FR3023548A1 - DEVICES FOR TREATING WASTEWATER BY CULTIVATION OF MICROALGUES - Google Patents

Abstract

The invention relates to the treatment of domestic or industrial wastewater using microalgae. The invention particularly relates to an improvement of wastewater treatment devices by cultivating mixotrophic microalgae, energy gains and footprint. The invention also relates to a method for treating wastewater by culturing microalgae characterized in that it comprises a continuous or discontinuous injection of precultivated microalgae into a fermenter, said injected microalgae being advantageously in the growth phase, very advantageously at the beginning of the growth phase.

Description

The invention relates to the treatment of domestic or industrial wastewater using mixotrophic microalgae. It is also possible to say that the invention relates to the cultivation of microalgae through the depollution of wastewater, since the objectives of these two disciplines are entangled: depollution of the wastewater to produce a water usable by cultivating microalgae that can be used in many areas such as biofuel production, such as bioethanol, or in green chemistry for example by the production of biopolymers or polysaccharides. The invention particularly relates to an improvement of wastewater treatment devices by cultivation of microalgae in mixotrophy and by innoculating a raceway process by a culture highly concentrated in microalgae from fermentor cultures. The invention also relates to a method for treating wastewater by culturing microalgae characterized in that it comprises a continuous or discontinuous injection of precultured microalgae into a fermenter, said injected microalgae being advantageously in a growth phase, or at the beginning of the growth phase. The treatment of wastewater by microalgae (conversely the cultivation of microalgae by wastewater treatment) is relatively well known and documented in the prior art. In this regard, mention should be made of Abdel-Raouf et al. (Saudi Journal of Biological Sciences (2012) 19, 257-275). In summary, the wastewater can be treated by culture of microalgae in basins, called raceway or algal high efficiency lagoons, where the wastewater, advantageously previously cleared of their insoluble content (sludge and others), are incubated in Adapted basins in the presence of microalgae known for their ability to assimilate nitrogen (the step of depollution in nitrogen proves to be the most expensive in the usual processes of wastewater treatment) for example contained in nitrates (NO3 -), to assimilate nutrients contained in the wastewater to be treated such as easily assimilable organic carbon, soluble nitrogen (NH4) or soluble phosphorus (P043-), to assimilate also heavy metals such as zinc, cadmium, aluminum, chromium, copper, lead, mercury, nickel (see in this regard the review of Raul Muh-oz and Benoit Guieysse, Water Research, (2006) 40, 2799-2815). Thanks to the mixotrophic culture, the ammonium ions (NH4 +) will be transformed into nitrate ions (NO3-), this step in the conventional treatment process activated sludge wastewater represent the majority of energy costs, since it requires great amount of oxygen to introduce for bacteria and therefore large amounts of energy. It turns out that in addition to the growth of microalgae strains is favored by injecting CO2 into the culture medium. However, CO2 is a gas polluting the atmosphere generated by many industries and for which it is necessary to find either physical means of capture or other means to reduce the concentration in the ambient air. The treatment of wastewater by microalgae culture is one of the ways to recycle CO2 since it is easy to recover CO2 and inject it into microalgae culture basins in order to promote their growth.

A problem, however, well known in microalgae culture basins is their very large land use due to the need for large areas to plant culture basins. This problem has been partly solved by the immobilization of the microalgae strains on substrates immersed in raceways, which makes it possible, at the contact surface of the algae / identical culture medium, to reduce the footprint of the culture device (see in this respect, the review by Nirupama Mallick (BioMetals (2002) 15, 377-390) In addition, the immobilization of strains makes it possible to increase the cellular concentration in the wastewater to be treated and therefore to intensify the bioremediation process. algal, or the raceway or process of extensive algal culture, includes a smaller footprint, but the fact remains that another problem remains despite all the improvements made over time to the wastewater treatment devices. by microalgae culture: the loss of microalgae in the culture medium during the treatment process This loss can be mandatory because the device is by definition not only the treatment of wastewater but also the production of microalgae they grow during the culture and to avoid clogging the device it is necessary to regularly harvest microalgae produced and therefore to reduce the concentration in the device. Apart from this compulsory loss, the concentration of microalgae also decreases naturally during the cultivation. It is therefore necessary to find a way to maintain the constant amount of algae in the culture basin in order to maintain the rate of depollution of wastewater by the device and in parallel with the growth rate of microalgae grown.

Moreover, it is well known that the growth of microalgae is not linear but begins with a lag phase during which the rate of depollution of the culture medium will be almost zero, then continues with an exponential phase during which the growth rate of microalgae is maximum which is reflected in devices for treating wastewater by algae culture by a maximum of environmental pollution by the microalgae, then continues with a stationary phase followed by a decay phase during which the wastewater treatment device loses its effectiveness. It is therefore understood that it may be advantageous during the wastewater treatment cycle to have in the device as long as possible microalgae in exponential growth phase while avoiding as much as possible the initial latency phase, and the stationary phases and obviously of decay. It is an object of the present invention to provide a means of maintaining the amount of microalgae in a constant exponential growth phase in a wastewater treatment device.

Thus, the subject of the invention is primarily a device for treating wastewater by culturing microalgae, characterized in that it comprises at least one microalgae culture basin, a fermenter and at least one microalgae supplying means connecting said microalgae. fermenter said microalgae culture basin, in order to feed when necessary culture basin pre-cultured microalgae in said fermenter. The device according to the invention has the advantage of allowing almost constant maintenance in the wastewater treatment pond of a microalgae rate exponential phase sufficient so that the efficiency of wastewater treatment also remains almost constant. According to the invention, the fermenter may be smaller in volume than the microalgae culture basin. There may be a volume factor of at least 100 to 1000 between the two. The fermenter can be of any known type provided that it allows the cultivation of microalgae. In this regard, fermentors manufactured by the companies Pierre Guérin and Sartorius agitated tank type. These fermenters will produce the strains under controlled conditions to reach high cell densities at the site of the depollution plant and inject these strains in the raceway, place of depollution. A fed-batch fermentation strategy can be adopted and this strain culture will be done under sterile conditions. The strains will be produced one by one in this same fermenter. The medium used to grow the strains can be made from cheap carbon substrates such as sugar cane molasses or glucose monohydrate of moderate purity (> 80%) for example. According to the invention, said microalgae supply means connecting said fermentor to said microalgae culture tank may be any known means provided that it can be introduced at the desired time, namely rather during the growth phase of the strain. in the microalgae culture pond the microalgae grown in the fermenter. In this regard can be cited the withdrawal under sterile conditions fermenter also said sequenced batch reactor. The idea being to carry out a fermentation, to carry out the culture in exponential phase, to drain a big part of the volume (approximately 80% of the volume) in the basin or on the supports of immobilization and to leave with the rest of the medium of culture and the strain to start more quickly in the growth phase.

According to a first variant of the invention, said wastewater treatment device may further comprise a settling basin, advantageously disposed upstream of said microalgae culture basin, in which the solid components of the wastewater to be treated may be separated from water to clean up. The separation of the solid components of the wastewater to be treated may be carried out by any means known to those skilled in the art, advantageously by decantation, by filtration, or by filtration and decantation. According to a second variant of the invention, said wastewater treatment device may further comprise a separation basin, advantageously disposed downstream of said microalgae culture pond, wherein said microalgae may be separated from the water to be treated and possibly each used directly or for subsequent treatments. Indeed algae culture and therefore the treatment of wastewater, operating continuously, the algae that have cleaned the water of nutrients and consumed carbon dioxide, can be harvested regularly in the area of separation. The biomass suspended in the water can thus be concentrated. Any means of concentration can be used at this stage, such as, for example, the precipitation with iron salts (for example: ferric chloride, FeCl 3) with aluminum salts (for example: Alumina sulphate) and also more advantageously for the recovery of biomass flotation, autoflocculation, gravitational sedimentation then centrifugation, the addition of natural cationic or anionic organic polymers (example: chitosan) or even micro or ultrafiltration. The algae can then be harvested for example using a pump at the bottom of the book.

According to a third variant of the invention, said wastewater treatment device may further comprise one or more means (s) for supplying carbon dioxide (CO2) into the microalgae culture basin.

This means of supplying CO2 may be any means known to those skilled in the art. Advantageously CO2, for example from industry cement, food, energy (oil and gas, coal power plant), agro-food industry, chemical industries, or incinerators or treatment plants or industries fertilizer manufacturing, can be stored in compressed form and can be re-injected into the pond when microalgae need it, ie mainly during the day when the pond is lit by natural light, it is that is, when the microalgae are in the phase of photosynthetic metabolism (diurnal phase), this making it possible to optimize the uptake of CO2. CO2 can be injected by gas via medium or fine bubbles (maximum bubble sizes 3 to 4 mm). Fine bubbles may be favored to maximize the diffusion of CO2 in the medium. Indeed, the smaller the bubbles and the higher the transfer surface / volume ratio will be important so more transfer of CO2 in the liquid phase will be important. The diffusers may be in any known form, advantageously discs, plates or tubes. The injected gas may contain at least 4% of CO2, advantageously from 15% to 100%, preferably 15% or 99% (physical limit to the CO2 concentration, Air Liquide data).

According to a fourth variant of the invention, said wastewater treatment device may further comprise at least one microalgae fixing means. It is known that one of the interests of fixing algae is to partially overcome the constraint of the cell division time of the strains. Indeed, a fixed strain, immobilized on a support, because it is constantly fed has a lifespan 10 to 100 times longer and enzymatic activities tenfold compared to the same amount of algae in suspension. Any known means for fixing microalgae may be used in the device. According to the invention the fixing means may be of any type, in any material, of any shape and any volume, compatible with the function for which said fixing means is used and compatible with the device. Advantageously, said microalgae fixing means may be made of a porous material, such as, for example, pozzolan, vermiculite, perlite, alginate balls, carrageenan, oyster shells or polyurethanes or plastic resins made of polyethylenes. specific surface preferentially vermiculite and pozzolan.

