IT201800010683A1 - Integrated system of bioelectrochemical processes and photobioreactors for the cultivation of photosynthesising microorganisms with the recovery of carbon and nutrients from organic sources or wastewater - Google Patents

Description

Title: "Integrated system of bioelectrochemical processes and photobioreactors for the cultivation of photosynthesising microorganisms with the recovery of carbon and nutrients from organic sources or wastewater"

DESCRIPTION

It is possible to reuse organic substrates or treat wastewater through the cultivation of photosynthesising microorganisms (MF), in order to obtain, instead of a sludge, a biomass that can be a source of added value products, such as feed supplements, hydrolyzed compounds for the preparation of biofertilizers, biostimulants and plant growth promoters or molecules such as natural dyes, antioxidants, biopolymers, carotenoids.

The systems known in the art, however, have limitations relating to the use of organic sources of carbon and nutrients and to the treatment of wastewater, especially if with a high content of organic matter.

In fact, above certain organic load thresholds, MFs are progressively inhibited, with the simultaneous development of heterotrophic microorganisms, which causes the onset, in the long term, of anaerobic conditions and turbidity of the liquid medium.

The biomass obtained at the end of the process is therefore of low quality in most cases, due to the presence of high percentages of bacterial biomass, together with the MF biomass.

As a consequence, the value-added applications of this type of product, such as the production of food with organic certification (the Italian legislation on organic farming excludes the use of mineral fertilizers of synthetic origin), cosmetics, animal feed or for the extraction of pigments, are to be excluded in most cases.

In light of the known needs in the field, the authors of the present invention have developed a particular configuration and structure of microbial electrochemical cells (METs), to be integrated with crops of photosynthesizing microorganisms for the growth of the same microorganisms using sources of carbon and nutrients in organic form. , including by-products and waste from food production and wastewater.

Brief description of the figures

Figure 1 represents a diagram of operation of a microbial electrochemical technology that associates the use of photosynthesizing microorganisms according to the present invention;

Figure 2 shows a detail of the configuration of the system proposed by the present invention;

Figure 3 shows a representation of an experiment carried out to obtain information on the operation of the results obtained with the use of the present invention;

Figures 4 and 5 show, respectively, the results of the experiments performed in terms of current generation and growth of spirulina and residual losses of COD in the cathode chamber;

figure 6 represents the diagram of a plant according to the present invention.

Object of the invention

The present invention relates to a microbial electrochemical module integrated with a photobioreactor, a photobioreactor and a plant comprising this photobioreactor, as well as the method for the cultivation of photosynthesising microorganisms through the recovery of carbon, of nutrient elements contained in waste water and the simultaneous purification of waters containing these nutrients.

Detailed description of the invention

According to an object of the present invention, a MET technology (Microbial Electrochemical Technology) is described which uses photosynthesizing microorganisms.

For the purposes of the present invention, photosynthesising microorganisms include Chlorella vulgaris, Chlamydomonas reinhardtii, Dnaliella teriolecta, Ulva lactuca, Pseudokirchneriella subcapitata, Scenedesmus, Scenedesmus obliquus, Desmodesmus sp, Laminaria saccerosocharina, Chasystacterium Rhodopseudomonas palustris, Leptolyngbya, Acutodesmus, Chlamydomonaceae, Merismopedia glauca.

According to a first aspect, the population of microorganisms is homogeneous; in an alternative aspect, the population can be represented by one or more of the indicated species or by consortia of microorganisms.

For the purposes of the present patent application, the term "organic solution" means an aqueous solution comprising an organic fraction and a population of heterotrophic microorganisms.

In practice, these organic solutions contain soluble or suspended organic forms, coming from recovered organic materials, from by-products or waste from agro-food production, sewage water from settlements, wastewater of zootechnical origin or water from agro-food processing.

According to the present description, the organic solution comprises an organic fraction, rich in soluble organic carbon and nutrients (nitrogen, phosphorus, potassium, iron, calcium, magnesium, sulfur and other micronutrients such as cobalt, manganese, molybdenum, etc.)

