondary tubes
33 Collector
34 Collection pump
liquid injection means:
40, 40' Injection Sets
41 Main tube
42 Secondary tubes
44 injection pump
70 means of liquid distribution:
means of liquid extraction:
43 Pumping member
43', 43" Ends of 43
46 Extraction pump
45 purge
storage areas
47₁, 47₂ buffer zones
47₃, 47₄ storage areas
48 mixing medium

Vint interior volume of a compartment
Vl volume of liquid injected
Vlmin minimum value of Vl
Ti injection time
Timax maximum value of injection time

Detailed description of embodiments of the invention

As said previously, the installation and the process according to the invention aim to treat solid waste containing fermentable organic materials. Solid waste is, for example, household waste, agricultural by-products, waste from the chemical or agri-food industries.

An installation according to the invention essentially comprises at least one compartment, at least one cover, gas capture means and liquid injection means.

In an improved version as shown in the figures, the installation according to the invention essentially comprises a common functional space 1, placed centrally, and several compartments extending radially from this common functional space. More precisely, the common functional space 1 is hollow and has a polygonal shape, seen from above. It rests on a base 2, also polygonal which has radial dimensions greater than those of this space. The number of sides of the functional space corresponds to the number of compartments with which the installation is provided. Each peripheral wall 1A to 1F of the functional space, corresponding to one side of the latter, forms a first side 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 other side walls of a respective compartment. In addition to side walls, a compartment includes a bottom 10; the bottom 10 and the walls of a compartment together delimit on the one hand an interior 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.

In its simplest version, an installation according to the invention comprises a single compartment. In the example illustrated, the installation according to the invention comprises six waste reception and treatment compartments, which are assigned references 4A to 4F. However, a different number of compartments can be provided, in particular between 4 and 6. An installation comprising several compartments is more efficient. In fact, the compartments are used and work staggered in time relative to each other. Thus, as soon as one compartment is full, it is possible to fill a second compartment as the waste is collected, without waiting for the previous compartment to have been emptied after digestion. Also, this makes it possible to inject into one compartment liquid extracted from another compartment: on the one hand this limits the storage time of a liquid and on the other hand it makes it possible to have a large quantity of liquid and / or a quantity of liquid having biochemical and / or bacterial properties appropriate to the needs of a compartment to be watered.

The cover 20 is adapted to selectively cover the interior volume of one or 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 in compartment 4E (full and covered) in Figures 1 and 2. The number of covers 20 (at least one) of the installation depends on the number of compartments. Details on the choice of the number of compartments, on the concrete construction and dimensions of the compartments, on the number of covers 20, on the concrete construction and fixing of a cover 20 can be found in document D1, page 10 line 4 on page 14, line 14.

The collection means fitted to the installation according to the invention make it possible to extract, out of each compartment, the gas released by the waste during its treatment. These collection means are more particularly visible in Figures 5 and 6, as well as on the where the liquid injection means are however not shown, for the sake of clarity.

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

A collection assembly 30, 30' comprises a main tube 31 extending radially as well as secondary tubes 32. The latter extend in the horizontal plane obliquely, on either side of the aforementioned main tube 31. Advantageously, there are at least two similar tubular assemblies 30, 30' (see ), arranged one above the other inside a compartment. The different tubular assemblies, installed in the compartments of the installation, open radially inwards into the common collector 33, provided in the central common space (see in particular Figures 5 and 6). This collector 33, which makes it possible to centralize the gas flows, is associated with the pump 34, for example of the centrifugal type. Advantageously, the collector 33 extends outside the central common space 1 and opens into an energy production device not shown, for example of the engine (or turbine) type running on gas, driving an electric generator and operating advantageously in a combined cycle. Details on the concrete implementation of the sensing means can be found in document D1, page 10 line 4 to page 14, line 14. Advantageously, the sensing means are equipped with means not shown for measuring physical parameters. -chemical of the gas flows collected in each compartment. In particular, the volume of gas captured and/or the flow rate of gas captured can be determined, for each compartment, as well as the composition of the gas captured, in particular the proportion of methane (CH4) and/or the proportion of dihydrogen (H2) in the gas captured. These parameters are representative of the progress of waste digestion; they make it possible to identify the phases of methanization in an active bioreactor compartment.

