WO2009134358A1

WO2009134358A1 - Apparatus and method for producing biofuel from algae by application of shaped pulsed pressure waves

Info

Publication number: WO2009134358A1
Application number: PCT/US2009/002586
Authority: WO
Inventors: Tajchai Navapanich; David M. Giorgi
Original assignee: Optiswitch Technology Corporation
Priority date: 2008-04-28
Filing date: 2009-04-28
Publication date: 2009-11-05

Abstract

Biofuels may be produced from algae, and algae may be dewatered, by exposing the algae to shaped pulsed pressure waves. The shaped pulsed pressure waves are produced within the liquid medium containing the algae, and are designed to effectively disrupt the physical structure of the algae in the liquid medium to facilitate the release of biofuel, water, or both. Biofuel is obtained by separating the biofuel from the disrupted algae and liquid medium in any desired manner. Accordingly, the production of biofuel from algae may be performed efficiently, without pre-drying the algae. Dewatered algae is obtained by separating the disrupted algae from the liquid medium in any desired manner. Suitable pressure wave sources include electrohydraulic generators, electromagnetic generators, and piezoelectric generators. A drive pulse supply such as a Marx bank generator may be used to drive these sources to obtain the shaped pulsed pressure waves.

Description

TITLE OF THE INVENTION

Apparatus and method for producing biofuel from algae by application of shaped pulsed pressure waves

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of US Provisional Patent Application Serial No. 61/125,760 filed April 28, 2008, which hereby is incorporated herein in its entirety by reference thereto. This application also is a continuation-in-part of US Application Serial No. 11/904,393 filed September 27, 2007 and published as US Patent Application Publication NO. 2008/0311638 on December 18, 2008, which claims the benefit of US Provisional Patent Application Serial No. 60/934,782 filed June 15, 2007, all of which hereby are incorporated herein in their entirety by reference thereto.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] The present invention relates to the production of biofuel, and more particularly to the production of biofuel from algae.

[0003] Description of Related Art

[0004] Biofuel has been produced from algae. The algae are grown in a liquid medium, harvested, and processed in various ways to yield biofuel. In one technique, algae removed from liquid medium are dried and pressed in a press to extract the biofuel contained therein. In a technique known as solvent extraction, a solvent such as hexane is applied to the algae to dissolve the biofuel contained therein, the algae is removed from the solvent- biofuel combination, and the biofuel and solvent are separated by, for example, distillation. Subsequently, the solvent may be re-used. Solvent extraction may even be applied to pressed algae. [0005] Several problems are associated with the press and solvent extraction techniques as currently practiced. These include capture of only a small portion of the biofuel from the algae, slow processing time, and presence of hazardous materials. Other problems with known production methods include lack of scalability, energy intensiveness, and economical non-viability. Accordingly, improved apparatus and methods for production of biofuel from algae are needed.

[0006] Some industrial processes involve dewatering algae. However, even after various dewatering methods such as membrane filtration, flocculation, and centrifugation, the water content remaining can still be quite high; for example, around 85%. If less water is desired, a homogenizer may be used to mechanically break the cells, much like a blender.

[0007] Unfortunately, the homogenizer process is expensive, and also creates other processing issues like clogging of equipment. Accordingly, improved dewatering processes are needed.

BRIEF SUMMARY OF THE INVENTION

[0008] These and other problems in the prior art are solved in various ways by one or more of the various embodiments of the present invention.

[0009] One embodiment of the present invention is an apparatus for treating algae in a liquid-based algae-containing medium, comprising a pressure wave generator having a treatment region for containing the liquid-based algae-containing medium; and a drive pulse generator coupled to the pressure wave generator for supplying a drive pulse thereto to generate a shaped pulsed pressure wave in the treatment region. The shaped pulsed pressure wave comprises a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae-containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain a treated medium comprising algae having disrupted cellular structures. [0010] Another embodiment of the present invention is a method for producing biofuel from a liquid-based algae-containing medium, comprising directing the liquid- based algae-containing medium into a treatment region; applying a shaped pulsed pressure wave to the liquid-based algae-containing medium in the treatment region to obtain a treated medium comprising algae having disrupted cellular structures and biofuel from the disrupted algae; and separating the biofuel from the treated medium. The shaped pulsed pressure wave comprise a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae-containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain the treated medium.