Said fixing means may be used in suspension in water or packaged in mesh bags which will retain the supports and therefore the strains. The volume occupied by said fixing means may range from 1% to 50% of the volume of the basin. It is understandable that the size of the basin will be optimized.

According to a fifth variant of the invention, said wastewater treatment device may furthermore comprise at least one water recirculation means between said microalgae culture basin and said settling basin. This will allow, among other things, recirculation at the head of the device, in the settling basin which also forms an anoxic zone ensuring the denitrification of the water to be treated, nitrates contained in the water, which may allow the total elimination of water. nitrogen in the liquid phase. It is understood that the water recirculation means may be any means known to those skilled in the art such as a combination of tubing, valves, pumps and control means of the assembly.

According to this variant, it is possible to envisage a recirculation rate of between 50 and 500%, advantageously 100 and 400%; and very advantageously 150%. According to a sixth variant of the invention it is possible to envisage that said wastewater treatment device further comprises one or more means (s) of illumination. Any type of known lighting means may be used. Advantageously, the use of lamps, light ramps, or light piers as mentioned in patent Fermentalg, FR135364. We know that in the French latitudes, a factor of six exists between the maximum incident solar power in summer and the minimum power in winter. The addition of lighting means may make it possible to keep the device performance constant or almost constant throughout the year.

According to a seventh variant of the invention it is possible to envisage that said wastewater treatment device further comprises one or more means (s) for regulating the temperature. Any type of control means or thermal insulation of the raceway process (heat insulated walls) of the known temperature can be used. Advantageously, the use of a thermal insulation of the walls of the device, heating means (heat lamps, heating resistors, heat capture: placing in a greenhouse raceway for example etc., cooling means). Said wastewater treatment device may furthermore comprise any other known means for improving its performance, whether in the field of water treatment and / or in that of the growth of microalgae. The invention also aims at a process for the depollution of wastewater by microalgae culture, comprising a step of depollution of the waters by cultivation of algae in a Raceway-type basin, characterized in that culture strains are injected regularly or continuously into the culture basin; algae pre-cultured in a fermentor. According to a variant of the invention, the process for the depollution of wastewater by microalgae culture can implement a device as described above. Advantageously, the process according to the invention may use microalgae that can withstand high levels of dissolved CO2 (pH of the culture medium that can reach a value as low as 4) and high levels of nitrogen (maximum ammonium of 3 g NH 4 ± / L and preferably between 40 and 100 mg NH4 / L, maximum nitrates of 2 g N037L preferentially between 5 and 50 mgN037L). According to a variant of the invention, said process implements mixotrophic microalgae. According to another variant of the invention, said process uses microalgae of fresh water. According to yet another variant of the invention, said process implements mixotrophic microalgae of fresh water.

