EP2190791A2

EP2190791A2 - Method for continuous processing of solid organic products and installation for continuous processing of solid organic products

Info

Publication number: EP2190791A2
Application number: EP08836087A
Authority: EP
Inventors: Pierre Buffiere; Sylvain Frederic; Damien Delhomme
Original assignee: Naskeo Environnement; Institut National de la Recherche Agronomique INRA
Current assignee: Naskeo Environnement; Institut National de la Recherche Agronomique INRA
Priority date: 2007-09-11
Filing date: 2008-09-10
Publication date: 2010-06-02
Also published as: WO2009044076A3; WO2009044076A2; FR2920761A1; FR2920761B1; TN2010000083A1

Abstract

The invention relates to a method for continuous processing of solid organic products in a hydrolysis reactor (10). Said method provides for a modification of the residence time (TSL) for liquids in the hydrolysis reactor, independently of the residence time for the solid organic products(TSS) which itself can be modified such as to optimise the process as a function of a desired degradation degree for the solid organic products (?). The invention also relates to an installation for the continuous processing of solid organic products.

Description

PROCESS FOR CONTINUOUS PROCESSING OF SOLID ORGANIC PRODUCTS AND INSTALLATION FOR CONTINUOUS PROCESSING OF SOLID ORGANIC PRODUCTS

Field of the invention

The invention relates to a process for the continuous treatment of solid organic products in a hydrolysis reactor. More specifically, the invention relates to a process for the continuous treatment of solid organic products in which the residence time of the solids and the residence time of the liquids in the hydrolysis reactor are controlled and can be dissociated so as to optimize the treatment. solids. Controlled means that their values are chosen accurately by the user and are adjustable according to the needs. The invention also relates to a treatment plant for the continuous treatment of solid organic products. The invention has applications in any industry generating organic products, including food industries.

State of the art

Anaerobic digestion has been used for a very long time for the transformation of organic waste, soluble or solid, into biogas. This technique is applied to the depollution of polluting loads, such as urban or industrial waste water loaded with biodegradable organic matter, or organic products in solid form, such as sewage sludge, household waste, biowaste, waste from agro-food industries, waste from different agricultural or forestry activities, energy crops.

Methanation is a complex biological process, involving several stages of decomposition of organic matter, including: hydrolysis, in which macromolecules are transformed into low molecular weight molecules and soluble; acidogenesis, in which low molecular weight molecules are converted to short chain organic acids, alcohols, hydrogen and other simple compounds; acetogenesis, in which the alcohols and organic acids are converted into acetic acid; methanogenesis, during which methane is formed, either from hydrogen or from acetic acid. The treatment of solid charges by methanation requires, when carried out in a single step, a particularly long time. This is why it is known to carry out a treatment in two stages: on the one hand, hydrolysis and acidogenesis, which can rarely be dissociated, and, on the other hand, acetogenesis and methanogenesis, which can not be separated.

The first reaction step is the solid organic products processing step itself, the second step corresponding to the treatment of the liquid phase recovered at the end of the first treatment stage. The solid organic processing stage is characterized by the production of organic acids and is generally accompanied by a decrease in the alkalinity of the medium and a decrease in pH if the medium is not sufficiently buffered. Thus, the decrease in pH and the accumulation of organic acids result in a decrease in the overall biochemical activity of the system, such as enzymatic hydrolysis activity and acidogenic activity. In the second stage, acid methanation often leads to a rise in alkalinity, since these acids are consumed to be converted into methane. Also, it is interesting to introduce a fraction of the liquid phase from the second stage of the treatment into the solids treatment tank in order to drain and evacuate the acid soluble molecules.

Currently, to optimize the treatment of solid organic products, it is known to perform a hydrolysis pretreatment, to make a massive intake of microorganisms, to promote contact between microorganisms and decaying solid organic products, or to promote drainage and evacuation of potentially inhibitory soluble compounds to the methanogenic stage.

However, current processing methods do not allow satisfactory and continuous treatment of solid organic products. It is most often necessary, at the end of the treatment, to empty the solids treatment tank to fill it with a fresh mass of solid organic products before starting the process again. Conversely, a continuous treatment makes it possible to continuously feed the solids processing tank with fresh mass to be treated and to simultaneously discharge the treated mass from said tank. This has the main advantage, at the industrial level, of not having a storage tank in which accumulate solid organic products awaiting treatment. Furthermore, it is not necessary to regularly interrupt the entire process line to empty the tank and reset the process.

Presentation of the invention

In the invention, it is sought to provide a treatment process capable of continuously treating solid organic products, the treatment being able to be modulated according to the nature of the solid organic products to be treated and the degradation rate of the desired solid organic products. The rate of degradation of solid organic products can be fixed in particular according to its final destination, the law etc.

