EP4164990A1 - Method and device for treating organic waste, including the anaerobic digestion thereof and the composting of the digestates - Google Patents

Abstract

The invention relates to a continuous process for treating organic waste taking place in a plant, said process for treating organic waste comprising a process of anaerobic digestion of a first part of said waste, which takes place in at least one digestion chamber, and a process of aerobic composting of a second part of said waste, which takes place in at least one composting chamber, the process for treating organic waste comprising the steps of: - collecting digestate and biogas at the end of said anaerobic digestion process, - collecting compost and humic percolate at the end of said aerobic composting process, - feeding at least part of said digestate into said aerobic composting process, - feeding at least part of said humic percolate into said anaerobic digestion process.

Description

METHOD AND DEVICE FOR THE TREATMENT OF ORGANIC WASTE, INTEGRATING THEIR ANAEROBIC DIGESTION AND THE COMPOSTING OF THE DIGESTATE

Technical field of the invention

The present invention relates to the field of the biological treatment of volatile or non-volatile organic matter and waste. These organic materials and waste can be of various origins, such as slaughterhouse, kitchen and table waste, plants or woody products of agricultural, forestry or industrial origin. They can be liquid such as blood or waste from the dairy or wine industry, or solid such as viscera, spent grains, marc or the fermentable fraction of household and similar waste. More specifically, the invention concerns anaerobic digestion processes as well as aerobic composting processes for organic matter, but above all the coupling of these two treatment modes on a single station.

The invention therefore relates to a new process which couples in a single device a methanation process and a process for composting organic materials and waste. The invention also relates to a new device for implementing this method.

State of the art

WO 2017/109398 (JUA Group) describes an installation and a process for the biological treatment of organic waste and effluent by biodigestion. It is known that the treatment of organic materials by biodigestion is above all subject to bacterial ecology constraints which the techniques used to create and maintain an ecosystem favorable to the microorganisms particular to this type of bio-oxidation attempt to respect. Thus a biodigester is a reactor which accommodates and maintains populations of strictly anaerobic microbes which are brought to grow and reproduce on an organic substrate consisting of liquid or solid matter in the presence of water. Essentially, these specific microbial populations develop bio-oxidation activity, but in the absence of atmospheric oxygen. The reaction is only possible when the three bacterial communities typical of this trophism form a balanced ecosystem such that the bulk of the reducing equivalents (carbon and hydrogen atoms) produced as waste products during bacterial anabolism ( hydrolysis, acidogenesis and acetogenesis) are finally found in methane (CH ₄ , methanogenesis). The bacterial species concerned are complex and relatively varied, but we know quite well their biochemical characteristics and the main features of their ecology. They are generally classified into three groups: hydrolytic and fermentative bacteria, acetogenic bacteria, and methanogenic bacteria.

The management of the artificial ecosystem constituted by an anaerobic bioreactor requires dynamic intervention to ensure certain essential physico-chemical conditions; such as pH, temperature and redox potential and nutritional requirements. The availability of digestible carbon is particularly critical to avoid fatal inhibitions in the presence of volatile fatty acids (commonly abbreviated VFAs) or supernumerary ammonium and to optimize methane production.

The critical parameters in the conduct of the anaerobic biodigestion process are pH, temperature, redox potential, and nutritional and metabolic supply.

The optimum pH for anaerobic digestion is around neutrality. It is the result of the optimum pH of each bacterial population; that of acidifying bacteria is between 5.5 and 6, acetogens prefer a pH close to neutrality while methanogens have maximum activity in a pH range between 6 and 8. However, methanation can occur in slightly acidic or alkaline media.

The activity of the methanogenic consortium is closely related to temperature. Two optimal temperature ranges can be defined: the mesophilic zone (between 35°C and 38°C) and the thermophilic zone (between 55°C and 60°C) with a decrease in activity on either side of the these temperatures. The majority of bacterial species have been isolated from mesophilic environments, but all trophic groups of the anaerobic digestion steps have thermophilic species using the same metabolic pathways as mesophilic bacteria with similar or superior performance. It is nevertheless possible to work at temperatures different from the optimum with lower performance.

The redox potential represents the reduction state of the system, it affects the activity of methanogenic bacteria. These bacteria indeed require, in addition to the absence of oxygen, an oxidation-reduction potential of less than 330 mV to initiate their growth. The Redox potential (Eh) is an indicator of the bioelectric activity of a natural environment; the lower it is the more it indicates a high level of energy available for biochemical exchanges in the environment considered. Humic substances positively influence the redox potential.

With regard to nutritional and metabolic needs, like any micro-organism, each bacterium constituting the methanogenic flora requires a sufficient supply of macro-elements (C, N, P, S) and trace elements for its growth. The needs in macro-elements can be evaluated roughly starting from the raw formula describing the composition of a cell (C ₅ H ₉ O ₃ N). For methanogenic bacteria, the culture medium must have carbon contents (expressed in Chemical Oxygen Demand (COD), nitrogen and phosphorus at least in the COD/N/P proportions equal to 400/7/1. Ammonium is their main source of nitrogen. Some species fix molecular nitrogen while others need amino acids. Nitrogen requirements represent 11% of the volatile dry mass of the biomass and phosphorus requirements 1 /5 of those of nitrogen.

Methanogenic bacteria have high levels of Fe-S proteins which play an important role in the electron transport system and in the synthesis of coenzymes. Also the optimal concentration of sulfur varies from 1 to 2 mM (mmol/L) in the cell. This flora generally uses reduced forms such as hydrogen sulphide. Methanogens assimilate phosphorus in mineral form.

Certain trace elements are necessary for the growth of methanogens. These are more particularly nickel, iron and cobalt. Indeed, they are constituents of coenzymes and proteins involved in their metabolism. Magnesium is essential since it comes into play in the terminal reaction of methane synthesis as well as sodium appearing in the chemo-osmotic process of synthesis of Adenosine Tri-Phosphate (ATP).

There are growth factors that stimulate the activity of certain methanogens: fatty acids, vitamins as well as complex mixtures such as yeast extract or peptone trypticase.

In conclusion, if today we correctly master the macro-model which simulates a biodigestion process, to the point that we can summarily predict the magnitude and form of methane production and the composition of a digestate, it don't stay unless the methods are difficult to implement. Indeed, if one wants to treat a given organic effluent, the fermentable fraction of household and similar waste or certain industrial organic waste or waste from agricultural sectors, or even a mixture of inputs (co-digestion) it is necessary each time dedicate the process to achieve the best productivity because each substrate corresponds to an optimum microbiological ecosystem and the biochemical yield windows are narrow. In other words, the challenge is to design and implement a methane digester with low investment and low operating costs but perfectly versatile in terms of bacterial resources to ensure high methane productivity regardless of the variation in the constraints of the plant. inputs

A bioreactor under anaerobic condition is an artifact that tries to optimize the living conditions of a colony of given microorganisms at a given time and / or in a given place in order to concentrate in a minimum biological retention time, therefore in a minimum volume of bioreactor, the maximum production of methane which results from the digestion of the substrates placed in aqueous solution or more generally in the absence of gaseous oxygen. A biodigester consists of four major components: a sealed and often heat-insulated enclosure, a stirring or stirring device, a digestate heating device, and inlet/outlet devices for the substrate, the digestate and the biogas.

Depending on the processes implemented, two major types of ecosystems can be distinguished in such a reactor: fixed biomass and free biomass.