According to the invention, said microalgae may be chosen from the strains of the genera Botryococcus, Chlorella, Scenedesmus, Micractinium, Euglena, Nitzschia, Porphiridium, Chlamydomonas, Stephanodiscus, Monoraphidium and preferentially of the genera Chlorella, Botryococcus, Scenedesmus, Micractinium and Euglena. When microalgae are of the genus Botryococcus, they may be selected from the species B. australis, B. balkachicus, B. braunii, B. calcareus, B. canadensis, B. comperei, B. coorongianus, B. femandoi, B. giganteus. , B. neglectus, B. pila, B. protuberans, B. sudeticus, B. terribilis, B. terricola. Advantageously according to the invention the algae of the genus Botryococcus may be algae of the species B. braunii. When the microalgae are of the Chlorella genus, they may be selected from C. acuminata, C. anitrata, C. antarctica, C. botryoides, C. condtrix, C. con glomerata, C. desiccata, C. emersonii, C. fusca, C. glucotropha, C. homosphaera, C. infusionum, C. luteoviridis, C. marina, C. miniata, C. minutissima, C. mirabilis, C. noctuma, C. oocystoides, C. ovalis, C. parasitica, C. parva, C. peruviana, C. protothecoides, C. pyrenoidosa, C. regularis, C. rugosa, C. saccharophila, C. satina, C. sorokiniana, C. spaerckii, C. stigmatophora, C. subsphaerica, C. variabilis, C. variegata, C. vulgaris, C. xanthella, C. zopfingiensis. Advantageously according to the invention the algae of the genus Chlorella may be algae selected from the species C. sorokiniana or C. vulgaris. When microalgae are of the genus Scenedesmus, they may be selected from S. abundans, S. aciculatus, S. aculeolatus, S. aculeotatus, S. acuminatus, S. acutiformis, S. acutus, S. aldavei, S. ambuehlii. , S. anhuiensis, S. anomalus, S. apicauda tus, S. apicula tus, S. arcua tus, S. arista tus, S. arma tus, S. arvemensis, S. bacillaris, S. baculiformis, S. bajacalifomicus, S. balatonicus, S. basiliensis, S. bemardii, S. bicauda tus, S. bicellularis, S. bidenta tus, S. bijuga, S. bijuga tus, S. bijugus, S. brasiliensis, S. breviaculeatus, S. brevispina , S. caribeanus, S. cariatus, S. caudatoaculeolatus, S. cauda tus, S. chlorelloides, S. circumfusus, S. coalitus, S. costatogranulatus, S. crassidenta tus, S. curvatus, S. decorus, S. denticula tus, S. deserticola, S. dileticus, S. dimorphus, S. disciformis, S. dispar, S. distentus, S. ecomis, S. ellipsoideus, S. ellipticus, S. falca tus, S. fenestratus, S. grahneisii , S. granulatus, S. gujaratensis, S. hanleyi, S. hel veticus, S. heteracanthus, S. hindakii, S. hirsutus, S. hortobagyi, S. huangshanensis, S. hystrix, S. incrassatulus, S. indianensis, S. indicus, S. intermedius, S. jovais, S. jugalis, S. kerguelensis, S. kissii, S. lefevrei, S. littoralis, S. longispina, S. Ionus, S. mirus, S. multistria tus, S. naegelii, S. nanus, S. oahuensis, S. obliquus, S. obtusus, S. olvaltemus, S. opoliensis, S. ovaltemus, S. pannonicis, S. papillosum, S. parisiensis, S. parvus, S. pecsensis, S. perforatus, S. planctonicus, S. plarydiscus, S. platydiscus, S. pleiomorphus, S. polessicus, S. polyglobulus, S. polyspinosus, S. praetervisus, S. prismaticus, S. producto-capitatus, S. protuberans, S. pseudoarma tus, S. pyrus, S. quadrialatus, S. quadricauda, S. quadrispina, S. raciborskii, S. reginae, S. reniformis, S. rostrato-spinosus, S. rotundus, S. schnepfii, S. securiformis, S. semipulcher, S. senilis, S. serrato-perfora tus, S. serra tus, S. serrula tus, S. setiferus, S. smithii, S. sou, S. sooi, S. spinosus, S. spinula tus, S. stria tus., S. subspica tus, S. tetradesmiformis, S. tricosta tus, S. tschudyi, S. vacuolatus, S. velitaris, S. verrucosus, S. vesiculosus, S. weberi, S. wisconsinensis, S. wuhanensis, S. wuhuensis. Advantageously according to the invention the algae of the genus Scenedesmus may be algae selected from the species S. obliquus or S. quadricauda. When the microalgae are of the genus Micractinium, they may be selected from M. appendiculatum, M. belenophorum, M. bomhemiense, M. condtrix, M. conococcoides, M. crassisetum, M. crassispinum, M. elongatum, M. eriense. M. extremum, M. inermum, M. octospinum, M. parvisetum, M. parvulum, M. parvum, M. paucispinum, M. pusillum, M. pusillum f. quadrisetum, M. pusillum var. mucosum, M. pusillum var. elegans, M. pusillum var. longisetum, M. pusillum, M. quadrisetum, M. radiatum, M. reisseri, M. sp., M. strigoniense, M. viride. Advantageously according to the invention the algae of the genus Micractinium may be algae selected from the species M. sp. and M. pusillum. When the microalgae are of the Euglena genus, they may be chosen from the species E. acauda, E. acaulis, E. acus, E. acusformis, E. nadhaerens, E. agilis, E. ahi, E. alata, E. allorgei, E. americana, E. amphipyrenica, E. anabaena, E. anabaenaminima, E. anaerobica, E. anguillula, E. angusta, E. ante tossa, E. anura, E. aquaepurae, E. ara ci, E. archaeoplastidiata, E. arcus, E. ascusformis, E. astasioides, E. aumuelleri, E. austalica, E. australica, E. bacillaria, E. bacilliformis, E. baltica, E. basistellata, E. bellovacensis, E. bichions, E. bistellata, E. bivittata, E. boirsensis, E. bonettoi, E. brevicaudata, E. brevifilagellum, E. bucharica, E. caballeroi, E. calva, E. cantabrica, E. carterae, E. caudata, E. centralis, E. centrorubra, E. chadefaudii, E. chaetophorina, E. chamberlini, E. charkiensis, E. charkowiense, E. chemichromata, E. chlamydophora, E. chlorodictyon, E. chlorophoenicea, E. choretes, E. cingula, E. circularis, E. clara, E. clavata, E. communis, E. com Pressa, E. conca vus, E. con fusa, E. contabrica, E. convoluta, E. copula, E. cuvata, E. cyclopicola, E. demulcens, E. deses, E. detonii, E. dikaryon, E. discolor, E. Distinct, E. downiae, E. durbanica, E. ecaudata, E. ehrenbergi, E. elastica, E. elenkinii, E. elongata, E. estonica, E. ettlii, E. eutreptia, E. excavata, E. exilis, E. fenestrata, E. flagellata, E. flava, E. foliacea, E. fomicata, E. tracta, E. fundoversata, E. fusca, E. gastrosteus, E. gaumei, E. geniculata, E. gentilis, E. gibbosa, E. globosa, E. gojdicsas, E. gracilis, E. granulata, E. grisoli, E. guttula, E. gymnodinioides, E. haematodes, E. heimii, E. helicoideus, E. heliorubescens, E. hemichromata, E. hiemii, E. hirudo, E. hispidula, E. hyalina, E. iara, E. ignobilis, E. incisa, E. incurva, E. inflata, E. intermedia, E. interrupta, E. intervolans, E. iraci, E. jacira, E. jandira, E. jirovecii, E. juraci, E. kemenesii, E. klebsi, E. korshikovii, E. laciniata, E. laevis, E. tata, E. lepocincloides, E. leucops, E. li Mophila, E. limosa, E. longa, E. longicaudata, E. longotaulis, E. longissima, E. longuscula, E. lucens, E. lutaria, E. magnifica, E. maharastrensis, E. mainxi, E. mangenotti, E. mangini, E. matvienkoi, E. megalithus, E. mesnili, E. messula, E. metabolica, E. middelhoekii, E. minima, E. minuta, E. montanensis, E. mucifera, E. mucosa, E. mucronata, E. multiformis, E. mutabilis, E. nana, E. navicula, E. neglecta, E. neustonica, E. oblonga, E. obscura, E. obtusa, E. obtusa-claudata, E. obtusata, E. obtuso-caudata, E. olivacea, E. orientalis, E. orna ta, E. orthia, E. ostendensis, E. oxyuris, E. palmeri, E. paludosa, E. paradoxa, E. parasitica, E. pascheri, E. Pavlovskoensis, E. pedunculata, E. penardii, E. physeter, E. pigmaea, E. pisciformis, E. planctonica, E. pleuronectes, E. polymorpha, E. pringsheimii, E. pro wsei, E. proxima, E. pseudochadefaudii, E. pseudoehrenbergii, E. pseudospirogyra, E. pseudostellata, E. pseudoviridis, E. pseudoxyuris, E. pumila, E. purpurea, E. pusilla, E. py riformis, E. radians, E. ranunculformis, E. refringens, E. repulsans, E. reticulata, E. retronata, E. rhynchophora, E. rivulariarum, E. robertilamii, E. rostrata, E. rostrifera, E. rubida, E. rubra, E. rustica, E. ruttneri, E. sabulorum, E. sacculiformis, E. satina, E. sanguinea, E. sanguinea, E. scherffelii, E. sciotensis, E. seppiana, E. sessilis, E. sieminskiana, E. simulacra, E. slavjanskiensis, E. sociabilis, E. spadix, E. sphagnicola, E. spinifera, E. spirogyra, E. spiroides, E. splendens, E. srinagari, E. stellata, E. striato- punctata, E. subacutissima, E. subehrenbergii, E. subthinophila, E. sulcata, E. sulcifera, E. synchlora, E. tentans, E. tenuior, E. terricola, E. texta, E. thienemannii, E. E. tibetica, E. tiszae, E. torta, E. tripteris, E. tristella, E. truncata, E. truncatula, E. tuba, E. tuberculata, E. undulata, E. univittata, E. utriculus, E. vagans, E. vaginicola, E. van-gloori, E. variabilis, E. velata, E. velveta, E. vermicularis, E. vermiformis, E. ves terbottnica, E. vilmae, E. viridis, E. vittata, E. vivida, E. walneae, E. wangii, E. zocchioi, E. zonalis. Advantageously according to the invention the algae of the genus Euglena may be algae of the species E. gracilis or E. viridis. When the microalgae are of the genus Nitzschia, they may be selected from the species N. abbreviata, N. abonuensis, N. abridia, N. accedens, N. accommoda ta, N. aciculariformis, N. acicularioides, N. acicularis (in all these variants), N. acidoclinata, N. actinastroides, N. actydrophila, N. acula, N. acuminata (in all these variants), N. acuta, N. adamata, N. adamatoides, N. adapta, N. adducta, N. adductoides, N. admissa, N. admissoides, N. aequalis, N. aequatorialis, N. aequorea, N. aerophila, N. aerophiloides, N. aestuari, N. affinis, N. africana, N. agnewii, N. agnita, N. alba, N. albicostalis, N. alexandrina, N. alicae, N. allanssonii, N. alpina, N. alpinobacillum, N. amabilis, N. ambigua, N. americana, N. amisaensis, N. amphibia, N. amphibia (in all these variants), N. amphibioides, N. amphicephala, N. amphilepta, N. amphioxoides, N. amphioxys (in all these variants), N. amphiplectans, N. amphiprora, N. amplectens, N. amundonii, N. anassae, N. andicola, N. angularis (in all these variants), N. angulata, N. angustata (in all these variants), N. angustatula, N. angustiforaminata, N. aniae, N. antarctica, N. antillarum, N. apiceconica, N. apiculata, N. archibaldii, N. arcuata, N. arcula, N. arcus, N. ardua, N. aremonica, N. arenosa, N. areolata, N. armoricana, N. asperula, N. astridiae, N. atomus, N. aurantia, N. aurantia, N. aurariae, N. aurica, N. auricula, N. australis, N. austriaca, N. bacata (in all these variants), N. bacillariaeformis, N. bacilliformis, N. bacillum, N. balatonis, N. balcanica, N. baltica, N. barbieri (in all these variants), N. barkleyi, N. barronii, N. barrowiana, N. bartholomei, N. bathurstensis, N. bavarica, N. behrei, N. bergii, N. beyeri, N. biacrula, N. bicapitata (in all these variants),. bicuneata, N. bifurcata, N. bilobata (in all these variants), N. birostrata, N. bisculpta, N. bita, N. bizertensis, N. blankaartensis, N. bombiformis, N. borealis, N. bosumtwiensis, N. braarudii, N. brebissonii (in all these variants), N. bremensis (in all these variants), N. brevior, N. brevirostris, N. brevissima (in all these variants), N. brevistriata, N. brightwellii, N. brittonii, N. brunoi, N. bryophila, N. buceros, N. bukensis, N. bulnheimiana, N. buschbeckii, N. calcicola, N. caledonensis, N. calida (in all these variants), N. califomica, N. campechiana, N. capensis, N. capitata, N. capitellata (in all these variants), N. capuluspalae, N. camicobarica, N. camico-barica, N. challengeri, N. chalonii, N. chandolensis, N. chardezii, N. chasei, N. chauhanii, N. chungara, N. chutteri, N. circumsuta, N. clarissima, N. clausii, N. clementei, N. clementia, N. clevei, N. closterium (in all these variants), N. coarctata, N. cocconeiformis, N. communis (in all these variants), N. commutata, N. commutatoides, N. compacta, N. compressa (in all these variants), N. concordia, N. confinis, N. con formata, N. con