For this, the invention proposes dissociating the residence times of the liquid and solid phases in the solids processing reactor, so as to be able to modulate them independently of one another in order to optimize the treatment. Indeed, the solids processing times are much longer than those of liquid discharges. Thus, at the outlet of the solid-state treatment reactor, the liquid phase is separated from the solid phase. The solid phase is at least partially recycled to the solid-state treatment reactor, which makes it possible to increase the residence time of the solids. The liquid phase can be fed to a liquid treatment reactor to undergo anaerobic degradation of the dissolved organic compounds. In order to modulate the residence time of the liquids in the solids processing reactor, provision is made to introduce into said tank treated liquid, that is to say one which has undergone a methanization during which the acidified organic compounds are degraded. By modulating the residence time of solids, we play on the degradation rate of said solids, while by modulating the residence time of liquids, we play on the rate of hydrolysis of solid organic products by allowing a rapid evacuation of molecules potentially inhibitory effects of hydrolysis. Advantageously, it is possible to provide, in parallel with the treatment of the products organic solids, to treat liquid discharges in a liquid discharge treatment tank. Liquid discharges are directly subjected to anaerobic digestion. The treated liquid resulting from this treatment can be partly introduced into the solids treatment tank to modulate the residence time of the liquids. Thus, in the case where a user produces solid waste and liquid waste, he can simultaneously and simultaneously process in the same place both types of waste, the interconnection between the two tanks making it possible to optimize the treatment of the products. solid organic. In all cases, it is possible to provide a liquid waste treatment tank, in which at least the liquid phase recovered at the outlet of the solids treatment tank can be treated. The liquid treated at the outlet of the liquid waste treatment tank is characterized by a low content of residual organic pollution and a high alkalinity. Feeding the solids treatment tank treated liquid, through which said liquid will percolate or be mixed, allows to evacuate the solubilized elements from hydrolysis and acidogenesis. In addition to the evacuation of these compounds, the high alkalinity of the treated liquid makes it possible to counteract the drop in alkalinity due to acidogenesis within the mass of solids, which makes it possible to maintain the solubilization and acidogenesis rate of said solids. solid at a high level. It is thus possible to regulate the alkalinity in the solids treatment tank by controlling the treated liquid recycling rate to the alkalinity level at the outlet of the tank. It is also possible to add alkaline compounds to the treated liquid reinjected. The liquid that has passed through the solids treatment tank is then loaded into soluble molecules derived from acidogenesis and is returned to the anaerobic treatment tank of the liquid discharges.

The subject of the invention is therefore a process for the continuous treatment of solid organic products in which solid organic products are treated in a hydrolysis reactor, characterized in that a fraction of treated liquid is introduced into the hydrolysis reactor. in order to modify the liquid residence time in the hydrolysis reactor and

a fraction of treated solids leaving the hydrolysis reactor is reintroduced into said hydrolysis reactor, so as to modify the time of residence of the solid organic products in the hydrolysis reactor according to a desired degradation rate of the solid organic products.

Solid organic products are all types of waste that can undergo hydrolysis and acidogenesis. The solid organic products may comprise biodegradable solid organic material and / or biodegradable soluble material.

By hydrolysis reactor, or solids processing tank is meant a reactor in which the solid organic products undergo hydrolysis and / or acidogenesis so as to be at least partially degraded to alcohols and organic acids.

The treated liquid fraction is acetogenized liquid and / or methanogenesis so as to no longer contain organic alcohols or acids, or negligible amounts.

The liquid residence time, or hydraulic residence time, is the time spent by the liquid phase in the hydrolysis reactor. By adjusting the liquid residence time, the hydrolysis rate of the solid organic products is modulated in the hydrolysis reactor.

The residence time of the solid organic products is the time spent by the solid phase in the hydrolysis reactor. By adjusting the solid residence time, the degradation rate, that is, the degree of treatment of solid organic products, can be varied as needed.

Solids treated means the solid phase resulting from the phase separation at the outlet of the hydrolysis reactor.

The treated liquid fraction can be recovered at the outlet of a methanation reactor in which the liquid phase leaving the hydrolysis reactor, and / or a liquid effluent, is treated.

In order to adapt the treatment process to the waste to be treated and to the desired degradation rate, it is possible to provide all or part of the following additional steps: - The content of biodegradable solid organic matter and soluble organic matter biodegradable products is characterized solid organics to be treated, and the content of proteins, sugars, greases and fibers in said biodegradable solid organic material and in said biodegradable soluble organic matter is determined so as to adapt the hydrolysis constant in the hydrolysis reactor features solid organic products to be treated. By characteristics of the solid organic products to be treated is meant the content of biodegradable solid organic matter and biodegradable soluble organic matter as well as the content of proteins, sugars, fats and fibers of each of them. The working concentration of solid biodegradable organic material and the working concentration of soluble biodegradable organic matter in the hydrolysis reactor are set according to the nature of the solid organic products to be treated. The organic matter concentration refers to the average concentration in the hydrolysis reactor, in kilograms of organic matter per kilogram of solid organic products (kgMO / kg).