[0011] Another embodiment of the present invention is a method for dewatering algae contained in a liquid-based algae-containing medium, comprising directing the liquid-based algae-containing medium into a treatment region; applying a shaped pulsed pressure wave to the liquid-based algae-containing medium in the treatment region to obtain a treated medium comprising algae having disrupted cellular structures; and separating the disrupted algae from the treated medium. The shaped pulsed pressure wave comprises a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae- containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain the treated medium.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0012] FIG. 1 is a schematic block diagram of an illustrative apparatus for producing biofuel from algae by application of shaped pulsed pressure waves.

[0013] FIG. 2 is a graph of an exemplary shaped pulsed pressure waveform generated by a pressure wave generator upon application of a suitable drive pulse.

[0014] FIG. 3 is a schematic diagram of an illustrative Marx bank generator 100. [0015] FIG. 4 is a cross-section view of an illustrative mass transport device for applying shaped pulsed pressure waves to a liquid-based material stream in a continuous flow process.

[0016] FIG. 5 is a cross-section view of an illustrative array of points for applying shaped pulsed pressure waves to a liquid-based material stream in a continuous flow process.

[0017] FIG. 6 is a schematic block diagram of an illustrative apparatus for dewatering algae by application of shaped pulsed pressure waves.

[0018] FIG. 7 is a block schematic diagram of an illustrative apparatus for dewatering algae and for recovering biofuel from the material stream, by application of shaped pulsed pressure waves.

[0019] The Figures generally illustrate various exemplary implementations of the apparatus and methods. The particular exemplary implementations illustrated in the figures provide for ease of explanation and understanding, even while being fully descriptive. Variations of the apparatus and methods that differ from the illustrated implementations are contemplated. The extensions of the figures with respect to number, position, order, relationship and dimensions will be explained or will be within the ordinary skill of the art after the description has been studied. Furthermore, the apparatus, materials and other operational parameters to conform to specific size, force, weight, strength, velocity, temperatures, flow, and similar requirements will likewise be within the ordinary skill of the art after the description has been studied. Where used in reference to the figures, the terms "top," "bottom," "right," "left," "forward," "rear," "first," "second," "inside," "outside," and similar terms should be understood to reference the structure and methods described in the specification and illustrated in the drawings and are utilized for purposes of explanation. DETAILED DESCRIPTION OF THE INVENTION, INCLUDING THE BEST MODE

[0020] Biofuels are produced from algae by exposing the algae to shaped pulsed pressure waves generated by a pressure wave source. The shaped pulsed pressure waves may be produced within the liquid medium containing the algae, which may include the typically aqueous medium in which the algae is grown. The shaped pulsed pressure waves are designed to effectively disrupt the physical structure of the algae in the liquid medium, thereby facilitating the release of biofuel from the algae into the liquid medium. The shaped pulsed pressure waves may be applied to the algae in liquid media in a batch process, or as the algae, entrained in liquid media, flows through a treatment cell chamber in a continuous flow process, either with or without recirculation. The biofuel may be separated from the disrupted algae and liquid medium in any desired manner, illustratively by centrifuge. Accordingly, the production of biofuel from algae may be performed efficiently, without pre-drying the algae.

[0021] Suitable shaped pulsed pressure wave sources include electrohydraulic pressure wave generators, electromagnetic pressure wave generators, and piezoelectric pressure wave generators. Suitable pulse characteristics may be obtained from these sources by utilizing an appropriate pulse supply. Generally speaking, high voltage and high current pulse supplies are appropriate for electrohydraulic pressure wave generators, moderate to high voltage and high current pulse supplies are appropriate for electromagnetic pressure wave generators, and high voltage low current pulse supplies are appropriate for piezoelectric pressure wave generators.