fusa, N. congolensis, N. constricta (in all these variants), N. consummata, N. corpulenta, N. costei, N. coutei, N. creticola, N. cucumis, N. cursoria, N. curta, N. curvata, N. curvilineata, N. curvipunctata, N. curvirostris (in all these variants), N. curvula (in all these variants), N. cuspidata, N. cylindriformis, N. cylindrus, N. dakariensis, N. davidsonii, N. dealpina, N. debilis , N. decipiens, N. delauneyi, N. delicatissima, N. delicatula, N. delognei, N. denticula (in all these variants), N. denticuloides, N. desertorum, N. dianae, N. diaphana, N. diducta , N. didyma, N. dietrichii, N. dilata ta, N. diluviana, N. dippelii, N. directa, N. diserta, N. disputa ta, N. dissipa ta (in all these variants), N. dissipatoides, N. distans (in all these variants), N. distantoides, N. divaricata, N. divergens, N. Diversa, N. diversecostata, N. doljensis, N. draveillensis, N. droebakensis, N. dubia (in all these variants), N. dubiformis, N. dubioides, N. ebroicensis, N. eglei, N. elegans, N. elegantula, N. ele gens, N. elliptica, N. elongata, N. entomon, N. epiphytica, N. epiphyticoides, N. epithemiformis, N. epithemioides, N. epithemoides (in all these variants), N. epsilon, N. erlandssonii, N. erosa, N. etoshensis, N. examanda, N. eximia, N. famelica, N. fasciculata, N. febigeri, N. ferox, N. ferrazae, N. fibula-fissa, N. filiformis (in all these variants), N. flexa, N. flexoides, N. fluminensis, N. fluorescens, N. fluvialis, N. fogedii, N. fonticola (in all these variants), N. fonticoloides, N. fonticula, N. fontifuga , N. forfica, N. formosa, N. fossalis, N. fossilis, N. fragilariiformis, N. franconica, N. fraudulenta, N. frauenfeldii, N. frequens, N. frickei, N. frigida (in all these variants) , N. frustuloides, N. frustulum (in all these variants), N. fruticosa, N. fundi, N. fusiformis, N. gaarderi, N. gaertnerae, N. gandersheimiensis, N. garrensis, N. gazellae, N. geitlerii, N. gelida (in all of these variants), N. geniculata, N. gessneri, N. gieskesii, N. gigantea, N. gisela, N. glabra, N. glacialis (in all these variants), N. glandiformis, N. goetzeana (in all these variants), N. gotlandica, N. graciliformis, N. gracilis ( in all these variants), N. gracillima, N. graciloides, N. gradifera, N. graeffii, N. grana, N. grandis, N. granii (in all these variants), N. granulata (in all these variants), N. granulosa, N. groenlandica, N. grossestriata, N. grovei, N. gruendleri, N. grunowii, N. guadalupensis, N. guineensis, N. guttula, N. gyrosigma, N. habirshawii, N. habishawii, N. hadriatica, N. halteriformis, N. hamburgiensis, N. hantzschiana (in all these variants), N. harderi, N. harrissonii, N. hassiaca, N. heidenii, N. heimii, N. hemistriata, N. heteropolica, N. heuflerania, N. heufleriana (in all these variants), N. hiemalis, N. hiengheneana, N. hierosolymitana, N. hoehnkii, N. holastica, N. hollerupensis, N. holsatica, N. homburgiensis, N. hudsonii, N. hummii, N. hungarica (in all of these variants), N. hustedti, N. hustedtiana, N. hyalina, N. hybrida (in all these variants), N. hybridaeformis, N. ignorata (in all these variants), N. iltisii, N. impressa, N. improvisa, N. incerta, N. incognita, N. inconspicua, N. incrustans, N. incurva (in all these variants), N. indica, N. indistincta, N. inducta, N. inflatula, N. ingenua, N. inimasta, N. innominata, N. insecta, N. insignis (in all these variants), N. intermedia (in all these variants), N. intermissa, N. interrupta, N. interruptstriata, N. invicta (in all these variants), N. invisa, N. invisitata, N. iranica, N. irregularis, N. irremissa, N. irrepta, N. irresoluta, N. irritans, N. italica, N. janischii, N. jelineckii, N. johnmartinii, N. juba, N. jucunda, N. jugata (in all these variants), N. jugiformis, N. kahlii, N. kanakarum, N. kanayae, N. kavirondoensis, N. kerguelensis, N. kimberliensis, N. kittlii, N. kittonii, N. knysnensis, N. kolaczeckii, N. kotschyi, N. kowiensis, N. krachiensis, N. krenicola, N. kuetzingiana (in all these variants), N. kuetzingii, N. kuetzingioides, N. kurzeana, N. kurzii, N. kützingiana (in all these variants), N. labella, N. labuensis, N. lacrima, N. lacunarum, N. lacunicola, N. lacus-karluki, N. lacustris, N. lacuum, N. laevis, N. laevissima, N. lagunae, N. lagunensis, N. lamprocampa (in all these variants), N. lanceola (in all these variants), N. lanceolata (in all these variants), N. lancettula, N. lancettuloides, N. lange-bertalotii, N. latens, N. latestriata, N. latiuscula, N. lauenbergiana, N. lauenburgiana, N. lecointei, N. leehyi, N. legleri, N. lehyi, N. leistikowii, N. lesbia, N. lesinensis, N. laothensis, N. leucosigma, N. levidensis (in all these variants), N. liebetruthii (in all these variants), N. ligowskii, N. limicola, N. limulus, N. linearis (in all these variants), N. lineata, N. lineola, N. linkei, N. lionella, N. littoralis (in all these variants), N. littorea, N. longa, N. longicollum, N. longirostris, N. longissima (in all these variants), N. lorenziana (in all these variants), N. lucisensibilis, N. lunaris, N. lunata, N. lurida, N. luzonensis, N. macaronesica, N. macedonica, N. macera, N. machardyae, N. macilenta (in all these variants), N. magnacarina, N. mahihaensis, N. mahoodii, N. maillardii, N. major, N. majuscula (in all these variants) ), N. makarovae, N. manca, N. mancoides, N. manguini, N. margina ta, N. marginulata (in all these variants), N. marina, N. martiana, N. maxima, N. media, N medioconstricta, N. mediocris, N. mediterranea, N. metzeltinii, N. microcephala (in all these variants), N. migrans, N. minuta, N. minutissima, N. minutula, N. miramarensis, N. miserabilis, N. mitchelliana, N. modesta, N. moissacensis (in all these variants), N. moll is, N. monachorum, N. monoensis, N. montanestris, N. morosa, N. multistriata, N. nana, N. natalensis, N. natans, N. nathorsti, N. navicularis, N. navis-varingica, N. navrongensis, N. neglecta, N. nelsonii, N. neocaledonica, N. neoconstricta, N. neofrigida, N. neogena, N. neotropica, N. nereidis, N. nicobarica, N. nienhuisii, N. normannii, N. notabilis, N. novae-guineaensis, N. novaehollandiae, N. nova-zealandia, N. nyassensis, N. oberheimiana, N. obesa, N. obliquecostata, N. obscura, N. obscurepunctata, N. obsidialis, N. obsoleta, N. obsoletiformis, N. obtusa (in all these variants), N. obtusangula, N. oceanica, N. ocellata, N. oliffi, N. omega, N. osmophila, N. ossiformis, N. ostenfeldii var. minor, N. ovalis, N. paaschei, N. pacifica, N. palacea, N. palea (in all these variants), N. paleacea, N. paleacea, N. paleacea, N. paleaeformis, N. paleoides, N. palustris, N. pamirensis, N. panduriformis (in all these variants), N. pantocsekii, N. paradoxa (in all these variants), N. parallela, N. pararostrata, N. partita, N. parvula (in all these variants) ), N. parvuloides, N. paxillifer, N. peisonis, N. pela gica, N. pellucida, N. pennata, N. peragallii, N. perindistincta, N. perminuta, N. perpusilla (in all of these variants), N. N. perspica, N. persuiana, N. pertica, N. perversa, N. petitiana, N. philippinarum, N. pilum, N. pinguescens, N. piscinarum, N. plana (in all these variants), N. planctonica, N. plicatula, N. plioveterana, N. polaris, N. polymorpha, N. ponciensis, N. praecurta, N. praefossilis, N. praereinholdii, N. princeps, N. procera, N. prolongata (in all these variants), N. prolongatoides, N. promare, N. propin qua, N. pseudepiphytica, N. pseud oamphioxoides, N. pseudoamphyoxys, N. pseudoatomus, N. pseudobacata, N. pseudocapitata, N. pseudocarinata, N. pseudocommunis, N. pseudocylindrica, N. pseudodelicatissima, N. pseudofonticola, N. pseudohungarica, N. pseudohybrida, N. pseudonana, N. pseudoseriata, N. pseudosigma, N. pseudosinuata, N. pseudostagnorum, N. pubens, N. pulcherrima, N. pumila, N. punctata (in all these variants), N. pungens (in all of these variants), N. pungiformis, N. pura, N. puriformis, N. pusilla (in all these variants), N. putrida, N. quadrangula, N. quickiana, N. rabenhorstii, N. radicula (in all these variants), N. rautenbachiae, N. recta (in all these variants), N. rectiformis, N. rectilonga, N. rectirobusta, N. rectissima, N. regula, N. reimerii, N. reimersenii, N. retusa, N. reversa, N. rhombica, N. rhombiformis, N. rhopalodioides, N. richterae, N. rigida (in all these variants), N. ritscheri, N. robusta, N. rochensis, N. rolandii, N. romana, N. romanoides, N. romano wiana , N. ro R., N. rosenstockii, N. rostellata, N. rostrata, N. ruda, N. rugosa, N. rupestris, N. rusingae, N. ruttneri, N. salinarum, N. salinicola, N. salpaespinosae, N. salvadoriana, N. sylvophagum, N. scabra, N. scalaris, N. scaligera, N. scalpelliformis, N. schoenfeldii, N. schwabei, N. schweikertii, N. scutellum, N. sellingii, N. semicostata, N. semirobusta, N. separanda, N. seriata (in all these variants), N. serpenticola, N. serpentiraphe, N. serrata, N. sibula (in all these variants), N. sigma (in all of these variants), N. sigma formis, N. sigmatella, N. sigmoidea (in all these variants), N. silica, N. silicula (in all these variants), N. siliqua, N. similis, N. simplex, N. simpliciformis, N. sinensis , N. sinuata (in all these variants), N. smithii, N. sociabilis, N. socialis (in all these variants), N. solgensis, N. solida, N. solita, N. soratensis, N. sp., N. spathulata (in all these variants), N. speciosa, N. spectabilis (in all these va mites), N. sphaerophora, N. spiculoides, N. spiculum, N. spinarum, N. spinifera, N. stagnorum, N. steenbergensis, N. stellata, N. steynii, N. stimulus, N. stoliczkiana, N. stompsii (in all these variants), N. strelnikovae, N. stricta, N. strigillata, N. striolata, N. subaccommodata, N. subacicularis, N. subacuta, N. subamphioxioides, N. subapiculata, N. subbacata, N. subcapitata , N. subcapitellata, N. subcohaerens (in all these variants), N. subcommunis, N. subconstricta, N. subcurvata, N. subdenticula, N. subfalcata, N. subfraudulenta, N. subfrequens, N. subfrustulum, N. subgraciloides , N. subinflata, N. subinvicta, N. sublae vis, N. sublanceolata, N. sublica, N. sublinearis, N. sublongirostris, N. submarina, N. submediocris, N. subodiosa, N. subpacifica, N. subpunctata, N. subromana, N. subrostrata, N. subrostratoides, N. subrostroides, N. subsalsa, N. subtilioides, N. subtils (in all these variants), N. subtubicola, N. subvitrea, N. suchlandtii, N. sulcata, N. sundaens is, N. supralitorea, N. tabellaria, N. taenia, N. taeniiformis, N. tantata, N. tarda, N. taylorii, N. temperei, N. tenella, N. tenerifa, N. tenuiarcuata, N. tenuirostris, N. tenuis (in all these variants), N. tenuissima, N. tergestina, N. terrestris, N. terricola, N. thermalis (in all these variants), N. thermaloides, N. tibetana, N. tirstrupensis, N. tonoensis, N. towutensis, N. translucida, N. tropica, N. tryblionella (in all these variants), N. tsarenkoi, N. tubicola, N. tumida, N. turgidula, N. turgiduloides, N. umaoiensis, N. umbilicata, N. umbonata, N. vacilla, N. vacua, N. valdecostata, N. valdestriata, N. valens, N. valga, N. valida (in all these variants), N. vanheurckii, N. vanoyei, N. v. ventricosa, N. vermicularis (in all these variants), N. vermicularoides, N. vexans, N. victoriae, N. vidovichii, N. vildaryana, N. villarealii, N. virgata, N. visurgis, N. vitrea (in all these variants), N. vivax (in all these variants), N. vixnegligenda , N. vonhauseniae, N. vulga, N. weaveri, N. weissflogii, N. westii, N. williamsiii, N. wipplingeri, N. witkowskii, N. wodensis, N. woltereckii, N. wuellerstorfii, N. wunsamiae, N. Yunchengensis, N. zebuana, N. zululandica. Advantageously according to the invention, the algae of the genus Nitzschia may be algae selected from N. sp. Species.