In a preferred aspect, the organic solutions to be treated contain suspended solids in an amount not exceeding about 5 gTSS / L.

In another aspect, organic solutions can contain organic load levels up to about 10 gCOD / L.

According to a first object of the invention, the MET technology described is represented by a module (in the figures indicated with references 11,12,13,14,21,22,23,24) for a photobioreactor 100.

In particular, this module 11,12,13,14,21,22,23,24 includes a cathode 106 (or, better, biocathode, as it is structured) and an anode 104 (or, better, a bioanode, as it is structured).

For the purposes of the present invention, the biocathode 106 is in contact with a population of photosynthesizing microorganisms.

As regards the bioanode 104, on the other hand, this is in contact with a quantity of organic solution 30,31,33.

As stated above, the organic solution is rich in organic fraction and comprising a heterotrophic microbial population.

In the photobioreactor 100 of the invention, the biocathode 106 and the bioanode 104 are physically separated from each other thanks to a porous septum 105.

For the present purposes, this septum 105 is made of ceramic or ceramic / carbonaceous material.

More particularly, this porous septum 105 is represented by an element having a tubular shape.

According to a preferred aspect of the invention, the porous septum is prepared starting from a biomass or from a mixture of a biomass with clay; in this second case, the biomass inside the mixture can be replaced with biochar.

If necessary, the mixture is subsequently molded into tubular form.

Preferably, the diameter of the porous septum is about 20-100 mm and the thickness is between 3 and 10 mm.

In a subsequent phase, the element modeled in the form of a tube is subjected to pyrolysis; in this way a porous material is advantageously obtained, with a certain electrical conductivity (0.1 - 1000 mS / cm), suitable for the present uses.

The pyrolysis is preferably carried out according to a thermal ramp which comprises: a first heating phase up to 900 ° C, a second isothermal phase at 900 ° C for about 60 minutes and a third cooling phase.

In particular, the first heating phase provides for a temperature increase of about 10 ° C / minute.

The isothermal phase preferably has a duration of about 60 minutes.

The cooling phase provides for a decrease in temperature at a rate preferably of about 5 ° C / minute.

In an alternative aspect of the present invention, the MET described does not have a double chamber tubular configuration (with a physical separation between anode and cathode), but is a snorkel (with a continuity of electroconductive materials between anode and cathode).

The module of the photobioreactor of the invention also includes an element 101 for the distribution of the organic solution within the photobioreactor itself.

In one aspect of the invention, this element 101 is represented by a tube, preferably coaxial, possibly of plastic material, inside the module 11,12,13,14,21,22,23,24; thus a gap 103 is generated.

The interspace 103 is filled with a conductive and electrochemically stable material and preferably not subject to corrosion; in a particularly preferred aspect, this material can be selected from the group which comprises: electroactive biochar, carbon coke, optionally in granular form, or from carbon fiber fabrics.

The size of the granular material is preferably about 3-15 mm.

The cavity material is preferably pressed.

To allow a homogeneous distribution of the organic solutions, this tubular element has a plurality of openings 102, which allow the solution to pass from inside the tube 101 to the interspace 103 between this and the biocathode 106.

These openings 102 preferably have a diameter of about 1-2 mm; advantageously, this ensures an adequate flow of organic solutions to the anodic cavities.

For the purposes of the present invention, the cathode 106 is preferably exposed to the culture of photosynthesizing and electroactive microorganisms described above which is formed on the layer of conductive material and which reduces the oxygen produced by photosynthesis.

In another aspect of the invention, the anode 104 is exposed to organic solutions rich in organic content and in heterotrophic microorganisms, typical of organic materials and wastewater according to the above definitions; in fact, electroactive heterotrophic microorganisms are selected, which oxidize, by anaerobic anodophilic metabolism, the organic fraction contained in the organic solutions, releasing soluble forms of the minerals they contain.

The separation of the two microbial populations is maintained thanks to the porous septum 105.