[0022] A suitable type of high voltage high current pulse supply is the Marx bank generator, which is a capacitive store pulser that allows for fast high voltage waveforms to be delivered to a pressure wave generator load. The Marx bank generator is designed to shape the voltage pulse across the load.

[0023] The term "algae" as used herein includes algae (both prokaryotes and eukaryotes), diatoms, and similar organisms that form biofuel within their cellular structure. The algae are grown in a liquid media, which is generally aqueous but may contain salts, nutrients, and/or other materials and additives. The biofuel is generally held within the one or more cells of the algae.

[0024] The term "biofuel" as used herein includes lipids, oils, fats, fatty acids, and similar hydrocarbon materials that may be used as fuel, a precursor for the formation of fuel, an additive that may be blended with other materials to form fuel, or as lubricants. Biofuel may be usable as fuel and/or fuel component for use in internal combustion engines such as diesel, Otto cycle, and gasoline engines, and other types of engines such as jet engines.

[0025] Material stream, as used herein, includes the algae and the liquid media, and may include biofuel extracted from the algae, and solvents and other additives. Various additives may be used for various purposes, including conditioning the algae and adjusting the salinity and other characteristics of the liquid media in the material stream.

[0026] Biofuel Production

[0027] FIG. 1 shows an illustrative extraction apparatus which includes a electrical drive pulse generator 10, a shock wave generator 20, and a separator 30. Algae input stream 22 is supplied to a pressure wave generator 26 in the shock wave generator 20, where it is exposed in a treatment area to shaped pulsed pressure waves generated by the pressure wave generator 26 in response to a pulse from the drive pulse generator 10 and emerges as an algae output stream 28. The algae output stream 28, which contains disrupted algae and biofuel from the disrupted algae, is supplied to a suitable separator 30 such as a centrifuge, where it is separated into a biofuel stream 40 and a by-products stream 50.

[0028] FIG. 2 shows an exemplary shaped pulsed pressure waveform generated by the pressure wave generator 26 upon application of a suitable drive pulse from the drive pulse generator 10. Other suitable shaped pulsed pressure waves of varying amplitude and/or varying duration may be generated in various aspects. This waveform is characterized by a near instantaneous increase in pressure (the shock) as shown during phase 70, followed by a period of negative pressure as shown during phase 80. Both phases 70 and 80 of the pressure wave, one exerting compressive force and the other exerting tensile strain, profoundly affects the algae.

[0029] In various aspects, the material stream containing the algae may be static or flowing through the treatment area. A flowing cell or mass transport device is particularly suitable in various aspects. Although dependent on the type of technology and particular design used for the pressure wave generator 26, the voltage applied to the pressure wave generator 26 by the drive pulse generator 10 may be greater than about 10 kV and, in some aspects, may be greater than about 50 kV for a electrohydraulic pressure wave generator, for example. The shaped pulsed pressure waves should be greater than a few MPa and up to about 30 MPa or more. The shaped pulsed pressure waves transmit through the liquid medium in which the algae is being transported, which may be the water in which the algae is grown, so the algae does not need to be dried. The physical mechanisms that disrupt the cellular structure of algae include spallation, cavitation, shear stress and superfocusing, and squeezing (or expansion).

