WO2013006459A1

WO2013006459A1 - Pseudo column photobioreactor for photosynthetic microalgal culture

Info

Publication number: WO2013006459A1
Application number: PCT/US2012/045004
Authority: WO
Inventors: Qiang Hu; Milton Sommerfeld; Michael Mckay; Mark Kleshock
Original assignee: Arizona Board Of Regents For And On Behalf Of Arizona State University
Priority date: 2011-07-01
Filing date: 2012-06-29
Publication date: 2013-01-10

Abstract

A photobioreactor comprising a support structure and a flexible liner and a method of using said photobioreactor.

Description

DESCRIPTION

PSEUDO COLUMN PHOTOBIOREACTOR FOR PHOTOSYNTHETIC

MICRO ALGAL CULTURE

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to United States Provisional Patent Application Serial

Number 61/503,951 filed July 1, 2011, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

Embodiments of the present invention relate generally to flat panel photobioreactor designs configured to significantly reduce capital costs while facilitating high-yield cultivation of algae.

B. Background of the Invention

Photobioreactors (PBRs) play an important role in the production of algae-based biofuels and bioproducts. In general, PBRs accounts for more than sixty percent of capital investment and operation cost. PBR development is a key scientific and engineering challenge and a commercialization barrier. The following design principles should be applied to PBR design: design for productivity, scalability, energy consumption, land use, water requirement, cost of ownership, serviceability, and maintainability.

Flow characteristics (laminar vs. turbulent, C0₂ and 0₂ mass transfer, reactant gradient), light utilization (light absorption/scattering, light saturation and dilution, light fluctuation) and kinetics, (dynamics of photosynthesis, mass/energy balance, product gradient) are all important factors to be considered for PBR design. A cost effective solution will have a cost-cutting impact on algae-based biofuel and high value product (by-product) markets. Flat plate-type photobioreactors are promising culture devices for cultivation of photosynthetic microalgae for various applications. This type of photobioreactor (PBR) was first described by Samson and Leduy (1985) and by Ramos de Ortega and Roux (1986), and further refined by Tredici et al. (1991, 1997) and Hu et al. (1996, 1998a,b).

Flat plate-type designs offer greater advantages over the tubular-type systems including for example: (1) no "dark zone" is associated with the flat-plate design and the reactors are illuminated in their entirety, thus boosting photosynthetic productivity; (2) aeration that facilitates culture mixing and turbulence exerts little harm to algal cells because of the minimum hydrodynamic force created by air bubbling; (3) harmful levels of oxygen are not built up in flat plate-type system because of their short reactor heights (i.e., 3 to 10 feet); (4) flat-plate reactors can be set at various orientations and/or tilted angles aimed at maximal exposure to solar energy throughout the year to further enhance photosynthetic biomass yield; (5) flat plate PBRs can be installed close to each other to increase light utilization efficiency due to spatial dilution of photon fluxes by closely arranged PBRs; (6) compared to open raceway ponds, flat plate PBR occupies much less land area; and (7) compared to tubular reactors, flat plate reactors require considerably less capital and maintenance costs.

However, current large scale flat plate PBR design typically utilizes a flanged reactor tank fabricated primarily of acrylic plate that is glued and welded. Large PBR modules are formed by joining multiple tanks at the flanges. An acrylic PBR is relatively fragile and heavy, requiring it to be supported and secured by a substantial structure based on posts embedded in deep concrete footings. As such, the capital cost of such design is usually high, making it cost prohibitive for algal mass culture for - biofuels or other commodity products (e.g., food, feed, fertilizer).

One low cost version of flat plate PBRs is a "cage" based design, which includes both vertical support members as well as intermediate horizontal members between the upper and lower support members. This configuration greatly reduces the capital and maintenance costs compared to rigid tubular or flat panel PBRs. However, one major disadvantage of such design is that algae build up along vertical cage components due to the flow turbulence/recirculation cells formed by the horizontal dividers. This causes significant reduction in light penetration into the culture suspension due to biofouling (i.e., algal wall growth) and microbial contamination caused to a large extent by decay of algal cells accumulated in those dead spots created by the "cage" structure (horizontal dividers), which in turn promotes the occurrence and development of bacteria and predators in the culture. Several other issues are related to the usable lifetime of PBRs and increased operation and maintenance costs.

This limits the selection of the materials; for example, flexible materials typically cannot be used. Exemplary embodiments of the present disclosure overcome this issue by introducing the vertical beams at predefined intervals and enabling the use of cost-effective materials as the PBR construction components. SUMMARY

Embodiments of the present disclosure relate to systems and methods for simplified version of the flat panel PBR design to significantly reduce capital costs while facilitating high-yield cultivation of algae.