Solid organic products are by nature the content of biodegradable solid organic matter and biodegradable soluble organic matter. Advantageously, the working concentration of solid biodegradable organic material is between 0.005 and 0.3 kgMO / kg, so as to have a good compromise between the effectiveness of the biological reaction and the ease of pumping and stirring of the medium. The working concentration is also a function of the input concentration of the waste to be treated. Preferably, the working concentration of soluble organic biodegradable material is low compared to the working concentration of solid organic biodegradable material, and in particular less than 0.005 kg of MO per kg of reactor so that there is no too many molecules inhibiting the hydrolysis reaction in the hydrolysis reactor. The dimensions of the hydrolysis reactor and the fraction of treated solids to be reintroduced into said hydrolysis reactor are determined as a function of the biodegradable solid organic matter content of the solid organic products to be treated and of their protein content, of sugars, in fat and fiber, the content of biodegradable soluble organic matter of the solid organic products to be treated and their content of proteins, sugars, fats and fibers, the hydrolysis constant in the hydrolysis reactor, the solid biodegradable organic material working concentration, the soluble biodegradable organic material working concentration, and the degree of hydrolysis of the desired biodegradable material. The fraction of treated liquid to be reintroduced into the hydrolysis reactor as a function of the content of biodegradable soluble organic matter of the solid organic products to be treated is determined from the working concentration of soluble organic matter that is soluble in the hydrolysis reactor, the biodegradable solid organic matter content of the solid organic products to be treated, the feed rate of the solid organic products to be treated in the hydrolysis reactor, and the degree of hydrolysis of the desired biodegradable material.

The invention also relates to an installation for the continuous treatment of solid organic products comprising

a hydrolysis reactor;

a feed pipe for solid organic products able to supply the hydrolysis reactor continuously with solid organic products to be treated;

- Phase separation means capable of separating a liquid phase from a solid phase at the output of the hydrolysis reactor;

controlled reinjection means of a fraction of the solid phase in the hydrolysis reactor;

- Controlled supply means of the hydrolysis reactor treated liquid. By controlled means that the treated liquid supply as the reinjection of a fraction of the solid phase is at a desired rate, which can be changed at any time according to the needs.

The installation according to the invention may also comprise

an anaerobic digestion reactor; a liquid waste inlet conduit capable of supplying the methanisation reactor with liquid waste to be treated;

controlled re-injection means of a treated liquid fraction leaving the methanation reactor in the hydrolysis reactor.

Advantageously, the plant according to the invention is used to implement the process for treating solid organic products according to the invention.

Brief description of the figures The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented as an indication and in no way limitative of the invention. The figures represent:

- Figure 1: Graph showing the comparative evolution of the amount of organic material remaining in hydrolysis reactors, expressed as a percentage of the amount of initial organic material, as a function of time for different liquid residence times;

FIG. 2: Graph showing the comparative evolution of pH over time in hydrolysis reactors for different liquid residence times;

FIG. 3: Graph showing the comparative evolution of the amount of total volatile fatty acids measured in the hydrolysis reactors as a function of time for different liquid residence times;

FIG. 4: Graph showing the comparative evolution of the degradation of the organic matter over time as a function of the inoculum present in the hydrolysis reactor;

FIG. 5: Schematic representation of an example of an installation used to implement the treatment method according to the invention.

detailed description

I] Experiences

Firstly, the role of liquid residence time (TSL) and solid residence time (TSS) in the hydrolysis of solid organic products was investigated.

1- First experience: Interest in adjusting the TSL during the treatment of solid organic products

Three hydrolysis reactors of 10 liters were initially filled with 2 kg of solid organic waste, ie apple juice manufacturing waste. The volume of the reactors was then supplemented to 10 liters with water and an anaerobic inoculum, the amount of inoculum added in each reactor corresponding to 1 liter to 50 g / l of volatile materials.

Recycling of the percolation water was carried out for the three reactors. Two reactors were fed with water having the characteristics of a water treated by anaerobic digestion, and in particular a high alkalinity, at TSL = I day and TSL = 2 days.

The third reactor was not fed with water from outside, so the TSL in this reactor can be considered infinite. In order to maintain the same hydraulic characteristics in the three reactors, the water percolating into the third reactor is constantly reintroduced.

Samples are taken regularly from each reactor to determine the mass and concentration of remaining waste (Figures 1 and 4).

Liquid phase samples are also taken from the reactors to measure the pH (Figure 2) and the characteristics of the effluent, including the concentration of volatile fatty acids (Figure 3), which are the products of acidogenesis potentially inhibitory.

There is a surprising gap in residual organic matter between the three reactors (Figure 1). The best performance is observed for the shortest hydraulic residence time. In particular at TSL = 1 day, more than 70% removal of organic matter is obtained after about three weeks of treatment. Conversely, the hydrolysis reactor operating in closed loop, that is to say having an infinite TSL, degrades at the same time as 42% of the organic material. The hydrolysis reactor having a TSL = 2 days has intermediate performance. This difference is also found at the pH level (Figure 2); the pH of the hydrolysis reactor operating in closed loop decreases to 4, while those of the other two hydrolysis reactors rise more or less rapidly over time, and up to 6.5 at three weeks of treatment for the hydrolysis reactor having a TSL = I days. There is also a significant difference in the concentration of volatile fatty acids. For an infinite TSL, the amount of volatile fatty acids reaches up to 6 gDCO / L while it remains relatively low, less than 2 gDCO / L, in hydrolysis reactors where the TSL is short.

The pH level and the amount of volatile fatty acids are a function of the liquid residence time used. In all three reactors, the performances initials are similar and it is only when volatile fatty acids and pH are differentiated that the degradation performance of organic matter diverges.

It therefore appears necessary to adjust the residence time with respect to the initial rate of degradation of the solid.

