WO2011113974A1

WO2011113974A1 - Open reactor system for the cultivation of microalgae

Info

Publication number: WO2011113974A1
Application number: PCT/ES2011/000078
Authority: WO
Inventors: Antonio Marcilla; Juan Carlos GARCÍA; Amparo GÓMEZ; Ángela GARCÍA; Maria Isabel BELTRÁN; Lucia CATALÁ
Original assignee: Universidad De Alicante
Priority date: 2010-03-17
Filing date: 2011-03-17
Publication date: 2011-09-22
Also published as: ES2368282A1; ES2368282B1

Abstract

The invention can be used to obtain a final culture of microalgae from a seed culture, using the bed of a dry river. The invention comprises: an open reactor (1) consisting of the bed of a dry river or ravine, conditioned and divided to form rafts (2); nutrient supply means (7); water supply means (10); and seeding means (5) that provide the seed culture. The seeding means (5) may be closed photobioreactors (5) or part of the recycled final culture. The water supply means (10) are preferably wells (6) located in proximity to the system. The system is supplied with the energy resulting from the combustion of part of the final culture obtained.

Description

OPEN REACTOR SYSTEM FOR THE CULTURE OF

MICROALGAS

D E S C R I P C I Ó N

OBJECT OF THE INVENTION

The present invention can be included in the technical field of obtaining microalgae. Also, the invention has a place in the field of conditioning and recovery of deteriorated natural environments.

The object of the invention consists of an open reactor system for the cultivation of microalgae that allows the recovery of deteriorated natural environments.

BACKGROUND OF THE INVENTION

Microalgae are "carbon dioxide fixative" microorganisms, since because their diet is, in general, photosynthetic, they transform sunlight into chemical energy through photosynthesis, assimilating carbon in the form of carbon dioxide.

These organisms are a source of bioproducts of great economic importance. Some species store high concentrations of lipids. Its protein content is on average 65% dry basis, higher than other natural foods and have a high concentration of vitamins, minerals and other nutrients. They also contain gammalinoleic acid, stimulant of prostaglandins, regulators of the activity of body cells. Some species contain lutein, which can reduce the risk of various types of cancer, heart and ophthalmological diseases. Other microalgae compounds also have anticarcinogenic, antimutagenic, immune system stimulant, detoxifying and reducing cholesterol and hypertension. Certain species have high concentrations of beta-carotene, antioxidant and efficient radical scavenger. On the other hand, microalgae represent an important reserve of omega-3 fatty acids, whose derivatives are effective in the prevention and treatment of, among others, coronary heart disease, platelet aggregation, abnormal cholesterol levels, and some types of cancer, being also highly promising for the treatment of certain forms of mental illness.

Therefore, the use of microalgae includes very diverse applications (6-9), such as the manufacture of medicines, food additives or foods for human consumption. In addition to their forage use, microalgae are used in aquaculture in the growth of bivalves (9), for larval states of some species of crustaceans and for early stages of fish due to their high protein content. Additionally, in recent years its potential has been manifested as an energy source, given its high content of substances of high energy value. Thus, for example, the oil accumulated by the microalgae, after a transesterification process, could be destined to the production of biodiesel (10-1 1), and the waste used by its calorific value, and even the microalgae can be used directly as fuel in the appropriate systems or as a source of raw materials in thermal processes.

Among the open systems of industrial production of biomass, the carousel type, consisting of closed circuits of shallow channels (15-20 cm.), Where the culture medium is driven by pallets, requiring large areas of land (500-5000 m ² ) (19), but have the advantage of low cost of algal biomass production (20). However, they have several drawbacks: low productivity, easy contamination, difficult recovery of the product from diluted media and difficulty in temperature control. These systems must be sown with a flow and an algae concentration appropriate to the growth in the expected time.

There are numerous actions of various official bodies on ravines and dry riverbeds, with diversions from them by road infrastructure, access to different urban areas or by other concepts. Frequently, they are in a virgin and / or deteriorated state, even in areas close to urban centers. The maintenance of these environments is not always adequate and they are often neglected, dirty and even clogged, which makes them infunctional and dangerous.

