Device and method for the production of volatile fatty acids from the shells of soft-bodied molluscs or from the flesh

Abstract

The present invention belongs to the field of shellfish and mussel farming, and more particularly to the processing and recycling of products classified as "unmarketable" because they do not meet the quality criteria required by the various labels. The object of the present invention relates to a device for the production of volatile fatty acids from mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, comprising: a tank, a recirculation loop, outside the tank, the recirculation loop, the tank further comprising a filter arranged to prevent the passage of particles into the recirculation loop, and a process for the production of volatile fatty acids comprising a hydrolysis step under thermophilic conditions, implemented in a device according to the invention, from said mollusc shells with soft bodies or flesh, which have been sanitized.The invention further includes the use of the device according to the invention in the production of volatile fatty acids (VFAs) from shells and flesh of molluscs having soft bodies or flesh.

Description

Title of the invention: Device and method for the production of volatile fatty acids from mollusc shells having soft bodies or flesh Technical field

[0001] The present invention belongs to the field of shellfish and mussel farming and more particularly to the treatment and recycling of products classified as “unmarketable” because they do not meet the quality criteria required by the various labels.

[0002] The subject of the present invention relates to a device for producing volatile fatty acids from mollusc shells having soft bodies or flesh, classified as category 3 animal by-products, comprising: a tank, a recirculation loop, outside the tank, the recirculation loop, the tank further comprising a filter arranged to prevent the passage of particles into the recirculation loop and a method for producing volatile fatty acids comprising a step of hydrolysis under thermophilic conditions, implemented in a device according to the invention, from said mollusc shells having soft bodies or flesh. The invention further comprises the use of the device according to the invention in the production of volatile fatty acids (VFA) from mollusc shells having soft bodies or flesh. State of the art

[0003] Shellfish and mussel farming generates a substantial quantity of products classified as "unmarketable" because they do not meet the quality criteria required by the various labels. These rejects, mainly of the "undersized" type, are considered waste and must therefore be eliminated. Production sites are also subject to the presence of a competing and invasive species, slipper limpets, generating a drop in production in terms of quality and quantity.

[0004] Methods and devices for processing mollusk shells having soft bodies or flesh exist.

[0005] Currently, waste classified as "undersized", coarsely crushed or not crushed, is discharged into the sea. Slipper limpets are not recovered.

[0006] This practice, in addition to the potential generation of olfactory nuisances, can lead to pollution of the marine environment: the discharge of a significant quantity of organic matter can encourage bacterial development and harm water quality.

[0007] There is therefore a need to provide an outlet for this waste while recovering it.

[0008] Other processes for the recovery of mussels have been developed, whether or not using to methanization.

[0009] In document FR 3 037 481 for example, the process described uses enzymatic hydrolysis. The objective of the process described is not to produce AGVs but a dry powder rich in proteins. However, this solution involves a regular supply of enzymes, generating significant costs. The powder produced does not meet any standards and therefore retains its status as waste: the problem is shifted but remains the same.

[0010] The publication Biomass and Bioenergy, (2018)111,96-102, describes a process using methanization. It involves the coupling of two reactors: a first reactor containing unground mussels and a second of the UASB type (for Upflow Anaerobic Sludge Blanket). The process described is a solid phase process. The objective is not to separate the methanization phases but to consume VFAs directly as production progresses. The first reactor operates in the solid phase. The mussels are neither ground nor sanitized. The recirculation loop aims to feed a UASB reactor allowing the immediate consumption of the VFAs produced. The overflow of the UASB leads to the inoculation of the first reactor with bacteria allowing methanogenesis to take place. In this process, it is therefore not possible to separate the hydrolysis phase producing VFAs from the methanogenesis phase producing methane.Furthermore, this process does not comply with French regulations in terms of SPAN treatment: since the digestate is not standardized, it retains its status as waste and therefore cannot be used for soil improvement.

