U.S. patent application number 13/671064 was filed with the patent office on 2013-03-14 for system and method for high-voltage pulse assisted aggregation of algae.
This patent application is currently assigned to OLD DOMINION UNIVERSITY RESEARCH FOUNDATION. The applicant listed for this patent is OLD DOMINION UNIVERSITY RESEARCH FOUN. Invention is credited to Juergen F. KOLB, Gary C. SCHAFRAN, Karl H. SCHOENBACH, Aron STUBBINS.
Application Number | 20130061518 13/671064 |
Document ID | / |
Family ID | 43412880 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130061518 |
Kind Code |
A1 |
SCHAFRAN; Gary C. ; et
al. |
March 14, 2013 |
SYSTEM AND METHOD FOR HIGH-VOLTAGE PULSE ASSISTED AGGREGATION OF
ALGAE
Abstract
A method and device for aggregating algae in an aqueous solution
is disclosed. The method can include providing an algae feed
comprising a liquid and algae dispersed therein. The algae feed can
be aggregated by applying a nanosecond pulsed electric field to the
algae feed. The nanosecond pulsed electric field can include a
plurality of electric pulses having a pulse duration ranging from 1
to 1,000 nanoseconds. The method can also include separating an
aggregated algae stream from the algae feed and feeding the
aggregated algae stream to a lipid extraction operation.
Inventors: |
SCHAFRAN; Gary C.; (Norfolk,
VA) ; KOLB; Juergen F.; (Norfolk, VA) ;
STUBBINS; Aron; (Norfolk, VA) ; SCHOENBACH; Karl
H.; (Norfolk, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OLD DOMINION UNIVERSITY RESEARCH FOUN; |
|
|
US |
|
|
Assignee: |
OLD DOMINION UNIVERSITY RESEARCH
FOUNDATION
|
Family ID: |
43412880 |
Appl. No.: |
13/671064 |
Filed: |
November 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12823696 |
Jun 25, 2010 |
|
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13671064 |
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61220417 |
Jun 25, 2009 |
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Current U.S.
Class: |
47/1.4 |
Current CPC
Class: |
C12N 13/00 20130101;
C12N 1/12 20130101; C12M 33/00 20130101; C12P 7/649 20130101; A01G
2/00 20180201; Y02E 50/13 20130101; Y02E 50/10 20130101; Y02E 50/17
20130101 |
Class at
Publication: |
47/1.4 |
International
Class: |
A01G 1/00 20060101
A01G001/00; A01D 44/00 20060101 A01D044/00 |
Claims
1. A system for aggregating algae, comprising: an aggregation
reactor comprising at least one electrode, said at least one
electrode in electrical communication with a power supply and in
liquid communication with an algae feed contained in said
aggregation reactor, said power supply for applying nanosecond
electric pulses to said at least one electrode, said nanosecond
electric pulses having a pulse duration ranging from 1 nanosecond
to 1,000 nanoseconds.
2. The system according to claim 1, further comprising: a separator
in fluid communication with said aggregation reactor, said
separator for producing an aggregated algae stream from an
aggregated effluent from said aggregation reactor.
3. The system according to claim 2, wherein said aggregation
reactor comprises said separator.
4. The system according to claim 2, further comprising a lipid
extraction operation in fluid communication with and down-stream of
said aggregation reactor.
5. The system according to claim 2, further comprising a lipid
extraction operation in fluid communication with and down-stream of
said separator.
6. The system according to claim 1, wherein said nanosecond
electric pulses produce electric fields in said algae feed such
that algae in said algae feed lose less than 10 wt-% of a lipid
content of said algae as a result of said nanosecond electric
pulses.
7. The system according to claim 1, wherein a peak electric field
of said pulses ranges from 1 to 1,000 kV/cm.
8. The system according to claim 1, wherein a peak power of said
pulses is at least 1 megawatt.
9. The system according to claim 1, wherein a peak voltage of said
pulses ranges from 1 kV and 500 kV.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/823696, entitled "System and Method for High-Voltage
Pulse Assisted Aggregation of Algae," which claims priority to U.S.
