FR3108900A1 - Process for the pretreatment of fatty residues of animal and / or vegetable origin - Google Patents

Abstract

The invention relates to a process for the pretreatment of fatty residues of animal and / or plant origin, for example waste from industrial or urban wastewater or from industrial processes, in particular for a purification plant, comprising at least the following steps: a) physical separation of the greasy residues by static or aerated degreasing or by flotation, b) pumping of the separated greasy residues, c) conveyance of the pumped greasy residues to a main reaction vessel / a reactor, d) contacting the fatty residues in the main reaction vessel / reactor with a strong base to obtain hydrolysis in a basic medium by saponification, and stirring of the hydrolyzed mixture during the reaction until a homogeneous saponified liquid solution is obtained, e) storage of residues saponified greasy thus obtained, andf) recovery of said saponified residues to a recovery unit.

Description

Process for the pretreatment of fatty residues of animal and/or vegetable origin

Technical field of the invention

The present invention relates to a process for the pretreatment of fatty residues of animal and/or vegetable origin, for example waste from industrial, urban wastewater or from industrial processes, in particular for a purification plant, and more precisely a process for the pretreatment of fatty waste by saponification with a view to material and/or energy recovery.

It is common, in different fields of activity, to have to process greasy waste, for example in sanitation (fatty waste from wastewater treatment plant flotation/greasy waste from grease traps for catering trades), in the recovery of organic waste (mainly anaerobic digestion), and in certain specific industrial fields (agri-food/cosmetics).

Organic greasy residues, or fats, are mainly generated during processing operations, the use of agri-food products and the cleaning of associated equipment. This greasy organic waste represents a very significant source of pollution and nuisances of all kinds for the environment, mainly when their disposal is not well controlled. These are then evacuated with the waste water into the sewerage network, currently posing a major disposal problem. Indeed, they are the cause of major malfunctions in networks and treatment plants, such as accumulation and clogging or difficult biodegradation due to their physical properties (lower density than that of water , solidification at room temperature, insolubility in water), and odor nuisance due to their fermentable nature.

Another solution is to collect these fats to transport them in vehicles intended to then dump them on landfills. However, it is generally prohibited by law to spread or bury this type of waste.

Thus, various attempts have been proposed for the elimination or recovery of these fatty residues.

Energy recovery channels are possible via incineration or methanation processes (anaerobic biological treatment or biodigester). The first can be carried out by direct combustion (subject to pre-treatment) or by co-combustion with household waste. The main limitation of this is its cost due, among other things, to the necessary stages of dehydration upstream and processing of fumes downstream. Anaerobic digestion is a booming industry that is now strongly supported by local and national policies. Thanks to their high methanogenic power, fats improve biogas productivity. Currently, these are generally co-digested with sewage sludge or other organic waste, but only in small proportions because they are very difficult to degrade and can quickly unbalance the biological reaction (it is rarely added more than 10 -15% crude fat).

The most widely used treatment/elimination technologies currently used by well-known companies established worldwide in this sector are biological treatments that achieve dilution and partial biological hydrolysis of fatty materials.

Most of these processes are based on the same principle as the activated sludge tanks of wastewater treatment plants for which the operating parameters and the biomass have been adapted to this particular substrate: they consist of degrading the fats using bacteria through two successive phases of hydrolysis and oxidation (β-oxidation). These facilities have been tried and tested, but their implementation is far from trivial both in terms of costs (investment and operation) and monitoring. Indeed, they require long residence times (15 to 25 days) and dilution is often necessary using biological sludge from the treatment plant. However, this requires a large volume pool.

In addition, these different processes require the implementation and management of aeration, agitation, nitrogen and phosphorus nutrient supply systems (and sometimes even heating) to allow biological biodegradation and avoid any inconvenience (foaming , production of filamentous bacteria, etc.).

Finally, they also produce a large quantity of sludge so that no recirculation of this is necessary.