[0011] Thus, although there are processes for recovering mussels unfit for consumption by methanization, these processes do not, however, allow compliance with the SPAN regulations, nor do they only ensure the production of AGV. The products of these processes cannot be spread on French territory and are also not standardized, insofar as they do not allow compliance with the regulations in force.

[0012] There is thus a need for a device and a method which solve the problems encountered in known methods or provide solutions applicable in the territory, and in compliance with the regulations in force.

[0013] Description of the invention

[0014] The new device and the new method according to the invention make it possible to carry out biological hydrolysis without the addition of an enzyme. They make it possible to produce a significant quantity of VFAs and then possibly convert them into methane. The devices and method according to the invention thus aim to separate the methanization phases in order to optimize them. It is possible to obtain, for example, a concentration of more than 20 g / L of VFAs at the end of the hydrolysis phase by applying suitable parameters, which is not the case in known methods.

[0015] It should also be noted that the presence of crushed shell fragments is highly detrimental to conventional methanization processes, as this leads to blockage of the pumping and valve components. In addition, the accumulation of these fragments in continuously operating reactors reduces the useful volume of the reactor and the residence time, and thus negatively impacts the biogas conversion yields of these structures.

[0016] The device and method according to the invention make it possible to address these issues while also improving the operating efficiency of the equipment.

[0017] The device, while ensuring the hydrolysis of the material, is configured to liquefy the mussel flesh while keeping the crushed shell fragments in place. Thus, the hydrolyzate circulates continuously through the mixture of flesh and crushed shells (via the recirculation loop). The bacterial action degrades the flesh and converts the organic matter into VFA-rich hydrolyzate. At the end of the reaction, the shells are completely free of flesh and the hydrolyzate produced is rich in VFA, short-chain alcohols, and ammonium.

[0018] The preservation of the crushed shells also offers a definite advantage to the process according to the invention compared to an upstream decortication process. Indeed, biological hydrolysis is a reaction that is inhibited in an acidic medium. However, the biological hydrolysis implemented in the present invention produces VFAs, which are naturally acidic compounds. Thus, the presence of the crushed shells and the recirculation of the hydrolyzate during hydrolysis can lead to a slight dissolution of the shells which can thus buffer the pH of the medium. This association can have a synergistic effect on the hydrolysis yield which can be significantly improved. Without preservation of the shell fragments, the production of VFAs could be slowed down, or even stopped, by the acidification of the medium and the conversion yield would be limited.

[0019] The implementation of grinding and hygienization are regulatory obligations for recovery by methanization, for inputs falling into the category of animal by-products. The device and the method according to the invention also make it possible to comply with the regulations in force regarding animal by-products, and to overcome the constraints generated, which is not possible with known methods, following the evolution of the regulations: the characteristics of the device according to the invention make it possible to carry out grinding to 12 mm and hygienization, while remaining compatible with a large-scale methanization process.

[0020] An object of the invention is thus a device for producing volatile fatty acids from mollusc shells having soft bodies or flesh, classified Category 3 animal by-products, including: - a tank comprising an upper part equipped with an upper inlet and a lower part equipped with a lower outlet, - a recirculation loop connecting the lower outlet of the tank to the upper inlet of the tank, outside the tank, the recirculation loop being configured to suck hydrolysate from the lower outlet of the tank and discharge it towards the upper inlet of the tank, characterized in that the tank further comprises a filter having pores with a diameter less than or equal to 4 mm, the filter being arranged between the upper inlet and the lower outlet of the tank, inside the tank, so as to prevent the passage of particles into the recirculation loop.

[0021] The term "volatile fatty acids" means short carbon chain fatty acids (SCFAs) comprising less than six carbon atoms. These may be, for example, acetic acid, propionic acid and / or butyric acid.

[0022] The term "short-chain alcohol" means alcohols containing less than six carbon atoms. This may be, for example, ethanol, n-, iso-propanol, n- and / or iso-butanol.

[0023] The term "ammonium" means either the ammonia molecule itself or the ammonium ion, depending on the pH.