According to one embodiment, a pressure slightly lower than the pressure in the compartment is maintained inside the tubular assembly(s) 30, 30', so that the gases produced are sucked in by the collection means. This embodiment also has the advantage of limiting the risk of air entering the compartment during methanization.

In the example shown, the liquid injection means include in particular an injection member such as an injection pump 44 and, for each compartment, a tubular injection assembly 40 formed by a main tube 41, s 'extending radially, as well as 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 a compartment, there is a single tubular injection assembly 40, placed above the tubular collection assemblies 30, 30'. This tubular injection assembly 40 is more particularly visible in Figures 5 and 6, as well as on the where the means of capturing the gas are however not represented, for the sake of clarity. Details on the concrete implementation of the collection means can be found in document D1, page 10 line 4 to page 14, line 14. The pump 44 is arranged to supply liquid alternately to the injection assembly 40 from one or the other of the compartments.

According to the invention, the installation comprises liquid injection means 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 Vl of greater liquid at a minimum volume Vlmin of liquid capable of saturating the upper layers of the waste mass with liquid.

By saturating the upper layers with liquid, we ensure the most homogeneous percolation of liquids possible throughout the entire waste mass, thus allowing efficient methanization.

For this purpose, in one implementation mode, the volume Vlmin is determined by Vmin = S*H*M where
- S and H are respectively a surface and a height of the waste mass and
- M is an index of macroporosity of the waste mass.
S and H are linked to the structure of the compartment, and to the volume of waste in the compartment. M is defined as the ratio between the volume of voids in the waste mass and the total volume of the waste mass, expressed as a percentage. M is correlated to the particle size of the organic materials constituting the waste mass and is usually between 20% and 60% respectively for a fine particle size and a coarse particle size. M is for example determined from a measurement of the particle size of the waste in the waste mass and a correspondence table or an abacus.

In a practical example, the 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 into the compartment a large volume of liquid, and more precisely a volume of liquid greater than Vmin. As an order of magnitude, for a compartment with a section of around 130 m² to be modified and a height of around 6 m, Vlmin is around 160 m3.

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

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.

It is for example determined according to Darcy's law, a physical law which expresses the flow rate of an incompressible fluid filtering through a porous medium. The flow of fluid between two points is determined by the hydraulic conductivity or permeability coefficient of the substrate and the pressure gradient of the fluid. 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.).

N is a parameter representative of the conditions for effective percolation of the liquid injected into the waste mass; N is greater than 1; N is preferably chosen greater than 5 for average efficiency and N is ideally chosen greater than 10 to obtain very rapid accumulation of liquid in the mass. The parameter N is chosen by the operator of the installation, in particular depending on the waste to be treated, the desired duration of waste treatment and the injection capacity of the installed liquid injection means. order of magnitude, for a compartment of section S of the order of 130 m² and a height of the order of 6 m of waste presenting a hydraulic conductivity index C equal to 0.3, the maximum injection time of the volume Vlmin (calculated in the previous paragraph) is 240 minutes, 48 minutes or 24 minutes respectively for a factor N equal to 1, 5 or 10.

In addition, the installation comprises liquid distribution means 70 comprising liquid storage zones 47 and a mixing means 48 arranged to supply the injection means with a liquid mixture comprising liquid coming from at least one zone of storage.

Advantageously, in the liquid mixture, a proportion of liquid coming from each storage zone (47₁, 47₂, 47₃, 47₄) can be 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 waste mass contained in the active bioreactor compartment.

The liquid thus injected into the active bioreactor compartment is best suited to the progress of the methanization in progress and/or improves the average biochemical state of the waste mass for efficient methanization.

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 means of distribution.

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 in the waste, from the bottom of the compartment where this liquid accumulates by gravity, to a storage area.

In the example shown, the extraction means comprise an extraction pump 46 and, for each compartment, a pumping member 43.

The pumping member 43 has, in the example shown, a tubular shape and extends over substantially the entire height of the common space 1. A first end 43' of the pumping member opens near the bottom of the compartment in the accumulation zone, crossing the bottom of the separation wall 1A, and a second end 43'' of the pumping member is connected to an inlet of the extraction pump 46. The extraction means can 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 member.

The pumping member 43 is advantageously equipped with means (not shown) for measuring at least one parameter of the liquid present in each compartment. The liquid parameters likely to be measured or determined include the volume of liquid flowing into the accumulation zone, the composition of the liquid, the level 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.