Exemplary embodiments provide enhanced surface area to volume ratio and increase the illuminated surface area compared to the flat panels. Exemplary embodiments also allow for variable inside dimension of the reactor which allows the user to vary the growth conditions by varying light penetration into the reactor. Exemplary embodiments also allow the possibility of changing reactor light path (i.e., reactor width) in-situ allowing process flexibility. Widths may be varied by manual or automated means.

Exemplary embodiments with the flexible liner allow for a linear reactor to be configured with varying internal reactor widths which allows a single reactor to contain algae culture in various stages of growth (ie. growth phase, stress phase, etc.). This may allow for simplified continuous, multistage cultivation of algae, and/or continuous mode processing of algae. Exemplary embodiments also enhance ease of maintenance by allowing the reactor interior to be exposed for assembly, cleaning, and repair. As a result of using the flexible lining material to contain the algae, other features that may be implemented in this reactor design to include the possibility of incorporating temperature control and nutrient supply directly in the bag via manufactured channels for heating or cooling culture media and delivery of nutrients (such as nitrogen and phosphorus). The supporting structure, or outer skeleton may also be used to transport heating/cooling media, as well as nutrients and aeration to the reactor which negates the need for external piping.

Exemplary embodiments comprise many unique design features, including considerably increasing the surface to volume ratio as compared with existing alternative PBR designs. Exemplary embodiments also allow the light path (culture width) of the PBR to be readily adjusted within a single row or modified in different rows or modules. Furthermore, the pseudo column feature greatly improves culture mixing. In addition, exemplary embodiments provide for little oxygen accumulation and thus no oxygen-induced photoinhibition of photosynthesis. Exemplary embodiments also provide for low biofouling due to the pseudo-column geometry and improved culture mixing, and an internal thermal exchanger improves the maintenance of culture temperature. Furthermore, exemplary embodiments provide low water loss due to the internal thermal control rather than evaporative cooling used in existing technologies. Exemplary embodiments also provide a number of advantages over the existing PBRs in that it is (1) inexpensive to manufacture, (2) simple assembly, (3) fast installation; (4) low maintenance; (5) high reliability; (6) flexible bag/liner; (7) low capital cost; (8) consumable (annual); (9) flexible installation; (10) minimal surface prep; and (11) tolerant of outdoor environments.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method or system of the invention, and vice versa. Furthermore, systems of the invention can be used to achieve methods of the invention.

The term "conduit" or any variation thereof, when used in the claims and/or specification, includes any structure through which a fluid may be conveyed. Non-limiting examples of conduit include pipes, tubing, channels, or other enclosed structures.

The term "reservoir" or any variation thereof, when used in the claims and/or specification, includes any body structure capable of retaining fluid. Non-limiting examples of reservoirs include ponds, tanks, lakes, tubs, or other similar structures.

The term "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

The terms "inhibiting" or "reducing" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or."

As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include"), or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

As used herein, "biofuel products" and/or "precursors" include hydrocarbons derived from biomass or microorganisms. Non-limiting examples include metabolites that are directly suitable for combustion, or precursors requiring additional refinement to enable their use in said applications. Said metabolites may be produced by either natural or engineered organisms. Examples include, but are not limited to: alcohols (including, for example, all isomers of ethanol, propanol, butanol, pentanol, hexanol and all of their isomers), fatty acids (including, for example, decanoic, lauric, myristic, palmitic, and stearic acids) and their esters (including, for example, methyl and ethyl esters), alkanes (including, for example, undecane, tridecane, pentadecane, and heptdecane), and isoprenoids.

Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the examples, while indicating specific embodiments of the invention, are given by way of illustration only. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Exemplary embodiments of the present disclosure provide a pseudo-column geometry for PBR illustrated in the accompanying Figures.

FIG. 1 illustrates a perspective view of a PBR 100 comprising a support structure 110 in an open position, while FIG. 2 illustrates a more detailed view of a portion of support structure 110. As shown in FIG. 2, support structure 110 comprises one or more upper horizontal support members 115 and one or more lower horizontal support members 125. A plurality of vertical support members 135 extend between upper horizontal support members 115 and lower horizontal support members 125. As shown in this exemplary embodiment, no intermediate horizontal support members are placed between upper horizontal support members 115 and lower horizontal support members.

In the exemplary embodiment shown, a hinge 140 allows one side of vertical support members 135 to pivot away from the opposite side of the vertical support members 135 so that a flexible liner (discussed below) can be inserted between the vertical support members. In other embodiments, vertical support members 135 may be separated and then coupled together without the use of a hinge in order to insert a flexible liner.

FIGS. 3-4 illustrate PBR 100 with a flexible liner 150 supported by support structure 110. FIG. 3 provides a perspective view, while FIG. 4 illustrates a top-down view of the PBR 100.

In this embodiment, flexible liner 150 extends between vertical support members 135, so that flexible liner 150 is fully exposed to the environment in an area extending between the upper and lower horizontal support members 115, 125 and adjacent vertical support members 135.