[0030] Spallation is caused by the pressure waves. In materials that have an acoustic impedance higher than the surrounding medium, spall fractures occur at the distal end of the sample. When a pressure wave enters the sample and reflects off thedistal end, the reflected wave may be negative. This area of negative pressure is added to the negative pressure of the incoming pulse. Thus a region of low pressure is created in the sample, resulting in a large tensile stress near the distal end that results in material being ejected from the sample. For materials that have a lower acoustic impedance than the surrounding medium, which may be the case for algae under many conditions, the opposite is true: the wave reflected off the proximal end of the sample is negative and this negative pressure adds to the negative pressure of the incoming tail of the pressure wave. This creates an area of extremely low pressure just in front of the sample, which causes algae to expand rapidly in the direction of the incoming pressure wave. This large tensile stress spalls material off of the proximal end of the sample. The net result is that the algae is disrupted, and thus the biofuel is obtained. [0031] The negative pressure phase 80 of the pressure wave shown in FIG. 2 creates a cavitation bubble, which also results in significant disruption of the algae and thus again causes disruption of the algae so that the biofuel may be obtained. Cavitation refers to the creation of cavities (bubbles) when the negative pressure of the incoming shock wave is negative enough to tear apart the surrounding fluid (water). The negative pressure can also be caused by reflection of a positive pressure wave from a medium of lower acoustic impedance. A cavitation bubble may grow until the outside pressure (about 1 atmosphere) is higher than the near vacuum inside the bubble. For example, the collapse of the cavitation bubble, which occurs in 150 μs, results in the formation of a microjet of fluid with speeds upwards of 100 m/sec; see, e.g., Crum, L. A., Cavitation microjets as a contributory mechanism for renal calculi disintegration, ESWL. J. Urol., Vol. 140, 1988, pages 1587-90. These high speed jets cause disruption to the algae. The collapse of the cavitation bubble is extremely violent, and the gas that diffuses into these bubbles becomes superheated to an extent that light emission occurs; see, e.g., Coleman, AJ, Choi, MJ, Saunders, JE, Leighton, TG, Acoustic emission and sonoluminescence due to cavitation at the beam focus of an electrohydraulic shock wave lithotripter, Ultrasound Med Biol., Vol. 18, 1992, pages 267-81. The superheating is extremely concentrated and is not expected to cause significant heating of the algae. The collapse of a cavitation bubble may also cause secondary shock waves.

[0032] Tandem pressure wave generators, or one pressure wave generator operating two pulses in a bust mode, may be used to enhance the collapse of the cavitation bubble, thereby improving disruption of the algae. If, for example, a second shock wave arrives at the peak of the bubble formation (about 300 μs), then the compressive phase of the second shock wave enhances the bubble collapse caused by the negative pressure of the first shock wave. See, e.g., Bailey, MR₁ Cleveland, RO, Williams, JC Jr., Effect of increased ambient pressure on lithotripsy-induced cavitation in bulk fluid and at solid surfaces, Joint Meeting of the Acoustical Society of America, European Acoustics Association and German Acoustics DAGA Conference, Berlin, Germany: Deutsche Gesellschaft fur Akustik (DEGA), 1999. See also Sokolov, DL, Bailey, MR, Crum, LA, Use of dual-pulse lithotriptor to generate a localized and intensified cavitation field, J Acoust Soc Am., Vol. 110(3 Pt 1 ), 2001 , pages 1685-95. The growth of the cavitation bubble disrupts the algae. For example, biofuel or water present in the algae may expand during the formation of cavitation bubbles, to disrupt the algae and release the biofuel.

[0033] Algae material streams may include layers that are weak with respect to shear. Shear stresses develop as the pressure wave moves through the algae layers, and may be amplified by reflections at the boundary of dissimilar materials. Shear and tensile stresses may be amplified by the focusing of these waves due to refraction or diffraction of the sound waves by the physical geometry of the algae material stream.

[0034] For materials in which the speed of sound is higher than in water, the pressure wave moves faster in the material than in the surrounding medium. After the pressure wave leaves the material, the surrounding medium is still under high pressure and may result in the squeezing of the material. If the opposite is true and the pressure wave moves slower in the material than the surrounding medium, the region of higher pressure may still exist in the material after the shock has passed the surrounding medium. This may result in the expansion of the material, which may fail due to tensile strain. This may be the case for less dense materials such as algae.