For example, the pumping member 43 shown in the figures is positioned vertically and is equipped with a gauge adapted to measure a height of liquid in a tube. Outside of the liquid extraction phases, the liquid in the pumping member 43 is at the same altitude as the liquid in the associated accumulation zone. The accumulation zone Z having a perfectly defined geometry, the height of liquid in the tubular pumping member makes it possible to determine the volume of liquid present in the accumulation zone and to deduce the humidity level therefrom. interior of the compartment. It is possible for example to place, in the pumping member 43 or in the accumulation zone inside the compartment, a high level sensor and a low level sensor, to constantly maintain the accumulated liquid volume within a range given, corresponding to a target humidity level range in the compartment.

As another example, it is possible to place, in the pumping member 43 or in the accumulation zone or at the level of the pump 46, a device for taking a sample of liquid and provide a device for Spectroscopy analysis of the composition of the liquid sample.

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

According to one embodiment (represented , 6), the storage means comprise a single buffer storage zone and the liquid extracted from all of the compartments is stored in said buffer zone.

Alternatively ( ), the distribution means comprise at least two buffer storage zones (47₁, 47₂) and the extraction means are arranged to bring liquid extracted from a compartment to one or other of the buffer storage zones in function of at least one biochemical parameter of the extracted liquid. The pH of the liquid is a parameter likely to be taken into account when choosing the storage area.

The buffer zone(s) make it possible to temporarily store the liquid extracted from a compartment or several compartments, so as to have a quantity of liquid available at the time when an injection of liquid is envisaged to control the installation, as described above. will see better later. The duration of a methanization cycle being of the order of several weeks, the storage of the extracted liquid can last a few days to a few weeks, depending on the liquid needs in the compartments. The buffer storage zone(s) (47₁, 47₂) are for example concrete silos or large capacity stainless steel tanks, of the order of several tens of cubic meters, for example between 10 and 100 m³.

The buffer zone(s) (47₁, 47₂) also make it possible to pool the liquids extracted from several compartments, when the installation includes several, so as to have in advance the largest possible quantity of liquid in order to produce in a compartment a significant injection of liquid capable of saturating the upper layers of the mass of waste present in the behavior. Finally, the presence of several buffer zones makes it possible to store extracted liquids having different physico-chemical or bacteriological parameters, which can be subsequently injected into a compartment at the appropriate time depending on the digestion phase in progress, depending on their physico-chemical parameters. chemical or bacteriological.

For example, the liquids extracted from a compartment in the hydrolysis or acidogenic phase having a pH of around 5 to 7 can be stored in a first buffer zone 47₁, and the liquids extracted from a compartment in the hydrolysis phase methanogenesis having a pH greater than 7 can be stored in a second buffer zone 47₂. They can thus be used subsequently in a compartment, depending on their pH, to restore the biochemical balance of a compartment according to its specific needs to promote the methanization phase concerned.

The collection means can also include at least one purge member 45 at the level of the pump 46 or one purge member per compartment. The purge member 45 makes it possible to eliminate part of the liquid from a compartment. In particular, liquid can be purged if overall the quantity of liquid in the accumulation zone is too large and cannot be stored in full, or to protect the pump in the event of excessive viscosity of the liquids extracted from a compartment.

We can also purge part of the liquid if the parameters of the latter cannot easily be corrected, as will be better seen later. The purge member is preferably used when it is not appropriate to store the liquid in a buffer zone, for example when the liquid parameters are not suitable or when the buffer zone(s) are full.

In the installation according to the invention, the storage means can also comprise at least one storage zone for a liquid adjuvant (47₃, 47₄).

A first type of liquid adjuvant is for example a liquid containing inocula, typically consisting of previously selected bacterial colonies; inoculums make it possible to quickly inoculate the waste mass to promote or accelerate the completion of one of the phases (hydrolysis, acidogenesis, acetogenesis, methanogenesis) of the anaerobic digestion stage or the transition between two phases of anaerobic digestion. For example, in a 47₃ storage zone a liquid adjuvant containing bacteria promoting the hydrolysis of organic materials is stored. Typically, the liquid is highly concentrated in inoculum so that a small amount of liquid is sufficient for installation; the storage zone 47₃ of liquid containing inoculums can thus consist for example of carboys capable of containing a few liters or tens of liters of liquids and arranged to be emptyable in the liquid reinjection network of a given compartment on a regular basis and controlled, for example by Venturi effect.