This experiment shows that the best degradation performance of solid organic products is a function, on the one hand, of the presence of a liquid stream having the properties of a water treated by anaerobic digestion, which makes it possible at the same time to trace the pH and to lower the concentration of volatile fatty acids, these two elements being clearly inhibitors of the hydrolysis reaction, and, on the other hand, the level of flow rate applied for this flow of liquid, the adjustment of which allows to improve the rate of hydrolysis. This experiment therefore shows the advantage of the dissociation of the liquid residence time and of the solid residence time in the solid-state treatment reactor, and the need to adapt the hydraulic residence time to the rate of degradation of the solids since the speed The degradation of solid organic products is equal to the rate of production of the molecules that inhibit the reaction.

2- Second experiment: The interest of adjusting the solid residence time during the treatment of solid organic products

In a second experiment, we tried to demonstrate the interest of dissociating the TSL and the TSS. For this, we set up two reactors each dealing with a mixture of solid organic products and liquid discharges. In the first reactor, the TSL and the TSS are both 2 days. In the second reactor, a liquid-solid separation at the outlet of the reactor makes it possible to adjust the TSS to 30 days, the TSL remaining the same as in the first reactor.

Both reactors operate with the same applied organic load, ie 2.5 kg of organic material introduced per cubic meter of reactor per day.

The experiment is conducted on two types of organic waste, one containing 50% solid organic matter and 50% dissolved organic matter, the other containing 100% solid organic matter diluted with water. Table 1 below shows the removal efficiencies of the organic matter, in percentage of degraded organic matter, in the two reactors during the two experiments, after 30 days of stabilized operation, that is to say during where performance is established and no longer changes over time.

Table 1: Solid organic matter removal efficiencies for two types of waste, with and without STL and TSS dissociation

10

It is found that even for a low charge favorable to the complete degradation of the organic matter, the dissociation of the TSL and the TSS makes it possible to improve the yield of degradation of the organic matter by nearly 10%.

More generally, it is found that it is advantageous to control the TSS, for example by means of a liquid / solid separation making it possible to choose the quantity of solids to be reintroduced into the reactor.

3- Third experiment: Low influence of inoculation

In a third step, the influence of the inoculation of the hydrolysis reactor by anaerobic biomass on the level of degradation of the solid organic products was tested.

For this, two hydrolysis reactors similar to those used in the first series of experiments are used.

The same amount of organic waste is introduced into the two hydrolysis reactors.

The first hydrolysis reactor is filled with anaerobic inoculum, ie digestate recovered from the first experiment, in a proportion representing about 10% of the organic matter of the introduced waste. The second hydrolysis reactor is not inoculated.

The two hydrolysis reactors have a liquid supply having the characteristics of a water treated by anaerobic digestion, but not containing biomass, with a TSL = 2 days.

Figure 4 shows the organic matter curves remaining in the two hydrolysis reactors, as a percentage of the amount of initial organic material, as a function of time.

It is found that the removal performance of the two reactors are quite similar, and that the presence of an anaerobic inoculum is, in this case, not of interest to accelerate the hydrolysis of the organic material.

Solid organic waste already contains its own inoculum, already having enzymatic systems suitable for hydrolysis. This result goes against many lessons indicating that continuous recycling of bacteria is the only beneficial phenomenon to improve the treatment of solids.

II] Example of Implementation of the Treatment Process According to the Invention In FIG. 5 is schematically represented a solid organic product processing line according to the invention, in which concomitantly, additional liquid discharges may be treaties.

More specifically, the installation comprises a hydrolysis reactor 10 capable of receiving solid organic products D ₀ to be treated. A methanation reactor 11 is able to treat liquids directly from liquid discharges D ₉ , and / or from the liquid phase D ₃ recovered at the outlet of the hydrolysis reactor.

The hydrolysis reactor 10 may be an anaerobic or aerobic digestion reactor. The methanation reactor 11 is an anaerobic digestion reactor.

A separator 12 collects a mass of waste D at least partially treated at the outlet of the hydrolysis reactor 10, so as to separate the liquid phase D ₃ from the solid phase D ₂ . The liquid phase D ₃ is conveyed towards the methanation reactor 11, where it is treated at the same time as liquid discharges. Of course, the liquid phase D ₃ can be treated in another methanation reactor. The solid phase D2 may be wholly or partly conveyed out of the treatment chain. According to the invention, the installation comprises means 13 for reinjecting a fraction of treated solids D ₅ into the hydrolysis reactor 10. The reinjection means 13 comprise a channel capable of conveying the fraction of treated solids D ₅ from an evacuation pipe of the solid phase 14 in the hydrolysis reactor 10, or directly from the separator 12. The reinjection means also comprise flow control means adapted to modulate the feed rate of treated solids D ₅ as needed. Adjusting the treated solids streams D ₄ , D ₅ makes it possible to adjust the TSS in the solids processing reactor.