Thus, all these installations first of all generate a very significant investment, whether in civil engineering or in equipment. Then, the operating costs are also an important element to take into account and far from being negligible, whether they are energy (aeration, agitation), linked to the supply of nutrients / alkaline solution (nitrogen, phosphorus, lime or sodium hydroxide), monitoring of the biological reaction (online or via analysis) or management of the sludge produced. On average, these costs vary in terms of investment and operation respectively from 250 to 1150 € excluding tax and from 90 to 250 € excluding tax, all this per ton of greasy waste per year.

These installations have many shortcomings, including:
- Difficulties in controlling biological systems: bacteria have difficulty degrading fatty waste alone (even diluted) creating inhibitions and foaming. On the other hand, the waste often thickens in the reactor making the medium heterogeneous with mixing difficulties, etc. and finally a partial treatment of greasy residues.
- Significant operating costs (energy for continuous aeration of structures in particular and sometimes reactive): Process difficult to apprehend at the economic level. There are no clear figures on the economic reality of the process and associated operating efficiency. However, the energy costs of the process as well as the addition of any nutrients or soda-based reagents, or even dilution, suggest a minimum cost to be confirmed of €90 excluding tax/ton introduced. However, no figures relating to a technical and objective study have been put forward to date;
- Degradation and therefore elimination of fats alone, without possible recovery. This type of solution is no longer in phase with a market for the recovery of organic waste and the production of energy (methanation).

Biological treatments of crude fats generally do not carry out a specific initial fat hydrolysis step. Consequently, fats remain in an acidic environment and generate problems, namely:
- the use of a solid and hydrophobic material in a process leads to phenomena of clogging, flotation and crusting,
- biological treatments involve microbial processes which can, through biomass inhibitions, generate cell lysis and therefore uncontrolled expansive foaming, and
- non-negligible economic costs linked to significant direct expenses (energy and reagents), breakdowns and post-processing which is always necessary.

Thus, all the processes of the Prior Art (aerobic treatment by hydrolysis and biological oxidation, methanation by anaerobic digestion, emptying by transport to other sectors, addition of enzymes or bacteria) are not satisfactory and not optimized in terms of pre-treatment of greasy residues. They are often complex, extremely slow, expensive, bulky, poorly adapted to current environmental constraints and still have too low a productivity and profitability.

Presentation of the invention

The present invention aims to remedy these drawbacks and focuses on the realization of a hydrolysis in basic medium controlled and optimized on the technical plans (agitation / implementation / pumping / absence of the inconveniences mentioned above). In addition, economically, this pretreatment by saponification makes it possible to be competitive.

To this end, according to a first aspect, the present invention relates to a process for the pretreatment of fatty residues of animal and/or vegetable origin, for example waste from industrial or urban waste water or from industrial processes, in particular for a wastewater treatment plant, comprising at least the following steps:
a) physical separation of greasy residues by static or aerated degreasing or by flotation,
b) pumping of the separated greasy residues,
c) routing of the pumped greasy residues to a main reaction vessel/reactor,
d) bringing the fatty residues in the main reaction vessel/reactor into contact with a strong base to obtain hydrolysis in a basic medium by saponification, and stirring the hydrolyzed mixture during the reaction until a homogeneous saponified liquid solution is obtained ,
e) storage of the saponified fatty residues thus obtained, and
f) recovery of said saponified residues to a recovery unit.

The invention is implemented according to the embodiments and variants set out below, which are to be considered individually or according to any technically effective combination.

Advantageously, the method comprises a step b2) of grinding carried out before or after the step b) of pumping.

Preferably, the process comprises a step b3) involving an intermediate buffer tank to smooth the volumes of residues entering the main reaction tank/the reactor.

According to a particular aspect of the present invention, step a) is a degreasing step, with or without flocculation, by adding a bio-based polymer and/or of petrochemical origin.

More specifically, step a) comprises a coagulation step before the flocculation step.

According to a specific embodiment, the pumping step is carried out by a type of pump chosen according to the nature of the residues, advantageously by a worm screw pump and eccentric rotor if the residues in the main reaction vessel/the reactor contain more than about 12% to 25% by weight dry matter, and a rotary lobe pump if the tails in the main reaction vessel/reactor are less than about 12% by weight dry matter.