As shown in FIG. 4, a curvature of the flexible liner 150 may be either preformed or as a result of water column pressure. The vertical beams will provide the required mechanical strength to maintain the desired pseudo-column shape. This geometry is a novel modification to previous designs where cross bars were used as the external containments (i.e., cage-based designs). This geometry is not obvious even to the field experts because of the challenges in how to reduce this concept to the practice. The proposed pseudo-column geometry has the following advantages over either cage-based or vertical panel designs.

As shown in FIG. 5, a comparison of the increase in algae biomass (g/L) over an eight day period was performed in multiple acrylic panel reactors and compared with the increase in biomass in a an exemplary embodiment of PBR 100 (also labeled as a pseudo column reactor or PCR). There was no significant difference in the biomass yield between the high cost acrylic panel reactor and the lower cost pseudo column reactor design of PBR 100.

The following references are incorporated by reference:

l. International Patent Publication WO2010/076795 A 1.

2. Gitelson, A., Hu, Q & Richmond, A. (1996) Photic volume in photobioreactors supporting ultrahigh population densities of the photoautotroph Spirulina platensis. Applied Environmental Microbiology 62: 1570-1573.

3. Hu, Q., Guterman, H. & Richmond, A. (1996) A flat inclined modular

photobioreactor (FIMP) for outdoor mass cultivation of photoautotrophs. Biotechnology & Bioengineering 51 : 51-60.

4. Hu, Q., Hu, Z., Cohen, Z. & Richmond, A. (1997) Enhancement of eicosapentaenoic acid (EPA) and g-linolenic acid (GLA) production by manipulating algal density of outdoor cultures of Monodus subterraneus (Eustigmatophyte) and Spirulina platensis

(Cyanobacterium). European Journal of Phycology 32: 81-86. 5. Hu, Q., Kurano, N., Iwasaki, I., Kawachi, M. & Miyachi, S. (1998) Ultrahigh cell density culture of a marine green alga, Chlorococcum littorale in a flat plate photobioreactor. Applied Microbiology & Biotechnology 49: 655-662.

6. Hu, Q., Yair, Z. & Richmond, A. ( 1998) Combined effects of light intensity, light- path and culture density on output rate of Spirulina platensis (Cyanobacteria). European

Journal of Phycology. 33: 165-171.

7. Hu, Q., Faiman, D. & Richmond, A. (1998) Optimal orientation of enclosed reactors for growing photoautotrophic microorganisms outdoors. Journal of Fermentation &.

Biotechnoogy. 85: 230-236.

8. Hu, Q. & Richmond, A. (1996) Productivity and photosynthetic efficiency of

Spirulina platensis affected by light intensity, cell density and rate of mixing in a flat plate photobioreactor. Journal of Applied Phycology. 8: 139-145

Claims

CLAIMS:

1. A photobioreactor comprising:

a support structure comprising:

a plurality of vertical support members;

an upper horizontal support member proximal to a first end of the vertical support members; and

a lower horizontal support member proximal to a second end of the vertical; and

a flexible liner extending between the plurality of vertical support members, wherein the flexible liner is fully exposed to the environment in an area extending between the upper and lower horizontal support members and adjacent vertical support members.

2. The photobioreactor of claim 1 wherein the support structure does not comprise additional horizontal support members between the upper and lower horizontal support members.

3. The photobioreactor of claim 1 wherein the flexible liner extends outwardly from between adjacent vertical support members.

4. The photobioreactor of claim 1 further comprising a temperature controller configured to control the temperature of an inner volume of the flexible liner.

5. The photobioreactor of claim 1 further comprising a nutrient supply system configured to supply nutrients to an inner volume of the flexible liner.

6. The photobioreactor of claim 5 wherein the nutrient supply system is configured to supply nitrogen and phosphorous to an inner volume of the flexible liner.

7. The photobioreactor of claim 1 wherein the support structure is configured to transport temperature control media.

8. The photobioreactor of claim 1 wherein the support structure is configured to transport nutrients to an inner volume of the flexible liner.

9. The photobioreactor of claim 1 wherein the support structure is configured to aerate an inner volume of the flexible liner.

10. The photobioreactor of claim 1 further comprising a hinge proximal to the lower horizontal support member.

11. The photobioreactor of claim 10 wherein the hinge is configured to allow a first portion of the plurality of vertical support members to be pivoted away from a second portion of the plurality of vertical support members.

12. A method of cultivating cells, the method comprising:

providing the photobioreactor of any of claims 1-11; and

culturing photosynthetic cells in an inner volume of the flexible liner.

13. The method of claim 12, further comprising controlling the temperature of the inner volume of the flexible liner.

14. The method of claim 12 further comprising delivering nutrients to the inner volume of the flexible liner.

15. The method of claim 12 further comprising aerating the inner volume of the flexible liner.

16. The method of claim 12 further comprising adjusting a light path to the flexible liner.