WO1998051624A1

WO1998051624A1 - Aerobic biodegrading method and plant for lipid compositions

Info

Publication number: WO1998051624A1
Application number: PCT/FR1998/000902
Authority: WO
Inventors: Etienne Paul; Xavier Lefebvre
Original assignee: Biotrade
Priority date: 1997-05-09
Filing date: 1998-05-05
Publication date: 1998-11-19
Also published as: FR2763078A1; FR2763078B1; AU7659698A

Abstract

The invention concerns an aerobic biodegrading method for lipid compositions which consists in putting in a reactor (1) an amount of bacterial biomass, and sequentially supplying the reactor with the medium to be treated. If the amount of foam formed at the reaction medium surface exceeds a predetermined threshold, a regenerating step is carried out during which the reactor (1) is supplied with aqueous lipid medium so that the amount of foam is reduced to less than the threshold amount. The invention also concerns a plant for implementing the method.

Description

PROCESS AND PLANT FOR AEROBIC BIOLOGICAL DEGRADATION OF LIPID COMPOSITIONS

The invention relates to aerobic biological degradation of organic lipid compositions such as grease or fatty waste of animal or vegetable origin rejected by domestic or industrial installations. Such treatment of these lipid compositions can be incorporated in particular into a process for purifying waste water before discharge into the natural environment. It is known that organic fats can be degraded in an aqueous medium on contact with a bacterial biomass such as an activated sludge.

Thus, there is already known (cf. for example FR-2,669,916) an aerobic biological degradation process for fats in which fats are introduced into a tank of a sequential feed reactor, in the presence of activated sludge in an aqueous medium with air injection. The fats are introduced sequentially at intervals of 2 to 3 days with simultaneous removal, after decantation, of the supernatant from the medium treated in equivalent quantity.

Nevertheless, as indicated in the publication "OPTIMIZATION OF THE BIOLOGICAL TREATMENT OF FATS BY A CONTROLLED SEQUENTIAL FEEDING PROCESS", X. LEFEBNRE, E. PAUL, JIE 96, volume 2, pages 71-1; 71-10, 18-20 September 1996, POITIERS, such treatment of fatty residues poses the problem of too slow kinetics of biological degradation. In fact, an acceleration of biodegradation rates comes up against various physical limitations in practice: foaming, bioavailability of fats, oxygen transfer or heat production. This publication therefore recommends a prior saponification of fats and monitoring of the progress of the degradation reaction by detecting the concentration of dissolved oxygen.

However, despite the relatively high purifying performance announced in this publication, the elimination of fats (quantified by the measurement of extractable materials with hexane or MEH) is still incomplete, and we observe in practice the appearance, sometimes very brutal, of expansive foams. In addition, this foaming is favored by strong ventilation and by the use of saponified fats. This untimely foaming phenomenon is considered to be a malfunction for the development of industrial units.

Thus, FR-2 690 458 describes a process in which a prior saponification of the fats is carried out, and indicates that the development of the foams must be stabilized. To do this, this document recommends using intense agitation caused by a large air flow, considering that the phenomenon of expansive foaming would be linked to insufficient agitation. However, it is also rightly intended to incorporate an anti-foam product in the reaction medium.

However, it appears in practice that the use of such intense agitation does not make it possible to avoid with certainty the development of the foams. In addition, the incorporation of an anti-foam product is a source of impurities and is not economically compatible with industrial exploitation.

Consequently, we do not know how to avoid with certainty this phenomenon which remains a major obstacle to the development of industrial units with high yields. Furthermore, the online monitoring of dissolved oxygen recommended by the aforementioned publication does not allow optimal control of the reaction time since the kinetics of variation of the dissolved oxygen level is in fact linked to the importance of ventilation. Thus, if the aeration is too strong, the dissolved oxygen level can remain constant and close to saturation. If it is too low, the rise in the dissolved oxygen level will not be noticed until long after the actual end of fat breakdown.

The other solution envisaged so far for reactors with sequential feed consists in providing a residence time of the greases fixed in advance at a value large enough to ensure that the reaction is complete. This solution leads to very long treatment times important and is not satisfactory. Indeed, the fatty residues have a concentration of lipids and a composition very variable over time and according to the site, so that it is certain that this treatment duration, fixed independently of the actual duration of each reaction, is the more often too large. Consequently, this solution leads to low performance and productivity.