Advantageously, in step d), the stirring of the hydrolyzed mixture during the reaction is carried out continuously until a homogeneous saponified liquid solution is obtained, consisting essentially of fatty acid esters.

According to a complementary aspect, the process comprises a step of rapid agitation of the residues in the main reaction vessel/reactor, advantageously of the pendular type for a vessel with a capacity of less than or equal to approximately 5 m ³ or submerged for a vessel with a higher capacity. to about 5 m ³ , and recirculation stirring using an external lobe pump.

Advantageously, the recirculation stirring step is initiated as soon as the dry matter content of the greasy residues exceeds about 8%.

According to one embodiment, the recovery unit is an aerobic biological treatment.

According to a variant, the recovery unit is an anaerobic digester internal to the site.

According to another variant, the recovery unit is a biogas plant external to the site.

Finally, according to yet another variant, the recovery unit is a facility for extracting molecules of interest or transforming molecules into products with higher added value.

According to a characteristic specific to the invention, the strong base is washing soda or potash in a concentration of approximately 30 to 50%.

According to another preferred embodiment, the strong base is a milk of lime, for example in a concentration of approximately 600 g/L.

Preferably, the volume of strong base injected is continuously regulated according to the measured pH and/or conductivity of the hydrolyzed solution and/or the volume of fatty residues present in the tank.

Brief description of figures

Other advantages, objects and characteristics of the present invention emerge from the description which follows.

The process for the pretreatment of greasy residues in accordance with the present invention finds its application in particular in purification stations used for the treatment of domestic wastewater or wastewater from industry (factories for example), installation of anaerobic digestion or storage/transit centers for this type of waste.

Thus, the method in accordance with the present invention comprises, chronologically, the following main steps:
a) physical separation of greasy residues by static or aerated degreasing or by flotation,
b) pumping of the separated fatty residues,
c) conveying the pumped greasy residue to a main reaction vessel/reactor,
d) bringing the fatty residues in the main reaction vessel/reactor into contact with a strong base to obtain hydrolysis in a basic medium by saponification, and stirring the hydrolyzed mixture during the reaction until a liquid solution is obtained homogeneous saponified,
e) storage of the saponified fatty residues thus obtained, and
f) recovering said saponified residues to a recovery unit.

Saponification consists of injecting and bringing into contact a strong base and lipid molecule(s). More specifically, concerning the basic reagent used, it is soda or potash lye (in a concentration of around 30% to 50%) or milk of lime (in a concentration of around 600 g/L) , common reagents in the sanitation sector. This solution avoids the phenomena of foaming and clogging, has a high digestion capacity, and is odorless and fast.

The volume of strong base injected is continuously regulated according to the measured pH and/or conductivity of the hydrolyzed solution and/or the volume of fatty residues present in the tank, in order to optimize the reaction over time.

To this end, various probes allow the online measurement of physico-chemical and/or hydraulic parameters (in particular pH, level, flow) of pretreated fats, and therefore complete automation of the process. The reagent used is conveyed by a specific metering pump connected to a reserve of reagents. Various monitoring indicators are analyzed to better adapt the operation of the unit to the specificities of the production of fatty waste. When the fats are saponified, a pump transports the saponified materials to a sludge storage tank before disposal / recovery.

All the steps are therefore carried out continuously in a completely autonomous manner. Depending on the needs, the operation of the unit can be integrated into the supervision of the treatment plant of the industrial site (sending of alarms, monitoring of parameters, etc.).

These adjustments and this refining of constants make it possible to stabilize the operation of the process and to guarantee an optimal saponification threshold for the envisaged recovery (yield of the reaction preferably greater than 75% and close to 85%), with both optimized management of the quantity of reagents necessary for the reaction (neither too much nor too little) to obtain, for example, a pH of approximately 8 to 9, and a high rate of conversion of fatty residues.