A second type of liquid adjuvant is, for example, a liquid containing suspended organic matter (called the “organic load” of the liquid) capable of being methanized. Typically, liquid adjuvants contain an organic load varying between 5% and 20% by volume, an organic load which is in the form of particles with a size varying between 0 mm (corresponding to dissolved particles of unmeasurable size because too much low) and 13 mm (for the largest dimension of three-dimensional particles). Liquid adjuvants are for example liquid waste (also called “liquid digestates”) from other installations or food biowaste, collected in the form of “soup” and which can be temporarily stored for example in storage area 47₄ of the 'facility. Liquid adjuvants, easily hydrolysable, are for example used to trigger the hydrolysis phase of methanization, as will be better seen later. In a preferred embodiment, the liquid waste is injected into a compartment as soon as it arrives at the installation or at short notice so that the storage zone 47₄ can be for example a tank truck or containers dedicated to liquid waste, immobilized for a period of time from a few hours to a few days, the period of time necessary for the transfer of liquid waste to a specific compartment. Typically, liquid waste is transferred to a compartment in the hydrolysis phase, via liquid injection means.

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

There schematizes 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 appropriate quantities to maintain the biochemical state of the most appropriate waste mass. to the phase (hydrolysis, acidogenesis, acetogenesis or methanogenesis) of the digestion in progress. The extraction means are also controlled to store (flow 65₁ 65₂) the extracted liquid in an appropriate storage zone 47₁, 47₂ or to evacuate the extracted liquid via the purge member 45. The mixing means are controlled to provide ( flow 50A-50F) to the means for injecting the liquid coming (flow 66₁, 66₂, 66₃, 66₄) from one or more of the storage zones 47₁, 47₂ of extracted liquid, possibly supplemented by a liquid adjuvant stored in the zones 47₃ , 47₄ and/or possibly supplemented with water, depending on the composition of the liquid necessary to optimize the efficiency of the current digestion phase or prepare for the following decomposition phase.

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

Conventionally, the method of implementing an installation as described above comprises, 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 waste mass so as to make the active bioreactor compartment substantially waterproof,
- a step of at least partial anaerobic digestion of the fermentable organic materials 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 liquid injection step into the active bioreactor compartment.

The compartment is filled conventionally by any suitable mechanical means allowing the compartment to be loaded from the top. Emptying the compartment is done by the same means, possibly supplemented by the use of construction equipment equipped with buckets which can enter the compartment via the ramp provided for this purpose. Prior to filling, the waste can be crushed and/or mixed so as to obtain waste with a homogeneous particle size.

Control of the installation consists of optimizing the physicochemical and bacteriological parameters inside a compartment in which the anaerobic digestion stage is in progress, so that this stage is as complete and rapid as possible. The digestion step being carried out by bacteria, moreover bacteria of different natures depending on the successive phases of the anaerobic digestion step, the management of the installation consists of optimizing the physicochemical and bacteriological parameters in the compartment allowing good development of the bacterial colonies necessary for the completion of the current phase of the digestion stage. In the context of the invention, optimization is carried out in particular by optimizing the injection of liquid into the compartment as the digestion stage progresses.

The method 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 in the active bioreactor compartment:
- a temperature between 25°C and 65°C, and preferably between 45°C and 55°C
- a humidity level of 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 so as to allow at least 70%, and preferably at least 90%, of the methanogenic potential of the degradable organic materials present in the waste to be expressed. This anaerobic digestion step has a duration in a compartment typically between 1 and 10 months, and preferably between 2 and 3 months.

The method according to the invention can be implemented in an installation comprising a single compartment, as will be described below. Advantageously, however, it is implemented in an installation comprising several compartments (at least two); where appropriate, the process is implemented compartment by compartment, at times offset from each other, 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 delay between two bioreactor compartments is ideally 1.5 weeks.

In an installation with several compartments, the liquids extracted in one compartment can thus advantageously be used in another compartment, to accelerate the rate of injections of liquids into the other compartment for the purpose of accelerating digestion in said other compartment and, simultaneously, in order to reduce the storage time of the extracted liquid. In addition, the storage in the same storage zone of liquids extracted from several compartments makes it possible to have a large quantity of liquid available to implement the essential step of the invention described below.