When microalgae are of the genus Porphiridium, they may be selected from P. aerugineum, P. cruentum, P. griseum, P. marinum, P. purpureum, P. sordidum, P. violaceum. Advantageously according to the invention the algae of the genus Porphiridium may be algae selected from the species P. aeruginum and cruentum.

When the microalgae are of the genus Chlamydomonas, they may be selected from C. aalesundensis, C. abbreviata, C. acidophila, C. acies, C. actinochloris, C. aculeata, C. acuminata, C. acuta, C. acutata , C. acuteovalis, C. acutiformis, C. acutissima, C. aequabilis, C. aestivata, C. africana, C. agametos, C. agloeformis, C. akimovii, C. alaskensis, C. alata, C. alatapapilla, C. albo-viridis, C. allensworthii, C. allorgei, C. alpina, C. altera, C. alveolata, C. ambigua, C. ametastatos, C. amici-mei, C. amoena, C. amplissima, C. ampulla , C. anglula, C. angulosa, C. annula ta, C. antarcticus, C. anticontata, C. anulata, C. anuraea, C. apex, C. apiangulata, C. apicala, C. apiculata, C. apiocystiformis, C. appendiculata, C. applanata, C. arachne, C. arctoalpina, C. areolata, C. armata, C. asiatica, C. asterosperma, C. astigmata, C. asymmetrica, C. atactogama, C. attenuata, C. augustae, C. autumnalis, C. bacca, C. baccata, C. bacillaris, C. bacillus, C. badensis, C. ball C. basimellulata, C. basistellata, C. basistigmata, C. bebaryana, C. bella, C. bergii, C. bemardinensis, C. biarticulata, C. bicaudata, C. bichlora, C. biciliata, C. bicocca, C. biconica, C. bicon vexa, C. bifrons, C. bila tus, C. bipapillata, C. bipartita, C. biverruca, C. blatnensis, C. boldii, C. bolyaiana, C. botryodes, C. botryopara, C. botrys, C. botulus, C. bourrellyi, C. brachyura, C. brannonii, C. braunii, C. breviciliata, C. brezoviensis, C. bulla ta, C. bullosa, C. burchallii, C. bursiculaeformis, C. calatelensis, C. calcicola, C. callosa, C. callunae, C. calyptrata, C. calyptrocarpa, C. capitata, C. capitis, C. caput-sepiae, C. carolii, C. carpatica, C. carrizoensis, C. C. Caudata, C. cava, C. cavanillesiana, C. celerrima, C. chadefaudii, C. characioides, C. chlamydogama, C. chlorastera, C. chlorogoniella, C. chlorogonioides, C. chlorolobata, C. chodati , C. cholnokii, C. christensenii, C. chrysomonadis, C. cienkowskii, C. cistula, C. citriformis, C. clavat a, C. closter, C. coccoides, C. communis, C. compacta, C. complanata, C. completa, C. composita, C. concinna, C. concordia, C. concrescens, C. con finis, C. conica , C. coniformis, C. conjungens, C. conochilae, C. conocylindrus, C. conoides, C. constricta, C. contexta, C. conversa, C. con vexa, C. cordiformis, C. comuta, C. corrosa, C. corticata, C. corticatiformis, C. costata, C. crassa, C. crassicauda, C. cristata, C. cucculata, C. cuneata, C. curvicauda, C. cyanea, C. cylindrica, C. cylindrocystiformis, C. cylindrus, C. dactylococcoides, C. dalecarlica, C. damasii, C. dan geardiana, C. dangeardii, C. danica, C. dauciformis, C. debaryana, C. de-baryana, C. decipiens, C. deludens, C. depressa, C. desmidii, C. detata, C. dictyosphaeriae, C. difficile, C. diffusa, C. dilatata, C. dillii, C. dinobryonii, C. discifera, C. dissimilis, C. distracta, C. doliolum , C. dorsoventralis, C. dresdensis, C. duplex, C. durbanica, C. dysosmos, C. ehrenbergii, C. elegans, C. elliptica, C. elongatum, C. emaculata, C. endogloea, C. enteromorphae, C. epibiotica, C. epiphytica, C. epizootica, C. epsilon, C. eradians, C. eriense, C. ettlii, C. euchlorum, C. eudorinae, C. eugametos, C. euglenaeformis, C. eupapillata, C. euryale, C. eustigma, C. eustigmata, C. ecentrentra, C. fallax, C. fascia ta, C. fenestrata, C. ferrophila, C. fiscina, C. fissa, C. flavovirens, C. flosaquae, C. flosculariae, C. fluvialis, C. fonticola, C. foraminata, C. formosissima, C. fossalis, C. fottii, C. foveola, C. foveolarum, C. foveolata, C. fragilis , C. franki, C. franzei, C. friedmannii, C. frigida, C. fritschiana, C. fungicola, C. fusus, C. gallica, C. geminata, C. gerloffii, C. gibberula, C. glacialis, C. Glans, C. globosa, C. globulosa, C. globus, C. gloeogama, C. gloeopara, C. gloeophila, C. gordalensis, C. goroschankini, C. io gracilis, C. grandis, C. grandistigma, C. granula ta, C. granulosa, C. gregaria, C. grintzescui, C. grovei, C. guizhounensis, C. gutta, C. gymnogyne, C. gyroides, C. gyrus, C. haema tococcoides, C. hallensis, C. halophila, C. hartmanni, C. hebes, C. hedleyi, C. heimii, C. hemigymnos, C. hennessyi, C. heterogama, C. heverlensis, C. hexangularis, C. hiberna, C. hiemalis, C. holdereri, C. hovassei, C. huberi, C. humicola, C. hyalina, C. hydra, C. hypermaculata, C. hyperpapillata, C. hyperstigma, C. hypolimnica, C. imitans, C. C. incisa, C. incaerans, C. incrassata, C. incurvata, C. inermis, C. inertis, C. inflexa, C. inhabilis, C. insana, C. insolita C. intermedia, C. inversa, C. involucrata, C. irregularis, C. isabeliensis, C. isogama, C. iyengari, C. jemtlandica, C. kakosmos, C. kirchneriellae, C. klebsii, C. klinobasis, C. kniepii, C. kochii, C. koishikavensis, C. komarekii, C. komma, C. koprophilos, C. kronauensis, C. kuteinikowii, C. kuwadae, C. kvildensis, C. lacustris, C. laeve, C. lagenula, C. languida, C. lapponica, C. lata, C. lateralis, C. lateritia, C. latifrons, C. leiostraca, C. tenta, C. leptobasis, C. le ptochaete, C. leptos, C. lewinii, C. libera, C. libonica, C. limosa, C. lismorensis, C. lobulata, C. longeciliata, C. longeovalis, C. longirubra, C. longistigma, C. loricata , C. lunata, C. lunatopyrenoidea, C. mondi, C. lunulatiformis, C. macroplastida, C. macropyrenoidosa, C. macrostellata, C. macrostigma, C. madraspatensis, C. magnusii, C. magurensis, C. manshurica, C. maramuresensis, C. marina, C. marsupium, C. marvanii, C. matwienkoi, C. media, C. mediocris, C. mediostigmata, C. melanospora, C. meslinii, C. metapyrenigera, C. metastigma, C. meyeri, C. microcystiae, C. microhalophila, C. micropapillata, C. microscopica, C. microsphaera, C. mikroplankton, C. mimina, C. minor, C. minuta, C. minutissima, C. moewusii, C. monadina, C. monoica, C. monpulsata, C. montana, C. monticola, C. moorei, C. mucicola, C. muciphila, C. multigranulis, C. multiplex, C. multipyrenoidosa, C. multitaeniata, C. muriella, C. muscicola, C. musculus, C. mutabilis, C. nannostigma, C. napocensis, C. nas trochloris, C. nasus, C. nasuta, C. navicularis, C. neinhardii, C. neoplanoconvexa, C. nephroidea, C. nitens, C. nivalis, C. noctigama, C. nomadina, C. nonpulsata, C. nova, C. novaezealandiae, C. nygaardii, C. obergurglii, C. obesa, C. obliqua, C. oblonga, C. oblusa, C. obovata, C. 113 oboviformis, C. obscura, C. obtusa, C. obversa, C. ocellata, C. ohioensis, C. oleosa, C. olifaniae, C. oligochloris, C. oligothermica, C. oocysticola, C. oogamum, C. operuclata, C. opisthostigma, C. opulenta, C. orbicularis, C. oscillans , C. ovalis, C. ovata, C. oviformis, C. pachychlamys, C. palatina, C. palatina, C. palla, C. pallens, C. pallida, C. pallidostigmatica, C. paludosa, C. papillata, C. parallelitata, C. paramucosa, C. parietaria, C. parisii, C. parkeae, C. partita, C. parvula, C. pascheriana, C. passiva, C. patellaria, C. paupera, C. paupercula, C. pedalii, C. pelophila, C. penioides, C. penium, C. pennata, C. perforato-striata, C. perigranulata, C. peritopos, C. perpusilla, C. pertus a, C. pertyi, C. petasus, C. peterfii, C. phaseolus, C. philothermos, C. pigra, C. pila, C. pila, C. piriformis, C. pirum, C. pisiformis, C. pisum , C. pitschmannii, C. pitschmannii, C. plancon vexa, C. planctogloea, C. planocon vexa, C. platyrhyncha, C. platystigma, C. plena, C. plethora, C. pluviale, C. poljanskii, C. polychloris , C. polydactyla, C. polypyrenoides, C. porosa, C. praecox, C. primo yens, C. printzii, C. proboscigera, C. procera, C. prokudinii, C. prolifera, C. proteus, C. protracta , C. provasolii, C. pseudagloe, C. pseudeugametos, C. pseudintermedia, C. pseudobadensis, C. pseudocaeca, C. pseudococcum, C. pseudocon vexa, C. pseudocostata, C. pseudodangeardii, C. pseudodistracta, C. pseudoelegans, C. pseudoelliptica, C. pseudoepiphytica, C. pseudofonticola, C. pseudogloeogama, C. pseudohaematococcoides, C. pseudolunata, C. pseudomacrostigma, C. pseudomicrosphaera, C. pseudomutabilis, C. pseudopertusa, C. pseudopertyi, C. pseudopolypyrenoidea, C. pseudoprotracta, C. pseudopulsa tilla, C. pseudorecta, C. pseudoregularis, C. pseudoreticulata, C. pseudorotula, C. pseudostellata, C. pseudotarda, C. pseudotetraolaris, C. pseudotubulosa, C. pteromonoides, C. pulchra, C. pulsatilla, C. pulvinata, C. pulvisculus, C. pumilio, C. pumilioniformis, C. punctum, C. pusilla, C. pygmaea, C. pyramidalis, C. pyrenobractea, C. pyrenodiscus, C. pyrenogeiton, C. pyriformis, C. quadrilobata , C. quiescens, C. radiata, C. radiosa, C. ranula, C. rapa, C. rapida, C. rattuli, C. raudensis, C. recta, C. reginae, C. regularis, C. reinhardtii, C. Reisiglii, C. reniformis, C. retrona tans, C. retro versa, C. rhigophilos, C. rhinoceros, C. rhomboidalis, C. rhopaloides, C. rigensis, C. rigophilos, C. rima, C. romanica, C. rosae, C. rostrata, C. rotifera, C. rotula, C. rotunda, C. rubrifilum, C. rudolphiana, C. rugosa, C. sacculiformis, C. saccus, C. sagene, C. sagittula, C. salinophila , C. salviniae, C. sanguinea, C. saxonensis, C. scalpriformis, C. scarabaeus, C. schillerian a, C. schizochlora, C. scintillans, C. scutula, C. sectilis, C. securis, C. sedlicensis, C. semiampla, C. serbinowi, C. sessilis, C. sestinensis, C. shawii, C. sichuanensis, C. siderogloea, C. sigmoidea, C. silesiae, C. similis, C. simplex, C. simulans, C. simulans, C. sinica, C. skujae, C. skvortzowiana, C. smithiana, C. smithii, C. snowiae, C. snowii, C. soederi, C. solida, C. soosensis, C. sordida, C. speciosa, C. sphaera, C. sphagnicola, C. sphagnophila, C. spinifera, C. spinosa, C. spirochloris, C. spiridioides, C. splendida, C. spreta, C. springeri, C. squalens, C. stagnalis, C. stagnophila, C. starrii, C. steinii, C. stellata, C. stelliformis, C. stercoraria, C. stigma, C. strepta, C. stria ta, C. striola tus, C. strohschneideri, C. subanguliformis, C. subangulosa, C. subannulata, C. subasymmetrica, C. subcaudata, C. subcomposita, C. subconica, C. subcylindrica, C. subehrenbergii, C. subfusiformis, C. submarina, C. suboogama, C. subradiata, C. subreticulata, C. subtils, C. su Ngariensis, C. superiora, C. surtseyiensis, C. svitaviensis, C. sylvicola, C. synoica, C. tarda, C. tatrica, C. taurangensis, C. tauros, C. tecta, C. tenebraria, C. teodorescui, C. teractidis, C. terrestris, C. terricola, C. testudo, C. tetrabaena, C. tetrachloris, C. tetragama, C. tetraolaris, C. tetras, C. tetravacuolata, C. texensis, C. thiophila, C. thomassonii, C. tin people. C. tomensis, C. toveli, C. tremulans, C. triangularis, C. triplicanensis, C. trulla, C. truncata, C. tuberosa, C. tubulata, C. tumida, C. turicensis, C. typica, C. ucrainica, C. uglanii, C. ulla, C. ulotrichae, C. ulvaensis, C. umbonata, C. urceolata, C. uva-maris, C. vacuolata, C. van-straelenii, C. varians, C. vectensis, C. venusta, C. vemalis, C. versicolor, C. vestita, C. vibra tilis, C. virgata, C. viridemaculata, C. viastae, C. volvocicola, C. vorhiesi, C. vulgaris, C. waldenburgensis, C. wuhanensis, C. yellowstonensis, C. zebra, C. zero vii, C. zygnemoides. Advantageously according to the invention the algae of the genus Chlamydomonas may be algae of the species C. reinhardtii. When microalgae are of the genus Stephanodiscus, they may be selected from the species S. aegyptiacus, S. agassizensis, S. akanensis, S. alpinus, S. asteroides, S. astraea, S. atmosphaerica, S. balatonis, S. balticus , S. bellus, S. berolinensis, S. biharensis, S. bina tus, S. binderanus, S. biserialis, S. biwensis, S. bramaputrae, S. carconensis, S. carpathica, S. conspicueporus, S. costatilimbus, S. damasii, S. delicatus, S. densus, S. dubius, S. dzhilindus, S. elegans, S. entzii, S. epidendrum, S. eccentricus, S. exiguus, S. fenestralis, S. formosus, S. fossilis, S. galileensis, S. gayhartianus, S. gravitoides, S. hamadryas, S. hantzschi, S. hantzschianus, S. hantzschii, S. heterostylus, S. incognitus, S. inconspicuus, S. invisitatus, S. irregularis, S. jamsranii, S. kanitzii, S. khurseviczae, S. komoroensis, S. kuetzingii, S. kutzingiana, S. linea tus, S. lucens, S. major, S. makarovae, S. margina tus, S. matrensis, S. medius, S. minor, S. minuta, S. minutulus' S. min utus, S. miyagiensis, S. mongolicus, S. muelleri, S. nativus, S. nemanensis, S. neoaegypticus, S. neoastraea, S. nia garae, S. nipigonensis, S. novaezeelandiae, S. omarensis, S. oregonica , S. sp., S. pantocsekii, S. parvus, S. perfora tus, S. ponticus, S. popovskayae, S. prohantzschii, S. pseudosuzukii, S. puicherrimus, S. punctatus, S. pusillus, S. radia tus, S. rhombus, S. robustus, S. rotula, S. rugosus, S. sinensis, S. skabitschevskyi, S. socialis, S. soochowensis, S. speciosus, S. subsalsus, S. subtils, S. subtranssylvanicus, S. sudanensis, S. superiorensis, S. suzukii, S. symbolophora, S. tenuis, S. transsylvanicus, S. triporus, S. triporus, S. vesiculosus, S. vestibulis, S. volgensis, S. yellowstonensis, S. yukonensis, S. zachariasi. Advantageously according to the invention algae of the genus Stephanodiscus may be algae of the species S. astraea or S. sp.