DESCRIPTION OF THE INVENTION The present invention solves the aforementioned drawbacks by means of an open reactor system for the cultivation of microalgae comprising an open reactor consisting of a natural space, such as a ravine, an environmentally degraded area or the channel of a river, conveniently enabled to function as an open reactor.

The use or habilitation of these natural sites for use as reactors for the cultivation of algae provides the advantage of keeping them in operational conditions as a clean channel, free of obstacles and facilitates the evacuation of water accumulations from the floods of their origin and your current destination. The open reactor system for the cultivation of microalgae object of the present invention comprises: - an open reactor that supports the cultivation of microalgae producing a final culture of microalgae from a sowing crop;

- sowing means to provide a sowing culture to the open reactor;

- water supply means; Y

- nutrient delivery media;

As previously advanced, the open reactor consists of a natural space adequately conditioned to serve as a microalgae culture bed. As examples of natural spaces suitable for employees as an open reactor, ravines and riverbeds and, in general, environmentally degraded natural sites are mentioned. The conditioning of natural spaces includes the operations of compaction, cleaning and waterproofing, for example, by depositing a means of waterproofing comprising plastic materials or a layer of crushed rock on a bed of clay. Preferably and, to the extent that it is convenient and / or necessary, the natural space is compartmentalized, by means of dams, in consecutive rafts. The sowing means provide a sowing culture to the open reactor, said sowing culture is developed during its stay in the open reactor, resulting in a final culture of microalgae.

Preferably, two options for obtaining the sowing crop are considered: the use of sowing photobioreactors (open type or, more preferably, closed type) and use as a seed crop of a part of the crop in recirculation. These options constitute non-exclusive alternatives, and there is the possibility, depending on the needs of each particular case, to use more than one of them to the extent that is most appropriate.

In relation to sowing means, the use of open sowing reactors has the advantage that they involve lower operating and construction costs. When crop contamination is not a critical design parameter, said open seeding reactors are preferable. The use of a part of the final crop as a sowing crop is also a valid option when contamination is not a critical parameter.

However, closed sowing reactors have the advantage of significantly decreasing crop contamination by unwanted microalgae species or by predators, contamination that is expected to occur when the crops are exposed to the atmosphere. The probability of the presence of contamination is proportional to the exposure time of the crop abroad.

If the contamination appears in the middle or at the end of the bed, this could be acceptable and would hardly affect the process. However, if a recirculation flow rate is used as sowing, there would be almost a total probability that the crop would be contaminated at some point, and such contamination would be inoculated in the bed head; after several stages, the entire crop could be lost if the contamination were from a predator of the type of a ciliated protozoan.

The necessary water supply means are preferably constituted by wells located in the vicinity of the open reactor. In the case of locations near the coast, there is the advantage In addition, the water already has an adequate salt content. Other means of water supply are not ruled out, although direct use of seawater would cause pollution problems. The nutrient supply media provide the necessary nutrients for the development of microalgae, both macronutrients (carbon, nitrogen, phosphorus, silicon, magnesium, potassium and calcium) and micronutrients (iron, manganese, copper, zinc, sodium, molybdenum, chlorine and cobalt). The addition of nutrients can be carried out either in the initial area of the crop or staggered along the open reactor.

In the particular case of the carbon supply, several possibilities are contemplated: bicarbonate contribution, and the use of bubblers for the bubbling of CO ₂ . Because each of these options has disadvantages and advantages, it is also possible to use a combination of both.

Specifically, the bubbling of C0 ₂ is limited by the low water solubility of C0 ₂ , which facilitates its loss into the atmosphere. The contribution of carbon by means of sodium bicarbonate does not present such inconvenience, as well as it facilitates the concentration of carbon along the open reactor, although it implies the need to provide pH control means, since the presence of bicarbonates causes a increase in pH caused by the precipitation of said bicarbonates, not producing the expected carbon supply.

