Heavy metal decontamination process

Abstract

Process for the decontamination of organic matter from molluscs of the cephalopod or bivalve class with heavy metals, characterized by a succession of steps including an optional preliminary washing to remove undesirable elements, followed by progressive pressing of the material with a pressure of between 2% and 50%, allowing the digestive glands to burst with the addition of water, washing of the solid residue with an aqueous solution chosen from fresh or salt water optionally including an acid at a concentration of between 0 and 10%, then separation of the solid and liquid fractions through a perforated drum having perforations with a diameter of between 1 mm and 3 mm. The process makes it possible to obtain a reduction in the heavy metal contents in the solid fraction by a factor of 5 to 1000, making it compliant with the regulatory thresholds for use in human or animal food, in agriculture or in methanization.

Description

Title of the invention: Method for decontamination of heavy metals Field of invention

[0001] The present invention lies in the field of heavy metal decontamination. Its subject matter is more particularly a method aimed at significantly reducing the heavy metal content of organic matter and biological matrices.

[0002] This process applies particularly to the recovery of animals or parts of animals of the mollusc branch and particularly those of the cephalopod class and those of the bivalve class and particularly those of the Pectinida order and particularly of the Pectinidae family. Technological background of the invention

[0003] Among marine shellfish, several species of scallops represent an important target for commercial fisheries. However, bivalves are known to accumulate trace metals at sometimes high levels. Among these, scallops show significant levels of certain elements such as cadmium, arsenic, mercury and lead. Cadmium levels very often even exceed the maximum levels authorized by regulations. Analyses have nevertheless shown that most of these contaminants are found concentrated in certain organs and that, among the edible organs, only the adductor muscle contains a significant proportion of arsenic but in a non-toxic form. This is why today selective evisceration is practiced leading to the marketing of only the muscle (nuts) and sometimes the gonads (coral) while the rest (barbs) is eliminated or directed towards other sectors (animal feed, methanization, etc.)..). However, today, even these other outlets are no longer authorized because the cadmium levels exceed the maximum regulatory values. It is therefore a very high proportion of these bivalve molluscs which must be destroyed.

[0004] The present invention aims to overcome this problem by proposing a process which makes it possible to very significantly reduce the cadmium, arsenic, mercury and lead contents of these residual fractions and thus to authorize their use in numerous fields, starting with human food.

[0005] Cephalopods also concentrate in their viscera and particularly in their digestive glands (such as the hepatopancreas) many contaminants, starting with heavy metals. Commercial practices in use mean that these molluscs are sold gutted. The viscera, when not thrown into the sea, are used in the agricultural and animal feed sectors. (mainly in the form of flour). Here again, heavy metal levels now prevent these recoveries. The present invention aims to overcome this problem by proposing a process which makes it possible to significantly reduce the cadmium, arsenic, mercury and lead levels in these viscera and thus authorize their use in animal feed and agriculture. Summary of the invention

[0006] The present invention relates to a method characterized in that it comprises the following steps which consist of: 1. To subject the said viscera or barbs to pressure strong enough to burst the digestive glands including the hepatopancreas and to separate what they contain from the rest. 2. Wash the solid residue to remove any container remains. 3. At the end of this step, separate the solid and liquid fractions.

[0007] The decontamination levels obtained for the solid fraction are very significant and can range from 5 to 1000 times depending on the initial contamination in heavy metals.

[0008] According to other non-limiting characteristics: • A preliminary water wash can be carried out in order to eliminate as much as possible unwanted elements such as sand, mud, solid residues, algae, etc. • Pressing is carried out, for example, using a belt separator based on the principle of progressive crushing of the material (viscera and / or beards) between the belt and the perforated drum. It could also be carried out with a screw separator or other process for separating products of different viscosities / fibrousness. • Although not mandatory, adding acid to the wash water promotes decontamination, particularly that linked to cadmium. Any type of acid can be used, preferably citric acid and acetic acid.

[0009] Detailed description of a non-limiting example of the invention

[0010] The process according to the invention which uses a mechanical pressing process is particularly interesting since it makes it possible to very significantly reduce the content of heavy metals (Lead, Cadmium, Arsenic, Mercury, etc.) in scallop beards.