When the microalgae are of the genus Monoraphidium, they may be selected from M. affixum, M. arcuatum, M. braunii, M. capricomutum, M. carybeum, M. circinal, M. contortum, M. con volutum, M. dybowskii, M. flexuosum, M. fontinale, M. griffithii, M. indicum, M. intermedium, M. irregulare, M. komarkovae, M. littoral, M. longiusculum, M. lunare, M. minutum, M. mira bile, M. neglectum, M. obtusum, M. pseudobraunii, M. pusillum, M. raphidioides, M. saxatile, M. setiforme, M. skujae, M. sp., M. subclavatum, M. terrestrial, M. tortile . Advantageously according to the invention, the algae of the genus Monoraphidium may be algae of the M.sp species. The algal wastewater treatment method developed in this patent comprises at least: a first step of denitrification and separation of solid components of the wastewater, a step that can be carried out in a settling basin, advantageously disposed upstream of the microalgae culture basin, - a second step of water pollution control by algae culture, advantageously fixed on fixing means during which the nutrients and heavy metals will be removed from the water to be treated by the algae culture, a step that can be carried out in an algae or raceway culture basin, optionally provided with at least one means of regulating the temperature and / or at least one lighting means and / or at least one water recirculation means for returning the water from the culture pond in the upstream settling basin to create a recirculation of the water to be treated in order to essentially improve the denitrification; - A third step of separation of treated water and algae, a step that can be performed in a separation basin advantageously located downstream of the culture basin. At the end of these three stages treated water and algae can be used directly or to undergo other treatments in order to recycle them. For example, water can be made potable by the various conventional water purification treatments. In the same way the algae can for example be valorized in - hydrocarbons: certain strains, in particular those of the genus Botryococcus can produce interesting molecules valorizable in green chemistry: n-alkadienes, mono-, tri-, tetra-, and pentaenes, which are produced from fatty acids (eg C27 diene, C30 botryococcene, squalene, tetramethylsqualene). These molecules can represent up to 60% of the dry mass of the algal cell. This strain can also produce a tetraterpene known as licopadiene which can constitute up to 2 to 8% of the dry biomass. Botryococcus can also produce polymethylated botryococcenes (C30-C37). - lipids (triglycerides and fatty acids) usable in biofuel from the biomass developed in the basin. In this respect, if it is desired to favor this type of valorization, preference will be given to carbon injection (C / N ratio> 20) and its assimilation to direct the culture on lipid synthesis. polysaccharides such as sulfated exopolysaccharides produced by strains of the genus Porphiridium, for example strains of the species Porphiridium aeruginum. more classically and preferentially, in starch-type polysaccharides, cellulose, pectin, chitin, hemicellulose; polysaccharides which themselves are convertible and fermentable into bioethanol. However, as previously pointed out, these methods of treatment of waste water by algae culture present a problem since during the treatment the quantity of algae decreases which may result in the reduction of the effectiveness of the water pollution control rate. used to treat. The invention proposes to overcome this problem by regularly introducing, or continuously, new strains of algae previously precultured into fermenters and injected into the medium to be decontaminated in the culture basin of a wastewater treatment device. seaweed culture. By regularly it is understood in the present text that the injection of microalgae into the culture basin is not done continuously but either at predefined periods of the algae culture process, therefore the wastewater treatment process is on demand. that is to say, when judged by an operator or possibly by an automatic control means, it is necessary to add algae to the culture medium. Continuous is understood in the present text that the injection of microalgae in the culture basin is done without a period of interruption of the injection of precultured algae in the fermenter. Thus according to the invention, the strains of precultured algae can be injected regularly into the pond where CO2 pollution will be performed, organic carbon and nutrients to be cleaned (NH4 +, NO3-, P043-). The frequency of addition can be done according to the generation time of the strains. Thus the invention relates to a wastewater treatment process by algae culture in said wastewater to be treated comprising at least a first step of denitrification and separation of the solid components of the wastewater to be treated, a second step of depollution of water from the first step by cultivation of algae, said algae can be advantageously fixed on fixing means, a third step of separation of treated water from the second step and algae, characterized in that it is injected into the medium of algae cultures in the culture basin, regularly or continuously, strains of algae pre-precultivated in a fermenter. Advantageously, said injection may be made during the second step of the wastewater treatment process by algae culture. According to a variant of the process of the invention, said fermenter can advantageously be physically connected to said culture basin by any connecting means. In this variant it is possible to envisage that the device in which the method is implemented further includes any means of control of the culture and in particular one or more means (s) for controlling the injection of precultured microalgae in the culture medium.

