FR2838660A1 - MICROWAVE TREATMENT PROCESS FOR SODIUM CHLORIDE USED FOR RECYCLING - Google Patents

Abstract

The object of the invention is a process for the treatment of used salts originating from cured meats, characterized in that said salts are treated by passage in microwaves so as to destroy the microorganisms and make the treated salt suitable. in particular for salting hides leaving slaughterhouses or for salting roads.

Description

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PROCESS OF MICROWAVE TREATMENT OF CHLORIDE
SODIUM USED FOR RECYCLING The present invention relates to a process for treating used salt, mainly sodium chloride, from cured meats, with a view to recycling it for other applications.

The industrial cured meat companies consume a lot of salt in the form of sodium chloride. It is generally sea salt which is of a very high quality both from the point of view of its chemical purity and from the point of view of its particle size regularity. This salt, for example in the case of salting hams in dry meats, is used to cover said fresh hams for a given period of several days, the amount being a function of the mass of meat. This salt is only partly absorbed by the meat and there remains a large amount of salt which has been contaminated by blood exudates and other fats. This excess salt also contains a large number of microorganisms whose origin is linked to the survival and / or development of germs following storage in the ambient air of hams during salting operations, handling of operators on the production chain, or the initial presence of microorganisms on fresh products and in new salt.

Also, this salt is not reusable for new salting to obtain dry hams. Indeed, such used salts could be, by successive recycling, sources of health risks for consumers.

The critical problem of disposing of such waste then arises.

Several solutions exist.

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The first is to recycle these salts for the treatment of roads in winter. However, this consists of spreading soiled products on the roadway and therefore in the environment, which is no longer acceptable today. In all cases, such a solution can only be envisaged for small quantities of used salts. It is not a global solution, capable of being transposed to industrial installations.

Another solution is to dispose of this waste by burying it in landfills. We know that this possibility will be eliminated in the near future because only the ultimate waste can be buried, the others having to be recycled. In addition, the cost of such a disposal service is not negligible.

As for incineration, which is also a disposal solution, we understand that it is prohibitively expensive for such waste and the strengthening of legislation, which aims to reduce atmospheric releases of chlorinated derivatives, will against disposal of sodium chloride by incineration.

 One solution is to recycle these salts after prior decontamination.

A known method consists in heating these used salts to temperatures of
108 to 110 C for periods of the order of 20 min then to store them hot in a large capacity hopper. The heating is generally of the burner type supplied with propane gas and the salt is contained in a drum, subjected to the action of heat.

 This method is reserved for heavily contaminated salts, in particular salts from slaughterhouses and tanneries. Indeed, after slaughter of cattle and sheep, the skins are salted and remain under the action of salt for a few days while waiting for the transfer to the tanneries. During the slaughterhouse storage stage, the salt aims to reduce the water content of the skins while ensuring the preservation of their intrinsic qualities.

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As a result, the salts leaving slaughterhouses are very dirty with blood exudates, excrement and the soil initially present on the skins. Mesophilic aerobic flora approaches 106 germs per gram of soiled salt.

Such a reprocessing installation by a 110 C process can only be envisaged for slaughterhouses or tanneries generating at least 1000 tonnes of used salt per year.

Finally, we also note that the sporulating microorganisms (certain bacteria and molds) even if they are present in a minority are not eliminated. A treatment at 121 ° C. for 20 minutes would provide sterile salts, but in this case, the investment and operating costs are inconceivable.

Another disadvantage of salts thus decontaminated or sterilized at temperatures above 100 ° C. is the degree of drying which is so advanced that it poses problems of melting these salts, whether they are reused for salting roads or skins. slaughterhouses.

The quality of used salts from the salting industries is far superior to that of salts from slaughterhouses and the salting of hides.

 The density is of the order of 1.02, close to that of coarse unseasoned salt which is 1.1.

 The humidity of a homogenized batch, because decantation rapidly causes a reduction in the quantity of water retained, is approximately 4% by weight of water relative to the weight of salt. This water comes from the water extracted from fresh hams.

 A draining phase allows the quantity to be reduced very quickly to a percentage of 2.9.

 Likewise, the fatty substances extracted from fresh meat are present in the used salts in an amount of 1.0% by weight of fat relative to the weight of used salt.

 Similarly, by simple draining, this percentage, partly linked to the presence of liquid fatty substances, can be reduced to 0.7%.

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Another advantage concerns the macroscopic aspect and, in particular, the maintenance of the white color of such used salts. Indeed, these salts only exceptionally have a slight yellow - brown tint, which, in this case, is due to fats and blood exudates sometimes present in small quantities.

The particle size is interesting because it has a varied spectrum with grains having a maximum size of 3 mm.

The microorganisms expressed in CFU / g are included in the following ranges: - 5 to 2000 for the total aerobic flora, centered on 300.

 - 2 and 60 for the micrococci, centered on 20.

 - 1 and 18 for staphylococci, centered on 5.

 - 1 and 67 for yeasts, centered on 14.

 - 1 and 32 for molds, centered on 7.

After study, we also note a significant evolution of these flora over time after three or four weeks of storage in packaging units at room temperature.

 Numerous salting tests are carried out on bovine and sheep skins with these contaminated used salts.

Whatever the treatment, used salt for salting alone, used salt with new salt added, used salt with additives, hot salting immediately after skinning or cold salting one or two days after, there is a degradation of the protein framework of the skins linked to a development of the microorganisms initially present in the used salts and, consequently, a downgrading of the skins in tanning.