[0024] “Shells of molluscs with soft bodies or flesh, category 3” means animal by-products (SPAN), generally mussels, sometimes unfit for consumption, identified by the official name of “Category 3 animal by-products”, according to EC Regulation 1069 / 2009, Article 10, § k).

[0025] Advantageously, the device according to the invention can be configured to operate in thermophilic conditions, preferably at a temperature greater than or equal to 45°C, preferably from 45 to 70°C, and more preferably at 55°C.

[0026] Advantageously, the device according to the invention can be configured to operate in an anaerobic environment. Under anaerobic conditions, the reactor is airtight and can withstand a pressure ranging from 10 to 80 mbar. The device can also be equipped with pressure relief and vacuum valves to prevent the structure from being destroyed in the event of damage, the presence of biogas also requiring compliance with specific ATEX regulations to limit the risk of explosion.

[0027] Advantageously, the device comprises a tank. The tank comprises an upper part provided with an upper inlet and a lower part provided with a lower outlet. The tank may have a cylindrical shape extending around a substantially vertical extension axis. The tank may have a cross-section relative to the extension axis. The cross-section may be of various shapes; for example example of circular, rectangular or square shape. The cross-section can have a diameter ranging from 1 m to 30 m. The tank can have a height ranging from 1 m to 20 m. The volume of the tank is generally of the order of a hundred cubic meters. For example, to treat a volume of mollusk shells with soft bodies or flesh of 1 m3, a tank with a volume of at least 2 m3 will be required. A person skilled in the art will know how to size the tank according to the volume of inputs to be treated and the configuration of the location where the device according to the invention will be placed.

[0028] Advantageously, the upper inlet of the tank comprises at least one injector, preferably the tank comprises one injector per m2 of cross-sectional area of ​​the tank. The at least one injector may be a sprinkler (or nozzle). The sprinkler may comprise, for example, circular orifices with a diameter greater than 4 mm. The injector allows a homogeneous distribution of the liquid circulating in the recirculation loop by distributing it over the surface of the bed of the reaction medium.

[0029] Advantageously, the lower part of the tank may have a funnel shape, a lower end of which defines the lower outlet of the tank. This shape facilitates the routing of the liquid into the recirculation loop. The lower outlet of the tank may further be connected to an evacuation system, said evacuation system making it possible to extract the hydrolyzate from the device, when the hydrolysis reaction is complete.

[0030] Advantageously, the tank further comprises a filter having pores with a diameter less than or equal to 4 mm. The filter is preferably removable. The filter is arranged between the upper inlet and the lower outlet of the tank, inside the tank, so as to prevent (or prevent) the passage of particles into the recirculation loop (in particular shell fragments). The filter may be a perforated mesh basket, preferably a round mesh. Preferably, the filter is made of stainless steel material. The filter preferably has substantially the same cross-section as the tank, so as to prevent (or prevent) the passage of particles into the recirculation loop.

[0031] Advantageously, the tank may further comprise a filling opening through which the mollusc shells having soft bodies or flesh, classified as category 3 animal by-products, crushed and hygienic, are introduced into the tank. The filling opening may be closed by means of a lid or a stopper. The opening may also be a flexible cover integrated on the upper part of the tank, also having the function of a gasometer.

[0032] Advantageously, the tank may further comprise a gasometer in the upper part of the tank.

[0033] Advantageously, the tank may comprise a heating means. The heating means may be positioned inside or outside the tank. Preferably, the heating means is positioned outside the tank and only heats the liquid fraction. It may be a tubular exchanger supplied with heat transfer fluid or an external tube immersion heater. The hydrolyzate recirculation loop ensures homogeneity in the heating.

[0034] Advantageously, the device comprises a recirculation loop connecting the lower outlet of the tank to the upper inlet of the tank, outside the tank. The recirculation loop is configured to draw hydrolyzate (liquid) from the lower outlet of the tank and discharge it to the upper inlet of the tank. The recirculation loop may comprise at least one pump. The pump may be a peristaltic, lobe, or eccentric rotor volumetric pump. The recirculation loop may further be connected to a discharge system.