[0035] All or some of the above mechanisms result in the disruption of the algae without the need to completely remove the water. In various aspects, these processes may be augmented by the presence of chemicals and solvents.

[0036] In summary, the use of shaped pulsed pressure waves in the disruption of algae may be characterized as follows. First, the shaped pressure waves exhibit both a compressive phase (positive pressure) and tensile phase (negative pressure) (most materials are weaker in tension than in compression). Second, the tensile phase may be enhanced by reflections from boundaries of different acoustic impedance. Third, shear stress may be generated by a combination of both shear waves and compressive waves that develop as the pressure wave passes through material of different acoustic impedance. Fourth, negative pressure may generate cavitation bubbles which disrupt the algae during periods of rapid expansion and collapse. During the collapse, a high speed jet of water may be generated which may further disrupt the algae. Moreover, by timing two pressure waves from different pulsed power systems the collapse of the cavitation bubbles may be enhanced. Fifth, due to the geometry of the algae material stream, superfocusing of the pressure wave may occur. Superfocusing may occur due to diffraction or refraction of the pressure waves.

[0037] Various types of apparatus may be used for the pressure wave generator

26. One type is the electrohydraulic pressure wave generator, which includes electrodes that are submerged in a fluid-filled housing (a suitable fluid is water, for example). The electrohydraulic pressure wave generator initiates the pulsed pressure wave by an electrical discharge between the electrodes. Vaporization of fluid molecules between the electrodes produces vapor bubbles that grow and rupture, resulting in explosive force that creates the pulsed pressure wave.

[0038] Other types of apparatus include the electromagnetic pressure wave generator and the piezoelectric pressure wave generator. In the electromagnetic pressure wave generator, opposing metal membranes are connected to electromagnetic coils. When a high current passes through one coil, a strong magnetic field is generated that induces a high current in the opposing membrane and accelerates the metal membrane away from the coil, which generates the pulsed pressure wave in various aspects. In the piezoelectric pressure wave generator, pulsed pressure waves are formed by the application of high voltage to piezoelectric crystals. The crystals immediately contract and expand to generate the pulsed pressure waves in various aspects.

[0039] The electrohydraulic pressure wave generator advantageously generates a fast pressure wave rise time and provides focused energy over a broader area, thereby delivering a greater amount of positive pressure wave energy than the electromagnetic pressure wave generator or the piezoelectric pressure wave generator. In addition, the pressure waves may be focused through the use of focusing reflectors.

[0040] FIG. 3 is a schematic diagram of a Marx bank generator 100, which is a particularly suitable voltage source for powering the electrohydraulic type of pressure wave generator to obtained a suitably shaped pulsed pressure wave. The Marx bank generator 100 shown in FIG. 3 has four stages, but the number of stages may be varied to achieve the desired voltage pulse characteristics. Generally, Marx bank generators include a capacitive store (illustratively capacitors 104, 114, 124 and 134) which are switched by solid state switches (illustratively solid state switches 106, 116 and 126). Alternatively, the Marx bank generator may be configured as a Pulse Forming Network ("PFN") Marx bank generator, in which the capacitors are replaced by transmission lines or by multiple capacitors and multiple inductors to form a transmission line. In various aspects, the solid state switches are capable of fast current rise (high di/dt), high blocking voltage, and large peak current. An example of a type of switch suitable for the Marx bank generator 100 is a Light Activated Silicon Switch (LASS) such as the LAS 010 and LAS 020 manufactured by Optiswitch Technology Corp. of San Diego, California. Other types of switches suitable for the Marx bank generator 100 include the thyristor, the Reverse Blocking Diode Thyristor ("RBDT") which is also known as the Reverse Switching Rectifier ("RSR"), the Breakover Diode ("BOD") including the XBOD® device manufactured by Optiswitch Technology Corp. of San Diego, California, the Gate Turn-Off Thyristor ("GTO"), the Super-GTO such as the Solidtron CCSTA14N40 available from Silicon Power Corp. of Malvern, Pennsylvania, the Insulated Gate Bipolar Transistor ("IGBT") such as the DIM900ESM45-F000 available from Dynex Semiconductor of Lincoln, UK., four layer (pnpn) diodes commonly referred to as Shockley diodes, the MOS Controlled Thyristor ("MCT"), current or voltage controlled solidtrons, and avalanche transistors.