The method according to the invention is in fact characterized in that the liquid injection step consists of introducing a volume Vl of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass.

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 uniform humidity level over the entire mass, facilitating more homogeneous digestion of the waste mass.

The first liquid injection step is preferably carried out between the covering step and the anaerobic digestion step. The introduction of liquid thus makes it possible to initiate the hydrolysis phase just after covering the compartment. And the introduction of a large quantity of liquid makes it possible to homogenize the hydrolysis phase in the mass, to accelerate the hydrolysis phase and to shorten this phase during which no gas is produced.

Other liquid injection steps can then be carried out during the anaerobic digestion step. The times at which such steps are carried out, as well as the quantity and quality of the liquid injected each time, may depend on the progress of the anaerobic digestion reaction, physico-chemical parameters of the captured gas and/or physico-chemical parameters. of the extracted liquid, as will be better seen later.

The liquid injected into the waste mass can come from a source external to the installation according to the invention. Advantageously, the injected liquid comes at least partially from the installation itself.

For this purpose, the method according to the invention may comprise a step of extracting at least part of the liquid from the accumulation zone, the extracted liquid being brought into a storage zone 47₁, 47₂. The liquid extraction step is carried out during the digestion step.

During the digestion stage, the liquid extraction stage can be carried out one or more times. The extraction step can be carried out at predefined time intervals, for example from 1 to 40 times per week, depending on the processing step in which the compartment concerned is located. Alternatively, the extraction step can be carried out depending on the liquid saturation rate of the compartment. Said saturation rate can for example be determined indirectly by the installation control means or directly from a measurement of a height of liquid in the pumping member 43 as mentioned above.

In practice, the physicochemical parameters of the extracted liquid, as well as the variety and quantity of the majority bacteria in the extracted liquid, evolve as the anaerobic digestion reaction progresses, and in particular depending on the phases of the digestion stage: hydrolysis, acidogenesis, acetogenesis and methanogenesis.

To be able to make 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 47₁ or a second storage zone 47₂ depending on at least one biochemical parameter of the extracted liquid.

In one embodiment, the biochemical parameter taken into account is the pH of the extracted liquid, the pH of the extracted liquid being for example measured in the pumping member 43; the extracted liquid is in this case brought into the first storage zone 47₁ or into 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.

To control the progress of the anaerobic digestion step, the process according to the invention also comprising, carried out 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 liquid injection step or a gas injection step in the active bioreactor compartment is carried out.

The monitoring step consists of acquiring parameters of the accumulated liquid and/or parameters of the gas captured in the compartment, and of comparing the acquired parameters to expected parameters representative of optimal digestion; the acquired parameters of the gas are compared to expected parameters relating to digestion at optimal efficiency, and the acquired parameters of the liquid are compared to expected parameters representative of a biochemical state in line with the growth and activity of the required bacterial colonies to optimize the efficiency of the current digestion step and/or to prepare in advance for the next step.

Some parameters are acquired directly by 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 are obtained from a measurement of the height of the liquid in the pumping member 43 and the shape and dimensions of the accumulation zone, the volume of extracted gas is determined from the captured gas flow rate, measured continuously, and the section of the main collection tubes 31, etc. Still other parameters require analyzes which cannot be carried out in real time and which are carried out at predefined intervals, for example every hour, every day, every month, etc. The level of organic matter in the liquid is for example determined by mass spectrography; the nature of the bacterial colonies present in the liquid is for example determined by culturing a sample of liquid in a Petri dish and analyzing it.

The monitoring step is ideally carried out throughout the anaerobic digestion step; some parameters are measured or determined in real time, others at predefined time intervals. For example, samples and analyzes are carried out every hour or twice an hour. They can be carried out by automatons present in the installation or in the immediate vicinity of the installation.

In one example, during the monitoring step, a height of the liquid in the active bioreactor compartment is measured and, if said height is less than a low alert height, the step of injecting liquid into the active bioreactor compartment is repeated. A liquid height lower than the low alert height may in fact be representative of a liquid saturation rate, in the waste mass, insufficient to allow the proper development of the bacterial colonies necessary for digestion.