Patent Application No. 61/220,417, entitled "High Voltage Pulse
Assisted Aggregation and Separation of Algae," filed Jun. 25, 2009,
the entirety of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to high voltage pulse assisted
aggregation and separation of algae for dewatering and harvesting
of algae.
BACKGROUND OF THE INVENTION
[0003] There is an increasing desire to develop sustainable fuel
options that are not reliant of fossil fuels. One option being
evaluated is the production of biofuels obtained from algae. The
commercialization of such biofuels will likely require cultivating
algae in large ponds. The ponds of algae would then be harvested
and the lipids within the algae extracted and converted into
biofuel. Existing methods of harvesting the algae have not proven
commercially viable for numerous reasons, which include, but are
not limited to: (i) too much water remains in the extracted algae
for efficient lipid extraction, (ii) the algae cell walls are
ruptured prematurely causing release of the valuable lipids before
the extraction and conversion processes, and (iii) the algae cell
walls are ruptured preventing the algae from being reused. Thus,
there is a need for improvements related to the harvesting and
processing of algae for the production of biofuels.
SUMMARY OF THE INVENTION
[0004] In one embodiment, a method of aggregating algae in a
solution is disclosed. The method can include providing an algae
feed comprising a liquid, e.g., water, and algae dispersed therein.
The algae feed can then be aggregated by applying a nanosecond
pulsed electric field to the algae feed.
[0005] The nanosecond pulsed electric field can be generated by a
plurality of electric pulses having a pulse duration ranging from 1
to 1,000 nanoseconds. The peak electric field of the pulses can
range from 1 to 1000 kV/cm. The peak power of the pulses can be at
least 1 megawatt and the peak voltage of the pulses can range from
1 kV and 500 kV. The nanosecond pulsed electric field can be of an
intensity and duration that the nanosecond pulsed electric field
does not produce a plasma discharge or an arc discharge.
[0006] The method can include separating an aggregated algae stream
from the algae feed. The aggregating step and the separating step
can be performed continuously. The method can also include
processing the aggregated algae stream to produce an algae-based
biofuel.
[0007] The nanosecond pulsed electric fields can be applied for a
duration sufficient to neutralize repulsive charges of the algae.
The aggregating step can include adding one or more aggregating
agents. The aggregating step can cause the algae in the feed stream
to lose less than 10 wt-% of the lipid content of the algae.
[0008] Also disclosed is a system for aggregating algae. The system
can include an aggregation reactor having at least one electrode.
The at least one electrode can be in electrical communication with
a power supply for applying nanosecond electric pulses to the
electrodes. The electrodes can be in liquid communication with an
algae feed contained in the aggregation reactor. The aggregation
reactor can be in fluid communication with a separating reactor,
which can be in fluid communication with a lipid extraction
operation.
[0009] These and other embodiments are described in more detail
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] A fuller understanding of the present invention and the
features and benefits thereof will be obtained upon review of the
following detailed description together with the accompanying
drawings, in which:
[0011] FIG. 1 is a schematic of a system for high-voltage pulse
assisted aggregation of algae (not to scale).
DETAILED DESCRIPTION
[0012] The invention is drawn to a method and device for harvesting
algae suspended in a liquid feed stream. It has been unexpectedly
discovered that when nanosecond electric pulses are applied to a
solution containing algae, the algae aggregate without the need for
the addition of an aggregation agent. While not wishing to be bound
by theory and while not necessary for practicing the invention, it
is believed that the nanosecond pulsed electric fields produce
nanopores which allow transport of ions, such as sodium, potassium
and calcium, across the algae cell membrane thereby neutralizing
the repulsion between individual alga. However, the nanopores
produced by the nanosecond electric pulses are not large enough to
allow lipids found in the algae to be released. Nanosecond pulsed
electric fields of high field strength may also change membrane
morphology and in particular dipole alignments in the membrane. In
addition, nanosecond pulsed electric fields may change surface
charge layers and the distribution of free and bound charges in the
matrix in general.