Preferably, the carbonates used as a carbon source can be obtained by fixing the carbon dioxide present in the flue gases of a chimney with the aid of carbonate / bicarbonate solutions following the Benfield process. In this way, the carbon contribution is given through HCO3 ^" obtained by the absorption of the C0 ₂ contained in a chimney gas stream of some industry close to the installation or the combustion of the same biomass obtained in the process, by countercurrent treatment with a carbonate solution. In this case, the chimney gas stream is brought into contact, in an absorption column, with the culture medium that is obtained at the exit of the channel, after carrying out the separation of the biomass, and having modified adequately pH to obtain a carbonate solution. The products of the absorption column constitute a gas stream which is depleted C0 ₂ and a liquid stream at a concentration sufficient to allow growth bicarbonates biomass to the desired level. The reaction that takes place in the absorption column is:

C0 ₂ + C0 ₃ ^{2 '} → 2 HC0 ₃ ^"

In this sense, the absorption process could be carried out in facilities attached to the flue gas emitting industry, or, if it is located near the dry riverbed, the carbon dioxide fixing unit could be included in the complex of the facilities and suppose the carbon source for both the algae present in the channel and in the sowing photobioreactors.

The energy necessary for the operation of the open reactor system of the invention is preferably obtained directly from the combustion of a part of the microalgae obtained in the final culture. Even more preferably, the C0 ₂ obtained in this combustion can be used as carbon source for the cultivation itself, as explained above. At the end of the journey in the open reactor, the current obtained can be used directly as food for aquaculture or undergo some process of biomass separation, such as sedimentation, tangential filtration, flocculation, centrifugation, etc. In any case, after the separation or use of the biomass generated, a stream of water is obtained, which after a conditioning process would be able to be recirculated to the process as mentioned above. Alternatively and, as previously mentioned, prior to the collection and separation of the cultured microalgae, this stream can be partially recirculated to constitute (suitably diluted) the sowing crop.

In short, the present invention proposes the use of a ravine or the river bed to obtain microalgae. The main idea is to enable a dry riverbed, or a place adapted as such, as a means of circulating a stream of water, conveniently conditioned as a culture medium for the growth of a certain species of microalgae. The seeding of the riverbed reactor is carried out with cultures from photobioreactors, or with culture from the recirculation of part of the current obtained in the riverbed. Throughout it the growth of the microalgae, the dosage of the necessary nutrients and carbon sources, is carried out to collect it at the end of the route.

A series of advantageous aspects of the present invention are listed below:

- The landscape recovery of the environment and the positive environmental impact on the area. - The fixation by said microorganisms of carbon dioxide and the reduction of its negative effect on the phenomenon of global warming. - The use of biomass generated for energy purposes, for the feeding of other species or for obtaining valuable chemical products, useful in different sectors, such as the pharmaceutical or foodstuffs up to the fuel sector.

DESCRIPTION OF THE DRAWINGS To complement the description that is being made and in order to help a better understanding of the features of the invention, according to a preferred example of practical realization thereof, it is accompanied as an integral part of said description, a set of drawings in which, with an illustrative and non-limiting nature, the following has been represented:

Figure 1.- Shows a scheme of the system of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the invention is described below with the aid of the attached figure 1: The open reactor system for obtaining microalgae of the invention comprises an open reactor (1) consisting of the channel of a dry river. The riverbed is previously compacted, cleaned and waterproofed. The open reactor (1) thus obtained is divided into consecutive rafts (2) by means of dams (3). In order to provide adequate solar lighting to the crop, the invention incorporates stirring means (4) from the cultivation of the rafts (2). Alternative and / or additionally, the depth of the rafts (2) is adapted for the correct lighting of the crop. As an example, a depth of between 15 and 25 cm is proposed. There is an initial zone (9) of the system in which a plurality of closed sowing photobioreactors (5) are located, which allow obtaining a sowing culture with a certain concentration of microalgae. The system of the invention incorporates wells

(6) as water supply means (10) and also incorporates (not represented) nutrient supply means (7). Periodically said photobioreactors (5) are partially emptied in order to feed the culture. After said partial emptying, the photobioreactors (5) are refilled with water (10) and enough nutrients (7). The current from the area of the photobioreactors (5) is mixed with a stream of water (10) obtained after the biomass separation stage (8), with a new one of water (10) whose purpose is the compensation of all the losses that may occur along the open reactor (1) and with a stream of nutrients (7). The addition of nutrients

(7) necessary for the growth of the microalgae can be carried out in the initial zone (9) or progressively along the bed. The nutrient stream (7) should contain the necessary amounts of both macronutrients and micronutrients. As an example, the following Table 1 shows a possible nutrient composition (7), where for each compound in the left column its average concentration in grams per liter is shown in the right column: Compound C _NC ( _medium gil)