In another example, during the monitoring step, a parameter of the captured gas representative of progress in the anaerobic digestion step is monitored and, when repeating the liquid injection step, a composition of the injected liquid is adjusted as a function of at least one parameter of the captured gas. For example, at any time, the quantity of methane CH4 and the quantity of oxygen O2 present in the captured biogas provides information on the progress of the reaction of the anaerobic digestion stage: 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 methanogenesis stage; etc.

The expected parameters for the accumulated liquid or the captured pile can be determined from average values of measurements carried out during previous implementations of the process, or from charts taken from the literature.

Alternatively, the method according to the invention can advantageously comprise an initialization step during which the expected theoretical results of the anaerobic digestion step are determined. Said results are for example obtained by the following steps:
- 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 charts; the characteristic parameters include in particular:
* the theoretical quantity of CH4 (called “methanogenic potential”, or BMP) that we can hope to obtain during the anaerobic digestion of said 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 kinetic factor or k factor) of said identified biochemical component; this rate of degradation is usually expressed in % of degradation per day and finally
- we determine, for example by a weighted average calculation, the expected results of the anaerobic digestion step 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 t0 (time of triggering of the hydrolysis phase by the first injection of liquid) and t0 + D (D being the expected duration of anaerobic digestion)

The expected theoretical degassing curve makes it possible to optimally control the digestion step, the control consisting of bringing the real curve as close as possible to the theoretical curve.

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 zone(s) 47₁, 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 physico-chemical parameters of the liquid extracted and stored are not in line with the physico-chemical parameters chemicals of the liquid which must be injected at a given moment, it is possible to inject, in addition to or instead of the extracted and stored liquid, one or more liquid adjuvants which can be a liquid containing targeted inoculums, or a liquid containing suspended organic matter, as described above, or even water.

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 adjuvant. From a practical point of view, in the installation, from the liquids contained in the storage means of the installation, and the parameters measured for the liquid extracted or the gas captured, the distribution means provide the means of injection a liquid mixture comprising liquid extracted from at least one compartment of the installation and/or a liquid adjuvant, according to an appropriate composition

Also, during the monitoring step, a level of di-hydrogen (H2) in the captured gas is measured and, if said level of di-hydrogen is less than a low alert value, a step of injection of di-hydrogen into the compartment is carried out. The presence of H2 promotes the development of hydrogenophilic bacteria at the end of acidogenesis and the beginning of acetogenesis. The addition of hydrogen makes it possible to seek a balance between the types of bacteria present in the compartment to optimize the transition from one phase to another.

At the end of the anaerobic digestion step, the process may further comprise 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 at inside the compartment. Thus, at the end of the anaerobic digestion step, aerobic digestion (or composting) can be carried out directly in the active bioreactor compartment, without it being necessary to empty the compartment and spread the residual waste over an area. annex spreading.

Ideally, the air injection is carried out in a coordinated manner with the removal of the cover 20 and can be continued during all or part of the aerobic fermentation (composting) stage so as to accelerate its completion. The withdrawal of coverage may be total or partial; it can also be carried out gradually in order to control the discharge of effluvia, and possible olfactory nuisances. The aerobic digestion stage typically lasts between 1 and 6 weeks, preferably between 2 and 3 weeks.

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

Thus, air injection does not require additional means. Alternatively, the means 40, 40' previously used to inject the liquid can be dismantled. At the end of the aerobic digestion stage, the compartment is emptied, in particular thanks to the mechanical means used for the initial filling of the compartment supplemented by the use of construction equipment capable of entering the compartment via the ramp. access provided for this purpose.

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

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.

First of all, before filling the compartment, the waste to be treated can be crushed so as to have waste with a homogeneous particle size and adapted to the duration of the desired process.

Also, 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 always greater than 10 cm, the said fraction of structuring waste constituting at least 10% and preferably at least 30% by volume of the waste mixture.
Ideally, to form the mass of waste during the filling stage, alternating layers of structuring materials and layers of methanogenic organic materials are introduced into the compartment.