The treated liquid D ₆ at the outlet of the methanation reactor 11 is characterized by a low content of residual organic pollution and a high alkalinity, due to the different biochemical reactions that have taken place during the transformation into methane of the soluble organic compounds. A treated liquid fraction D ₈ from the treated liquid D ₆ from the methanation reactor is used to supply the hydrolysis reactor 10, through which it will percolate or be mixed, and cause the solubilized elements resulting from the hydrolysis and acidogenesis. The remainder of the treated liquid phase D ₇ is discharged out of the treatment system. For this, the plant for the treatment of solid organic products according to the invention comprises controlled reinjection means 16 of a treated liquid fraction D ₈ capable of bringing said fraction D ₈ from an evacuation pipe 15 of the treated liquid to the hydrolysis reactor 10, or directly from the methanation reactor 11. The reinjection means 16 also comprise flow control means adapted to modulate the feed rate of the fraction of treated liquids D ₈ , that is, to say the flow, according to the needs. Adjusting the treated liquid flows D _7, D ₈ makes it possible to adjust the TSL in the solid-state treatment reactor 10.

The use of a solid / liquid separator 12, for example a centrifuge, makes it possible not only to control the TSS, but also to adjust, via the treated solid fraction reinjected D5, the dry matter content in the hydrolysis reactor. 10, dry matter among which found a high density of microorganisms, the concentration of which in the solids processing reactor favors the rate of biological reaction.

In another embodiment, it is possible not to provide separator 12 itself, while keeping the phase separation step. Indeed, in the case where the solid is sufficiently heterogeneous to form a layer through which the liquid can flow without causing solid, or percolate, the solid can be directly removed from the reactor by a suitable extraction system, such as an Archimedean screw pump or other, liquid being the percolation residue, or leachate leaving the hydrolysis reactor 10.

In the invention, an adjustable fraction of treated liquid Ds is reused to redilute or percolate through the mass of solid organic products contained in the hydrolysis reactor 10. The evacuation level of the soluble organic acid compounds is thus adjusted and Raises the pH in the hydrolysis reactor. The high alkalinity of the treated liquid fraction D ₈ makes it possible to counteract the drop in alkalinity due to acidogenesis within the mass of solid organic products, and thus to maintain the rate of solubilization and acidogenesis of said organic products. solid at a high level.

This method of treatment thus makes it possible, on the one hand, to treat liquid Dg and solid Do discharges together by anaerobic digestion, and to optimize the solids treatment phase by adjusting both the residence time of the solids and the time of residence of liquids. The liquid D ₃ having passed through the hydrolysis reactor 10 and recovered at the exit of the separator 12 is loaded with soluble molecules originating from the acidogenesis and is returned to the methanation reactor 11.

Advantageously, the liquid treatment reactor 11 is a high-load anaerobic digestion reactor, capable of tolerating a certain amount of suspended solids, and more particularly a fixed bed having a continuous declogging system such as that described in the application FR2885126.

In a particular embodiment of the treatment method according to the invention, it is possible to treat waste containing both suspended solids and liquids. In this case, the liquid and solid are separated by any known means so as to separate in two streams solids and liquids which are then treated according to the steps described above.

III] Parameterization Method of the Process for the Treatment of Solid Organic Products According to the Invention

In order to adapt the treatment process to the solid organic products to be treated, it is possible to specifically parameterize the hydrolysis reactor in particular to adjust the TSS and the TSL.

A method of parameterizing the characteristics of the installation according to the desired treatment objectives and the waste to be treated is proposed below, it being understood that it is not limiting. For this, reference is made to FIG.

1- Notations: D ₀ to D ₈ : mass flow rates (in kg / day)

Xo to Xs: concentration of biodegradable solid organic matter in streams 0 to 8 (in kgMO / kg);

X'o to X'β: concentration of inert solid (non-biodegradable) in streams 0 to 8 (in kg / kg); So at Ss: concentration of soluble organic matter in streams 0 to

8 (in kgMO / kg);

M _R : mass of the hydrolysis reactor (in kg); s: solids recycling rate in the hydrolysis reactor 10 (s = D ₅ / D ₂ ), t: separation efficiency of the solids in the separator, t = D ₂ X ₂ / DiXi, intrinsic property of the separator; c: D2 / D1 flux ratio, intrinsic property of the separator, p. : degradation yield on the biodegradable solid, dimensionless Rx: specific rate of solubilization of the biodegradable solid in the reactor (in kgX / kg of reactor / day)

2- Problematic:

Taking into account a given input mass flow Do and a given input concentration Xo, how to calculate the reactor size, that is to say the mass M _R , as well as the level of solid recycling, that is to say the treated solids fraction reinjected, to obtain a desired level of degradation p.

The solid residence time, TSS, is understood as the average time spent by an inert substance, that is to say non-biodegradable, of concentration X 'in the assembly comprising the hydrolysis reactor 10 and the separator 12. .

The TSS can be expressed as follows:

M _n X, ^'

TSS = - R ^yi ~ 1

D ₄ X ₄

Thus, for a stream of solid organic products to be treated entering D given and a given D ₈ treatment liquid feed rate, which will be a function of the waste and their degradation rate, the TSS depends on two parameters: the total mass of the reactor M _R and the fraction of treated solids recycled in the reactor 10, the parameters c and t being intrinsic properties of the separator 12.

It is sought to obtain degradation performance for solid organic products having given characteristics D ₀ , Xo, in a yield p fixed for example by the user according to the final destination of the waste to be treated in an installation comprising a separator having performances c, t data, the flow of treated liquid reinjected D ₈ being also fixed. For this, it is necessary to determine the dimensions of the reactor M _R and the fraction of treated solid to reinject in the hydrolysis reactor 10 to achieve the objectives.