[0035] The invention also relates to a unit for producing volatile fatty acids from mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, comprising: - a first reactor equipped with a grinding means, preferably a grinder, - a second reactor equipped with a heating means, preferably a sanitizer, - a third reactor comprising at least one device according to the invention, and - optionally a fourth reactor configured to operate under mesophilic conditions, preferably an infinitely mixed reactor, in which the first, second, third and possibly fourth reactors are arranged in series.

[0036] Advantageously, the second reactor is identical or different to the third reactor. That is to say that the device according to the invention can be configured to allow the sanitization of mollusc shells having soft bodies or flesh, classified as category 3 animal by-products. In this variant, the second and third reactors are one and the same reactor: a device according to the invention.

[0037] Advantageously, the transfer of material from one reactor to another can be ensured by automatic or manual transfer. In the case of automatic transfers, the adjacent reactors can be connected to each other by material transfer devices, said material transfer devices possibly being equipped with pumps, a network of valves and tanks (to allow a buffer effect and avoid overflows and clogging).

[0038] Advantageously, the first reactor is provided with a grinding means. The grinding means may be a shaft grinder provided with a 12 mm screen. The first reactor may be a simple grinder provided with an inlet and an outlet.

[0039] Advantageously, the second reactor is provided with a heating means. The heating means may be an immersion heater, a heating resistor or implemented via steam injection into the second reactor. The heating means is configured to allow a temperature of at least 70°C to be reached at the core of the second reactor. The volume of the second reactor is adapted to the quantity of inputs to be treated; it preferably allows the material to be kept heated for a residence time of 1 hour. A person skilled in the art will therefore be able to determine the dimensions of the second reactor. The second reactor may be configured to withstand a pressure ranging from 1 to 12 bars and temperatures greater than or equal to 165°C. The reactor is preferably made of stainless steel material, for example 316L stainless steel. Preferably, the second reactor is a hygienizer or a pasteurizer.When the device according to the invention is configured to allow the sanitization of mollusc shells (case where the second and third reactors are identical), these parameters of resistance to pressure and temperature apply to the third reactor (and therefore to each of the devices which compose it).

[0040] Advantageously, the third reactor comprises at least one device according to the invention. Preferably, the third reactor may comprise at least two devices according to the invention, and more preferably, it may comprise three. When the third reactor comprises several devices according to the invention, said devices according to the invention are arranged in parallel. The recirculation loop may be shared with a hydrolyzate evacuation system, common to all the devices. For example, each device according to the invention may comprise a recirculation loop, each of said loops being connected to a single outlet, allowing the extraction of the VFA-rich hydrolyzate at the end of the reaction.

[0041] Advantageously, the volatile fatty acid production unit according to the invention may comprise a fourth reactor configured to operate under mesophilic conditions. The volume of the fourth reactor is generally of the order of a few hundred cubic meters. For example, to treat a volume of hydrolyzate of 1 m3, a tank having a volume of at least 15 m3 will be required.

[0042] Advantageously, the fourth reactor may comprise a heating means. The heating means may be as described above. The fourth reactor is generally designed to offer a pressure resistance of 10 to 80 mbar and may be equipped with valves to secure the installation in the event that these thresholds are exceeded. The fourth reactor may be equipped with a mixing system of the recirculation pump or pendulum stirrer type, for example, as well as a hydraulic guard system allowing the liquid to exit without gas leakage.

[0043] The first, second, third and possibly fourth reactors are arranged in series. They can be connected to each other. When they are connected to each other, the outlet of reactor n (n being an integer ranging from 1 to 3) is connected to the inlet of reactor n+1, by means of piping, possibly equipped with one or more pumps in order to ensure the transfer of material from one reactor to another. Buffer tanks, making it possible to regulate the circulation of material from one reactor to another, can be positioned between two successive reactors. When the third reactor comprises several devices according to the invention, the second and third reactors can be connected via a distributor making it possible to evenly distribute the mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, crushed and hygienized, in the devices according to the invention arranged in parallel. These elements can be configured for operation by manual or automatic transfer from one reactor to another.

