FR2646989A1 - Pool for growing seaweed and method for implementing it - Google Patents

Abstract

The present invention relates to a pool 10 for growing macroscopic seaweed supplied with water, having the shape of a more or less flattened ring defined between an outer wall 11 and a central core 12, at least one paddle wheel 14 arranged radially and obstacles 18, 20.

Description

 The present invention relates to an outdoor pool for the cultivation of macroscopic algae, in which the algae floats in the water of er which circulates therein and to a cultivation method using this basin.

 Seaweed is widely used by the phariaceutical, chemical and food industries as a source of raw materials, some species are even eaten fresh or rehydrated in different countries; but the harvest of wild algae, on the French coasts in particular, is decreasing, and it is desirable to produce algae at least certain species - by culture in basins supplied with sea water and located in the open air on the shore, far storms and tidal phenomena.

Many species of algae can thus be cultivated, such as Chondrus crispus, Gigartina stellata, Calliblepharis ciliata and lanceolata, Laminaria sp., Solieria Chordalis, Cystoclonium purpureun,
Palmaria palmata, Gracilaria sp., Ulva sp., Enteromorpha sp., Bryopsis
Sp.

 For some such as Chondrus, a red alga from which carrageenans, thickening food-grade polysaccharides are extracted, and more particularly for Chondrus crispus whose tonnages processed in Europe are significant, it is entirely desirable to find culture conditions economically competitive. Some teams of specialists have already studied this question, such as that of R.G.S.

Bidwell in Canada, which described in Botanica Marina vol. XXVIII p. 8797 (1985) a basin for the cultivation of Chondrus crispus, also called
Irish osts, supplied with sea water, nutrients and carbon dioxide, the mixing of the algae being ensured by bubbling air from the bottom of the basin, about 80 to deep;
According to the authors, this device provides intermittent illumination of the algae, favorable to their development, and distributes only the sources of carbon and other necessary nutrients well known to the specialist, while the paddle wheel system previously used for agitation by Simpson and Colt. and described in Bot. nar. 21
P. 229-235 (1978), is clearly less efficient and profitable because the plants circulate poorly and tend to settle at the bottom of the basin, resulting in slower growth and easier development of epiphytes and diseases. , it was desirable to find another device, because the agitation of the basin by air bubbling presents various disadvantages including a high consumption of energy and carbon dioxide, as well as a higher cost of making the basins: k these must be fitted with non-codroductable air supply pipes, and their depth must be 4 to 5 times that of light penetration to ensure correct mixing.

 The basin according to the invention, because of its particular shape and the presence of obstacles placed on the path of the liquid medium set in motion by a paddle wheel, allows the cultivation of algae, in particular Chondrus crispus, in an area moderately sunny, like the English Channel and Atlantic coasts, with excellent yields.

 Algae develop rapidly, under conventional culture conditions, such as those described by R. G. S. Bidwell in the document cited above, or by Neish et Col. in Canadian Journal of Botany 55 p. 2 2632 271 (1977).

 Productivity per unit area is ten to fifteen times higher than when the alga is in its natural environment; a slight difference in appearance was also observed between the wild algae and that cultivated in the basins according to the invention and above all a difference in composition since in the cultured algae there is practically no mu fraction, precursor of Kappa carrageenan, but only this carrageenan; this allows extraction by maceration of the plant in slightly alkalized water, while a basic treatment at pH 12 is necessary to transform the precursors and extract all the carrageenan from the wild plant.

 The pelvis according to the invention has in horizontal plane the shape of a more or less flattened crown defined between an outer wall and an inner core. It can for example be substantially elliptical, the internal core then being able to be reduced to a simple plane, located in the major axis of the ellipse; this plane will be materialized for example by a wall which stops from each caté at a distance from the external wall of the basin approximately equal to the minor axis of the ellipse, so that the liquid medium can circulate continuously around the central core ; an equivalent basin, although more cumbersome on the ground and slightly less efficient, consists of a circular or elliptical cylindrical crown. In the case of an elliptical basin, it is preferred that the length of the major axis is 2 to 8 times that of short axis and that the wall has a thickness just sufficient to ensure its resistance, that is to say from 8 cm to 1.80 m approximately, depending on the material which constitutes it (earth, concrete, cemented bricks).

 The basin 10 illustrated by way of example in horizontal plan view in FIG. 1 has an elongated elliptical shape. Only half of the pelvis has been illustrated, the other half being symmetrical with respect to a vertical transverse plane of trace XX.

 The basin is delimited between an outer wall 11 and a central core 12, reduced in this embodiment to a wall stopping at a certain distance from the two ends of the basin, which defines in the latter a closed flow circuit for the water contained in the basin.

 As already mentioned, the pelvis can be in the form of a circular crown, in which case the outer wall and the central core will have concentric circular traces; or again, the pelvis may have the shape of an elliptical crown, the outer wall and the central core having substantially concentric elliptical traces.

 The basin can be placed on the ground, half-buried or buried. I1 is, in addition, provided with at least one paddle wheel 14, the rotation of which ensures the circulation of the liquid medium around the central core 12 of the basin; its axis is therefore coincident with the radius of the basin at the point considered and its blades 16 soak in water to a depth sufficient to set in motion the liquid medium over its entire height. The specialist will be able to calculate the size of the blades, their diving height in the water, the axis rotation speed depending on the shape and dimensions of the pool - and in particular the height of the water , knowing that the speed of movement of the liquid must be sufficient to avoid significant development of macrophyte algae, that is to say practically greater than 0.30 seconds.