Furthermore, a method is proposed below for jointly dimensioning the D ₈ flushing stream, associated with the residence time of the liquids, depending on the nature of the solid organic products to be treated and their rate of degradation. For this purpose, the system is characterized from a system of simple algebraic equations derived from the mass balances associated with the operation of the installation in continuous mode, as well as from the Expert knowledge acquired on the kinetics of hydrolysis and solubilization of biodegradable organic matter.

2.1- First equation: definition of the yield The yield p is defined as being the rate of reduction of organic solid between the entry and the exit, that is to say the flow of digestate D ₄ :

D ₀ X ₀ -D ₄ X ₄

D ₀ X ₀

Knowing that X4 = X ₅ = X2, and knowing the relations connecting the properties of the solid liquid separator, we also have: D ₄ = (I- ^ D ₁

X ₄ = X ₂ ⁼

VS

And so: p = l- {l- s) t ^DχXχ

D ₀ X ₀

Moreover, Di is known from the mass balance on the reactor:

D ₁ = D ₀ + D _& + D ₅ with D ₅ = ScD ₁

Therefore :

D ₁ {\ -S) IX ₁ p = l- 1 + - [Equation 1] D ₀ 1-sc X ₁

2.2- Second equation: mass balance on the biodegradable solid organic matter

The material balance on the biodegradable solid organic material is based on the non-accumulation of biodegradable organic material in the balance chamber, defined as the hydrolysis reactor; it is written as follows:

D ₀ X ₀ + D _% X _% + D ₅ X ₅ -D ₁ X ₁ = T _x M, Among the input terms, the term D ₈ Xs consists of the fraction of treated liquid reinjected from the methanation reactor 11. It is therefore possible to assume that this flow represents a negligible contribution of biodegradable solid organic matter by relative to the input streams D ₀ X ₀ and to the recycling stream D ₅ X ₅ representing the fraction of treated solid organic products reinjected into the hydrolysis reactor.

The balance sheet is therefore reduced to:

D ₀ X _{0 +} D ₅ X ₅ - D ₁ X ₁ = T _x M,

Moreover, it is known from numerous experimental studies, that the hydrolysis rate r _x is proportional to the concentration Xi of biodegradable organic material in the hydrolysis reactor 10. Moreover, it is known that the concentration of of a stirred reactor is equal to the concentration in said reactor. We can then write r _x = kX _λ k being the coefficient of proportionality, or kinetic constant, explained below.

Knowing the relation allowing to express X ₅ according to Xi (X ₅ = tXi / c), associated with the properties of the separator;

Knowing the relation that allows to express D ₅ according to D ₀ and

l - sc Knowing the relationship that expresses Di in terms of D ₀ and

_D ,: _A = .Vt-i l - sc The balance can therefore be written, after rearrangement:

M _R _ 1 D _{0 +} D, 1 - St

[Equation 2] k * 1 D ₀ 1 - SC

2.3- Third equation: assessment of the soluble phase

This equation makes it possible to account for the dilution effect associated with the treated liquid flow of the methanation reactor 11 reinjected into the hydrolysis reactor 10. If the material balance is written on the material solubilized organic, and assuming that the contribution of organic matter solubilized by the flow Ds is negligible, then we can write:

D ₀ S ₀ + D ₅ S ₅ - D _x S _x = -r _x M _R It is noted that the kinetic term is the opposite of the term of disappearance of solid organic matter, since all the solid biodegradable organic material which is hydrolysed is found in soluble form.

Knowing the relation between S ₅ and Si, namely S ₅ = Si; Knowing the relations allowing to express Di and D ₅ according to D ₀ and D ₈ ;

We can write :

D ₀ (S ₀ - S,) + kX, M _R Z) ₈ = - ^ - ^ - ^ι - - - [Equation 3]

The liquid residence time in the hydrolysis reactor 10 is given by: TSL = ^MR

D _n + A

3- Method of solving equations

The system consisting of Equations 1, 2 and 3 involves the following variables:

D ₀ , Xo, SO, t, c: are input data that do not vary; p is the treatment goal;

M _R , Ds and s: are the sizing parameters; Xi and Si: respectively are the working concentration of biodegradable solid organic material and soluble in the reactor, which must be adjusted to optimal values; k: is the hydrolysis constant, which depends on the nature of the solid organic products to be treated.

The sizing method therefore proposes: setting the desired working concentration Xi in the hydrolysis reactor; to deduce the Si concentration desirable in the hydrolysis reactor; to propose a value of k, which depends on the nature of the solid organic products to be treated; to complete the calculation by deducing M _R , D ₈ and s from equations 1, 2 and 3.

3.1- Value of Xi:

The value of Xi is set so as to obtain a good compromise between the efficiency of the biological reaction and the ease of pumping and stirring of the medium; this value also depends on the input nature of the solid organic products to be treated, if they are more or less concentrated.

The value chosen is between 0.005 and 0.3 kg of organic matter per kg of reactor, the value of 0.005 corresponding to the lower limit below which the efficiency of the biological reaction is low, and 0.3 corresponding to the upper limit above from which the pumping and mixing of the product are compromised.