[0044] “Connected” means a direct or indirect connection between two elements of the device. For example, the lower outlet of the tank can be connected directly to the evacuation system and to the recirculation loop (via a distributor) or the lower outlet of the tank can be connected to the evacuation system via the recirculation loop.

[0045] The invention further relates to a method for producing volatile fatty acids comprising a hydrolysis step under thermophilic conditions, implemented in a device according to the invention, from mollusc shells having soft bodies or flesh, classified as category 3 animal by-products, previously ground and sanitized.

[0046] Advantageously, the method according to the invention can comprise the ordered steps: (a) crushing of mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, to a cutting threshold of less than or equal to 12 mm, b) sanitizing the ground mixture obtained at the end of step a) at a temperature greater than or equal to 70°C, for a duration preferably greater than or equal to 1 hour, c) hydrolysis of the organic matter included in the hygienized mixture obtained at the end of step b), under thermophilic conditions, at a temperature greater than or equal to 45°C, preferably from 45°C to 70°C, and more preferably at 55°C.

[0047] Advantageously, step a) of grinding of the process according to the invention is carried out in the first reactor. The duration of step a) may vary depending on the size of the grinding means and the volume to be ground. Those skilled in the art will be able to adapt the duration of step a) depending on the nature and quantity involved. Step a) is generally carried out at room temperature, i.e. between 15 and 25°C. When carrying out step a), the mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, are ground to form a mixture comprising organic matter (from soft bodies or flesh) and shell fragments. The size of the shell fragments obtained at the end of step a) is around 4 to 12 mm.

[0048] Advantageously, step b) of sanitization of the process according to the invention is carried out in the second reactor. The mixture comprising organic matter (from soft bodies or flesh) and shell fragments obtained at the end of step a) is subjected to a high temperature so as to eliminate any pathogens present in the mixture and in particular any sporulating bacteria. The sanitization is carried out at a temperature greater than or equal to 70°C. Step b) of sanitization may have a duration greater than or equal to 1 hour. The temperature rise is not included in this duration. Depending on the equipment and the volume to be treated, the temperature rise may range from a few minutes to several hours. Step b) may be a pasteurization (stricter conditions), over a shorter time.For example, pasteurization can be carried out at a temperature greater than or equal to 140°C, at a pressure ranging from 1 to 10 bars.

[0049] Advantageously, hydrolysis step c) of the process according to the invention is carried out in the third reactor. The hydrolysis is carried out under thermophilic conditions, at a temperature greater than or equal to 45°C, preferably from 45°C to 70°C, and more preferably at 55°C. Step c) is preferably carried out in an anaerobic environment. Step c) may further comprise a sub-step of inoculation of the reaction medium (i.e. the tank(s) of the device(s) according to the invention) by means of a thermophilic digestate originating from a conventional methanization unit. The digestate may originate from a methanization unit under thermophilic conditions or be produced by recycling a portion of the digestate produced during the hydrolysis step (from a previous implementation of the process). It can also be a mixed microbial community or an open microbial community.The inoculation sub-step is preferably carried out in each of the devices of the third reactor, prior to the introduction into said devices of the hygienized mixture obtained at the end of step b). During step c) of the process, the hydrolysis of the organic matter included in the mixture is carried out in the presence of the shell fragments resulting from the grinding which have not been separated following grinding and hygienization. The presence of the shell fragments has a buffering effect on the pH of the hydrolysis reaction, which does not decrease as the reaction progresses. Step c) of hydrolysis is carried out in a closed circuit. The circulation and homogenization of the reaction mass is ensured by the recirculation loop which sucks the filtered suspension (liquid hydrolyzate) to reinject it via the at least one injector of the device. During the implementation of step c), the recirculation loop. The recirculation loop can ensure homogenization of the reaction mass continuously or alternately. For example, it may only be in operation for 5 to 15 minutes per hour (for the entire duration of step c)). The recirculation loop can operate in alternating continuous (60 minutes per hour) and discontinuous (5 to 15 minutes per hour) cycles. The shell fragments are retained by the filter, which prevents the fragments from circulating in the recirculation loop. The filter retains the mixture of shells and flesh while allowing the circulation of the filtered liquid, ensuring the homogeneity of the reaction mass, for the duration of the hydrolysis reaction.