In a fixed biomass digester, the enclosure serves not only to contain the substrate and isolate it from the air, but also to fix anaerobic bacterial colonies on suitable supports. Some liquid-phase techniques use self-contained fixative cells that are immersed in the flux. In general, the advantage of this process lies in the maintenance of the availability of the bacterial strains despite the permanent or sequential transfer of the flows of treated substrates, the desired objective being not to have to restart bacterial seeding or to avoid specializing the flora by chemical inputs. Several types of fixing processes are available, some for example granulate the substrate or part of the incoming substrate before seeding it and circulating it within the enclosure of the biodigester. As a general rule, the operations of bio-oxidation of waste or organic matter must satisfy several criteria of efficiency and biosafety which are carried out by carrying out critical settings and adjustments. Thus, in a free or fixed biomass digester, active biomass reinforcement processes are used which result from the heating and the circulation of the juices and possibly from the addition of trace elements and pH correctors. The process is adaptive and relies on the spontaneous ability of the bacterial flora to specialize according to the constraints of the environment, in particular with regard to the presence of nutrients in large quantities. The adaptability of the biomass, left free to leave the enclosure with the sequential or continuous flow of flows, and to evolve according to the constraints of the ecosystem is reinforced by "external" thermal actions (maintenance in mesophilic at 38°C or thermophilic at 55°C), chemical (neutralization of acid or alkaline pH) and mechanical (transfers, fluidification and mixing). As a general rule, a biodigester therefore requires either good monitoring of the indications provided by the sensors, in order to allow a human adjustment response in deferred time, or the analysis and automatic processing of the signals transmitted by the sensors inferring in real time the actuation of effectors.

Beyond the differentiation between fixed biomass and free population, manual or automated settings, there are also two types of flow dynamics: the process can be sequential loading (“batch” process) or continuous feeding.

Sequential loading processes have the major characteristic that they seek to establish, in the same enclosure for a single dose of substrate, the succession of the major phases of methane digestion. To put it another way, we can consider that in this context the bacterial populations evolve on an identical substrate from the beginning to the end of the cycle and therefore do not need to expend energy to adapt to unexpected changes in their ecosystem, it is they who transform it and not the other way around. Thus, as soon as the loading of the tank is completed, and it can be done in one day or in three or four, the optimum conditions for starting the hydrolysis phase are provided (temperature, pH, nutrients, inoculation). It is then the turn of the transitory phase of acidogenesis which is regulated to allow the triggering of acetogenesis and finally of methanogenesis. In theory, this process has the advantage of having a Hydraulic Retention Time (HRT) shorter than that of continuous flow protocols and of being easier to master. In general, it is necessary to have several tanks operating in parallel which are activated one after the other as they are filled. In the event of dysfunction of a cell, the treatment can be continued with the others. It is also a process where the tanks are smaller and which generally accept substrates denser in dry matter. Nevertheless, the sequential loading makes it necessary to multiply the enclosures and the ancillary devices such as the loading hoppers, the valves and other pumps. Furthermore, the spontaneous evolution of anaerobic microbiomes in correlation with the succession of phases of digestion is not guaranteed and often requires external interventions to counter inhibitions, regulate nutrient demands and acid-base dynamics.

However, continuous feeding is strictly opposed to sequential loading on several planes. Firstly because in the first case the ecosystem and particularly the bacterial flora are brought to be versatile, or rather to make coexist in the same enclosure and at the same time but not necessarily in the same zone of the volume of bioreaction of the bacteria and their co-enzymes for the four phases of the cycle. Then because to obtain a sufficient TRH it is necessary to size the tank on very large volumes which leads to proportional energy expenditure to maintain a suitable temperature and especially to stir the mixture continuously in order to avoid the formation of a crust on the surface , an accumulation of excessively dense sediments at the bottom of the tank and to ensure minimal circulation inside the bioreactors so that the transit of the substrates traverses the whole variety of bacterial biomes.

It should nevertheless be noted that this process, which is very old since domestic biodigesters or Chinese farmers are mainly fed continuously, is well suited to micro-deposits of homogeneous organic substrates with very low variability. Indeed with very small dimensions (a few tens of m ³ ), waste of stable quality and quantity, they are easy to maintain if indeed one does not seek to evacuate the sediments in real time but rather the flows in phase liquid or turbid (eluates) which can then be recovered by spreading. The fact remains that after several operating cycles these small units must be shut down and emptied of their sediments which, by dint of accumulating, reduce the useful volume of the installation and harm the development of the bacterial flora. Only certain industrial processes manage to produce, in addition to biogas, highly loaded flows from which digestates are extracted by decantation and/or spin-drying, which are generally difficult to recover as biological fertilizer. The advantage of this process, at the industrial or domestic level, therefore lies essentially in its ability to accept a continuous flow of waste or effluents with a low organic load with average biogas production but possible recovery of the extracted effluents and more difficultly of the "solid" fraction of the digestates.

Based on what has just been described, two major types of processes continue to compete with each other, namely single-phase processes and differentiated-phase processes.

In the first case, whether the biodigester is of the sequential or continuous type, with fixed or free biomass, all the phases take place in the same enclosure. This subsystem is either gravitational (sedimentation) or counterflow and is by far the majority. The fundamental technological variations concern the modalities of the sequential or linear mixing of the substrates (stirred vs pulsed vs infinitely mixed), the modalities of introduction of the substrates and extraction of the digestates and eluates.

In the second case and in theory, each of the four phases can be confined in a separate tank and the passage of the modified substrate at the end of each phase to the next is ensured by a mechanical or hydraulic system. In reality, the state of the art clearly favors two-phase systems in which hydrolysis and acidogenesis are confined in a first enclosure while acetogenesis and methanogenesis are ensured together in the second enclosure. The goal sought by these multiphase processes is to better manage the phases individually by playing on the micro conditions optimizing these different ecosystems.

More complex and expensive, differentiated-phase processes nevertheless have a better yield in terms of biodegradability, in particular for substrates which require strong enzymatic speciation and/or a particular chemical or thermal environment. On the other hand, for a stream of waste that is homogeneous over time and whose composition does not offer any particular risks (especially at the acetogenesis stage), it is generally considered that this process does not provide sufficient added value to legitimize the complexity and investment required.

Finally, a distinction is made between three types of biodigesters according to the concentration of Total Suspended Solids (STS) in the flows, ie the proportion of Dry Matter (DM) dissolved in the digester. Thus we distinguish the low DM biodigesters with less than 10% STS, medium DM biodigesters, containing between 15% and 20% STS, and high DM biodigesters, containing between 22% and 40% STS ; all these indications are given in mass percentage.

Flow biodigesters with a low STS content have as main inputs industrial or domestic effluents, as is the case for wastewater treatment plants or highly volatile solid inputs rich in inhibiting components (AGV, NhV) strongly diluted. These biodigesters have a particular configuration; the principle consists in using the biodigester as a sedimentation tank where the STS are retained and treated anaerobically while a flow of more or less purified water escapes. Thus, the Biological Retention Time (TRB) of the STS is greater there than that of the total flow (TRH) because the biodigester integrates a passive or active settling system and a system of retention / anaerobic degradation of the sedimented digestible MS.