3.2- Value of Si:

It is interesting to keep the value of Si as low as possible. In fact, a value that is too high can lead to rapid acidification of the fermentation medium and stop the hydrolysis reaction. It is relatively advantageous to use a proportionality criterion f between Xi and Si:

The value of f is chosen so that the concentration of soluble organic matter remains low in front of Xi: 0.001 </ <0.2

3.3- Value of k:

The kinetic constant k depends on the nature of the solid organic products to be treated. It is known that the hydrolysis constant of solid organic compounds varies depending on whether it is sugars, proteins or fats.

A method for fractionating organic waste material based on the determination of fat content has been developed. sugars, proteins and fibers (Buffière et al., 2005, Water Science and Technology, 53 (8) pages 233-241). Fractions obtained can be associated with kinetics of hydrolysis. The hydrolysis constants thus obtained are noted:

- k _s : hydrolysis constant associated with the degradation of sugars;

- k _P : hydrolysis constant associated with the degradation of proteins;

- k _G : hydrolysis constant associated with the degradation of fats;

- kF: hydrolysis constant associated with fiber degradation.

Thus, if the organic matter consists of a fraction of fs, fp, fol and ff, the hydrolysis constant associated with the degradation of organic matter as a whole can be calculated according to the formula next :

i F ⁿ F

Table 2 below shows, by way of example, the recommended values for the various hydrolysis constants at a temperature of 37.degree.

Table 2: Recommended values for hydrolysis constants (in j; -1)

3.4- Solving the sizing problem

The problem resolution procedure is as follows:

Characterize the incoming waste, in particular the content of biodegradable solid organic matter (Xo) and soluble biodegradable matter (So), and determine the fractions of proteins, sugars, fats and fibers as described in the state of the art (Buffer and coll., 2005, Water Science and Technology, 53 (8) pages 233-241); Choose, depending on the nature of the incoming waste, the values of Xi and Si which are optimal with respect to the desired treatment;

Calculate, from the data in Table 1, the kinetic constant of the process; - Solve the system of three equations with three unknowns consisting of equations 1, 2 and 3 in order to know M _R , D _S and s.

4- Example of application of the parameterization method

4.1- Input data

It is desired to treat solid organic products according to the following characteristics:

Flow of solid organic products to be treated: D ₀ = 1000 kg / day. Biodegradable solid organic material Xo = 0.2 kgMO / kg of waste, or solid organic products to be treated; consisting mainly of sugars (f _s = 0.8) and fibers (f _F = 0.2).

Biodegradable soluble organic material: So = 0.1 kgMO / kg of waste.

The separator used has the following characteristics: t = 1, that is to say that there is a total separation of the solid at the separator; c = 0.2 It is desired to obtain a biodegradable organic matter hydrolysis rate of 70% (ρ = 0.7).

4.2-Dimensioning: a- Choice of Xi: We choose the value of 0.05 kgMO / kg b- Choice of Si: Given the high sugar content and the risk of rapid inhibition associated, we take a low value for f = 0.1; c- Calculation of k: We take k _s = 0.18 and k _F = 0.03, which are values frequently encountered in the bibliography; he comes k = 0.15 j ^"1 .

Since t = 1, equations 1 and 2 can be combined to directly give the value of M _R : M- = P

^R X, k by reinjecting into equation 3: D ₈ = - ^ι - - ^ - ¹ D ₀

X, 1 - p

• s,

And for s s = Xo $ o + P ^ o

A_ _c »- P _{g |}

4.3- Results:

M _R = 18667 kg

D ₈ = 47000 kg / d

S = 0.98

TSL = 0.4 days TSS = I 5.6 days

Of course, it is possible to do otherwise to set according to the invention the plant for the treatment of solid organic products according to said waste to be treated. For example, it is possible to set the dimensions of the reactor and carry out two or three tests in which the TSL and / or the TSS are varied to get as close as possible to the desired yield.

PUBLICATIONS

- Z. Wang and CJ. Banks [2000], Accelerated hydrolysis and acidification of municipal solid waste in anaerobic flushing bio-reactor using treated leachate recirculation, Waste Management and Research, 18, 215-223;

- Wang, Z. and Banks, CJ. [2003] Evaluation of a two-stage anaerobic digester for the treatment of mixed abattoir wastes. Process Biochemistry. 38, 1267-1273.

- Buffière et al., 2005, Water Science and Technology, 53 (8) pages 233-241

- US 4,022,665 (Sambhunath Ghosh and garlic) "Two phaser anaerobic digestion" published May 10, 1977 - FR 2 324 581 (HITACHI) "Method and system for the anaerobic treatment of biochemical waste" published April 15, 1977

- GB 2013170 (Patrick Joseph Nawell et al.) "Anaerobic treatment of waste to produce methane" published August 8, 1979

EP 0 142 873 (GIST BROCCADES) "Process and apparatus for anaerobic fermentation of solid wastes in water in two phases" published on May 29, 1985

DE 40 00 834 (Eisenmann MaschienenbauKG) "Verfahren und Anlage zur Biomethanisierung von organischen Reststoffen" published on 13 January 1990 - EP 0 484 867 (ECOLMARE) "process for the utilization of organic wastes for producing biogas and agricultural products" published on 13 May 1992

US 4,396,402 (Sambhunath Ghosh) "Gas production by accelerated bioleaching of organic materials" published August 2, 1983 - NL8001997 published November 2, 1981