[0011] It can be applied to fresh beards or those of a more advanced age, or even frozen / thawed beards. A detailed example of the different stages of the process on scallop beards is given below: 1. The first (optional) step of the process consists of washing the beards in water (fresh or sea) to remove unwanted items such as sand, mud, solid debris such as shells, algae, etc. This first wash is not not obligatory although preferable to limit damage to the equipment and in particular to the pressing belt. 2. Pressing is carried out using a mechanical belt separator (Sepamatic type for example). 3. The diameter of the drum perforations is chosen carefully because it strongly influences the efficiency of the process. For the decontamination of beards, this is between 1 mm and 3 mm, ideally 1.3 mm. 4. The pressure exerted by the belt is also very influential. The stronger it is, the more solid matter will be able to pass through the holes in the drum (extrusion). For decontaminating beards, this pressure is between 2 and 50%, preferably between 10 and 30%, ideally 15%. 5. The whiskers are introduced into the separator hopper. The concomitant addition of water is not mandatory but can promote decontamination. 6. At the end of this mechanical separation, the solid and liquid fractions are separated. The solid fractions are then cleaned by washing with water in order to eliminate contaminant residues such as heavy metals and any residual solid particles (especially if prior pressure washing has not been carried out). 7. Although not mandatory, adding acid to the wash water promotes decontamination, particularly that linked to cadmium. Any type of acid can be used, preferably citric acid and acetic acid. The acid concentrations to be used vary from 0 to 100%, preferably from 0 to 10%, ideally from 0 to 4%. 8. Depending on its residual heavy metal content, the resulting solid fraction can be used in human food (PAI), animal feed, agriculture, or methanization for example.

[0012] Non-limiting examples of possible uses of the products resulting from the invention

[0013] Possible uses of the solid fraction of scallop beards obtained after implementing the method according to the present invention are described below.

[0014] A first possible use is energy and agricultural through its methanization. The gaseous fraction (biogas) thus obtained can be used as fuel after purification (biomethane) while the residual solid residue (digestate) can be used in agriculture (spreading).

[0015] This fraction can also be used directly in animal feed (e.g. fur animals) but more likely after certain treatments. in particular stabilization (cooking and / or drying for example) and / or shaping (grinding, hydrolysis, etc.). It can then be used for its nutritional properties (source of proteins and amino acids), but also as ingredients for domestic animals and aquaculture in particular.

[0016] This fraction can also be used for human consumption, the most interesting area from an economic point of view with the highest added value. Many recipes are already available and some examples (non-exhaustive) are given below: • Smoke • Scallop butter • Scallop beard tart • Risotto with scallops • Stewed scallops • Scallop sauce

Claims

Claims

1. A method for decontaminating organic matter from molluscs of the cephalopod or bivalve class with heavy metals, selected from cadmium, arsenic, mercury and lead, characterized in that it comprises progressive pressing of the material allowing the digestive glands, including the hepatopancreas, to burst, with the addition of water facilitating the separation and extraction of contaminants, said pressing being carried out using a mechanical separation device selected from a belt separator or a screw separator, washing of the solid residue with an aqueous solution selected from fresh or salt water, optionally comprising an acid, separation of the solid and liquid fractions, said method making it possible to obtain a reduction in the heavy metal content in the solid fraction by a factor of 5 to 1000.

2. Method according to claim 1, characterized in that the organic matter comes from bivalve molluscs of the order Pectinida.

3. Method according to one of the preceding claims, characterized in that it comprises an optional preliminary washing step to remove undesirable elements chosen from sand, mud, solid residues and algae.

4. Method according to one of the preceding claims, characterized in that the pressing is carried out with a relative pressure of between 2% and 50% of the maximum capacity of the mechanical separation device, preferably between 10% and 30%, ideally 15%.

5. Method according to claim 1, characterized in that, when the mechanical separation device is a belt separator, the latter comprises a perforated drum having perforations with a diameter of between 1 mm and 3 mm, ideally 1.3 mm.

6. Method according to any one of the preceding claims, characterized in that, when the aqueous washing solution comprises an acid, its concentration is between 0 and 10%.

7. Solid fraction obtained by the process according to any one of the preceding claims, characterized in that it has a reduction in the heavy metal content by a factor of 5 to 1000 compared to the initial organic matter, making it suitable for use in human or animal food.

8. Use of the solid fraction according to claim 7 for the preparation of food products intended for human consumption, chosen from culinary preparations based on scallops and food ingredients.

9. Use of the solid fraction according to claim 7 for animal feed, after stabilization treatment by cooking and / or drying, or shaping by grinding or hydrolysis, for organic amendment in agriculture by spreading, and for methanization for the production of biogas usable as fuel after purification, and of digestate usable in agriculture.