As such, these biodigesters are unsuitable for the treatment of solid organic waste except that the latter are ground and put into solution with effluents which will always constitute the majority of the input or which are highly diluted. Under these protocols, the production of biogas and digestates (in this case in the form of sludge) is relatively low, but above all their capacity for primary purification of an effluent is sought, and their energy balance is balanced with the cogeneration of the biogas. Eventually, the productivity of these subsystems improves with the resale of digestate liquors (eluates) as liquid organic fertilizers when they can, on the one hand, demonstrate proven biological stability and be transported to areas extended in order to guarantee a low concentration when spreading, which is always difficult to ensure under normal operating conditions, except by accepting significant logistical costs to widen the spreading area sufficiently. With this type of process, the maximum applicable volume loads are of the order of 2 to 5 kg of COD/m ³ /d.

The family of biodigesters with an average STS concentration is the most common. In this configuration, a solid digestible substrate is dissolved in two to three times its weight in water. This modality of organic matter density in solution corresponds to a search for balance between the quantity of digestible matter, its viscosity and its coalescence in the enclosure of the digester and the capacity of the medium. anaerobic to harbor and maintain bacterial populations without risking their inhibition by way of biochemical saturation. In fact, for bacterial activity to operate under the best conditions, the digestate must not compact as long as it can be mobilized as the different phases of biodigestion progress. This process is therefore suitable for the treatment of the digestible fraction of solid organic waste subject to effective sorting upstream to evacuate the undesirable and relatively fine grinding which allows the hydraulic transfer of the digestible mass and the proliferation of high bacterial diversity.

More suitable for continuous rather than sequential loading processes, medium DM concentration biodigesters particularly benefit from fixed biomass systems because the flow of substrate has a flow rate large enough to deplete the resident flora. In general, the volume loads to be applied can reach 15 to 20 kg COD/m ³ /d. Hydraulic residence times vary between 4 and 5 weeks. Under this configuration, the biogas yields are good and the production of digestates in the form of a more or less fibrous substrate requires at least a decantation if not a centrifugation.

Some organic waste deposits consist of a large solid fraction with low digestibility: the mass of DM is high but the proportion of Volatile Organic Matter (VOM) on the DM is low. Insofar as it is not possible to validly concentrate the VOM of this waste, it is desirable to have a technology which authorizes their treatment anaerobically. Some biodigesters are designed for this type of application; they are said to have a high concentration in DM.

The specificity of these biodigesters lies in the mode of advancement and mixing of the substrate and in the fact that they are almost exclusively sequential loading and free biomass bioreactors, but with seeding. In general, it should be noted that beyond a certain threshold of VOM content, there is a risk of overload which can lead to inhibition of methanogenesis, which is especially valid for waste rich in animal proteins. (carcasses and fat) or ammonium (litter and slurry). In addition, the volume loads to be applied can reach 40 kg COD/m ³ /d. Hydraulic residence times vary between 2 and 3 weeks.

It is thus necessary to take into account the fact that above 3 g/I, ammonium (NH4 ⁺ ) is an inhibitor of methanogenesis. We also know that this limit of 3 g / 1 of NH4 ⁺ must not not be exceeded for waste whose C/N ratio is equal to or less than 20 with a VOM rate of around 60% of the MO.

Beyond and in addition to dilution with water, the most common technique for keeping these particular organic substrates below the inhibition threshold consists of mixing waste that is too rich in protein (viscera, fish, dairy products, carcasses and other meat waste) with carbonaceous substrates.

The alternative to the mixture control approach consists in reducing the MOV rate of the waste (especially the proportion of ammonium) by subjecting it to a preliminary phase of intense thermophilic aerobic fermentation, but this requires in any case that meat waste is mixed with carbonaceous substrates.

Another alternative consists of a heat treatment at low temperature inducing thermolysis which particularly affects the VFAs and restores them in a configuration of increased digestibility. These three techniques can be used together, with heat treatment occurring sequentially first.

To conclude, regardless of the methane digestion process chosen, four parameters strongly contribute to ensuring satisfactory biological productivity and proven economic feasibility:

First, the deep mixing in positive, non-destructive displacement of the structured biomes established by the bacterial colonies within the digestates undergoing anaerobic maturation in the presence and their enzymatic commensals. This mixing is particularly necessary in the compacting sedimentation zone where it must promote active bioturbation dynamics.

Secondly, the processing of digestates to make them recoverable as biofertilizer, without environmental or biological risk. This is usually completed after liquid/solid phase separation or more rarely by aerobic thermophilic maturation.

Third, the availability of digestible organic carbon in a progressively mobilizable form and in proportion to the particular demand of each methane digestion phase in order to always remain below the VFA and ammonium inhibition threshold.

Fourthly, the thermal management of bioreactors to reach and maintain an optimal temperature which requires energy inputs that are all the more significant as the volume of the tanks is large, or in other words, all the more so as the dilution is significant within the bioreactors

The present invention seeks to provide an integrated solution to the difficulties encountered by the various existing methane digestion processes confronted with the risks of inhibition by lack of digestible carbon or by lack of dilution water, the impossibility of rejecting into the environment raw digestates and the energy expenditure required due to the thermal needs of the bioreactors.

Objects of the invention

The present invention relates to continuous loading as well as infinitely mixed sequential multi-phase anaerobic digestion processes, regardless of their volatile organic solids content, whether they are free or fixed biomass, mesophilic or thermophilic.

The invention preferably relates to multi-phase, continuous feed, mesophilic and thermophilic, high volatile solids and attached biomass processes.

According to an essential aspect of the invention, a methane digestion equipment is coupled with a composting equipment in a closed vessel, which makes it possible to carry out the addition of raw compost and the injection of composting percolates into the digester, ensure the treatment of digestates by co-composting with woody materials to produce a stable and balanced biofertilizer. This also makes it possible, and advantageously, to capture heat in the composting silo to transfer it to the tanks of the bio-digester.

Thus, a first object of the invention is a continuous process for the treatment of organic waste taking place in a coupled installation, said process for treating organic waste comprising a process for the anaerobic digestion of a first part of said waste, which takes place in at least one digestion enclosure, and an aerobic composting process for a second part of said waste which takes place in at least at least one composting enclosure, in which a process for treating organic waste: digestate and biogas are collected at the end of said anaerobic digestion process, compost and humic percolate are collected at the end of said aerobic composting process, at least a portion of said digestate is introduced into said aerobic composting process, at least a portion of said humic percolate is introduced into said anaerobic digestion process.

Typically, said first part of said organic waste mainly comprises volatile organic waste, selected from the group formed by: slaughterhouse waste, dairy waste, winemaking waste, fish processing waste, meat, stable livestock waste, kitchen and table waste, organic waste from the agro-food industries.

Typically, said second part of said organic waste mainly comprises structuring organic waste, which is mainly organic polymers of lignin, cellulose, hemicellulose, and/or keratin type, and/or said second part of said organic waste mainly comprises waste selected from the group formed by: sawing waste (such as sawdust or sawmill wood waste), shredded forest waste, shredded wood waste or products, brown cardboard, shredded plants of various origins such as pruning, clearing, picking up dead leaves, various agricultural waste such as straw.

In a preferred embodiment, said aerobic composting process takes place in at least one composting chamber, preferably vertical to ensure sufficient height for the percolation process, and provided with a first heat exchanger through which said composting chamber heats a heat transfer fluid to a first temperature, and/or said aerobic digestion process takes place in at least one digestion chamber provided with a second heat exchanger through which said at least one digestion chamber is heated by said heat transfer liquid being at a second temperature, lower than said first temperature. Very advantageously, said first part of said organic waste is subjected to a thermal pretreatment in a thermal pretreatment enclosure, at a temperature above 45°C, and preferably between 70°C and 80°C, before being cooled and admitted into said anaerobic digestion chamber.