Na ₂ EDTA 4.16 · io- ³

FeCl ₃ -6H ₂ 0 3.15 · io- ³

CuS0 ₄ -5H ₂ 0 1.0010 ^"5

ZnS0 ₄ -7H ₂ 0 2.2010 ^"5"

CoCl ₂ -6H ₂ 0 1.0010 ^"5

MnCl ₂ -4H ₂ 0 1.80 · io- ⁴

Na ₂ Mo0 ₄ -2H ₂ 0 6.0010 ^-6

Vitamin B ₁₂ 5.00 · io- ⁷

Vitamin Bj 1.00 · io- ⁴

Biotin 5.00- io- ⁷

NaN0 ₃ 7.50 · io- ²

NaH ₂ P0 ₄ -2H ₂ 0 5.65- io- ³

NaHC0 ₃ 1.01 - 10 ⁺¹

Table 1. Average composition of nutrients.

The optimal residence time of the crop is set taking into account that one of the main problems of open systems is pollution, and the probability that it occurs as well as its severity decreases as it decreases. Taking this into account, together with the fact that under the optimal conditions of a photobioreactor (5) crops can double the amount of biomass in one day, an approximate value of 3 days has been considered for the case of the riverbed, given that in reactors with this last configuration, the growth rates of microalgae are usually lower. The residence time should be adjusted according to, among other factors, the weather conditions and the type of microalgae considered. In this case, and post that the only thing that is recirculated is a stream of water (10), capable of being sterilized, the risk of contamination is low.

The appropriate circulation speeds in the open reactor are between 0.15 and 0.25 m / s to prevent sedimentation. Under certain circumstances, such as the case of the proposed configuration, the circulation speed may be lower (0.02 m / s), it being advisable to equip the crop with static mixing devices (not shown) that successively break the front of the flow current. water (10), getting a mixture of the different layers of fluid. Alternatively, the rafts (2) can be agitated by an external agitator (4).

The biomass concentration required to be used as a sowing crop is one of the parameters to optimize. For example, an output concentration of about 2 g / L would allow a dilution factor of 4 to be used to feed a 0.5 g / L solution to the bedside. The required residence time of the crop in the sowing photobioreactor (5) depends on the temperature, the solar radiation, the type of seaweed selected, etc; however, a reference value may be close to 24 hours (with approximately 8 hours of sunshine per day), time needed to obtain a sufficiently concentrated sowing crop. Although, from the point of view of reagent dosing and control in the reactors, the most appropriate configuration is their arrangement in a given area, it is possible that said photobioreactor reactors (5) can be placed along the bed and integrated In the landscape.

To achieve a carbon contribution, the invention contemplates the presence of carbon supply means (1 1) in the form of bubbles (1 1) of CO ₂ , as well as bicarbonate contribution. In the case of the contribution of bicarbonates, the invention incorporates pH control means that provide a solution of HCI properly distributed throughout the culture followed by a possible separation of carbonate precipitates or alkaline earth hydroxides, and a pH rectification.

Claims

1. - Open reactor system for the cultivation of microalgae characterized in that it comprises:

- an open reactor (1) consisting of a natural space selected between a ravine or the river bed, which supports the cultivation of microalgae producing a final culture of microalgae from a sowing crop;

- sowing means (5) to provide a sowing culture to the open reactor;

- water supply means (10) to provide the open reactor (1) and the sowing means (5) with the water (10) necessary to carry out the cultivation;

- nutrient supply means (7) to provide the open reactor (1) and the sowing means (5) with the nutrients (7) necessary for the cultivation, as well as carbon supply means (1 1); Y

- open reactor waterproofing means (1).

2. - Open reactor system for the cultivation of microalgae according to claim 1, characterized in that the open reactor (1) is compartmentalized in consecutive rafts (2) by means of dams (3).

3. - Open reactor system for the cultivation of microalgae according to claim 1, characterized in that the sowing means (5) are selected from at least one of the following:

- closed photobioreactors (5), and

- a portion of the final crop;

4. - Open reactor system for the cultivation of microalgae according to claim 1, characterized in that the water supply means (10) comprise at least one well (6) located in the immediate vicinity of the system.