[0050] Advantageously, step c) of hydrolysis of the process according to the invention has a residence time ranging from 2 to 7 days, preferably from 2 to 5 days, and more preferably 3 days.

[0051] Advantageously, step b) and c) of the method according to the invention can be implemented, successively, in a device according to the invention. In this variant, the second reactor and the third reactor are identical, and are a device according to the invention.

[0052] Advantageously, the method according to the invention may further comprise a step d) of extracting the crushed shell fragments from the hydrolyzed mixture obtained at the end of step c). The extraction consists of separating the shell fragments from the rest of the reaction medium (liquid fraction, hydrolyzate). When the filter has a basket shape, the extraction step d) may consist of removing said filter from the tank. The filter is removed from the reactor; it contains only shells without flesh. The remaining suspension (hydrolyzate rich in AGV) can then be transferred to the fourth reactor or recovered.

[0053] Advantageously, the process according to the invention may further comprise a step e) of methanogenesis under mesophilic conditions, preferably at a temperature ranging from 33 to 42°C, preferably 37°C, of ​​the liquid fraction obtained at the end of the extraction step d). Step e) of the process according to the invention is carried out in the fourth reactor. Step e) may be carried out under conventional methanogenesis conditions known to those skilled in the art. Step e) may comprise a dilution (with water) of the liquid fraction obtained at the end of step d). Step e) may further comprise an inoculation of the medium, prior to methanogenesis.

[0054] The device and method according to the invention also have the following advantages: - to allow and comply with the regulations in force concerning SPAN for mollusc shells with soft bodies or flesh, classified as category 3 animal by-products; - to ensure a high conversion of organic matter into AGV, alcohols, ammonium, carbon dioxide, methane, dihydrogen and hydrogen sulfide and shift the reaction equilibrium through the conservation during the implementation of the process of crushed shell fragments providing a strong buffering capacity to the reaction medium; - to separate the AGV production phase and the methane production phase, thus allowing direct operation of the AGVs; - to enable the production of fragments of shells without flesh and an organic amendment; - to protect industrial equipment by preventing the circulation and accumulation of shell fragments, resulting from the presence of shell crushing; - to reduce the volume of the hydrolysis reactor and therefore its manufacturing and implementation cost by accelerating the conversion of organic matter into AGV, alcohols, ammonium, carbon dioxide, methane, dihydrogen and hydrogen sulfide: recirculation through the bed of crushed shells promotes exchanges and allows the material being degraded to be heated to the core; - to enable the AGV production and methane production phases to be implemented differently with reactors adapted to the dry matter and particle content of their contents.

[0055] [Fig.l] [Fig.l] represents a device 10 according to the invention comprising: - a tank 110 comprising an upper part 111 provided with an upper inlet 112, itself provided with injectors 113 and a lower part 114 provided with a lower outlet 115, - a recirculation loop 116 connecting the lower outlet 115 of the tank 110 to the upper inlet 112 of the tank 110, outside the tank 110, the recirculation loop 116 being configured to suck hydrolyzate from the lower outlet 115 of the tank 110 and discharge it towards the upper inlet 112 of the tank 110, - a filter 117, said filter 117 being arranged between the upper inlet 112 and the lower outlet 115 of the tank 110, inside the tank 110 - a heating means 118, - an evacuation system 119, - a set of 120 valves, and - a 121 pump.