Advantageously, said thermal pretreatment enclosure is provided with a third heat exchanger.

In an advantageous embodiment, at least part of said heat transfer fluid heated by said first heat exchanger is led into said second heat exchanger.

The biogas generated by the anaerobic digestion process or the biomethane extracted from it by filtration. It can supply fuel to a burner provided with a fourth heat exchanger which heats a coolant, which is in thermal communication with said second heat exchanger and/or said third heat exchanger.

In a particular embodiment, said burner is in energy communication with an electrical energy generator, which preferably supplies electrical energy to at least part of said installation.

Another object of the present invention is an installation configured to perform the method according to the invention. This facility includes:

- an anaerobic digestion unit for the treatment of said first part of the organic waste, comprising successively a first enclosure intended for the progress of hydrolysis and acidogenesis, a second enclosure intended for the progress of acetogenesis, a third enclosure intended during the methanogenesis, and a fourth enclosure intended for degassing, said four enclosures being successively in fluidic connection (preferably not assisted overflow) to allow the transfer of treated waste from one enclosure to the next, said digestion unit anaerobic being configured to produce essentially digestate and biogas; - a composting enclosure intended for carrying out the aerobic composting of said second part of the organic waste, configured to produce essentially compost and humic percolates;

- means for transferring said digestate from said degassing enclosure to said aerobic composting unit;

- Means for transferring said compost and said percolate to said anaerobic digestion unit.

Very advantageously, the installation comprises a thermal pretreatment enclosure arranged upstream of said anaerobic digestion unit so that said first part of the organic waste intended to enter said anaerobic digestion unit passes through said thermal pretreatment enclosure .

In an advantageous embodiment, the installation is configured so that: at least one of said enclosures of said anaerobic digestion unit is heated using a heat transfer liquid; said thermal pretreatment chamber is heated using a heat transfer liquid; said aerobic composting chamber is cooled by a heat transfer liquid; the heat recovered from said aerobic composting enclosure is used to heat at least one of said enclosures of said anaerobic digestion unit, and/or said thermal pretreatment enclosure is heated using a heat transfer liquid.

At least part of the heat transmitted by the aerobic composting chamber to the heat transfer liquid which cools it can be used to heat at least one of the anaerobic digestion units.

Advantageously, the installation comprises a burner configured to burn the energy fraction of the biogas (which mainly comprises methane) produced by said anaerobic digestion chamber. This thermal energy can be used in two different ways, which can be combined within the installation: on the one hand, said burner can be configured to heat a heat transfer fluid which is in thermal communication with at least one of said enclosures of said anaerobic digestion unit and/or with said thermal pretreatment enclosure. On the other hand, said burner can be associated with an electrical energy generating device. The installation can be configured in such a way that said electrical energy generating device can supply said installation with electrical energy, for part or all of its needs, knowing that the installation includes accessory means, such as pumps, conveyors, solenoid valves, which use electrical energy.

Thus, the invention makes it possible to produce an organic waste treatment installation, combining anaerobic digestion with aerobic composting, and involving the composting of digestates and the recycling of humic percolates in anaerobic digestion, which can cover at least part of its own electrical and/or thermal energy needs.

tricks

[Fig.1] presents a diagram of an advantageous embodiment of the method according to the invention.

[Fig. 2] presents a first detail of the diagram according to figure 1.

[Fig.3] presents a second detail of the diagram according to figure 1.

[Fig.4] is a simplified schematic representation of a device that can be used to implement the method according to the invention.

The three-digit numerals refer to elements of the device, while the four-digit numerals designate steps or aspects of the method.

detailed description

In general, the process according to the invention makes it possible to use organic waste of very diverse origins. This may include slaughterhouse waste, kitchen and table waste, plants or wood products of agricultural, forestry or industrial origin. In general, the method according to the invention makes it possible to use liquid waste such as blood or scrap from the dairy or wine industry, and solid waste such as viscera, spent grains, marc or the fermentable fraction household and similar waste.

The method according to the invention will be described here in detail first in relation to Figure 1.

The process according to the invention mobilizes two different raw materials, which are both organic materials or waste. The first raw material consists of so-called structuring organic materials or waste (essentially organic polymers of the lignin, cellulose, hemicellulose, keratin type). The second raw material consists of volatile organic matter and waste (essentially organic molecules such as sugars, proteins, carbohydrates, therefore weakly polymerized).

These raw materials and their biological transformations will be explained with reference to FIG. 1 which schematically shows an embodiment of the invention. In this figure, the solid lines represent a material flow, the dotted lines an energy flow. The thick boxes represent a reactor, the other boxes represent a product or a process step.

The process according to the invention uses as raw material organic waste supplied in the form of structuring organic materials and waste (item 1000). It is mainly solid, highly polymerized waste, which is difficult to degrade by anaerobic biological means; as such, they may comprise ligneous material or other cellulosic materials and/or keratin. This may include, in particular, sawing waste, sawdust, shredded plants of various origins (pruning, clearing, collection of dead leaves or straw), shredded forest waste, shredded wood products, cardboard (in particular brown cards). This waste is supplied in a divided form, for example in the form of aggregate or crushed material not exceeding a typical dimension of approximately 50 mm x 20 mm (and preferably not exceeding a dimension of approximately 30 mm x 20 mm). They can be dry or wet.

This solid organic waste can undergo a new grinding which makes it possible to bring them to a finer particle size (reference 1010). This grinding can be carried out for example in a device of the slow grinder type with a double-axis knife, supplied with material by a loading hopper. They are then transferred, typically via a hopper, into a composting enclosure (item 1020) which acts as a bioreactor. As will be described below, according to an essential characteristic of the process according to the invention, this structuring waste will be mixed with a view to their composting with another fraction resulting from the process according to the invention, namely the digestate resulting from the anaerobic digestion of volatile organic waste.

The composting process is an aerobic process that takes place in two distinct phases; for this reason, said composting enclosure, which is typically made in the form of a vertical silo, has two compartments, each of which is dedicated to one of the two phases of the composting process. These two phases are shown in Figure 2.

The first phase 1022 of the composting process 1020 is an aerobic, thermophilic and exothermic process which takes place at a temperature of the order of 65°C to 75° or 80°C under the combined effect of various micro-organisms. The treated material must be supplied with wetting water (which typically includes, or is, recirculated humic percolate) and fresh air. The second phase 1024 of the composting process 1020 is mesophilic. Composting generates two fractions, namely a liquid fraction, called humic percolate (reference 1030) and a solid product called compost (reference 1040). As indicated above, it is necessary to maintain circulation of the humic percolate (item 1090) in the aerobic composting chamber.

Each of these two by-products can be recovered outside the process according to the invention according to methods known as such; this output of the process is called here “export”. For example, compost can be exported (reference 1070) to be used to improve an agricultural or horticultural growing medium, being rich in humic matter and minerals. The humic percolate is rich in humic acids and co-enzymes. Its dry matter content is low, preferably less than 5% by mass, typically less than 4%. It can also be exported (item 1060) to be used as a biostimulant of soil life and plant growth.