As described above, the septum is porous; pyrolysis is carried out at the end of obtaining pores having a distribution in a range of less than 500 nm (and in fact, they do not allow microbial cells to pass) and to obtain a material with adequate electrical conductivity.

The electric circuit is closed by a resistance of known value, for example of about 20-500 Ω or by the electroconductive material of which the porous septum is made, which has an electrical conductivity of known value (0.1-1000 mS / cm) .

For the purposes of the present invention, the porous septum 105 allows the electrical and electrolytic connection between the bioanode 104 and the biocathode 106, so that the electrochemical reactions push the passage of protons (thus closing the electrochemical circuit) and of nutrients (preferentially in mineral form) recovered from organic solutions to the culture of photosynthesising microorganisms, fertilizing it and promoting its growth.

By "nutrients" we mean soluble ionic forms containing nitrogen, phosphorus, potassium, calcium, magnesium, iron, bicarbonate ions, sulfur, and other micronutrients such as cobalt, manganese, molybdenum, etc.

In a preferred embodiment of the invention, the population of photosynthesizing microorganisms is represented by a culture of spirulina (Arthrospira).

According to an aspect of the present invention, several modules 11,12,13,14,21,22,23,24 according to what has been described above, can be organized together forming a circuit 10,20.

Figure 6 is a schematic representation of how the technology described by the present invention can be used for the realization of a raceway type plant for the recovery of nutrient elements contained in organic solutions.

As shown, a circuit (10,20) can comprise a plurality of modules (11,12,13,14,21,22,23,24) connected to each other in series forming a photobioreactor.

According to a first embodiment, the technology of the present invention can be implemented in a vertical tubular-shaped photobioreactor or a raceway-type horizontal tank, where this second configuration is particularly preferred for the purposes of the present invention.

The 10.20 module or modules of the circuit are immersed in a culture of photosynthesising microorganisms (5 ').

For the purposes of the present invention, a plant 200 for the purification of organic solutions and for the cultivation of photosynthesising microorganisms starting from recovered carbon and nutrients, included in said organic solutions, comprises a photobioreactor 100 as described above, comprising one or several circuits 10, 20, operating in parallel with each other, and one or more further elements for its operation and management.

Preferably, therefore, a plant 200 comprises:

- a tank (5) or more tanks containing the culture of photosynthesising microorganisms (5 '),

- a first tank (1) for the organic solution (30,31,33),

- a pump (P2, P3) for feeding the organic solutions (30,31,33) to each of the circuits (10,20) of the photobioreactor (200), - a pump (P4) to regulate the level of the photosynthesising microorganisms (5 ') inside the tank (5), - a vibrating screen (3) for the filtration of the culture of photosynthesising microorganisms (5'), - a second tank (2) for the discharge of the supernatant or for its recirculation of the same in the culture of photosynthesising microorganisms (5 ') or in the first tank (1).

The plant 200 of the invention may also include:

- a collector (4) for the collection of the organic solution (30,31,33) to be purified in the plant,

- a pump (P1) for pumping said waters (30,31,33) from the collector to the first tank (1).

Inside the tank 5 of a photobioreactor, a culture level of photosynthesizing microorganisms of about 10-25 cm is maintained.

Preferably, the pipes that make up the modules and the circuits are kept at a distance of about 20 mm from the bottom of the tank; this guarantees the mixing of photosynthesising microorganisms in the culture waters, avoiding areas of stagnation and accumulation of biomass.

According to a preferred aspect of the present invention, the plant is made in such a way as to satisfy the following parameters:

Cathode surface / Anode volume: ≥ 100 m <2> / m <3>

Photobioreactor / exchange surface volume: ≥ 0.05 m <3> / m <2>

In accordance with an object of the invention, a method is described for the purification of organic solutions and for the cultivation of photosynthesizing microorganisms, which recovers carbon and nutrients in organic form, which uses MET technology (Microbial Electrochemical Technology) and, in particular , the photobioreactor described above.