Thus, despite all the efforts made to date, industrial exploitation, under satisfactory economic and practical conditions, of aerobic biological degradation of organic lipid compositions comes up against the following antagonistic problems: (i) the foaming phenomena which appear inadvertently without being able to control, predict or avoid them, (ii) an improvement in the treatment kinetics and (iii) precise control of the reaction time, in particular when it is carried out under conditions high kinetics.

The invention therefore aims to solve these problems by proposing a method and an installation for aerobic biological degradation of organic lipid compositions such as fats and fatty wastes of animal or vegetable origin, thanks to which:

- one avoids without fail the dysfunctions linked to the untimely formation of foam, - one can implement operating conditions

(feeds, temperature, aeration, biological activity ...) allowing to obtain kinetics of degradation and improved purification efficiency.

The invention further aims to allow the residence time in the reactor to be managed optimally and automatically as a function of the actual reaction time.

The invention aims more particularly to propose such a method and such an installation which are furthermore extremely simple, reliable, and compatible with the constraints of exploitation on an industrial scale.

To do this, the invention relates to a method of aerobic biological degradation of organic lipid compositions such as waste fatty of animal or vegetable origin, in which a quantity of a bacterial biomass is placed in a reactor, the reactor is fed sequentially with an aqueous lipid medium containing the lipid compositions, added to the reactor (mixed with the aqueous lipid medium or separately) an appropriate amount of nitrogen and phosphorus amendment, air is introduced into the reaction medium, and the reactor is purged sequentially by extracting a quantity of liquid reaction products, and maintaining in the reactor a minimum quantity of reaction medium, characterized in that, if the quantity of foam exceeds a predetermined threshold quantity, a step, called regeneration step, is then carried out during which the reactor is supplied with an aqueous lipid medium containing lipid compositions at a concentration sufficient for there to be a minimum amount of this milie u aqueous lipid which can be introduced into the reactor for which the quantity of foam formed on the surface of the reaction medium, after introduction of this minimum quantity of aqueous lipid medium, becomes again below said threshold quantity, the quantity of aqueous lipid medium introduced into the reactor during this regeneration step being greater than or equal to this minimum quantity.

Whereas the appearance of foaming phenomena, in particular those of an expansive nature, was until now considered to be impossible to predict (or linked to the degree of aeration), and as a source of dysfunction incompatible with operation on a scale industrial, the invention makes it possible to control these foaming phenomena in an extremely simple manner.

Indeed, the inventors have demonstrated that: - lipid compositions, even in saponified form, have the property of preventing or suppressing any expansive foaming when they are used at a certain minimum concentration (the value of which depends in particular on the nature of the fats and the reaction parameters) and introduced in sufficient quantity into the reactor, - the appearance of expansive foaming is in fact linked to the decrease the fat concentration in the supernatant below a certain critical value (the value of which also depends on the nature of the fats and the reaction parameters) and is therefore characteristic of the almost total degradation of the fats in the medium, - it is possible, even under the most severe reaction conditions (very fast kinetics) to detect the appearance of expansive foaming, and to interrupt this expansive foaming and to make disappear most of the foam simply, by feeding to again the reactor with a sufficient quantity of lipid compositions, even when these are saponified. Thus, contrary to the immediate reflex which consisted in avoiding any new introduction of fats (all the more when these fats are saponified) when an expansive foaming was observed, the inventors have demonstrated that such foaming is not due to a excess of materials to be treated or of reaction parameters providing kinetics that are too rapid, but can on the contrary be simply absorbed by a new supply of lipid compositions. Therefore, thanks to the invention, the degradation reaction can be carried out under optimal kinetic conditions without fear of triggering an expansive untimely foaming.

Advantageously and according to the invention, the evolution of at least one parameter representative of the quantity of foam formed on the surface of the reaction medium is monitored so as to be able to detect any increase in this quantity of foam beyond said quantity of threshold, after which a regeneration step is carried out.

In an advantageous embodiment and according to the invention, as a representative parameter, the presence of foam is monitored opposite at least one foam presence detector fixed at a predetermined location of the reactor above the surface of the medium. reactive.

The simplest is to directly monitor the presence of the foam. As a variant, or in combination, it is nevertheless possible to monitor any other parameter which can be correlated with the appearance of foaming. expansive. Thus, in the case where the process can be implemented with good temporal reproducibility (the characteristics of the aqueous lipid medium to be treated remaining stable), nothing prevents, for example, from indirectly monitoring the appearance of expansive foaming, which will be repeated inevitably at regular time intervals, according to a time table, the duration between the regeneration steps then being fixed and predetermined.