It is noted that the solubilization of humic acids in the percolate requires a long residence time in a permanent thermophilic zone (temperature typically between 65°C and 80°C) which forms in a composting enclosure of size (and in particular of height ) sufficient; this enclosure must have a sufficient level of maturity. These conditions typically require that the thickness (height) of the windrow in the enclosure be at least 3 meters, and preferably at least 3.5 meters, and even more preferably at least 4 meters. Furthermore, it is advantageous to permanently recirculate the effluents in the composter (step 1090 of FIG. 1) so that they gradually become loaded with humic acids. Thus a humic percolate is formed, which typically has a coffee color, and which differs notably from the simple effluents of a composting reactor of known type. The process according to the invention also uses volatile organic materials and waste as raw material. The term "volatile" here refers not to a gaseous nature but to their easier biochemical decomposition: These materials and waste are weakly polymerized. They can be liquid, muddy or solid; they can comprise for example proteins, lipids, carbohydrates or sugars. This may include, in particular, slaughterhouse, dairy, winemaking, fish and meat processing, stable livestock, kitchen and table waste, and more generally organic waste from agro-industry. food. They typically include solid fractions and liquid fractions; their liquid fraction can comprise water and various liquid organic wastes, such as blood, oils, various juices.

These volatile organic materials and waste (item 1100), in whole or at least their solid fraction, can first be crushed to reduce them to an acceptable particle size (item 1110). Then they are subjected to a thermal pretreatment 1120 which will be explained below.

According to the invention, after their heat treatment, these volatile organic materials and waste are subjected to an anaerobic digestion process (reference 1150), also called methane digestion because it produces methane. Anaerobic digestion 1150 is an endothermic process that takes place in several phases, which are shown in greater detail in Figure 3. It takes place by successive passage of the mass in several enclosures hydraulically connected in series.

In a first step 1152 carried out in a first heated enclosure, two anaerobic microbiological processes are carried out which take place at the same time, using two different microbial strains which can coexist within the same mass, namely hydrolysis and acidogenesis . These two processes typically take place at a temperature of the order of 38° C. to 40° C., with a residence time of between three and ten days. In a second step 1154, the mass is transferred (preferably by assisted overflow) into a second heated enclosure and it is subjected to an acetogenesis process; the residence time is of the order of eight to twelve days. In a third step 1156, the mass is transferred to a third heated enclosure and it is subjected to a methanogenesis process; the residence time is of the order of twelve to eighteen days. In a fourth step 1158, the mass is transferred to a fourth degassing chamber to collect the small fraction of biogas which remained fixed in the digestates by surface tension (reference 1160). The biogas produced during the 1150 anaerobic digestion, rich in methane, is trapped in the gaseous sky which covers the three tanks of the digester in a single flexible and sealed envelope.

According to an essential characteristic of the invention, the method couples aerobic composting 1020 to anaerobic digestion 1150 by carrying out reciprocal exchanges of solid and liquid matter from one to the other of these two bioreactors.

Thus, the enclosures in which the different digestion phases 1152,1154,1156 take place can be supplied with humic percolate (item 1053) from the composting enclosure. More specifically, the humic percolate 1030 is preferably added to one of the enclosures (or to both at the same time) in which the acetogenesis 1154 and the methanogenesis 1156 take place, these additions being identified in FIG. 3 by the marks 10534 and 10536, respectively, and/or upstream of the anaerobic digestion 1150, namely in the thermal pretreatment enclosure (item 1051) and/or, possibly, in the grinder 1110 located upstream of the thermal pretreatment enclosure (item 1052), and/or optionally, in an optional mixer 1140, which is located between the thermal pretreatment enclosure 1120 and the anaerobic digestion 1150. In a preferred embodiment, the humic percolate 1030 is introduced into the enclosure heat pretreatment 1120.

Subject to the presence of sensors measuring the Redox potential (Eh) in each of the three tanks of the methane digestion cycle, it is possible to inject humic percolates in a singular and automated way into each tank to induce a fine regulation of the bio - optimum chemical reactivity which is specific to them.

Furthermore, the anaerobic digestion process 1150 can be supplied with compost 1040 from the composting enclosure. Preferably, this compost 1040 is added during the homogenization step 1120, namely in the thermal pretreatment enclosure 1120 (this addition route bears the mark 1051) and/or in the grinder 1110 located upstream of the thermal pretreatment enclosure (this addition channel is marked 1081).

As indicated above, the correct operation of the anaerobic digestion process 1150 requires the presence of a sufficient quantity of digestible organic carbon (which typically amounts to about half of the organic dry matter for a waste given organic) to avoid inhibition of the process. It is the addition of percolate 1050,1051,1052,1053 to the materials and waste 1100 entering the composting chamber which makes it possible to control the correct content of digestible carbon in the digestion chambers 1150.

As indicated above, the anaerobic digestion process according to the invention can use volatile organic materials and waste (item 1100), typically present in a fluid form, that is to say liquid or muddy or loaded with particles. ground solids. It can be waste of various origins, crushed and/or homogenized. This waste is advantageously rich in proteins, lipids and sugars. Sludge from biological treatment plants can also be used, but on condition that it does not contain chemical substances likely to interfere with the final use of exported compost 1260 and percolate 1240.

Depending on their origin, it may be necessary to heat pre-treat said volatile organic materials and waste 1110 in a heat treatment enclosure (reference 1110). For example, waste food products collected after they have been placed on the market (kitchen waste from households or the catering sector) or from the food industry, as well as more specifically the by-products animals and the products derived from them must undergo appropriate heat treatment (hygienization, pasteurization, or even sterilization in the event of a high health risk) with a view to their recovery and elimination in biological processes. As described above, compost and humic percolate from the composting chamber are added to the mass intended for anaerobic digestion. According to a very advantageous embodiment, the compost added is also subjected to the heat treatment 1120, and for this reason it is added either at the grinding/mixing stage 1110 or directly in the heat treatment enclosure 1120. Indeed, the Heat treatment of compost removes certain strains that may interfere with the anaerobic digestion process. The percolate can also be subjected to the heat treatment, together with the mass to which it has been added.

Anaerobic digestion 1150 generates biogas (item 1160). Biogas is rich in methane; it also includes nitrogen, water and carbon dioxide. It is subjected to a 1170 filtration process to separate the methane. The latter can be the subject of energy recovery 1190, in a burner, and/or it can be exported. Anaerobic digestion generates a muddy or pasty residue called digestate (item 1200) which is mixed with crushed structuring waste and this mixture is transferred to the composting enclosure (item 1210) to be broken down into compost 1040 and humic percolates 1030, such as described above.

According to a very advantageous implementation of the method according to the invention, the anaerobic digestion enclosures 1150 and the aerobic composting enclosure 1020 are connected not only by material flows, but also by energy flows. Indeed, the overall process comprises at least one exothermic step, namely the first thermophilic phase 1022 of the aerobic composting 1020 (and, where applicable, also the energy recovery 1190 of the biogas), and at least one endothermic step, namely the anaerobic digestion 1150 (and, if applicable, also thermal pretreatment 1120 of fluid waste). These energy flows are represented in FIG. 1 by dotted lines. The thermal energy released during the cooling 1130 of fluid organic materials and waste after their heat treatment 1120 can also be recovered.

Thus, in a very advantageous embodiment of the installation according to the invention, the aerobic composting enclosure 1020, and more precisely its compartment dedicated to the thermophilic reaction 1022, comprises a heat exchanger capable of absorbing the reaction heat produced during the thermophilic phase of composting, and to transfer it, via an appropriate heat transfer fluid which may be water, to a heat exchanger associated with the aerobic digestion enclosure 1150, capable of heating the mass contained in this chamber. Alternatively, said heat transfer fluid heated by the aerobic composting chamber 1020 can also heat the thermal pretreatment chamber 1120.