[0013] The method of harvesting algae can include providing an
algae feed that includes algae dispersed in a liquid, e.g., water,
brackish water, saline water or brine. The algae feed can be
aggregated in a step that includes applying a nanosecond pulsed
electric field to the algae feed. The nanosecond pulsed electric
field can be produced by delivering a plurality of electric pulses
having a pulse duration ranging from 1 nanosecond to 100,000
nanoseconds, 1 to 1,000 nanoseconds, or even 1 to 500 nanoseconds
or even 10-300 nanoseconds to the electrodes. The duration of the
electric pulses can be selected such that the algae aggregate while
the cell walls of the algae do not lose their integrity.
[0014] The strength of the electric fields applied to the algae
feed can depend on the pulse duration and can be selected so that
they remain below the dielectric strength of water for a given
pulse duration. Under these conditions, no breakdown (i.e.,
discharge between the high voltage electrode and the ground
electrode) will occur. This is beneficial because such breakdowns
have the potential to disrupt internal and outer cell membranes of
the algae. The electric fields to which the algae feed is exposed
can range from 0.1 to 100,000 kV/cm or from 10-1000 kV/cm.
[0015] The method can also include separating an aggregated algae
stream from the algae feed after the nsPEFs have been applied.
Depending of the pulsed exposure conditions, the aggregated algae
may float to the top of the harvest tank, sink to the bottom of the
harvest tank, or remain suspended in the harvest tank. Depending on
the relative location of the aggregated algae, the aggregated algae
can be harvested using an appropriate technology. Exposure
conditions can also be varied to control the aggregation time,
which can be as short as second, e.g., 1-60 seconds, or can take
minutes, e.g., 1-60 minutes.
[0016] The aggregating step and separating step can occur as part
of continuous flow reactor(s). In some embodiments, no aggregating
agents are added during the aggregating step. The method can also
include processing the aggregated algae stream to produce an algae
biofuel. As used herein, the term "algae biofuel" is used to refer
to algae-based fuels that include, but are not limited to,
vegetable oil, biodiesel, bioethanol, biogasoline, biomethanol,
biobutanol and other biofuels.
[0017] As used herein, the terms "aggregate" and "aggregation" are
used to refer to a process where particles, e.g., algae, of a
dispersion agglomerate or coagulate into larger groups of
particles. As used herein, the term "aggregating agent" is used to
refer to additives, such as salts, that facilitate aggregation of
particles in dispersion. Exemplary aggregating agents include, but
are not limited to, alum, aluminum chlorohydrate, aluminum sulfate,
calcium oxidecalcium hydroxide, iron (III) chloride, iron (II)
sulfate, polyacrylamide, polyDADMAC, sodium aluminate, sodium
silicate, chitosan, Moringa oleifera seeds, papain, strychnos
seeds, isinglass, and combinations thereof.
[0018] The nanosecond pulsed electric field can neutralize
repulsive charges of the algae. In some embodiments, the nanosecond
pulsed electric field does not produce a plasma discharge or arc
discharge.
[0019] An unexpected benefit of the claimed method and device is
that the algae do not undergo electroporation, which could cause
premature release of lipids from the algae. As used herein,
"electroporation" refers to a process where the cell membrane is
temporarily made permeable enough to allow large molecules, such as
propidium iodide or lipids, to cross the cell membrane. The algae
can lose less than 10 wt-% of the lipid content of the algae as a
result of the aggregating step, less than 5 wt-% of the lipid
content of the algae as a result of the aggregating step, or less
than 1 wt-% of the lipid content the algae as a result of the
aggregating step, or even less than 0.5 wt-% of the lipid content
the algae as a result of the aggregating step.
[0020] The peak electric field delivered to the algae feed by the
pulses ranges from 0.1-100,000 kV/cm, or from 10 to 1,000 kV/cm, or
from 50 to 500 kV/cm, or from 100 to 400 kV/cm. The peak power of
the pulses can be at least 500 kW, or at least 1 megawatt. The peak
voltage of the pulses can range from 1 kV and 500 kV, or from 10 kV
to 450 kV, or from 50 kV to 300 kV.
[0021] It should be noted that while the delivery power is
extremely high, the energy that is delivered can remain low due to
the minimal pulse duration. The energy delivered with a single
pulse can range from 0.1 to 100 joules, or 1 to 10 joules.