[0056] [Fig.2] [Fig.2] represents an AGV production unit 20 according to the invention comprising: - a first reactor 21 equipped with a grinding means 23, - a second reactor 22 equipped with a heating means 24, - a third reactor consisting of three devices 25 according to the invention in parallel and a recirculation loop 26 shared between the different devices 25.

[0057] [Fig.3] [Fig.3] represents the monitoring of the operating parameters of the thermophilic hydrolysis reactor, A: VFA production (g / L) as a function of time (days), B: buffer capacity (g / L) as a function of time (days) and C: pH as a function of time (days). [Fig.3] thus represents a VFA production kinetics with an increase in the VFA concentration until the 3rd day then a plateau to reach a maximum VFA concentration of 20 g / L on the 7th day. The buffer capacity increases until the 4th day then peaks at an approximate value of 6 g / L. This increase in the alkalimetric titer allows the medium to be well buffered, thus the pH increases during the first days of hydrolysis then peaks at a value of 7.3 after the 3rd day.

[0058] The invention will be better understood by reading the following non-limiting example.

[0059] Example: Production of a hydrolyzate rich in AGV

[0060] The method according to the invention is implemented on a laboratory model representative of the device of [Fig.l] and comprising: - a tank 110 comprising an upper part 111 provided with an upper inlet 112, itself provided with injectors 113 and a lower part 114 provided with a lower outlet 115, - a recirculation loop 116 connecting the lower outlet 115 of the tank 110 to the upper inlet 112 of the tank 110, outside the tank 110, the recirculation loop 116 being configured to suck hydrolyzate from the lower outlet 115 of the tank 110 and deliver it to the upper inlet 112 of the tank 110, - a filter 117, said filter 117 being arranged between the upper inlet 112 and the lower outlet 115 of the tank 110, inside the tank 110 - a heating means 118, - an evacuation system 119, - a set of valves 120, and - a pump 121.

[0061] A first reactor and a second reactor adapted to the model are used.

[0062] Material and method

[0063] a) Grinding (first reactor): 2.5 kg of mussels from Mont Saint Michel, classified as category 3 by-product, ground to 12 mm with a knife grinder then placed in jars.

[0064] b) Hygienization in a hygienizer (second reactor): the crushed mussels are then hygienized in a jar hygienizer, with a volume of 60 liters, 20 min of temperature rise to 70°C, then 1 h of holding at 70°C, followed by stopping the process.

[0065] c) Hydrolysis in a reactor configured to operate under thermophilic conditions (third reactor comprising a device according to the invention): the volume of the tank is 5 liters. The reactor is 40 cm high and has a circular section with a diameter of 15 cm. The lower part of the tank is heated evenly by a double jacket. The applied temperature allows a stable temperature of 55 °C to be reached. The reactor used is the BPC CSTR 5S model from BPC Instruments®.

[0066] A perforated mesh basket (filter, mesh size = 2 mm) is placed in the tank. The residence time of the hydrolysis reaction is 7 days. Quantitative and qualitative monitoring of the biogas is carried out with a pFlow meter from BPC Instruments® and the use of gas chromatography.

[0067] The recirculation loop (collection from the lower part of the tank and discharge to the upper part of the tank) has a flow rate of 30 L / h with operation of 10 min per hour.

[0068] At the end of the hydrolysis reaction, a hydrolyzate rich in AGV is obtained.

[0069] In [Fig.3] we observe a production of AGV, which stabilizes at a concentration of 20 g / L of hydrolyzate with a buffer capacity of 9.3 g / L and a pH of 7.2. We observe a low production of biogas which stabilizes at 2 L / d with a methane content of approximately 30%: methanogenesis is therefore not launched, the production of AGV is not transformed into biogas and the hydrolysis phase is well isolated.

[0070] No system blockage, malfunction, sedimentation, or foaming was observed.

[0071] The method and device according to the invention thus enabled a high production of AGV, for a total yield of 59 g of AGV for 210 g of raw mussels, i.e. 28%.