According to another advantageous aspect of the installation according to the invention which can be combined with the previous one, the burner which ensures the energy recovery 1190 of the biomethane, heats a heat transfer fluid (item 1240), typically water (for example under the form of superheated steam) which supplies the heat exchanger of the anaerobic digestion enclosure (item 1250) and/or the thermal pretreatment enclosure (item 1260). The rest of the energy from the energy recovery of biomethane can be exported (reference 1270); it can be thermal or electrical energy, the latter being generated either by generators with cogeneration or by a turbine driven by a gas heated by the combustion of biomethane. At least one part of said electrical energy can be used by the installation itself, which comprises material flow transfer means (such as pumps for fluid organic waste 1100, wet percolates 1030 and digestates 1180, and conveyors for compost 1040) which consume electrical energy. These energy flows are not shown in Figure 1 so as not to overload it.

Thus, the invention makes it possible to produce an installation which is completely self-sufficient in energy, and which is also capable of producing a very significant surplus of energy.

An important advantage of the process according to the invention lies in the fact that it is carried out continuously, as opposed to discontinuous processes (“batch” mode), the flows of material take place almost continuously, the enclosures do not have no need to be drained and restarted periodically.

The process according to the invention makes it possible to valorize the digestate resulting from an anaerobic digestion process. In the known processes, the digestate still contains volatile matter which is not mineralized, which poses a problem when spreading the digestate on agricultural land surfaces. The method according to the invention recovers these volatile materials in a composting process. The supply of digestate with equivalence of mass of dry matter with structuring waste not only improves the dynamics of the thermophilic phase of composting but also significantly increases the level of nitrogenous nutrients in the compost.

Finally, the process according to the invention very partially reintroduces the percolate resulting from this composting process into the anaerobic digestion process. Thus, the volatile material is best utilized in a cyclic process.

With reference to Figure 4 we now describe an installation according to the invention which makes it possible to implement the method according to the invention which has just been described.

The installation according to the invention comprises an anaerobic digestion unit 110. It comprises four enclosures accommodating liquid phases, and an enclosure accommodating the biogas generated, as will now be explained. The first enclosure 120 is a heated enclosure in which hydrolysis and acidogenesis take place at the same time. The second enclosure 122 is a heated enclosure in which the acetogenesis takes place 1154. The third enclosure is a heated enclosure 124 in which takes place the methanogenesis 1156. The fourth enclosure 130 is a degassing enclosure 1158 in which the biogas is separated from the digestate (degassing phase

1158).

Said first 120, second 112 and third 124 enclosures are heated by a heat transfer liquid. The successive transfer of the liquid phase from one tank to another can be done by assisted overflow of the contents of one enclosure into the next enclosure, as symbolized in the figure by the difference in height of the enclosures. The biogas accumulates in the fifth enclosure 112 which is closed by a flexible roof which is extensible according to the pressure of the biogas.

The anaerobic digestion unit is loaded by a loading means 180 which can be a belt conveyor or, preferably, a pneumatic conveyor. The raw material enters a hopper then a mixer 188, before being admitted to the thermal pretreatment enclosure 184. The latter is typically a water bath, with a heat transfer fluid which is typically water. A pump 138 transports this pre-treated waste to the anaerobic digestion unit 180. The digestate is evacuated by a pump 131 to a mixing tank 133.

The installation also includes an enclosure 150 for aerobic composting. The enclosure can be a cylindrical or parallelepipedal and vertical silo, with a bottom, a lid and an envelope made of sheet metal, preferably stainless steel, or coated on the inside with a plastic film, which is preferably polypropylene. The enclosure has in its upper part admission means 148, 149 of volatile organic matter and waste and liquid digestate. This enclosure comprises a first zone 152 in which the thermophilic phase 1021 takes place, and a second zone 154 in which the mesophilic phase 1022 takes place. In one embodiment, said first zone 152 is located in the upper part of the enclosure 150 and the second zone 154 in the lower part of the enclosure 150.

At least on the part corresponding to the first zone 152, the wall of the enclosure is surrounded by a heat exchanger, typically a coil 156, connected to a circuit in which circulates a heat transfer fluid, which is typically water. At the bottom of the enclosure are means 158,159 for outputting the humic percolates and compost to an intermediate tank 160. The transfer to the anaerobic digestion unit 110 will be described in greater detail below. A more detailed description is given here of certain important aspects of the invention, so that those skilled in the art can implement the objects of the invention.

1. Adding raw compost and composting percolates to the anaerobic digester

The harvest of raw compost and raw composting percolates is carried out during the co-composting of the digestates resulting from a complete cycle of the methane digester within a composting silo, according to methods known as such, for example like this described in WO 2017/109398. Raw composts are particularly rich in digestible carbon and in simple, non-saturating nitrogen compounds, compatible with the nutrient demand of anaerobic bacteria. Percolates rich in humic acids, tannins, carbonaceous colloids result from the liquid/solid phase separation of digestates mixed with ground ligneous or cellulosic materials (the composting substrate) subjected to intense and thermophilic then mesophilic reactions of bacterial bio-oxidation. Although containing only very little dry matter, typically around 2% to 4% by mass, it is known that these percolates contain biochemical mediators and co-enzymes suitable for intensifying anaerobic bacterial activity by promoting in particular cell growth.

It is important to emphasize the stable quality over time of the composts and humic percolates which are produced in just-in-time flows at the same rate as that of the upstream biodigestion process. The additions of composting products to the digester tanks are therefore regular with dosages that are easy to perform.

According to the invention, the doses of compost and raw percolates are injected in three modes. They are first injected at the start of the methane digestion process to replace other carbonaceous additions and dilution water. It is also advantageous to integrate them into the feed dose of the digester subjected to a thermal pretreatment if such a thermal treatment is practiced. Finally, it is possible and profitable to inject them in an appropriate manner into each of the three digester tanks according to data provided by biochemical index sensors (Eh, pH, biogas production and biogas composition, total alkalinity, total carbon) ; in fact, during the anaerobic digestion process on the basis of biochemical indices the injection of compost and raw percolates has a particularly high impact in multiphase processes because the injection of these carbonaceous and humic compounds is carried out there in a much more targeted manner.

The additions thus obtained of digestible carbonaceous organic matter and of bacterial metabolism intensifiers in aqueous dilution not only make it possible to optimize the biochemistry of the process but also constitute one of the vectors of a circular economy which has the great advantage at the end of cycle to produce digestates transformed into highly recoverable compost as biofertilizers, without any of the disadvantages of spreading raw digestates, the negative impact on the environment of which is known.

Another positive consequence of this process is that the partial recycling of the liquid phase of the digestates percolated through the composting silo saves all of the dilution water requirements necessary for a non-inhibiting dosage of the volatile fraction which feeds the digester. while leaving available for agronomic use these particularly effective humic liquors after aerobic bubbling to regenerate soils and support their biotic activity.