In particular, this method comprising the steps of:

a) make a quantity of organic solution (30,31,33) flow inside the tube (101) of a module (11,12,13,14,21,22,23,24) and allow said organic solution (30,31,33) passes through the openings of the module (102) towards the gap of the bioanode (103),

b) allow the oxidation of the organic forms of carbon and nutrients (nitrogen, phosphorus, potassium, iron, magnesium, calcium, sulfur and other elements) of the organic solution (30,31,32) by said electroactive microbial population, combined with the reduction of oxygen to the biocathode, obtaining the release of nutrients in mineral form,

c) allow the passage of said nutrients through the porous septum (105) of said module (11,12,13,14,21,22,23,24) towards the culture of photosynthesizing microorganisms (5 ').

In a preferred aspect of the invention, the method comprising the further step d) of letting said mineralized nutrients in step c) fertilize the culture of photosynthesizing microorganisms (5 ').

For the purposes of the present invention, the method is carried out in the presence of one or more of the following preferred conditions:

1. Organic substance concentration in the organic solution: ≤3,000 mgsCOD / L.

2. Specific daily organic load sCOD / anodic volume / d: ≤500 mgsCOD / Lan / d.

3. Specific daily organic load sCOD / Cathodic surface / d: ≤5000 mgsCOD / m <2> / d.

4. Specific daily organic load sCOD / Photobioreactor volume / d: ≤130 mgsCOD / Lpr / d.

Removal rate per unit of total volume: ≤ 120 mgsCOD / L / d.

In one aspect of the present invention, the described method allows not only the purification of organic solutions, such as wastewater, but also the production of a nutrient-enriched biomass.

The biomass thus obtained, which represents a further object of the present invention, is characterized by an added value that fully justifies its use for the production of food according to the current legislation for organic farming, for the extraction of pigments, for the production of feed, for the production of cosmetic products or for the production of hydrolysates and phytostimulating and soil improver preparations for crops.

Example 1

The following table shows the dimensional characteristics and the main process parameters of a laboratory plant and a pilot plant, sized with specific tests.

Operating according to the above conditions, high COD removal rates were obtained in the anodic compartment (0.65 gCOD L <-1> d <-1>), with negligible COD losses towards the cathode compartment, containing the culture of photosynthesising microorganisms. The oxygen produced through photosynthesis was found to be sufficient for the METs to function (Pmax about 4 W / m <2>, with an internal resistance of the system of about 40 Ω). Spirulina growth was approximately 40 mgTSS L <-1> d <-1>.

The analysis of the anode and cathode solutions made it possible to evaluate the transport of ions through the separator during the operation of the MFC.

The purity of the obtained Spirulina culture was confirmed by microbiological analyzes.

From reading the above description of the present invention, the numerous advantages offered by the proposed microbial electrochemical systems will be evident to the person skilled in the art.

First of all, the proposed system is economical, thanks to the use of non-precious materials, easy to find and widely available commercially.

The configuration with which the system can be built, with the circuits consisting of modular elements in series, and operating with each other in parallel, allows the operation of the system to be adapted to the needs; furthermore, maintenance is easier, thanks to the possibility of isolating a single circuit on which maintenance is to be carried out, without blocking the entire system.

Furthermore, the method for the purification of organic solutions, such as waste water, according to the present invention, allows to recover a stream of purified water and a biomass enriched with nutrients which, being able to be used in other sectors, has a high added value. .

To the process of the present invention described above, an expert person, in order to meet contingent and specific needs, may make adaptations, modifications and replacements of elements with other functionally equivalent ones, without however departing from the scope of the claims set out below.