According to the invention, the culture conditions of the algae strains in the fermenter may be the usual conditions known and used to cultivate the strains of algae used. Advantageously, the conditions that will allow the best yield of algae strains at the desired stage for their injection into the culture medium, namely algae in the growth phase, advantageously algae at the beginning of the growth phase, will be advantageously used. very advantageously algae at the end of the lag phase. At the end of the preculture phase, the operator will check that little or no carbon, nitrogen or phosphorus elements remain in the algae culture medium contained in the fermenter. These soluble elements have been consumed and the operator will check that the organic carbon remains for example only at a quantity "10g / L; that the total dissolved nitrogen remains, for example only at a quantity <100 mg / L; and that the total dissolved phosphorus remains, for example, only at a quantity <40 mg / L. In this way, the nutrient flow from the fermentor culture medium will account for less than 10% of the flows from the wastewater. Flow is here understood to mean the product of a concentration (often in mg / L) with a volume of water, in liters. According to the invention, the strains can be added regularly so as to increase the amount of strains in the culture medium by at least 1 log so as to increase the treatment performance. The table below shows the concentration of cells, depending on the season, with and without addition of new precultivated fermenter strains, in a culture pond during a wastewater treatment process according to the invention. Season Winter Spring Summer Autumn Concentration in cells (nb of 105 5.1 05 5.106 5.105 cells / mL) Concentration to reach after addition of 106 5.106 5.107 5.106 cells (nb of cells / mL) According to the invention, there may be a factor volume of 100 to 1000 between the fermenter and the culture basin of the wastewater treatment device used according to the process according to the invention, the fermenter being smaller than the basin in volume.

Thus, to increase the quantity of active cells in the pool by one log, a biomass with an average total concentration of 2 to 5 log, advantageously 3 to 4 log, more than the average total concentration of the biomass, must be produced in the fermenter. strains of the culture medium contained in the culture basin used for the process according to the invention. As an example for a 100m3 pond, a 100-liter fermentor will be needed, capable of producing the strains in a total concentration averaging 3 log more than in the basin. Of course, those skilled in the art will be able to adapt the concentration of the added biomass according to the strains used in order to respect the ratios desired to achieve the desired objective of increasing the concentration in the culture basin of at least one log. According to a variant, when the method according to the invention includes the use of algae fixing means, it may be advantageous for injection of the precultivated microalgae to be carried out at the level of said microalgae fixing means so that the precultivated microalgae are injected. are fixed as soon as possible to said fixing means. The level of the pool can then be lowered and the algae will be injected directly onto the supports. The algae will be placed in contact with their support for about one to two hours, allowing time for the algae to settle on the supports. A nitrogen deficiency in the preculture medium will also favor the production of polysaccharides thus allowing the algae to attach to the supports. Once the algae are fixed on the supports, the level of the basin will be reassembled, the raceway will then be fed continuously by raw sewage, preferably pretreated. As indicated previously, it may be advantageous for the microalgae to be fixed to a support itself immersed in the culture basin. Thus the process according to the invention may advantageously use microalgae fixed on a support. Any known means for fixing microalgae may be used according to the method of the invention. Said fixing means may be of any type, in any material, of any shape and any volume, compatible with the function for which said fixing means is used according to the method of the invention. Advantageously, said microalgae fixing means may be made of a porous material such as, for example, pozzolan, vermiculite, perlite or polyurethanes, alginate balls; carrageenan; polyethylene resins with a high specific surface area (m 2 / m 3 greater than 50, for example Bio Hel-X elements); silicate beads; oyster shells preferentially vermiculite; pozzolan and high surface area polyethylene resins. According to the method of the invention, said fixing means may be used in suspension in water or packaged in mesh bags which will retain the supports and therefore the strains. According to the method of the invention, the volume occupied by said fixing means may range from 1% to 50% of the volume of the basin, preferably 2%, 5% or 10%.

According to the process according to the invention, the temperature of the culture medium can be maintained at the temperature at which the strains used have a maximum of growth. Those skilled in the art will easily adapt the temperature used according to the method of the invention to the strain used.

Advantageously, the temperature of the culture medium or of the wastewater may be between 10 ° C. and 30 ° C., advantageously between 20 ° C. and 30 ° C. As also indicated above, it may be advantageous for the method according to the invention to include illumination of the culture medium in order to optimize the growth of the algae and hence the efficiency of the wastewater treatment. According to the invention the illumination of the culture medium may be carried out continuously or discontinuously. It will be understood that those skilled in the art will be able to adapt the lighting periods not only to the needs of the strain used according to the process but also according to the natural lighting which is subjected to the culture basin of the wastewater treatment device. wherein the process according to the invention is carried out.

According to a variant of the invention, the process may be applied preferably to mixotrophic microalgae, and the compounds they contain starch, cellulose, pectin, chitin, hemicellulose, are convertible and fermentable bioethanol.

The following examples illustrate the present application without limiting it. Example 1: Interest in immobilizing the strains Objectives of the tests: Demonstrate the advantage of immobilizing cells in a medium polluted with CO2 and dissolved nitrogen. io Methodology: The following tests were conducted on the strains Chlorelle vulgaris (optimal generation time: 3.5h, in mixotrophy, Ogawa & Aiba, 1981) and Botryococcus braunii (optimal generation time: between 50 and 60h, A. Lemonnier , 2013). Precultures of these strains on optimized media were previously carried out in Erlenmeyer flasks simulating the effect of a fermentor culture. The strains, in the growth phase, were then inoculated on a vermiculite support at different concentrations: 0% (control medium without strain); 0.5% (in% vermiculite relative to the weight of the medium to be cleaned); 1 and 2%. These supports containing the fixed microalgae were then immersed in other Erlenmeyer flasks containing the mixture of carbon dioxide and domestic wastewater. The composition of the effluent has been cleaned up as follows: Initial synthetic medium: "reconstituted waste water + bicarbonates = CO2 equivalent Elements Concentration Remarks Pollutant range of the element pollutant concentration Carbon Carbon mineral 489 mg 55 to 550 mg dissolved, CO2 CO2 / L CO2 / L dissolved Nitrogen Total nitrogen 27, 5 mg Nt / L 20 to 100 mg Nt / L Nitrogen 27.1 mg N- 2 to 47 mg N-Ammoniacal NH4 / L NH4 / L Nitric nitrate (<5) 0.35 "Value 5 to 35 mg N- mg N-NO3 / L - less than NO3 / L range Phosphorus Phosphate 16.1 mg P- 1.6 to 29 mg PO4 / L P-PO4 / L Application" 190 Mg 15 to 150 mg chemical content in 02 / L 02 / L oxygen greater than pH 8 NB: To avoid working with CO2 in the form of gas, bicarbonate of formula HCO3- was added to the effluent synthetic, bicarbonate being the dissolved form of carbon dioxide.