2. Creating and maintaining a bioturbation zone in a digester tank

Its main objective is the intensification of biogenic and biochemical exchanges in the most turbid horizon which tends towards coalescent and solid sedimentation. Non-destructive positive displacement mixing, combined with a bubbling cycle by recirculation of desulfurized biogas and possibly enriched in hydrogen, prevents the solidification of the bottom sediments and allows the intensification of exchanges. Indeed, the movements of sediments do not occur to the detriment of the accretive structures built by assembling the exopolymers of biofilms resulting from bacterial activity on fixing bases or nodules. In the process according to the invention, the fixing nodules can be exogenous, that is to say introduced as artefacts into the tanks to promote the fixing of biomass, or even more favorably endogenous, that is to say generated as and as anaerobic digestion occurs due to the degradation of organic matter such as flesh still attached to bony structures or bones, digestible plant seed coats supported by a woody skeleton, nails, hairs and other rich organic compounds into polymers such as keratin.

In a continuous feed process it is necessary to prevent the excessive accumulation of endogenous fixing nodules; for this reason we prefer to carry out this operation by pumping on the critical lower horizon by regularly extracting doses that do not jeopardize the fixing functionality of this horizon.

We always observe a sedimentation of indigestible residues rich in calcium or keratin, moreover the contribution of raw compost still structured in partially digestible fibers is either absolutely necessary in the case of substrate poor in endogenous fixing nodules or recommended to enrich the base fixing. Be that as it may, the formation of a biofilm anchored on these fibrous or calcified particles which brings together in a holistic densitometric horizon a wide variety of bacterial colonies forms a complex ecosystem which not only provides resistance to disturbances (trophic or physical) of the environment but above all allows an organization in a trophic chain with dynamics of very active exchanges, starting from activated sediments and traversing the whole of the column of substrates in dilution.

It should be emphasized that when the calcium nodules are maintained in the deep sedimentary horizon, the solid fibrous materials from the raw compost, which have a lower density, are maintained in the upward flow within the tank in the presence of the solutes of dilution and metabolic intensification, the composting percolates being close to the density of water are indeed present in the entire volume of the tank while the denser mineral co-enzymes will migrate rapidly to the bottom of the tank.

To promote this dynamic of bioturbation in the sedimentary horizon and in the upper layers of the flow of materials, the reactor according to the invention can comprise a system of convergent hydraulic deflectors. Advantageously, these deflectors are positioned at two specific heights in the anaerobic digestion tanks, ie at approximately the lower third and at mid-height of the tank. The deflectors can be made in the form of simple plates of rigid plastic, ideally in polypropylene 3 mm thick, fixed to bars crossing the tanks laterally (these bars acting as rigidity tie rods). The plates or deflectors function as directional flaps placed facing each other in symmetrical opposition with a distance between the upper edges of the flaps which is preferably not less than 300 mm. Advantageously, the inclination of the flaps respects an angle of between approximately 20° and approximately 45°, and preferably of approximately 30° on the lower flaps, and between 40° and 60°, and preferably of approximately 50° on the upper flaps; the angle can vary in opening or closing depending on the turbidity of the substrate in the tank as well as the gap between the upper edges of the flaps.

This system of deflectors promotes an upward flow dynamic in the center of the tanks by channeling the rise of sediments in the form of a current with particles carried as generated by bubbling.

3. Details on certain aspects of the device according to the invention

Among the means mobilized to qualify the invention, the coupling with a composting unit and the mixing and heating equipment by submerged flexible tanks can be distinguished. Practical embodiments of these aspects are indicated here.

Regarding coupling with a composting unit:

According to one embodiment, a digestate transfer path to the composting unit consists of a digestate degassing tank 130, a viscous fluid pump 131 with a high total solids content, a pipe 132 of a sufficient diameter (at least DN80) having a purge device, a mixing tank 133 which receives the digestates on a sufficient dose of crushed structuring ligneous waste.

According to one embodiment, a route for transporting composting percolates consists of a raw percolates containment tank 160 connected to a slurry pump 161, a pipe 134 connecting said pump 161 to the pretreatment tank thermal 184 where organic matter 1080/1081; 1051/1052 entering the digester 110 are preheated 1120 (advantageously after grinding 1081/1052), a device 135 for measuring the volume of percolate transferred, and at least one valve 136 which can be a manually operated valve or an automated solenoid valve.

A heat exchange device can consist of an isothermal wall supporting a network of water pipes and whose contact face for heat transfer will be fixed to the metal walls of a composting silo in the thermophilic zone. The circulation of water with a demand at 40°C can be regulated by thermosiphon with a gradient of the order of 25°C. With regard to mixing and heating equipment using submerged flexible tanks:

According to one embodiment, a device for heating water or a heat transfer fluid consists of a water bath heating tank, a boiler powered by biomethane or biogas, a solar thermal station or PV and thermal combination, a passive heat recovery system on the walls of a composting silo in a thermophilic zone, or the assembly of all or part of these means.

Such a device also advantageously comprises a pump capable of moving hot water up to 60°C with a setting adapted to the configuration of flexible tanks on the following basis (without inferring pressure drops). This setting is described by two parameters:

The first parameter is the nominal flow rate of the pump Dp=(Vi-Vm)/T, expressed in m ³ /h; in this equation Vi is the intermediate volume of a flexible tank, Vm is the minimum volume of a flexible tank and T the time (expressed in hours) taken to pass from state Vm to state Vi.

The second parameter is the nominal operating pressure that the pump must deliver Pp=((cf.Hs)/10).1.25, expressed in bar (10 m of water column) with a prudence factor of 1, 25; in this equation d is the bulk density of the digestates, and Hs the height of the column of digestates above the surface of the bladders at stage Vm.

Such a device also advantageously comprises a digital transmission flowmeter and a thermal regulation device by thermocouple or a programmable automaton system connected to one or more temperature sensors and to a digital transmission flowmeter which controls the power supply of the pump and solenoid valves.

Such a device also comprises hydraulic connections through sealed walls making it possible to connect the flexible inlet and outlet pipes of the heat transfer flow of the submerged flexible tanks with the exterior of the digester. He understands also connections suitable for waterproof and durable fixing of heat transfer flow pipes on submerged flexible tanks.

Such a device includes, as already mentioned, flexible tanks. The latter allow the perfect containment of hot water at 60°C or of a heat transfer stream with aggressiveness parameters equivalent to or less than hot water and resistance to chemical and mechanical attack from hot water. or a heat transfer fluid. They must withstand a certain water column pressure, which is typically a maximum of 8 meters (0.8 bar) with a minimum, intermediate or maximum filling. They must be resistant, at least on their outer face, to chemical and mechanical attack from the digestates.

A system for fixing said flexible tanks at the bottom of the tank allows both their deployment for the different filling phases, and prevents the interference of digestates between the bottom of the tank and the tank.

Advantageously, a system for fixing flexible tanks submerged in the walls of the tank completes the main device for flexible tanks submerged in the bottom of the tank.

The device according to the invention may comprise auxiliary means which facilitate its use or which make it more versatile.

Thus, it may include a system for grinding incoming waste and substrates to reduce their relative size in a particle size preferably not exceeding 25 mm. This system can take the form of a slow double-shaft knife mill served by a loading hopper ensuring the protection of the operator.

It can also include a preheating and mixing system can be made in the form of a water bath or any other equivalent device loaded by gravity with organic substrates and raw compost from the grinder and receiving the dilution liquid consisting of percolates.

It can also include a lift pump accepting highly turbid flows with a maximum particle size of 35 mm is provided to supply the bioreactor in the upper part. It can also include a network of sensors capable of and configured to measure, in real or slightly delayed time, the values of temperature, pH, turbidity of the digestates during the different phases, chemical composition, temperature and relative humidity of biogas and purified biomethane.