Advantageously and according to the invention, the reactor is a tank adapted to be able to contain a maximum volume Nmax of reaction medium and to define a volume NM above the surface of the reaction medium (that is to say above Nmax) greater than the volume of foam corresponding to said threshold quantity. Said quantities are therefore expressed in volumes and heights in the tank. To monitor the quantity of foam, the height of the foam formed on the surface of the reaction medium is then monitored, in particular by means of means for detecting the presence of foam attached to the tank at a sufficient height always greater than a nominal height of the foam in the tank (non-expansive foaming) during the degradation reaction, taking into account the maximum volume Nmax that can be occupied by the reaction medium, and other parameters of the reaction influencing the foaming (air injection, stirring, etc.). .).

Advantageously and according to the invention, the detection of expansive foaming can be used as a parameter, possibly combined with other parameters, to control the sequence of the supply of lipid compositions.

Thus, a process according to the invention is advantageously characterized in that a step of supplying the reactor with an aqueous lipid medium, in the form of a regeneration step, is carried out only after having detected an increase in the quantity of foam beyond said threshold amount.

Expansive foaming detection can also be used in combination with one or more other parameters, for example the dissolved oxygen concentration, the redox potential, the pH, a predetermined maximum admissible value of the time between two feeds or a variation profile in the time for this maximum admissible value (time table) ... The process according to the invention is therefore, in this last variant, characterized in that a step of feeding the reactor with lipid medium is carried out when the first of the events following occurs:. an increase in the quantity of foam is detected beyond said threshold quantity, said feeding step then forming part of a regeneration step,

. the end of the reaction is detected by monitoring one or more parameters chosen from the concentration of dissolved oxygen; the redox potential; pH; a predetermined maximum admissible value of the time elapsed since the last supply of lipid compositions; a profile of variation in the predetermined time for the durations between the supplies of lipid compositions and / or between the stages of purging (time table).

It should therefore be noted that it is possible to supply lipid compositions when no expansive foaming has been detected beforehand.

Furthermore, advantageously and according to the invention, a regeneration step is carried out immediately after detecting an increase in the amount of foam beyond said threshold amount. In addition, advantageously and according to the invention, immediately after detecting an increase in the quantity of foam beyond said threshold quantity, the introduction of air into the reaction medium is interrupted. Thus, a regeneration step begins with an interruption in the introduction of air into the reactor. In addition, advantageously and according to the invention, during a regeneration step, it is possible to start feeding the reactor in an aqueous lipid medium to be treated, immediately after having detected an increase in the quantity of foam beyond said quantity. threshold, that is to say simultaneously with the interruption of the introduction of air. The regeneration step then essentially consists of a feeding step. As a variant, advantageously and according to the invention, during a regeneration step, the reaction medium is left without the introduction of air for a predetermined period before starting the supply of the reactor with an aqueous lipid medium Advantageously and according to the invention , during a regeneration step, the introduction of air into the reaction medium is interrupted and the introduction of air is restarted after having completely introduced into the reactor said quantity of aqueous lipid medium greater than or equal to the quantity minimal.

In an advantageous variant and according to the invention, during a regeneration step, a purging step is carried out before performing a feeding step.

Throughout the text, the term purge designates any stage during which a certain quantity of treated reaction medium is extracted.

In the process of the invention using an aerobic biological degradation reactor with sequential feed, the purges are never total. In fact, in a manner known per se, a minimum quantity of reaction medium is always maintained in the reactor corresponding at least to the quantity of acclimated bacterial biomass used for the degradation reaction.

Advantageously and according to the invention, at each step of purging the reactor, an amount Nt of reaction products is extracted corresponding to the total amount of aqueous lipid medium introduced into the reactor from the previous purging step.

It should also be noted that, according to the invention, the reactor can be fed after each purging step, but also without having previously carried out a purging step (that is to say between two purging steps), as long as that the maximum capacity of the reactor has not been reached.

Advantageously and according to the invention, the appearance of expansive foaming is also used to control and optimize the stages of purging the reactor, and therefore the residence time of the medium in the reactor, and the amount of lipid compositions treated per unit. of time. Advantageously, in a method according to the invention, one performs a step of purging the reactor when: a) the total quantity in an aqueous lipid medium introduced into the reactor in one or more feed (s) since the previous purging step reaches a predetermined value Nt corresponding to the capacity of the reactor, b ) an increase in the quantity of foam is detected beyond said threshold quantity.

Thus, it should be noted that it is not necessary to carry out a purging step after each detection of an expansive foaming.