 This depreciation of the skins can lead to significant financial losses greater than the savings made by the use of used salts.

 There is no point in using used, uncontaminated cured salt for the treatment and preservation of hides and skins in slaughterhouses before being sent to the tannery.

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Knowing that the addition of germicidal chemicals is prohibited on the skins of slaughterhouses, it is necessary to resort to a physical treatment of the salts coming from cured meats in order to make them usable for the treatment of skins leaving slaughterhouses.

It is the aim of the method according to the present invention to propose steps leading to a reprocessed salt which can be used for salting hides and skins leaving slaughterhouses before going to the tannery, which is inexpensive or at least the cost of which can be envisaged as alternative to elimination and which is effective for the intended application.

This treatment method is now described in detail in comparison with other methods.

The first possible means is a heat exchanger. This means consists of passing a hot fluid through ramps in a container in which the used salt is placed. This mode is effective on microorganisms and remains well controlled but is only applicable on solids in a thin layer.

The use of infrared heating allows continuous treatment, or even of the product in its packaging, but such radiation is only effective on the surface.

 Ohmic heating techniques are very effective in that the treatment times are very short and do not require any heat transfer fluid. On the other hand, they are difficult to apply to solid products and are very expensive.

 Another thermal process is the current flow tube whose heating is homogeneous but which is reserved for liquids.

 Pulsed light is very fast and very effective on microorganisms but the costs are high.

 Hot pulsed air is effective on all microorganisms but on the other hand in the case of used salts, a crusting phenomenon occurs, which makes the

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 difficult salting and spreading steps on the skins. Regular brewing is required. The duration of treatment is also longer.

The method according to the present invention consists in resorting to a microwave treatment of the used salts to ensure their desiccation and the reduction of the microbial load.

The tests are carried out on quantities of used salting salts of the order of 1 to 10 kilograms.

The frequency range used is that which is authorized to comply with the standards and more particularly, the frequency of 2450 MHz 50MHz (wavelength 12 cm). This corresponds substantially to the size of the used salt layers to be treated.

1000 W power generators are used. These generators emit microwaves which are diffused by waveguides, preferably with slits.

The heating times and kinetics, the spatial distribution of temperatures during the treatment and the specific microwave consumption are measured. For temperature control, fluoroptic probes are provided.

The advantage of microwaves is to generate the release of heat in the product itself, which avoids the transfer time by conduction, which in the case of salt can prove to be quite long.

 The results obtained lead to an average temperature between 70 and 80 C.

 The duration of emission at a power of 370 W / kg is between 15 seconds and 6 min for the duration of rise to the temperature level and 10 to 30 minutes of regulation for salt thicknesses of a few centimeters, in l 'occurrence 4.5 centimeters.

 Dissolution:

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 It is found that the dissolution of the used salts after treatment is equivalent to that of a new salt.

Bacteriological analysis: The different treated samples ~ contain less than 10 germs / g compared to more than 300 microorganisms / g for an untreated used salt. A complete elimination of vegetative bacteria resistant to high salt pressures such as micrococci or staphylococci is ensured.

There is therefore an average reduction of 97% of the microorganisms initially present in the used salts. Only a few microorganisms known for their ability to sporulate are insensitive to treatments under the conditions of its application. These sporulating microorganisms, ubiquitous in the air, although capable of surviving under such conditions in terms of saline concentration, are however incapable of developing under the conditions of salting of the skins.

It should be noted that these sporulating microorganisms can be found in new salt.

We show that the optimal conditions can be of the order of: - temperature rise time: 65 seconds - bearing temperature: 70 to 80 C - temperature regulation time: 600 seconds - salt temperature before treatment: ambient, i.e. around 20 C - applied power density: 1.12 kW / kg - production rate from 300 to 600 kg / hour - consumption of 0.03 kWh / kg of treated salt.

It is found that microwaves prevent the formation of a crust during treatment, unlike, for example, treatment with hot air.

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 The salt obtained contains an amount of water of 1.04% by weight of water relative to the weight of salt, which can be considered to be close to that of new salts.

In addition, the treatment does not significantly modify the particle size of the salt.

This salt thus treated was used, alone and in admixture with new salt, for the salting of hides leaving the body of a slaughterhouse and gave satisfactory results, comparable to salting with new salt alone.

The skins are not downgraded because there is no microbial proliferation, which avoids the corresponding financial losses.

Claims (6)

 CLAIMS 1. Process for the treatment of used salts from cured meats, characterized in that said salts are treated by passage through the microwave so as to destroy the microorganisms and to make the treated salt suitable in particular for salting skins in leaving slaughterhouses or salting roads. 2. A method of treating used salts from salting according to claim 1, characterized in that a microwave emission is carried out for a rise in temperature of the salt up to a determined threshold, followed by an emission of microwave for temperature regulation for a fixed period. 3. A method of treating used salts from salting according to claim 1 or 2, characterized in that the salt is arranged in a layer of substantially constant thickness of the order of a few centimeters. 4. A method of treating used salts from cured meats according to any one of the preceding claims, characterized in that microwaves are used in the range from 2450 MHz to 50 MHz. 5. A method of treating used salts from cured meats according to any one of the preceding claims, characterized in that the temperature necessary to obtain an eradication of the vegetative bacteria and a reduction greater than 95% of the total microbial flora is between 70 and 80 C. 6. A method of treating used salts from salting according to any one of the preceding claims, characterized in that a power density of 1.12 kW / kg is applied with a consumption of 0.03 kWh / kg of processed salt.