In one embodiment, the installation according to the invention comprises a plurality of sensors configured to deliver data, installed in the enclosures of the anaerobic digestion unit, and in that said installation is configured to operate in real time and at each stage of the anaerobic digestion process said data to inject determined quantities of humic percolates.

It is also possible to provide a set of several programmable industrial automatons configured to process the signals received from the sensors, analyze the behavior of effectors and report the state of the system to a remote control station.

It is also possible to provide a network of effectors such as hydraulic or pneumatic solenoid valves which can regulate the circulation of the flows of substrates, digestates, eluates; these devices are controlled by programmable logic controllers or directly by the human operator.

We can provide one or more tanks acting as bioreactors to house the different phases of the biodigestion with the means of introduction and evacuation of the treated materials.

A digestate degassing system can be provided at the end of the methane digestion cycle. This system can be a simple gas-tight settling chamber with or without specific mixing devices.

In one embodiment, the installation according to the invention is configured to recirculate the percolates recovered in the lower part of a composting enclosure in said composting enclosure in order to maintain the relative humidity level necessary for the composting phases, and for settling and possibly stabilizing the humic percolates by air bubbling before their recovery or reinjection into the methane digestion enclosure. One or more biogas treatment devices can be provided. As such, a biogas filtration device can be provided, with the function of separating and treating CO2 and CH ₄ , and which can take the form of a solubilization cell with water, solvents, reagents, filters osmotic devices or any other equivalent device. It is also possible to provide a device for dehumidifying the biogas to extract the H2O water by condensation. A biogas filtration device can be provided to separate and treat hydrogen sulphide (H ₂ S), siloxanes and nitrogen oxides; this filtration device can take the form of a capture cell by biological means, activated carbon, or any other equivalent device.

The dimensioning of the installation according to the invention can be adapted to the needs of a site, within fairly broad limits.

Claims

1. Continuous process for the treatment of organic waste taking place in an installation, said process for treating organic waste comprising a process for the anaerobic digestion of a first part of said waste, which takes place in at least one digestion chamber, and a process aerobic composting of a second part of said waste which takes place in at least one composting enclosure, in which process for treating organic waste: at the end of said anaerobic digestion process, digestate and biogas are collected, At the end of said process for aerobic composting of the compost and the humic percolates, introducing at least a part of said digestate into said aerobic composting process, introducing at least a part of said humic percolate into said anaerobic digestion process.

2. Process according to claim 1, in which a part of said humic percolate is introduced into said aerobic composting process.

3. Method according to claim 1 or 2, characterized in that: said first part of said organic waste mainly comprises volatile organic waste, selected from the group formed by: slaughterhouse waste, dairy waste, winemaking waste , fish processing waste, meat processing waste, stable livestock waste, kitchen and table waste, organic waste from agro-food industries, and/or in that said second part of said organic waste mainly comprises structuring organic waste, mainly comprising organic polymers of the lignin, cellulose, hemicellulose and/or keratin type, and/or in that said second part of said organic waste mainly comprises waste selected from the group formed by : sawing waste (such as sawdust or sawmill wood waste), forestry waste shredded waste or shredded wood products, brown cardboard, shredded plants of various origins such as pruning, clearing, collection of dead leaves, various agricultural waste such as straw.

4. Method according to any one of claims 1 to 3, characterized in that said aerobic composting process takes place in at least one composting enclosure provided with a first heat exchanger through which said composting enclosure heats a heat transfer fluid at a first temperature, and/or in that said aerobic digestion process takes place in at least one digestion chamber provided with a second heat exchanger through which said at least one digestion chamber is heated by said heat transfer liquid located at a second temperature, lower than said first temperature.

5. Method according to any one of claims 1 to 4, characterized in that said first part of said organic waste is subjected to a thermal pretreatment in a thermal pretreatment enclosure, at a temperature above 45 ° C, and preferably between between 50°C and 80°C, before being cooled and admitted into said anaerobic digestion chamber, said thermal pretreatment chamber being preferably provided with a third heat exchanger.

6. Method according to claim 5, characterized in that at least a portion of said heat transfer fluid heated by said first heat exchanger is led into said second heat exchanger.

7. Method according to any one of claims 1 to 6, characterized in that said biogas, preferably after at least one purification step, supplies fuel to a burner provided with a fourth heat exchanger which heats a heat transfer liquid, which is in thermal communication with said second heat exchanger and/or said third heat exchanger.

8. Method according to any one of claims 1 to 7, characterized in that said burner is in energy communication with an electrical energy generator, which preferably supplies electrical energy to at least part of said installation.

9. Installation configured to perform the method according to any one of claims 1 to 8, comprising: an anaerobic digestion unit (110) for the treatment of the said first part of the organic waste, comprising successively a first chamber (120) intended for the progress of the hydrolysis and the acidogenesis, a second chamber (122) intended for the progress of acetogenesis, a third enclosure (124) intended for the progress of methanogenesis, and a fourth enclosure (130) intended for degassing, said four enclosures (120,122,124,130) being successively in fluidic connection to allow the transfer of treated waste from a enclosure to the next, said anaerobic digestion unit (110) being configured to produce essentially digestate and biogas; a composting chamber (150) intended for carrying out the aerobic composting of said second part of the organic waste, configured to produce essentially compost and humic percolates; means for transferring said digestate from said degassing enclosure (130) to said aerobic composting unit (150); means for transferring said compost and said percolates to said anaerobic digestion unit (110).

10. Installation according to claim 9, characterized in that it comprises means for transferring said humic percolate into said composting enclosure.

11. Installation according to claim 9 or 10, characterized in that it comprises a thermal pretreatment enclosure (184) arranged upstream of said anaerobic digestion unit (110) so that said first part of the organic waste intended for entering said anaerobic digestion unit (110) passes through said thermal pretreatment enclosure (184).

12. Installation according to any one of claims 9 to 11, characterized in that: at least one of said enclosures of said anaerobic digestion unit is heated using a heat transfer liquid; said thermal pretreatment chamber is heated using a heat transfer liquid; said aerobic composting enclosure is cooled by a heat transfer liquid; the heat recovered from said aerobic composting enclosure is used to heat at least one of said enclosures of said anaerobic digestion unit and/or said thermal pretreatment enclosure is heated using a heat transfer liquid.

13. Installation according to claim 11 or 12, characterized in that it comprises a burner configured to burn the energy fraction of the biogas produced by said anaerobic digestion chamber, said burner being configured to heat a heat transfer fluid which is in thermal communication with at least one of said enclosures of said anaerobic digestion unit and/or with said thermal pretreatment enclosure.

14. Installation according to claim 13, characterized in that said burner is associated with an electrical energy generating device, and preferably configured so that said electrical energy generating device can supply said installation with electrical energy, for some or all of its needs.

15. Installation according to any one of claims 9 to 14, characterized in that it comprises a plurality of sensors configured to deliver data, installed in the enclosures of the anaerobic digestion unit, and in that said installation is configured to use said data in real time and at each stage of the anaerobic digestion process to inject determined quantities of humic percolates.

16. Installation according to claim 15, characterized in that it is configured to recirculate the percolates recovered in the lower part of a composting enclosure in said composting enclosure in order to maintain the relative humidity level necessary for the composting phases, and for settling and possibly stabilizing the humic percolates by air bubbling before their recovery or reinjection into the methane digestion enclosure.