EP 0 152 730, (The Belgian State) "Process for the production of methane by anaerobic digestion of organic materials" published on May 13, 1987

- GB 2 230 004 (Ivor Pallett and Garlic) "Method for treating solid waste" published October 10, 1990 - FR 2 702 764 (GAZ DE France) "Process and installation for anaerobic fermentation of organic matter" published on September 23, 1994

EP 0 566 056 (REA GESELLSCHAFT) "Verfahren zur biologischen Aufbereitung organischer Substanzen, insbesondere zur anaeroben biologischen Hydrolysis zur anschliessenden Biomethanisierung, und Vorrichtung zur Durchfahrung des Verfahrens" published on October 20, 1993

- US 2006/0151004 (Yioshio Terada and garlic) "Cleaning sheet and method for cleaning substrate processing apparatus" published on July 13, 2006

- WO2006 / 048008 (BRANDENBURGISCHE TECHNISCHE UNIVERSITAT COTTBUS) "Method for decomposing biogenic material" published on November 3, 2005.

Claims

Process for the continuous treatment of solid organic products in which solid organic products are treated in a hydrolysis reactor (10), characterized in that

a fraction of treated liquid (D ₈ ) is introduced into the hydrolysis reactor so as to modify the liquid residence time (TSL) in the hydrolysis reactor and a treated fraction of treated solids (D ₅ ) is reintroduced of the hydrolysis reactor in said hydrolysis reactor, so as to modify the residence time of the solid organic products (TSS) in the hydrolysis reactor as a function of a desired degradation rate of the solid organic products (p). 2- Treatment process according to claim 1, characterized in that

a liquid phase (D ₃ ) leaving the hydrolysis reactor is treated in a methanation reactor, the fraction of treated liquid introduced into the hydrolysis reactor being at least partially withdrawn at the outlet of the methanation reactor.

3- treatment method according to one of claims 1 to 2, characterized in that

in parallel, liquid discharges (D ₉ ) introduced directly into a methanation reactor (11) are treated in parallel, the fraction of treated liquid introduced into the hydrolysis reactor being at least partially withdrawn from the methanation reactor.

4- Treatment method according to any one of the preceding claims, characterized in that

the content of biodegradable organic solid matter (Xo) and of biodegradable soluble organic matter (So) is characterized by the solid organic products to be treated, and

the content of proteins, sugars, fats and fibers in said biodegradable solid organic material and in said biodegradable soluble material is determined, in order to adapt the hydrolysis constant (k) in the hydrolysis reactor to the characteristics of the solid organic products to be treated.

5- Treatment method according to any one of the preceding claims, characterized in that - one sets the working concentration of solid organic biodegradable material (Xi) and the working concentration of soluble biodegradable organic material (Si) in the reactor of hydrolysis depending on the nature of the solid organic products to be treated.

6. Process according to claim 5, characterized in that the working concentration of solid organic biodegradable material (Xi) is between 0.005 and 3 kgMO / kg.

7- Method according to one of claims 5 to 6, characterized in that the working concentration of soluble organic biodegradable material (Si) is low compared to the working concentration of solid organic biodegradable material (Xi).

8- Treatment process according to one of claims 4 to 7, characterized in that

the dimensions (M _R ) of the hydrolysis reactor and the fraction of solids treated (s) to be reintroduced into said hydrolysis reactor are determined according to:

the content of biodegradable solid organic matter (Xo) of the solid organic products to be treated and their content of proteins, sugars, fats and fibers;

- the content of soluble biodegradable matter (So) of the solid organic products to be treated and their content of proteins, sugars, fats and fibers,

- the hydrolysis constant (k) in the hydrolysis reactor;

- working concentration of solid biodegradable organic matter (Xi); - working concentration of soluble organic biodegradable material (Si); and

the degree of hydrolysis of the desired biodegradable material.

9- Treatment process according to one of claims 4 to 8, characterized in that the fraction of treated liquid (D ₈ ) to be reintroduced into the hydrolysis reactor is determined as a function of:

the content of biodegradable soluble organic matter (So) of the solid organic products to be treated; the working concentration of soluble biodegradable organic material (Si) in the hydrolysis reactor;

the content of biodegradable solid organic matter (Xo) of the solid organic products to be treated;

the input flow rate of the solid organic products to be treated in the hydrolysis reactor, and

the degree of hydrolysis of the desired biodegradable material.

10- Installation for the continuous treatment of solid organic products comprising

a hydrolysis reactor (10); a feed pipe for solid organic products able to continuously supply the hydrolysis reactor with solid organic products;

- Phase separation means (12) capable of separating a liquid phase from a solid phase at the output of the hydrolysis reactor;

controlled reinjection means (13) for a fraction of the solid phase in the hydrolysis reactor

- Feeding means (16) controlled hydrolysis reactor treated liquid.

11- Installation according to claim 10, characterized in that it comprises - an anaerobic digestion reactor (11),

a liquid waste inlet pipe suitable for supplying the methanization reactor with liquid waste to be treated

- Controlled reinjection means (16) of a treated liquid fraction leaving the methanation reactor in the hydrolysis reactor. 12- Use of the installation according to one of claims 10 to 11, to implement the method according to one of claims 1 to 9.