[0041] The Marx bank generator 100 operates as follows. The capacitors 104,

114, 124 and 134 are charged in parallel from voltage source V|_N. Resistors 102, 112, 122, 132, 108, 118 and 128 are included for charging; inductors may be used instead, if desired. When a pulse is desired, the switches 106, 116 and 126 are closed and capacitors 104, 114, 124 and 134 discharge in series into load 142 through the closed switches 106, 116 and 126. The voltage discharged into the load 142 is essentially the cumulative charge placed on the capacitors 104, 114, 124 and 134. Marx bank generators are generally described in various publications, including, for example, US Patent Application Publication No. US 2008/0311638, published December 18, 2008 in the name of Navapanich et al.

[0042] Instead of a Marx bank generator, other types of high voltage systems may be utilized in various aspects. These may be various modulator schemes that can apply a high voltage pulse across the electrodes of the electrohydraulic shock wave generator. The switch may be Silicon or other semiconductor types (SiC₁ GaN or GaAs, for example). If the switch is a LASS and the material is not silicon, then the wavelength of light may need to be different depending on the material bandgap, and the encapsulation medium may be different depending on the absorption.

[0043] The shaped pulsed pressure waves may be delivered to the algae in liquid media in a batch process, or as the algae, entrained in liquid media, flows through a treatment cell chamber in a continuous flow process, either with or without recirculation. FIG. 4 shows an example of a mass transport device 150 for applying the shaped pulsed pressure waves to a liquid-based material stream in a continuous flow process. The mass transport device 150 includes an outer pipe 160 and a concentric interior rod or pipe 170, which function as electrodes and are coupled to the Marx bank generator 100 (FIG. 3) as the load 142. Illustratively, the pipe 160 functions as an anode and the rod 170 functions as a cathode. Alternatively, the pipe 160 may function as the cathode, and the rod 170 may function as the anode. The liquid-based material stream flows through the pipe 160 and is subjected to shaped pulsed pressure waves generated in the liquid by the voltage pulse applied to the anode pipe 160 and the cathode rod 170 by the Marx bank generator 100.

[0044] The implementation of FIG. 4 is only an example of a mass transport device for applying a shaped pulsed pressure wave to a liquid-based material stream. In other variations, a plurality of anodes and a plurality of cathodes may be placed generally about the interior of a pipe circumferentially and/or axially in various ways to provide the shaped pulsed pressure waves. Moreover, two or more drive pulse generators may be used to apply suitable voltage pulses to various anodes and cathodes to provide shaped pulsed pressure waves to the liquid-based material stream. Moreover, pipes and rods used for generating the shaped pulsed pressure waves may be shapes in various ways, including rectangular, square, or other cross-sectional shape.

[0045] In various aspects, electrodes may be used to create localized or nonuniform pressure waves across the material treatment area. One concept is to create a uniform sea of sharp points. FIG. 5 is a cross-section view of an illustrative sea or array of points for applying shaped pulsed pressure waves to a algae-containing liquid medium 160. Three points 170, 180 and 190 are shown, although a fewer or greater number of points may be used as desired. Point 170, which is illustrative of points 180 and 190, includes a high voltage electrode 172 and a ground electrode 174, which are designed to cause breakdown over a well defined region in liquid medium. The pressure wave generated by the discharge between the electrodes 172 and 174 is focused by an acoustic reflector 176 and coupled through a liquid coupling region 178 into the algae-containing liquid medium 160. The gap between the electrodes 172 and 174 is located, for example, at one of the foci of the acoustic reflector 176, and the zone of algae-containing liquid medium to be treated is located at the other foci. Once the gap breaks down, the shock wave is focused to the other foci. If necessary, multiple gaps and reflectors (e.g. points 180 and 190) can be used to treat a larger volume of material. If focusing is not required, the reflector can simple collimate the acoustic energy and direct it onto the algae-containing liquid medium as it passes by the treatment zone. This will result in a larger treatment zone, albeit at a lower maximum pressure for the same energy in the discharge.