The mixture of this solution will generate a basic hydrolysis of the triglycerides and/or a salification of the fatty acids to form a solution of fatty acid esters and, where applicable, glycerol.

The advantage of this reaction is mainly based on the change of state of the fats: transition from a hydrophobic state which is difficult to biodegrade to a hydrophilic state which is easily biodegradable.

Step a) is preferably a degreasing step (with or without flocculation) by adding a biosourced polymer and/or of petrochemical origin. Among the various flocculants or polymers used to better separate fats from water, mention may be made, for example, of polyacrylamide but also of numerous types of cationic or anionic polymers.

Step a) advantageously comprises a coagulation step before the flocculation step. This step removes the inter colloidal repulsions by adding metallic salts (for example iron or aluminium): the metallic cations used (Al ³⁺ and Fe ³⁺ ) neutralize the colloids which can now easily be flocculated. This makes it possible to make a certain number of materials insoluble which can be flocculated and then floated with the fats.

In order to improve the process, and depending on the type of fatty waste (viscosity, density, size of the residues), a crushing step b2) is carried out before or after the pumping step b). For this, an in-line cutter mill can be used.

A step b3) involving an intermediate buffer tank is also provided to smooth the volumes of residues entering the main reaction tank/reactor, which allows optimal operation of the saponification process, in particular in the management of the quantity of reagent to be used according to the volume of residues to be treated (avoid that the treatment is incomplete or, on the contrary, to use excess reagent). This also makes it possible to smooth the volume of residues treated so that their recovery and recycling are also optimized.

The pumping stage is carried out by a type of pump chosen in particular according to the nature of the greasy residues to be treated (and therefore their origin). Thus, a worm gear pump with an eccentric rotor is preferably (but not exclusively) used if the residues in the main reaction vessel contain more than approximately 12% to 25% by mass of dry matter, and a rotary lobe pump is used preferably (but not exclusively) if the residues in the main reaction vessel contain less than about 12% by mass of dry matter.

However, a lobe pump can still be used if the conditions are suitable if the main reaction vessel contains a little more than 12% by mass of dry matter.

In the same way, a worm screw pump with an eccentric rotor can be used if the residues in the main reaction vessel contain a little less than 12% by mass of dry matter.

It is also provided that in step d), the stirring of the hydrolyzed mixture during the reaction is carried out continuously until a homogeneous saponified liquid solution of fatty acid esters is obtained, this in order to optimize the saponification reaction and not form more or less well treated zones in the reactor (local accumulation of residues more difficult to saponify).

Agitation by submerged agitator and recirculation via a lobe pump (by regular crushing of the material putting the reagent in good contact with the grease) or by endless screw and eccentric rotor makes it possible to optimize reaction times and the quantity reagent used, to improve the acceptability of all types of greasy waste from wastewater (from very liquid to very pasty), and to better control the phenomena of foaming and/or re-agglomeration of greasy residues during the reaction .

A stage of rapid agitation of the residues in the main reaction tank is also provided as an option, the latter being advantageously of the pendular type for a tank with a capacity of less than or equal to approximately 5 m ³ , or of the submerged type for a tank with a capacity greater than about 5 m ³ . Stirring by recirculation using an external lobe pump is also recommended.

To this end, the recirculation agitation step is initiated as soon as the dry matter content of the fatty residues exceeds approximately 8%, always to homogenize the contents of the reaction vessel as well as possible and facilitate saponification.

The optimized recirculation rate makes it possible to carry out the reactions in a large volume of fats already saponified in successive batches and to minimize the reaction times as well as the quantities of reagent used.

According to the invention, different types of recovery units are adapted to the process thus presented.

For example, the recovery unit can be an aerobic biological treatment, but it can also be an anaerobic digester internal to the site, an methanizer external to the site or even an installation for extracting molecules of interest or for transforming molecules into products with higher added value (fatty acids, biopolymers, surfactants, etc.).