Claims (13)

CLAIMS 1. A module (11,12,13,14,21,22,23,24) for a photobioreactor (100) comprising a biocathode (106) and a bioanode (104), in which said biocathode (106) is in contact with a photosynthesizing microbial population and said bioanode (104) is in contact with an organic solution (30,31,33) comprising an organic fraction and an electroactive heterotrophic microbial population, said biocathode (106) and bioanode (104) being separated from each other from a porous septum (105) in ceramic or ceramic / carbonaceous material. The module (11,12,13,14,21,22,23,24) for a photobioreactor (100) according to the previous claim, in which said porous septum (105) is represented by a tubular element. The module (11,12,13,14,21,22,23,24) for a photobioreactor (100) according to any one of the preceding claims, comprising a distribution element of said organic solution (30,31,33) comprising an electroactive microbial population inside the photobioreactor (100) represented by a tube (101) comprising a plurality of openings (102) for the diffusion of the organic solution (30,31,33) to the outside of the tube (101). The module (11,12,13,14,21,22,23,24) for a photobioreactor (100) according to any one of the preceding claims, wherein said porous septum (105) is prepared from a biomass or a mixture of a biomass with clay, in which said biomass in mixture can be replaced with biochar. 5. The module (11,12,13,14,21,22,23,24) for a photobioreactor (100) according to the preceding claim, in which said biomass or said mixture is modeled and subsequently undergoes a pyrolysis step , comprising the following steps: - heating, with a temperature increase of about 10 ° C / minute up to 900 ° C, - isothermal at 900 ° C for about 60 minutes, - cooling, with a decrease in temperature of about 5 ° C / minute. 6. The module (11,12,13,14,21,22,23,24) for a photobioreactor (100) according to any one of the preceding claims 3 to 5, in which between said porous septum (105) and said tube (101) a cavity (103) is formed which is filled with an electroconductive material represented by electroactive biochar, carbon coke, possibly in granular form, or by a fabric. 7. A circuit (10,20) for a photobioreactor (100) comprising a plurality of modules (11,12,13,14,21,22,23,24) according to any one of the preceding claims, wherein said modules at inside of each circuit (10,20) are connected in series with each other. 8. A photobioreactor (100) comprising one or a plurality of circuits (10,20) according to the previous claim immersed in a culture of photosynthesizing microorganisms (5 '). 9. A method for the purification of organic solutions and for the cultivation of photosynthesizing microorganisms through the use of a photobioreactor (100) according to the previous claim, comprising the steps of: a) slide inside the tube (101) of a module (11,12,13,14,21,22,23,24) a quantity of organic solution (30,31,33) comprising an electroactive heterotrophic microbial population and allowing said organic solution (30,31,33) to pass through the openings of said tube (102) towards the bioanode (104), b) allow the anodic oxidation of the organic fraction of the organic solution (30,31,32) by said electroactive microbial population obtaining the release of nutrients and carbon, c) allow the passage of said nutrients and carbon through the porous septum ( 105) of said module (11,12,13,14,21,22,23,24) towards said culture of photosynthesizing microorganisms (5 '). 10. The method according to the previous claim, comprising the further step d) of letting said nutrients released in step c) fertilize said culture of photosynthesizing microorganisms (5 '), producing a biomass enriched with nutrients. 11. A plant (200) for the purification of organic solutions, for the cultivation of photosynthesising microorganisms and for the recovery of carbon and nutrients from organic solutions comprising: - a photobioreactor (100) according to claim 8, - a tank (5) containing a culture of photosynthesizing microorganisms (5 '), - a first tank (1) for said organic solutions (30,31,33), - a pump (P2, P3) for feeding the organic solutions (30,31,33) to each of the circuits (10,20) of the photobioreactor (200), - a pump (P4) to regulate the level of the photosynthesising microorganisms (5 ') in the tank (5), - a vibrating screen (3) for the filtration of the culture of photosynthesising microorganisms in the tank (5 '), - a second tank (2) for the discharge of the supernatant or for its recirculation in the culture of photosynthesising microorganisms (5') or in the first tank (1), and optionally comprising: - a collector (4) for said organic solutions (30,31,33), - a pump (P1) for pumping said organic solutions (30,31,33) to said first tank (1). The nutrient enriched biomass obtained by the method according to claim 9 or 10. 13. Use of biomass according to the preceding claim for the production of food, also according to the applicable legislation for organic agriculture, for the extraction of pigments, for the production of feed, for the production of cosmetic products or for the production of hydrolysates and phytostimulant and soil improver preparations for crops.