[0046] A feedback control to automatically adjust the voltage, current, and pulse width based on the load impedance of the material being processed. FIGS. 1 , 6 and 7 show a feedback sensor 24, which illustratively is a device of known geometry that passes a current through the algae stream 22. The impedance of the algae stream 22 is determined from the voltage, current, and geometry of the feedback sensor 24. In addition to improving the treatment, the feedback control may also be used to extend the life of the electrodes, which is particularly beneficial for the case where the system generates the shock wave from an electrical breakdown between electrodes in a fluid. Depending on the final voltage, other types of modulator schemes could be used.

[0047] Dewatering

[0048] The apparatus and methods described herein may be modified to reduce the water content of an algae-containing medium. FIG. 6 is a schematic block diagram of an illustrative apparatus for dewatering algae by application of shaped pulsed pressure waves. The interior of the algae cells retain a great deal of water, even after the medium is processed by such dewatering techniques as filtration, flocculation and centrifugation. Processing an algae-containing medium by exposure to a shaped pulsed pressure wave in accordance with the apparatus and methods described herein increases the cell membrane permeability, thereby allowing the water to come out of the algae cell more readily. The water and other byproducts 220 are separated and removed by separator 200. The resulting dewatered algae 210 may be processed further as desired. Illustratively, the dewatered algae 210 may be exposed to a solvent, or may be exposed to a further shaped pulsed pressure wave treatment to further disrupt cellular structures to enhance biofuel recovery, either with or without solvent. Dewatering may be enhanced by further processing the algae remaining after the shaped pulsed pressure wave treatment with a press, a centrifuge, a distillation column, an adsorption column, or any other such apparatus (not shown).

[0049] Dewatering of algae may be practiced as an additional operation in the processes of biofuel production from algae as described herein, or may be seen as an integral part of biofuel production. FIG. 7 is a block schematic diagram of an illustrative apparatus for dewatering algae and for recovering biofuel from the material stream, by application of shaped pulsed pressure waves. After dewatering treatment, the output algae stream 28 may contain biofuel released from the algae cells, in addition to water released by the algae cells. Where the amount of released biofuel is not sufficient for recovery, the treatment may be viewed as part of a dewatering operation in which the water in the material stream (which includes water released from the algae cells) is removed (FIG. 6). However, where the amount of biofuel released is significant enough to warrant recovery from the material stream, a suitable separator 230 is used to separate algae 210 and biofuel 240 from the output algae stream 28, leaving byproducts 250. If sufficient biofuel remains within the dewatered algae, it may be extracted by further processing of the algae.

[0050] The description of the invention including its applications and advantages as set forth herein is illustrative and is not intended to limit the scope of the invention, which is set forth in the claims. Variations and modifications of the embodiments disclosed herein may be made, and practical alternatives to and equivalents of the various elements of the embodiments may be substituted. These and other variations and modifications of the embodiments disclosed herein, including of the alternatives and equivalents of the various elements of the embodiments, are contemplated, and may be made without departing from the scope and spirit of the invention.

Claims

1. An apparatus for treating algae in a liquid-based algae-containing medium, comprising:

a pressure wave generator having a treatment region for containing the liquid- based algae-containing medium; and

a drive pulse generator coupled to the pressure wave generator for supplying a drive pulse thereto to generate a shaped pulsed pressure wave in the treatment region;

wherein the shaped pulsed pressure wave comprises a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae-containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain a treated medium comprising algae having disrupted cellular structures.