Advantageously and according to the invention, one or more other parameters can be used, in combination with the detection of expansive foaming, to control and optimize the reactor purging steps and the residence time. Thus, advantageously and according to the invention, a step of purging the reactor is only carried out when condition a) defined above is satisfied. Advantageously and according to the invention, a purging step is carried out when the condition a) defined above is satisfied and when the first of the following events occurs: b) an increase in the amount of foam is detected beyond said threshold quantity, c) the end of the reaction is detected by monitoring one or more parameters chosen from the concentration of dissolved oxygen; the redox potential; pH; a predetermined maximum admissible value of the time elapsed since the last supply of lipid compositions; a profile of variation in the predetermined time for the durations between the supplies of lipid compositions and / or between the stages of purging (time table). Advantageously and according to the invention, the concentration of materials extractable with hexane from the aqueous lipid medium is measured before feeding and an aqueous lipid medium for which this concentration is greater than 1 is used during a regeneration step. g / 1, in particular 5 g / 1, preferably between 10 and 500 g / 1. Preferably and according to the invention, a medium is used aqueous lipid formed from an aqueous solution of the lipid compositions previously saponified. If the above-mentioned concentration of the aqueous lipid medium is not sufficient, it is modified before feeding, in particular by introducing less water during saponification. The invention also extends to an installation for implementing a method according to the invention. The invention therefore relates to an installation comprising at least one reactor capable of receiving a quantity of a bacterial biomass, and an aqueous lipid medium to be treated, this reactor being provided with an aqueous lipid medium supply, means for introducing air in the reaction medium, and purging means, characterized in that the reactor is provided with means for detecting the quantity of foam formed on the surface of the reaction medium, arranged so as to be able to detect any increase in the quantity of foam beyond a predetermined threshold quantity, and in that it comprises means for automatically triggering a regeneration step as defined above, after detection by the detection means of an increase in the quantity of foam beyond said threshold amount.

Advantageously, an installation according to the invention is further characterized in that the reactor is a tank adapted to be able to contain a maximum volume Nmax of reaction medium, and to define a volume NM above the surface of the reaction medium greater than the volume of foam corresponding to said threshold quantity. This tank is high enough (NM is large enough) to be able to contain a predetermined volume of expanding foam above the reaction medium.

Advantageously and according to the invention, the tank has vertical walls whose height is greater than the width of the tank.

Advantageously and according to the invention, said automatic triggering means comprise a programmed system, for example a microcomputer or an automaton, for implementing the method according to the invention.

The invention also extends to a method and an installation characterized in that they have all or some of the characteristics in combination mentioned above or below.

Other objects, characteristics and advantages of the invention will appear on reading the following description of the examples of a method according to the invention and of an installation according to the invention which refers to the attached single figure which is a functional diagram of an installation according to the invention.

The installation shown in the figure comprises a reactor 1 in the general form of a cylindrical tank with vertical walls 2, with bottom 3, and which defines a maximum volume Nmax for the reaction medium, that is to say a maximum height Hmax that the reaction medium must not exceed. The reactor 1 is provided with an agitator 4 coupled to a stirring motor 5, and nozzles 6 for injecting compressed air from a compressed air pump 7 (compressor).

Each step of purging the reactor is done in the embodiment shown, by a purge line 8 which opens into the bottom 3 and is connected to a purge pump 9.

A thermal control coil 10 is immersed in the reaction medium in the tank 1, and is supplied with thermal cooling fluid (for example water) by an inlet pipe 1 1, the fluid emerging through an outlet pipe 24. The aqueous lipid medium to be treated is contained in a storage tank 12 provided with an agitator 13 with its stirring motor 14. The medium to be treated is extracted from this tank 12, discharged and supplied above the level of the reaction medium in the tank by a line 16 and a pump 15.

A foam detector 17 is fixed to the tank 1 so as to be able to detect the presence of the foam at a predetermined threshold height Hs, so as to always be placed above the reaction medium 25 and the foam 26 normally formed in reaction course. The tank 1 defines above its lower part of height Hmax, a guard volume NM adapted to be able to contain the foam when an expansive foaming occurs. The total height HT of the tank 1 defining the volumes Nmax and NM is greater than the height Hs. The height of Hs threshold corresponds to a predetermined amount of foam threshold above the reaction medium.

Preferably, the tank 1 is not closed at its upper part so as to allow the evacuation of the gases formed. The height HT of the vertical walls 2 is greater than the width of the tank 1.