 It is preferable, in order not to have a dead zone, next to very stirred zones, to have two wheels 14, 14 ′ in the basin, in diametrically opposite position particularly in the basins in crown, or for the basins with flattened central core, in the elongated part of the ellipse and cutting the 2 currents in opposite directions as shown in Fig. 1, but the wheels may not be in the axis of symmetry of the pelvis. The distance between their axes can be up to 2/3 of the length of the basin.

 The height of the calf in the basin depends on the species of algae cultivated, their density and size, as well as the average sunshine; it will generally be between 0.3 m and 1 m, preferably close to 0.40 m to ensure satisfactory circulation of the liquid and the illumination over a maximum depth.

 Finally, the basin is also provided with obstacles 18, 20 located on the path of the liquid medium, consisting for example of small vertical or slightly inclined walls, preferably flush with the upper level of the liquid, which form an angle between the current between 90 and 1600, and preferably 900 for the obstacles 20 located in the axis of the central core 12, and 1300 for those 18 downstream of the impellers 14,14 'whose length is at most equal to the half-width of the liquid current. These obstacles create vortices and locally accelerate the current ensuring better homogenization of the medium and the ascent of the algae to the surface of the water; the productivity of the culture is very appreciably improved in the presence of some obstacles, suitably placed, preferably in the zones where the current tends towards a laminar regime or those where the current is slowed down.

 Thus, in the case of the basin shown in FIG. 1, equipped with the 4 obstacles indicated, the productivity in an average year is 2.5 times that of a basin of the same shape, but stirred only by the paddle wheels.

 There is furthermore, as in conventional basins, a seawater inlet not shown and, preferably, at the other end, a pipe 22 for leaving the water; this outlet is advantageously located behind an obstacle, so that the density of algae in the area is low.

The water supply can be continuous or sequential; it must be sufficient to bring the quantity of trace elements and potassium necessary for the development of algae and compensate for natural evaporation.

 The configuration of the basin makes it possible to avoid recycling of the water, which is frequently installed on rectangular basins to create a current in the environment.

 Another object of the invention is the process for obtaining macroscopic algae, which consists in cultivating them in a basin according to the invention, supplied with sea water and supplemented with sources of carbon, nitrogen and phosphorus. The usual nutrients, nitrogen and phosphorus, are injected at regular intervals, preferably by interrupting the seawater circuit, which improves the absorption of the compounds by the algae and avoids a significant loss in the effluents.

 Carbon is also introduced into the culture medium in the form of carbon dioxide, a carbonate or an organic carboxylic acid; the pH of the culture medium is generally between 8 and 9 and preferably between 8.5 and 8.8 during periods of significant photosynthesis; a mineral acid can be introduced into the medium to keep it within these limits.

 According to another aspect of the process of the invention, an oxidizing aqueous solution is introduced into the basin during the culture, when the level of algae foreign to the culture resulting from the germination of the spores brought by the sea water becomes troublesome. containing an alkaline hypochlorite. The amount of NaOC1 depends on the characteristics of the basin and the amount of algae present, and the specialist will be able to determine it.

 A rapid treatment can be carried out, during which the oxidant is destroyed after a few minutes by the addition of a reducing agent, such as a thiodulfate or an alkaline hydrogen sulfite, or a simpler treatment in which the oxidant is allowed to eliminate spontaneously; it is obvious that in the second case, its initial concentration must be lower, by 15 to 25 X lower.

 In an elliptical basin of approximately 980 m2, in which the major axis is 7.2 times the minor axis, 40 cm deep and comprising two obstacles of 1 m and two obstacles of 2 m long, arranged as shown in the figure 1, 253 g / m2 by dry weight of red algae of the species Chondrus crispus were harvested in 4 weeks, from which carrageenan was extracted.

 For comparison, in a small round basin of 3 m in diameter, stirred by a strong bubbling of air, we harvested simultaneously with the same enriched marine environment, only 234 g / m2 of algae and that for a cost of significantly better operation, given the air circulation.

Claims (9)

 1. Basin (10 for growing macroscopic algae supplied with water, characterized in that it has a more or less flattened crown shape defined between an outer wall (II) and a central core (12), which it comprises at least one impeller (14) arranged radially and obstacles (18, 20).  2. Basin according to claim 1, characterized in that the central core (12) is reduced to a plane.  3. Basin according to claim 2, characterized in that it has a sensitive form of an ellipse are the length of the major axis is 2 to 8 times that of the minor axis.  4. Method for obtaining Chondrus crispus which consists in cultivating algae in a basin according to one of claims 1 to 3, supplied with sea water and supplemented with sources of carbon, nitrogen and phosphorus;  5. Method according to claim 4, characterized in that the carbon source is carbon dioxide, a carbonate or a carboxylic acid;  6. Method according to one of claims 4 or 5, characterized in that the pH of the medium is maintained between 8 and 9.  7. Method according to claim 6, characterized in that the pH of the medium is maintained between 8.5 and 8.8 by possible addition of a mineral acid during periods of significant photosynthesis.  8. Method according to one of claims 4 to 7, characterized in that it further comprises the addition of an alkaline hypochlorite to remove foreign algae;  9. Process according to reverxilcations 8, characterized in that the excess of hypochlorite is destroyed by the addition of an alkali metal thiosulphate or thiosulphate.