2. The apparatus of claims 1 further comprising a separator for recovering biofuel from the treated medium.

3. The apparatus of claims 1 further comprising a separator for recovering dewatered algae from the treated medium.

4. The apparatus of claims 1 further comprising a feedback sensor coupled to the drive pulse generator for adjust characteristics of the drive pulse generator based on load impedance of the liquid-based algae-containing medium.

5. The apparatus of claim 1 wherein the treatment region comprises a static region for maintaining the liquid-based algae-containing medium in a static condition during application of the shaped pulsed pressure wave.

6. The apparatus of claim 1 wherein the treatment region comprises a material stream flow path for maintaining the liquid-based algae-containing medium in a flowing condition during application of the shaped pulsed pressure wave.

7. The apparatus of claim 1 wherein the pressure wave generator comprises electromagnetic pulsed pressure wave generation elements.

8. The apparatus of claim 1 wherein the pressure wave generator comprises piezoelectric pulsed pressure wave generation elements.

9. The apparatus of claim 1 wherein the pressure wave generator comprises electrohydraulic pulsed pressure wave generation elements.

10. The apparatus of claim 9 wherein:

the electrohydraulic pulsed pressure wave generation elements are electrodes fluidly coupled to the liquid-based algae-containing medium; and

the drive pulse generator is a Marx bank generator comprising a capacitor store and a plurality of solid state switches adapted for high di/dt, high blocking voltage, and large peak current.

11. A method for producing biofuel from a liquid-based algae-containing medium, comprising:

directing the liquid-based algae-containing medium into a treatment region;

applying a shaped pulsed pressure wave to the liquid-based algae-containing medium in the treatment region, wherein the shaped pulsed pressure wave comprises a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae-containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain a treated medium comprising algae having disrupted cellular structures and biofuel from the disrupted algae; and

separating the biofuel from the treated medium.

12. The method of claim 11 further comprising adjusting characteristics of the shaped pulsed pressure wave based on load impedance of the liquid-based algae- containing medium in the treatment region.

13. The method of claim 11 further comprising maintaining the liquid-based algae-containing medium in a static condition in the treatment region during the applying step.

14. The method of claim 11 further comprising maintaining the liquid-based algae-containing medium in a flowing condition in the treatment region during the applying step.

15. The method of claim 11 wherein the applying step comprises generating the shaped pulsed pressure wave electromagnetically.

16. The method of claim 11 wherein the applying step comprises generating the shaped pulsed pressure wave piezoelectrically.

17. The method of claim 11 wherein the applying step comprises generating the shaped pulsed pressure wave electrohydraulically.

18. A method for dewatering algae contained in a liquid-based algae-containing medium, comprising:

directing the liquid-based algae-containing medium into a treatment region; applying a shaped pulsed pressure wave to the liquid-based algae-containing medium in the treatment region, wherein the shaped pulsed pressure wave comprises a first phase characterized by a near instantaneous increase in pressure to exert a compressive force on the algae in the liquid-based algae-containing medium, followed by a second phase of negative pressure to exert a tensile strain on the algae in the liquid-based algae-containing medium, to obtain a treated medium comprising algae having disrupted cellular structures; and

separating the disrupted algae from the treated medium.

19. The method of claim 18 further comprising adjusting characteristics of the shaped pulsed pressure wave based on load impedance of the liquid-based algae- containing medium in the treatment region.

20. The method of claim 18 further comprising maintaining the liquid-based algae-containing medium in a static condition in the treatment region during the applying step.

21. The method of claim 18 further comprising maintaining the liquid-based algae-containing medium in a flowing condition in the treatment region during the applying step.

22. The method of claim 18 wherein the applying step comprises generating the shaped pulsed pressure wave electromagnetically.

23. The method of claim 18 wherein the applying step comprises generating the shaped pulsed pressure wave piezoelectrically.

24. The method of claim 18 wherein the applying step comprises generating the shaped pulsed pressure wave electrohydraulically.