The foam detector 17 may simply consist of an electrical conductive wire whose free end 18 is stripped, so as to form an electrical contact when the foam reaches the height of this free end 18. This conductor 17 may simply be resting on the upper edge of the tank 1, so as to extend vertically downwards with the free end 18 in the lower position above the reaction medium as shown in the figure. If an electrical voltage is formed between this electrical conductor 17 and the tank 1 with metal walls (or another conductor immersed in the reaction medium), the appearance of expansive foaming will result in an electric current through the conductor 17.

A microcomputer 19 for controlling automatically manages the entire operation of the installation. This microcomputer 19 collects electrical signals from the foam detector 17, a pH meter 20, an oximeter 21, and a device 27 for measuring the redox potential, making it possible respectively to measure the pH, the concentration in dissolved oxygen in the reaction medium and the redox potential. Furthermore, the microcomputer 19 controls a power card 22 developing control signals for the three pumps 7, 9, 15 (air pump 7, purge pump 9, supply pump 15 in lipid medium) which are preferably electric motor pumps.

The microcomputer 19 is programmed to implement the method according to the invention, in particular to automatically trigger a regeneration step, comprising a step of supplying the reactor 1 in an aqueous lipid medium, if the detector 17 detects foam, that is to say after the appearance of an expansive foaming phenomenon. From then on, the pump 15 feeds the tank 1 in an amount of aqueous lipid medium coming from the storage tank 12. This amount is adapted to be sufficient to eliminate the phenomenon of expansive foaming. The concentration of lipid compositions in the aqueous lipid medium of the storage tank 12 is sufficient for there to be a minimum quantity of lipid medium from which the expansive foaming disappears and the height of foam decreases. Before starting up the installation, it is in fact verified that this concentration is sufficient and that there is a minimum quantity allowing, by simple supply of lipid medium, to break the phenomenon of expansive foaming and to return to nominal foaming. low height above the surface of the reaction medium, or even a complete absence of foaming. In general, the concentration of extractable materials with hexane (MEH) of the aqueous lipid medium is between 1 g / 1 and 500 g / 1.

The microcomputer 19 is also programmed to control and manage the steps of purging the tank 1 in the following manner. When all of the feeds carried out since the last purging step are such that the reaction medium reaches the maximum admissible height Hmax, the tank 1 is kept in the state until the next detection of an expansive foaming, it is that is to say until the next detection of the foam by the detector 17, and / or until the next detection of the end of the reaction by monitoring another parameter (pH, dissolved oxygen, redox potential, time limit or time table). When this expansive foaming and / or this end of reaction are detected, the microcomputer 19 interrupts the air supply (air pump 7) and purges (by actuation of the purge pump 9) a volume of reaction medium corresponding to the total volume Vt of aqueous lipid medium introduced into reactor 1 from the previous purging step. In this way, a minimum volume of reaction medium is maintained in reactor 1. Once the purging step has been carried out, the microcomputer 19 triggers the feed pump 15 again to introduce a new appropriate quantity of aqueous lipid medium.

The control microcomputer 19 can also be suitably programmed to manage the thermal control of the reactor 1, preferably to maintain the temperature of the reaction medium at a value below 40 ° C, in particular of the order of 35 ° C, by means of the coil 10 or any other suitable thermal control device.

The microcomputer 19 can be replaced by any other programmable device making it possible to manage the method according to the invention, for example an automaton.

Also, it should be noted that if the appearance of the phenomenon of expansive foaming is used, according to the invention, as a parameter for controlling the feeds and purges, that is to say the residence time of the medium in the reactor 1, other parameters can be used in combination or as a variant to manage the supplies and / or the purges. For example, if no detection of expansive foaming occurs for a predetermined minimum admissible duration, it is possible to provide a new supply in an aqueous lipid medium. Thus, the time intervals between two feeds can be determined by the appearance of expansive foaming phenomena or, if such phenomena do not appear, limited to a maximum admissible value. This maximum admissible value can be fixed in advance to a constant, or according to a predetermined profile varying over time (time table).

The tank 1 also comprises, in a manner known per se, a bacterial biomass formed from an activated sludge acclimated to fats. In steady state, it is known that each volume of aqueous lipid medium treated generates an additional quantity of activated sludge. In addition, the nitrogen and phosphorus amendment necessary for the degradation reaction is preferably introduced with the aqueous lipid medium in the reactor 1. To do this, this amendment can be simply mixed in the storage tank 12 with the aqueous lipid medium . The activated sludge used in reactor 1 has a concentration of suspended matter (bacteria and mineral matter) which is generally between 0.4 g / l and 200 g / l.