The solid structuring materials, due to their shape, dimensions and rigidity, limit the compactness of the mass when filling the compartment; in addition, the structuring materials contain a high proportion of carbon compounds of the lignic or ligno-cellulosic type, their decomposition under anaerobic conditions is limited or even insignificant during the progress of the digestion stage, which limits the compaction of the waste mass during the digestion stage; the massif thus maintains its homogeneous character throughout the anaerobic digestion stage; the structuring materials thus facilitate the digestion stage. The mixture of structuring organic materials and methanogenic organic materials optimizes the yield (in terms of quantity of methane produced and duration) of the digestion stage.

Claims (21)

Installation for processing solid waste containing fermentable organic materials 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, an opening waste intake and a liquid accumulation zone coming at least in part from the decomposition of organic materials,
- at least one cover (20) adapted to cover and close at least one compartment in a gas- and liquid-tight manner,
- means for capturing (30, 30', 33, 34) a gas coming 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 (Vl) of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass. 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 and a height of the waste mass and
- M is an index of macroporosity of the waste mass. 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 = [Vl/(S*C)]*N where:
- S is the surface of the waste mass,
- It is an index of hydraulic conductivity of the waste mass, and
- N is a parameter representative of the expected efficiency of percolation of the liquid injected into the waste mass, N being greater than 1, preferably greater than 5 and ideally greater than 10. Installation according to one of the preceding claims also comprising liquid distribution means (70) comprising liquid storage zones (47₁, 47₂, 47₃, 47₄) and mixing means arranged to supply the injection means with a mixture liquid comprising liquid from at least one storage zone. Installation according to the preceding claim in which, the mixing means is configured to supply the liquid mixture comprising a proportion of liquid coming from each storage zone (47₁, 47₂, 47₃, 47₄) depending on the parameters of the gas previously captured in the bioreactor compartment active and representative of progress in 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 waste mass contained in the active bioreactor compartment. 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. Installation according to the preceding claim, in which the distribution means (70) comprise at least two buffer storage zones (47₁, 47₂) and in which the extraction means are arranged to bring extracted liquid towards one or the other buffer storage zones as a function of at least one biochemical parameter of the extracted liquid. 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). Method for implementing a waste treatment installation containing fermentable organic materials to produce gas and recover the gas produced, said installation 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 admission opening and an area accumulation (Z) of liquid coming at least in part from decomposition of organic matter in the 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 waste mass so as to make the active bioreactor compartment substantially waterproof,
- a step of at least partial anaerobic digestion of the fermentable organic materials 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 liquid injection step into the active bioreactor compartment,
process characterized in that the liquid injection step consists of introducing a volume (Vl) of liquid greater than a minimum volume Vmin of liquid capable of saturating the upper layers of the waste mass. Method according to claim 9 in which the liquid injection step is carried out before the anaerobic digestion step. 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 zone storage (47₁, 47₂). Method according to claim 11 wherein, during the anaerobic digestion step, the extracted liquid is brought into a first storage zone (47₁) or a second storage zone (47₂) depending on at least one biochemical parameter of the extracted liquid. 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 liquid injection step or a gas injection step in the active bioreactor compartment is carried out. Method according to claim 13 in which, during the monitoring step, a height of the liquid in the active bioreactor compartment is measured and, if said height is less than a low alert height, the injection step of liquid in the active bioreactor compartment is repeated. Method according to claim 14 in which:
- during the monitoring step, a parameter of the captured gas representative of progress in the digestion step is monitored, and
- when repeating the liquid injection step, a composition of the injected liquid is adjusted as a function of the at least one parameter of the captured gas. Method according to one of claims 9 to 15 in which, during the liquid injection step, the injected liquid comprises liquid extracted from at least one compartment of the installation and/or a liquid adjuvant. Method according to one of claims 13 to 16 in which, during the monitoring step, a level of di-hydrogen (H2) in the captured gas is measured and, if said level of di-hydrogen is less than a low alert value, a step of injecting di-hydrogen into the compartment is carried out. 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. Method according to claim 18 in which, during the air injection step, the air is injected via means previously used for extracting the liquid and/or via means previously used. used for gas capture. Method according to one of claims 9 to 19 in which, to form the mass of waste during the filling step, solid structuring materials of elongated shape having a width or diameter of 1 to 10 are introduced into the compartment. cm, a length equal to 5 to 10 times the width or diameter and greater than 10 cm, the said fraction of structuring waste constituting at least 10% and preferably at least 30% by volume of the waste mixture. 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 materials are introduced into the compartment.