[0022] There are several additional unexpected advantages of the
methods and devices disclosed herein. First, the method eliminates
the need to use an agglomerating agent, which can provide a
substantial cost savings. Second, the nanosecond pulses do not
produce excess free charges in the algae feed, which limits
galvanic processes that can lead to corrosion and eliminates the
need for a sacrificial anode or other similar devices. Finally, the
nanosecond pulses disclosed herein use substantially less energy
than the continuous electrical energy required for
electro-flocculation.
[0023] The invention also includes a system for harvesting algae.
In the exemplary system shown in FIG. 1, the system 10 can include
an algae reservoir 12 or other source. The algae reservoir 12 can
include an algae feed 13, which can be an aqueous suspension
containing algae 14. In the algae reservoir 12, the algae will
generally be separated by the naturally-occurring repulsive forces
of the algae 14.
[0024] An aggregation reactor 16 can be in fluid communication with
the algae reservoir 12. The aggregation reactor 16 can include a
nanosecond pulsed electric field (nsPEF) system 18. The nsPEF
system 18 can include at least one electrode 20 and 22. The at
least one electrode can include a working electrode 20 and a ground
electrode 22. As shown in FIG. 1, the ground electrode 22 can be a
cylindrical electrode that is concentrically arranged with a pipe
of the aggregation reactor 16.
[0025] The at least one electrode 20, 22 can be in electrical
communication with a power supply 24. At least one of the at least
one electrodes 20, 22 can be in liquid communication with an algae
feed 13 within the aggregation reactor 16. The power supply 24 can
be designed for applying nanosecond electric pulses to the at least
one electrode 20, 22. In alternative embodiments, the arrangement
of the working and ground electrodes can be reversed.
[0026] The nanosecond electric pulses can have a pulse duration
ranging from 1 to 1,000 nanoseconds. The pulse duration of the
nanosecond electric pulses can be less than 500 nanoseconds, or
less than 250 nanoseconds, or less than 100 nanoseconds, or less
than 10 nanoseconds, or less than 1 nanosecond. The pulse duration
of the nanosecond electric pulses can be at least 1 nanosecond, or
at least 5 nanoseconds, or at least 10 nanoseconds. The pulse
duration can range from any combination of the above minimum and
maximum pulse durations, e.g., from 5 nanoseconds to 100
nanoseconds.
[0027] The system 10 can also include a separator 28 for separating
aggregated algae 30 that have been treated by the aggregation
reactor 16. The separator 28 can be part of the aggregation reactor
16. Alternatively, as shown in FIG. 1, the separator 28 can be
separate from, but in fluid communication with, the aggregation
reactor 16. For example, the aggregation reactor 16 can be a
cylindrical reactor, e.g., a pipe reactor, connected to the
separator 28 and the aggregated algae 30 can be separated from the
aggregator effluent 32 using a raking technique.
[0028] The system 10 can also include a lipid extraction operation
34 in fluid communication with and down-stream from the aggregation
reactor 16. The separator 28 can be in fluid communication with the
lipid extraction operation 34. An aggregated algae stream 36 can
exit the separator 28 and the aggregated algae stream 36 can be fed
to the extraction operation 34 via a pipe 38.
[0029] The nanosecond electric pulses of the aggregation reactor 16
can be applied such that algae 14 in the algae feed 13 supplied to
the aggregation reactor 16 lose less than 10 wt-% of a lipid
content of the algae 14 as a result of the nanosecond electric
pulses. The low lipid loss during the aggregation stage, simplifies
the process by retaining the lipids in the algae until the algae
are harvested and concentrated for lipid extraction. This enables
higher efficiency harvesting of algae and results in higher
efficiency production of algae biofuels.
[0030] It is to be understood that while the invention in has been
described in conjunction with the preferred specific embodiments
thereof and that the foregoing description is intended to
illustrate and not limit the scope of the invention. Other aspects,
advantages and modifications within the scope of the invention will
be apparent to those skilled in the art to which the invention
pertains.
* * * * *