Tests were carried out to characterize the results obtained and to confirm/reject certain technological choices if necessary. For this, greasy residues from one or more wastewater treatment plant sites are sampled. Different saponifications of these fats are carried out using 30.5% washing soda. The objective of this manipulation is to reproduce "on a laboratory scale" (1 L) the operation of the process that is the subject of this patent application with a view to integrating it into an existing wastewater treatment plant.

The test phase was carried out in beakers agitated by different methods (pendulum agitation, magnetic bar, etc.). Successive additions of reagent were made until a stable and homogeneous liquid was obtained.

During the reactions, the pH, conductivity and temperature parameters are monitored. A posteriori, raw and saponified fats are characterized by carrying out physico-chemical analyses.

At the macroscopic level, the liquid obtained is quite uniform and homogeneous. Quantitatively, the characterization of the different samples before and after saponification highlights several consistent and conclusive results, namely:
- Notable reductions in Hexane Extractable Substance (SEH) and Suspended Matter (SS) of 60% and 40% respectively: fat liquefaction and transformation into soaps (it should be noted that fat liquefaction should be further improved scale 1 thanks to the agitation/homogenization system which is difficult to reproduce on a laboratory scale),
- Low COD/BOD ₅ ratio: decrease in this ratio with a value close to 2 (very easily biodegradable effluent) after saponification,
- Parameters, NTK & PT remaining similar before or after saponification.

This characterization also makes it possible to determine the carbon, nitrogen and phosphorus flows associated with the elimination / recovery of this saponified effluent.

During this test, the volume of 30.5% sodium hydroxide injected is proportional to the dry matter content of the sample of fats analyzed and is generally between 0.5% and 3% of the total volume of fats (3% in this case, evening 120 mL / 4 L). This value is completely consistent with the usual data for such concentrations of dry matter.

Another test under similar conditions provided consistent and conclusive measured results in terms of:
- Low COD/BOD ratio ₅ : significant decrease (31%), this one approaching 2 (very easily biodegradable effluent) after saponification,
- Significant reductions in SEH & MES (63% & 52%): liquefaction of fats and transformation into soaps (It should be noted that the liquefaction of fats should be further improved at scale 1 thanks to our agitation / homogenization system which is difficult to reproduce laboratory scale),
- Increase in BOD ₅ (45%): improved biodegradability,
- Parameters, NTK & PT remaining similar before or after saponification.

During this test, the volume of 30.5% soda lye injected is 2% of the total fat volume (60 mL / 3 L). This value is entirely consistent with the usual data for such concentrations of dry matter.

In summary, the method according to the present invention thus carries out pumping of the fats after separation by flotation by grinding (depending on the case) for transport to the reaction vessel, an automated cyclic chemical reaction by injection of reagent, controlled agitation (possibly continuous and with recirculation) by monitoring the pH level and/or conductivity of the environment, storage of saponified fats and discharge to a material and/or energy recovery sector (aerobic treatment plant / anaerobic digester internal / external methanizer / biosourced products).

This robust and easy-to-use technology thus makes it possible to provide an innovative response to the problems of treating greasy residues and to reduce the technical, economic and environmental impacts associated with the management of these often critical by-products.

Saponified fats offer various advantages to the operator of the saponification unit as well as to the sanitation manager receiving the effluent, namely:
- The biodegradability ratio of saponified fats is less than or very close to 2, characteristic of an effluent/waste that is very easily biodegradable and this beyond domestic effluent or conventional sludge. It is thus a pollution very easily accepted and biodegraded in all types of treatment plant or as a booster in methanation;
- This supply of easily bio-available carbon can improve the purification performance of the aerobic or anaerobic biological system receiving the effluent concerned,
- In the context of integration into anaerobic digestion, saponification makes it possible to increase the digestion capacity, to preserve methanogenic potential over time, to reduce crusting, precipitation, biological inhibitions and thus foaming due to fats.

These greases will at the same time counter the residual acidification of the effluents in the biological system concerned and thus reduce the effects of corrosion and production of H ₂ S which are recurring problems in these installations.