In steady state, after each regeneration step, the previously observed expansive foaming is broken and the foam height decreases up to a nominal foam height, of low value, which depends on many parameters, and in particular on the quantity of air injected into reactor 1.

In an alternative embodiment, the tank 1 can also be supplied with an aqueous lipid medium, after detection of expansive foaming, not according to a predetermined fixed quantity, but according to a variable quantity. For example, for each supply of aqueous lipid medium of a regeneration step, aqueous lipid medium is introduced into the tank 1 at least until the detector 17 no longer detects foam at the threshold height Hs. Preferably, an aqueous lipid medium is introduced for a sufficient time to detect a reduction in the height of foam below this threshold height Hs, and for a complementary predetermined duration making it possible to bring the height of foam down to its nominal height, provided that the reaction medium does not exceed the maximum admissible height Hmax.

In an alternative embodiment, during a regeneration step, the reaction medium is left without introduction of air (but while stirring) for a predetermined period before starting the supply of reactor 1 in an aqueous lipid medium. Thus, the tank 1 is only started to be supplied with an aqueous lipid medium after having detected an expansive foaming, and after a stop time Ta of the aeration between 0 and 72 h has elapsed. After this time Ta, an amount of aqueous lipid medium is introduced into the reactor 1, making it possible to break the expansive foam until the height of the foam returns to the nominal height. Aeration is preferably restarted only after having completely carried out the step of supplying an aqueous lipid medium allowing the foam to be broken, or even after having left the medium without aeration for a duration Tb of between 0 and 72 h after end of feeding in an aqueous lipid medium. These down times Ta and Tb make it possible, for example, to adapt the operation of the process to a momentary deficit in lipid compositions which can be encountered in practice.

In the examples, A denotes the speed of agitation, B denotes the air flow injected into the reactor, Qi the volumes of lipid medium introduced into the reactor, ti the time elapsed since the last feeding step in an aqueous lipid medium or since the last purging step, Nt the purged volume, MEHt the total concentration of hexane extractable materials present in the purged volume, MEHs the concentration of hexane extractable materials solubilized in the purged volume, MES the concentration of suspended matter (biomass) in the purged volume, CNE the volume load of hexane extractable materials eliminated per cubic meter of useful reactor volume and by day.

The lipid compositions are formed from fats subjected beforehand to a saponification from a concentrated potassium hydroxide solution, so as to form an aqueous lipid medium which is an aqueous emulsion comprising a total concentration of extractable materials with hexane MEHto.

This medium is supplemented with nitrogen and phosphorus by adding ΝH4 and KH2PO4 in a C / N / P ratio of 100/5/1.

Bacterial biomass is an activated sludge previously acclimated with saponified domestic fats.

EXAMPLE 1: In this example, we have: Nmax ≈ 8 1

Detection height Hs - Hmax = 25 cm A = 500 revolutions per minute (52.36 rad / s) B = 40 1 / h

Type of fat = animal fat Origin of fat = MEHto canning = 45 g / 1 Qi is constant and equal to 200 ml The nominal height of foam observed during the reaction is between 0 and 2 cm. In this example, a feeding step is carried out after detecting an expansive foaming or after a maximum duration of 3 h, even if no expansive foaming is detected.

The successive time intervals ti between the supply stages are then as follows: tl = 2.5 h (since the previous purge stage); t2 = 2h; t3 = 2h; t4 = 1.5h; t5 = 2h.

Expansive foam was detected at tl, t2, t3, t4 and t5. After t5, a purging step (which requires 5 min) is carried out, and we have:

Nt = 1 1 MEHt = 0.5 g / 1

MEHs = 0.13 g / 1

MES - 16.5 g / 1

CNE = 13.5 kg / m3 / d

The process is continued after this purging step with t6 = 2.2 hours (since the end of the purging step); t7 = 2.2h; t8 = 2h; t9 = 2.2h; tl0 = 2.8h.

Expansive foam was detected at t6, t7, t8, t9 and t10. After 10, a purging step is carried out, and we have:

Nt = 1 1

MEHt = 0.5 g / 1 MEHs = 0.15 g / 1

MES = 16.5 g / 1

CVE = l 1.8 kg / m3 / d.