[0072] Liquefaction of the flesh and separation into two distinct phases were observed: a liquid phase of hydrolyzate and a solid phase of crushed shells without the presence of organic matter.

Claims

Claims

1. Device for producing volatile fatty acids from mollusc shells having soft bodies or flesh, classified as animal by-products of category 3, comprising: - a tank comprising an upper part provided with an upper inlet and a lower part provided with a lower outlet, - a recirculation loop connecting the lower outlet of the tank to the upper inlet of the tank, outside the tank, the recirculation loop being configured to suck hydrolysate from the lower outlet of the tank and discharge it towards the upper inlet of the tank, characterized in that the tank further comprises a filter having pores with a diameter less than or equal to 4 mm, the filter being arranged between the upper inlet and the lower outlet of the tank, inside the tank, so as to prevent the passage of particles into the recirculation loop.

2. Device according to claim 1, configured to operate under thermophilic conditions, preferably at a temperature greater than or equal to 45°C, preferably from 45 to 70°C, and more preferably at 55°C.

3. Device according to claim 1 or 2, in which the upper inlet of the tank comprises at least one injector.

4. Device according to any one of the preceding claims, in which the filter is a perforated mesh basket, preferably round mesh, preferably made of stainless material.

5. Device according to any one of the preceding claims, in which the lower part has a funnel shape, a lower end of which defines the lower outlet of the tank.

6. Unit for producing volatile fatty acids from mollusc shells with soft bodies or flesh, classified as category 3 animal by-products, comprising: - a first reactor equipped with a grinding means, preferably a shaft grinder equipped with a 12 mm screen, - a second reactor equipped with a heating means, - a third reactor comprising at least one device according to any one of the preceding claims, and - optionally a fourth reactor configured to operate in mesophilic conditions, in which the first, second, third and possibly fourth reactors are arranged in series.

7. Production unit according to the preceding claim, in which the third reactor comprises at least two devices according to any one of claims 1 to 5, preferably three, arranged in parallel.

8. Process for the production of volatile fatty acids comprising a step of hydrolysis under thermophilic conditions, carried out in a device according to any one of claims 1 to 5, from mollusc shells having soft bodies or flesh, classified as animal by-products of category 3, previously ground and hygienized, the hydrolysis of the organic matter included in the mixture being carried out in the presence of the fragments of shells resulting from the grinding which have not been separated following grinding and hygienization.

9. A process for producing volatile fatty acids comprising the steps: a) grinding mollusc shells having soft bodies or flesh, classified as category 3 animal by-products, to a cutting threshold of less than or equal to 12 mm, b) hygienization of the ground mixture obtained at the end of step a) at a temperature greater than or equal to 70°C, for a duration preferably greater than or equal to 1 hour, c) hydrolysis of the organic matter included in the hygienized mixture obtained at the end of step b), in the presence of shell fragments resulting from the grinding and under thermophilic conditions, at a temperature greater than or equal to 45°C, preferably from 45 to 70°C, and more preferably 55°C.

10. Method according to the preceding claim, in which step c) of hydrolysis is carried out in an anaerobic environment.

11. Method according to claim 9 or 10, in which step c) comprises a sub-step of inoculating the reaction medium.

12. A method according to any one of claims 9 to 11, wherein the residence time of step c) is 2 to 7 days, preferably 2 to 5, and more preferably 3 days.

13. Method according to any one of claims 9 to 12, in which steps b) and c) are carried out, successively, in a device according to any one of claims 1 to 5.

14. A method according to any one of claims 9 to 13, comprising furthermore a step d) of extracting the crushed shell fragments from the hydrolyzed mixture obtained at the end of step c).

15. Method according to claim 14, further comprising a step e) of methanogenesis under mesophilic conditions, preferably at a temperature ranging from 33 to 42°C, preferably 37°C, of ​​the suspension obtained at the end of step d) of extraction.

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