The complete operating costs of the process in accordance with the present invention per m ³ of fat treated are at least two to three times lower than the costs of current processes.

Finally, this innovative sector makes it possible to divide the overall environmental impact of the management of this waste by at least two and thus to be integrated in a more global way, at the scale of a territory, in the procedures for setting up “short circuits” and more sustainable solutions by companies and/or associated communities.

It should be understood that the detailed description of the subject of the invention, given solely by way of illustration, does not in any way constitute a limitation, the technical equivalents also being included in the scope of the present invention.

Thus, the process also finds its application in the pretreatment of tallow and fat from cutting or cooking, slaughterhouse/butchery from slaughtering and meat processing activities.

Depending on the type of greasy residue to be treated, it is possible to implement a certain number of mechanical pre-treatments or post-treatments (grinding / sieving).

Claims (16)

Process for the pretreatment of fatty residues of animal and/or vegetable origin, for example waste from industrial, urban wastewater or from industrial processes, in particular for a purification plant, comprising at least the following steps:
a) physical separation of greasy residues by static or aerated degreasing or by flotation,
b) pumping of the separated greasy residues,
c) routing of the pumped greasy residues to a main reaction vessel/reactor,
d) bringing the fatty residues in the main reaction vessel/reactor into contact with a strong base to obtain hydrolysis in a basic medium by saponification, and stirring the hydrolyzed mixture during the reaction until a homogeneous saponified liquid solution is obtained ,
e) storage of the saponified fatty residues thus obtained, and
f) recovery of said saponified residues to a recovery unit. Process according to Claim 1, characterized in that it comprises a step b2) of grinding carried out before or after the step b) of pumping. Process according to any one of the preceding claims, characterized in that it comprises a step b3) involving an intermediate buffer tank to smooth the volumes of residues entering the main reaction tank/the reactor. Process according to any one of the preceding claims, characterized in that step a) is a degreasing step, with or without flocculation, by adding a biosourced polymer and/or of petrochemical origin. Process according to claim 4, characterized in that step a) comprises a coagulation step before the flocculation step. Process according to any one of the preceding claims, characterized in that the pumping step is carried out by a type of pump chosen according to the nature of the residues, advantageously by a worm screw pump and eccentric rotor if the residues in the tank main reaction vessel/reactor has more than about 12% to 25% by mass dry matter, and a rotary lobe pump if the tailings in the main reaction vessel/reactor has less than about 12% by mass solids dried. Process according to any one of the preceding claims, characterized in that in stage d), the stirring of the hydrolyzed mixture during the reaction is carried out continuously until a homogeneous liquid solution saponified of esters of Fatty acids. Process according to any one of the preceding claims, characterized in that it comprises a stage of rapid agitation of the residues in the main reaction tank/the reactor, advantageously of the pendular type for a tank with a capacity of less than or equal to approximately 5 m ³ or submerged for a tank with a capacity greater than approximately 5 m ³ , and recirculation agitation using an external lobe pump. Process according to Claim 8, characterized in that the step of agitation by recirculation is initiated as soon as the dry matter content of the fatty residues exceeds about 8%. Process according to any one of Claims 1 to 9, characterized in that the recovery unit is an aerobic biological treatment. Process according to any one of Claims 1 to 9, characterized in that the recovery unit is an anaerobic digester internal to the site. Process according to any one of Claims 1 to 9, characterized in that the upgrading unit is a methaniser external to the site. Claim 13. Process according to any one of Claims 1 to 9, characterized in that the upgrading unit is an installation for extracting molecules of interest or for transforming molecules into products with higher added value. Process according to any one of the preceding claims, characterized in that the strong base is sodium hydroxide or potash lye in a concentration of approximately 30 to 50%. Process according to any one of Claims 1 to 14, characterized in that the strong base is a milk of lime, for example in a concentration of approximately 600 g/L. Process according to any one of the preceding claims, characterized in that the volume of strong base injected is continuously regulated as a function of the measured pH and/or conductivity of the hydrolyzed solution and/or the volume greasy residues present in the tank.