EXAMPLE 2: In this example, we have:

Nmax = 8 1 Detection height Hs - Hmax = 25 cm

A = 550 revolutions per minute (57.60 rad / s)

B = 25 1 / h

Nature of fats = fats of animal and vegetable origin

Grease source = MEHto treatment plant = 40 g / 1

Qi = 200 ml

The nominal height of foam observed during the reaction is also between 0 and 2 cm. A feeding step is carried out after detecting an expansive foaming, or at the end of a maximum duration of 4 h, even if no expansive foaming is detected. The time intervals between the feeding steps are as follows: tl = 3.25h; t2 = 3.5h; t3 = 2.75h; t4 = 3.25h; t5 = 3h.

The foam was detected in all cases. After t5, a purging step is carried out, and we have: Nt = 1 1

MEHt = 0.28 g / 1

MEHs = 0.08 g / 1

MES = 16.4 g / 1

CNE = 7.6 kg / m3 / d. The process is continued with a new series of feeding steps separated by the following successive time intervals: t6 = 4h; t7 = 2.5h; t8 = 2h; t9 = 2.5h; tl0 = 3.25h.

The foam was detected except for t6. Indeed, t6 corresponds to a predetermined maximum admissible duration between two feeding stages (4 h in this example). Similarly, if it is found that this duration is reached before detection of the expansive foaming and when the total capacity of the reactor is reached (Nt = 1 1 in this example), a purging step will be carried out. In this example, a purging step is carried out after tl 0, after detection of the expansive foaming, and we have: Nt 1 1

MEHt = 0.3 g / 1

MEHs = 0.13 g / 1

MES = 16.7 g / 1

CNE = 8.4 kg / m3 / d. These examples demonstrate that the invention not only makes it possible to completely control the foaming phenomena, but also that an almost total elimination of fats (more than 98.5%) is obtained with a purification yield per unit of time ( CNE) much higher than that obtained in the previous processes for which CNE is rarely higher than 4 kg / m3 / d.

Claims

CLAIMS 1 / - Method of aerobic biological degradation of organic lipid compositions such as fatty waste of animal or vegetable origin, in which a quantity of a bacterial biomass is placed in a reactor (1), it is fed into the reactor (1 ) sequentially with an aqueous lipid medium containing the lipid compositions, an appropriate quantity of nitrogen and phosphorus amendment is added to the reactor (1), air is introduced into the reaction medium, and the reactor (1) is purged ) sequentially by extracting a quantity of liquid reaction products and maintaining in the reactor a minimum quantity of reaction medium, characterized in that, if the quantity of foam exceeds a quantity of predetermined threshold, then a step, known as regeneration step, during which the reactor (1) is supplied with an aqueous lipid medium containing compositions li pidiques at a sufficient concentration so that there is a minimum quantity of this aqueous lipid medium which can be introduced into the reactor (1) for which the quantity of foam formed on the surface of the reaction medium, after introduction of this minimum quantity of lipid medium aqueous, becomes again below said threshold quantity, the quantity of aqueous lipid medium introduced into the reactor (1) during this regeneration step being greater than or equal to this minimum quantity. 2 / - Process according to claim 1, characterized in that the evolution of at least one parameter representative of the quantity of foam formed on the surface of the reaction medium is monitored so as to be able to detect any increase in this quantity of foam beyond said threshold quantity, after which a regeneration step is carried out. 3 / - Method according to claim 2, characterized in that, as a representative parameter, the presence of foam is monitored opposite at least one foam presence detector fixed at a predetermined location of the reactor (1) above of the surface of the reaction medium.

4 / - Method according to one of claims 1 to 3, characterized in that one uses as a reactor, a tank (1) adapted to be able to contain a maximum volume Nmax of reaction medium and a volume NM above the surface of the reaction medium greater than the volume of foam corresponding to said threshold quantity.

5 / - Process according to claims 2 and 4, characterized in that the quantity of foam formed is monitored by monitoring the height of the foam formed above the reaction medium in the tank.

6 / - Method according to claims 3 to 5, characterized in that to monitor the amount of foam, at least one detector (17) of presence of foam is used which is fixed to the tank (1) at such a height that it will always be greater than a nominal height of the foam in the tank (1) during the reaction, taking into account the maximum volume Nmax that can be occupied by the reaction medium, and the other parameters of the reaction influencing the foaming

(air injection, agitation ...).

It - Method according to one of claims 1 to 6, characterized in that a regeneration step is carried out only after having detected an increase in the amount of foam beyond said threshold amount.

8 / - Method according to one of claims 1 to 6, characterized in that a step of feeding the reactor (1) is carried out in an aqueous lipid medium when the first of the following events occurs:. an increase in the quantity of foam is detected beyond said threshold quantity, said feeding step being part of a regeneration step,

9 / - Method according to one of claims 1 to 8, characterized in that one performs a regeneration step immediately after detecting a increase in the amount of foam beyond said threshold amount.