The elements of the table were determined by a Hach Lange DR 3900 spectrophotometer and assay kits of the various elements. A monitoring of the composition of the culture medium was done at the beginning and at the end of the manipulation (cf results). Experimental conditions Temperature 22 ° C Agitation 150 rpm Neon light big lux Incubator Type Innova Results: Strain Chlorelle vulgaris: Placement on reconstituted wastewater + bicarbonates, inoculation with preculture at 5% (volume / volume). Start of culture tO = 0 h End of culture tf = 120 h Percentage of vermiculite (mass / mass) in the medium 0, 5 ° / 0 added 1% 2% 0% (Control) Carbon Carbone mineral dissolved at tO (in mg CO2 / L) 489 489 489 489 Dissolved mineral carbon at tf (in mg CO2 / L) 487 443 439 33110 Nitrogen Total soluble nitrogen at tO (mg Nt / L) 27.45 27.45 27.45 27.45 Total nitrogen soluble at tf 24.4 11.29 6.04 0.649 (mg Nt / L) Ammonia nitrogen at tO 27.1 27.1 27.1 27.1 (mg N-NH4 / L) Ammonia nitrogen at tf 12.6 9.52 6.04 0.417 (mg N-NH4 / L) Nitric nitrogen at t0 (mg N-NO3 / L) 0.35 0.35 0.35 0.35 Nitrogen nitrate at tf (mg N-NO3 / L ) 11.8 1.77 0 0.232 Phosphorus Phosphate at t0 (mg P-PO4 / L) 16.1 16.1 16.1 16.1 Phosphate at tf (mg P-PO4 / L) 17.8 17.6 16.4 16 Chemical Oxygen Demand COD tO (mg 02 / L) 190 190 190 190 COD tf (mg 02 / L) 177 164 176 176 pH TO (pH Unit) 8 8 8 8 Tf (pH Unit) 8 8 9 to 10 9 to 10 Conclusion: We can see that the more support we put into the environment, the more the pollution (or consumption) of carbon (CO2) and dissolved nitrogen (total dissolved nitrogen, ammonia nitrogen), is effective. Vermiculite also has a positive effect on ammonia nitrogen adsorption and nitric nitrogen uptake. The depollution is greater at the end of the culture at 2% vermiculite than at 1% to 0.5% than the control.

There is no effect observed on phosphorus. Interpretation Hypothesis: The more support is added to the medium, the more strains can attach to vermiculite and the better the carbon and nitrogen decontamination.15 Botryococcus braunii strain: Placement on reconstituted waste water + Bicarbonates Remarks, inoculation with a preculture at 15% (volume / volume). Percentage of vermiculite added to the medium (mass / mass) 0% 0 '5% 1% 2% (Control) Carbon Carbone mineral 489 489 489 489 dissolved at Oh (in mg CO2 / L) Mineral carbon 428 422 468 299 dissolved at 216h (in mg CO2 / L) Mineral carbon dissolved at 217h (in mg CO2 / L) Mineral carbon 408 398 359 356 dissolved at 384h (in mg CO2 / L) Mineral carbon dissolved at 816h (in mg CO2 / L) Nitrogen Nitrogen total soluble at 0 ° (mg Nt / L) 27 27 27 27 Total soluble nitrogen at 216h 57 70 84 83 (mg Nt / L) Total soluble nitrogen at 216h + addition value max 82 95 109 108 Value (mg Nt / L) maximum calculated after addition Total soluble nitrogen at 384h 63 66 93 98 (mg Nt / L) Total soluble nitrogen at 816h 102 91 109 113 Lyse (mg Nt / L) cell at end of culture? Ammonia nitrogen at 27.1 27.1 27.1 27.1 (mg N-NH4 / L) Ammonia nitrogen at 216h 21.5 23.5 22.5 22.2 (mg N-NH4 / L) Ammonia nitrogen 24.1 26.1 25.1 24.8 Value at 216 + ap addition calculated max max (mg N-NH4 / L) after addition Ammonia nitrogen at 384h 23.0 20.8 8.8 9.8 (mg N-NH4 / L) Ammonia nitrogen at 816h 6.56 0 5.08 5.8 (mg N-NH4 / L) Nitric nitrate at 0 (mg N-NO3 / L) 0.35 0.35 0.35 0 Nitric nitric at 0.344 0.001 0.142 0.186 216h (mg N-NO3 / L) Nitric nitrate at 38 38 38 38 Value 216 + ap addition calculated val max (mg N-NO3 / L) maximum after addition Nitric nitrogen at 42.6 43.5 52.7 54.6 384h (mg N-NO3 / L) Nitric nitrogen at 47.5 49.8 57.2 58.4 816h (mg N-NO3 / L) Phosphorus Phosphate at Oh (mg P- PO4 / L) 16 16 16 16 Phosphate at 216h (mg P-PO4 / L) 26 26.6 29.4 28.4 Phosphate at 216h + ap addition max val (mg P-PO4 / L) 35 36 39 38 Value calculated maximum after addition Phosphate at 384h (mg P-PO4 / L) 32 29 33 33 Phosphate at 816h (mg P-PO4 / L) 39.3 36.8 40 41.5 COD application at Oh (mg 190 190 190 190 Chi 02 / L) Oxygen COD at 216h (mg 02 / L) 178 173 171 174 COD at 216h + ap? ? ? ? addition val max (mg 02 / L) COD at 384h (mg 02 / L) 174 180 171 178 COD at 0816h (mg 02 / L) 887 767 822 823 Cell lysis at the end of culture? pH pH to Oh (pH unit) 8 8 8 8 pH to 216h (pH unit) 8 8 8 8 pH to 216h + ap? ? ? ? addition val max (pH unit) pH at 384h (pH unit) 8 7 to 8 7 at 8 8 pH at 816h (pH unit) 8 8 8 8 NB: An addition of botryococcus braunii was made at 216h to boost the depollution, this addition contains nitrogen and phosphorus elements, the concentration values of these elements were calculated after addition of the strain and the associated culture medium. It is noted that the more support is placed in the medium, the more the pollution (or consumption) of carbon (CO2) and dissolved nitrogen (total dissolved nitrogen, ammoniacal nitrogen), is effective. Vermiculite has a positive effect also on the adsorption of nitrogen lo ammoniacal and nitric nitrogen. The depollution is greater at the end of the culture at 2% vermiculite than at 1% to 0.5% than the control. There is no effect observed on phosphorus. Assumption of interpretation: The more support is added to the medium, the more the strains can bind to vermiculite and the more carbon and nitrogen decontamination is effective. On the other hand, the strains mentioned in this patent can be precultured in fermenters with high cell densities, the following table shows the different strains and their associated cell density: Number of times Generation time in cells (in culture for Strains conditions cell number to reach optimal / mL) / Density start of mixotrophic Optic (DO) phase expo Botryococcus 48-72h OD (per OD -300h, braunii scanner): 3-4 if rate Corresponding to 3 g inoculation = of Dry matter 10% / L Chlorella 4-10h 1x106 to 1x108 12 to 24h vulgaris, Chlorella sorokiniana Scenedesmus 10-24h Approximately 1x106 24 to 72h quadricauda, Scenedesmus obliquus Micractinium 12-48h No data Fermentalg Euglena gracilis, 24-48h 0, 1 (OD near 24 to 48h (data erlen) infrared, OD-scanner) Chlamydomonas 4-12h No data reinhardtii Fermentalg Nitzschia 72-120h OD 600nm: -6-7 -70h Porphiridium 24-40h No data Fermentalg aeruginum N.B: To this list may be added a diatom of the genus Stephanodiscus and a chlorophyceae of the genus Monoraphidium5

Claims (20)

REVENDICATIONS1. Device for treating wastewater by mixotrophic microalgae culture, characterized in that it comprises at least one raceway-type microalgae culture basin, a fermentor and at least one alga-feeding means between said fermentor and said raceway of microalgae culture. 2. Device according to claim 1, characterized in that the fermenter is agitated reactor type. 3. Device according to any one of claims 1 or 2, characterized in that said means for supplying seaweed is by sterile withdrawal. 4. Device according to any one of claims 1 to 3, characterized in that it further comprises a settling basin or settling zone. 5. Device according to any one of claims 1 to 4, characterized in that it further comprises a separation basin. 6. Device according to any one of claims 1 to 5, characterized in that it further comprises a microalgae culture tank feed means carbon dioxide (CO2) containing compressed air CO2 and a fine or medium-sized diffuser. 7. Device according to any one of claims 1 to 6, characterized in that it further comprises at least one microalgae fixing means. 25 8. Device according to any one of claims 2 to 7, characterized in that it further comprises a water recirculation means between said microalgae culture basin and said settling tank or settling zone. 9. Process for the depollution of wastewater by cultivation of microalgae, comprising a step of depollution of water by cultivation of algae in a breed type basin characterized in that 302 3 5 4 8 38 are injected into the culture basin , regularly or continuously, strains of algae pre-cultured in a fermentor. 10. Method according to claim 9, characterized in that it implements a device as described in one of claims 1 to 8. 5 11. The method of claim 10, characterized in that the microalgae are mixotrophic microalgae. 12. Method according to any one of claims 9 to 11, characterized in that said microalgae are microalgae fresh water. 13. Method according to any one of claims 9 to 12, characterized in that the microalgae are selected from strains of the genera Botryococcus, Chlorella, Scenedesmus, Micractinium, Euglena, Nitzschia, Porphiridium, Chlamydomonas, Stephanodiscus, Monoraphidium. 14. Method according to any one of claims 9 to 13, characterized in that it comprises at least a first step of denitrification and separation of the solid components of the wastewater to be treated, a second step of depollution of water from the first step by cultivation of algae, a third step of separation of treated water from the second stage and algae, characterized in that is injected into the culture medium of algae in the culture basin, regularly or continuously, pre-cultured algal strains in a fermentor. 15. The method as claimed in claim 14, characterized in that the injected algae are in the growth phase, advantageously at the beginning of the growth phase, very advantageously at the end of the latency phase. 16. Process according to claim 14, characterized in that the injected algae are at an average total concentration of 2 to 5 log, advantageously 3 to 4 log, more than the average total concentration of the strains of the culture medium contained in the invention. culture basin used for the process according to the invention. 17. Method according to any one of claims 14 to 16, characterized in that said algae are fixed on fastening means immersed in the culture basin. 18. A method according to any one of claims 14 to 17, characterized in that the temperature of the culture medium is between 10 ° C and 30 ° C, preferably between 20 ° C and 30 ° C. 19. Method according to any one of claims 14 to 18, characterized in that the culture basin or raceway is illuminated artificially either continuously or discontinuously. 20. Method according to one of claims 14 to 19, characterized in that the mixotrophic microalgae, and the compounds they contain starch type, cellulose, pectin, chitin, hemicellulose, are convertible and fermentable bioethanol.