10 / - Method according to one of claims 1 to 9, characterized in that immediately after detecting an increase in the amount of foam beyond said threshold amount, it interrupts the introduction of air into the medium reactive.

11 / - Method according to one of claims 1 to 10, characterized in that during a regeneration step, the reaction medium is left without introduction of air for a predetermined period before starting the feeding of the reactor (1 ) in an aqueous lipid medium. 12 / - Method according to one of claims 1 to 1 1, characterized in that, during a regeneration step, it interrupts the introduction of air into the reaction medium, and in that restarts the introduction of air after having completely introduced into the reactor (1) said quantity of aqueous lipid medium greater than or equal to the minimum quantity. 13 / - Method according to one of claims 1 to 12, characterized in that during a regeneration step, a purging step is carried out before performing a feeding step.

14 / - Method according to one of claims 1 to 13, characterized in that at each step of purging the reactor (1), an amount Nt of liquid reaction products is extracted corresponding to the total amount of aqueous lipid medium introduced in the reactor from the previous purge step.

15 / - Method according to one of claims 1 to 14, characterized in that a step of purging the reactor (1) is carried out when: a) the total amount of aqueous lipid medium introduced into the reactor (1) in one or several feeding step (s) since the preceding purging step reaches a predetermined value Nt corresponding to the capacity of the reactor (1), b) an increase in the quantity of foam is detected beyond said threshold quantity . 16 / - Method according to one of claims 1 to 14, characterized in that the reactor (1) is only purged when the total quantity of aqueous lipid medium introduced into the reactor in one or more feed stage (s) since the preceding purge stage reaches a predetermined Nt value corresponding to the capacity of the reactor. 17 / - Process according to claim 16, characterized in that a step of purging the reactor (1) is carried out when the first of the following events occurs: b) an increase in the quantity of foam is detected beyond said threshold quantity, c) the end of the reaction is detected by monitoring one or more parameters chosen from the concentration of dissolved oxygen; the redox potential; pH; a predetermined maximum admissible value of the time elapsed since the last supply of lipid compositions; a profile of variation in the predetermined time for the durations between the supplies of lipid compositions and / or between the stages of purging (time table).

18 / - Method according to one of claims 1 to 17, characterized in that the aqueous lipid medium introduced into the reactor (1) during a regeneration step has a concentration of materials extractable with hexane which is greater than 1 g / 1 - especially between 10g / l and 500g / l -. 19 / - Method according to one of claims 1 to 18, characterized in that the aqueous lipid medium introduced into the reactor (1) is an aqueous solution of the lipid compositions previously saponified.

20 / - Installation for the implementation of a method according to one of claims 1 to 19, comprising at least one reactor (1) capable of receiving an amount of a bacterial biomass, and an aqueous lipid medium to be treated, this reactor (1) being provided with means (15, 16) for supplying an aqueous lipid medium, means (6, 7) for introducing air into the reaction medium, and means (8, 9) for purging , characterized in that the reactor (1) is provided with means (17, 18) for detecting the quantity of foam formed on the surface of the reaction medium. arranged so that any increase in the amount of foam can be detected beyond a predetermined threshold quantity, and in that it comprises means (19) for automatic triggering, after detection by the means (17, 18) for detecting an increase in the quantity of foam beyond said threshold quantity, of a regeneration step during which the reactor (1) is supplied, with an aqueous lipid medium containing lipid compositions at a concentration sufficient for there to be a minimum quantity of this aqueous lipid medium which can be introduced into the reactor (1) for which the quantity of foam formed on the surface of the reaction medium, after introduction of this minimum quantity of aqueous lipid medium, becomes again below said threshold quantity, the quantity of aqueous lipid medium introduced into the reactor (1) during this regeneration step being greater than or equal to this minimum quantity.

21 / - Installation according to claim 20, characterized in that the reactor (1) is a tank adapted to be able to contain a maximum volume Nmax of reaction medium, and a volume NM above the surface of the reaction medium greater than the volume of foam corresponding to said threshold quantity.

22 / - Installation according to claim 21, characterized in that the tank (1) is sufficiently high to be able to contain a volume of predetermined expanding foam above the reaction medium.

23 / - Installation according to one of claims 21 and 22, characterized in that the tank (1) has vertical walls whose height is greater than the width of the tank (1).

24 / - Installation according to one of claims 19 to 23, characterized in that said means (19) for automatic triggering comprise a programmed system.