JP2015515375A - Algae harvesting and dehydration using a two-step process - Google Patents

Abstract

The present invention is generally directed to an apparatus for harvesting algae using a two-stage approach. This two-stage approach includes an aggregation stage and a dehydration stage. The flocculation stage is carried out in a first stage flocculation tank in which suspended algae in the growth medium are flocculated. The agglomerated algae are then fed to a second stage flotation separation tank where hydrogen and oxygen bubbles are generated using electrodes that adhere to the agglomerated algae and cause the agglomerated algae to float to the surface. . The floating algal mat can then be scooped from the surface of the growth medium.

Description

  In some industries, including the wastewater treatment industry and the algae farming industry, separating materials from suspensions has long been practiced. The processes involved in achieving separation and the desired end result vary. For example, in the wastewater treatment industry, the desired result is usually treated water that can be released to the environment. In contrast, in the algae farming industry, the main desired result may be the harvesting of biomass that can be used for energy production.

  The history of electrocoagulation in the wastewater industry is long. Electrocoagulation has been found to be an effective method for separating solids from fluids in the secondary stage of purification. This wastewater stream contains all types of organic matter, and algae are considered a nuisance caused by the high nitrate counts common in wastewater streams. Thus, algae eradication efforts usually do not involve preserving mass integrity for other uses such as, for example, pharmaceutical feedstocks or other high value feedstocks.

  In electrocoagulation commonly used in wastewater treatment, metal ions or cations are added to improve aggregation by increasing the conductivity of the matrix. The following cations, Li +, Rb +, K +, Cs +, Ba2 +, Sr2 +, Ca2 +, Na + and Mg2 + (sodium and lithium are often used because they form cheap salts) have a lower electrode potential than H +. Therefore, it is considered suitable as an electrolyte cation in these processes. Other metals are used with electrocoagulation to help precipitate solids such as iron oxide and other oxidants from wastewater. These metals are very effective in precipitating solids from solution. However, these metals contaminate the product and water itself with inorganic chemicals. The inorganic chemical must then be removed in the tertiary wastewater treatment stage or otherwise treated.

  In practice, these processes are performed in large ponds and / or with large volumes of fluid flow typical of wastewater treatment plants that can be in the millions of gallons per day, so The current used by the system is generally small, usually less than 1 ampere. Due to the overwhelming size of the plant and the Ohm law (I = V / R), current requirements and process scale, it is impractical to use high energy electrocoagulation systems for long periods of time. Furthermore, the degradation and scaling of electrolytic plates that operate at high currents for extended periods of time hinder the effective use of this technology at high amperages. Therefore, as discussed above, metal ions must increase the conductivity of the wastewater stream to reduce energy requirements and make this process practical.

  In the cultivation and harvesting of algae products, these considerations are reversed because the biomass in suspension is considered an asset whose quality must be maintained. The use of metal irreversibly contaminates the product. Thus, most methods used to dehydrate algae in suspension consist of a centrifuge, membrane separation, air drying and may involve chemical treatment and decontamination.

  One method used to dehydrate algae is known as Dissolved Air Flotation (DAF). This agglomeration method usually involves the use of coagulants, emulsifiers or other chemicals, as well as air curtains generated by pumps or cyclones. This method is generally more efficient than the centrifuge technique from an energy point of view, but has the inherent disadvantage of requiring both chemical and independent tanks. Furthermore, the effectiveness of the DAF system as a continuous system is hampered by the generation of bubbles as a cause of turbulence in the reactor. The solution to this problem has been to increase the size of the flotation separation, which increases the footprint.

  In addition, the use of chemicals in dehydration generally prevents or limits the reuse of growth water. A related prior application 13 / 274,094 entitled “Systems, Methods, and Apparatuses for Dewatering, Flocculating, and Harvesting Algae Cells” filed Oct. 14, 2011 and incorporated by reference is a Several forms of the system are disclosed. This application focuses on cell lysis as the final result.

  Harvesting microorganisms such as algae and intracellular products of microorganisms are chemical petroleum derivatives or other chemicals used in the manufacture of products such as pharmaceuticals, cosmetics, industrial products, biofuels, synthetic oils, feeds, fertilizers, etc. Promising as a partial or complete replacement for substances. However, in order for these alternatives to be feasible, a cell harvesting method that includes the steps of recovering and processing the intracellular product is required in order to be able to compete with the refining costs associated with the chemical derivatives. Must be efficient, cost-effective. The current extraction methods used to harvest microorganisms such as algae and ultimately produce products for use as chemical petroleum substitutes are labor intensive and have a low net energy gain, so today's Not practical for alternative energy demand. Such previous methods can also produce significant carbon dioxide emissions, exacerbating global warming and other environmental issues. These prior art methods, when further scaled up, produce even greater efficiency losses due to the degradation of valuable intracellular components, and provide greater energy or chemistry than is currently feasible for funding from microbial harvests. Requires input of material. For example, the cost per gallon of microbial biofuel is currently about nine times that of fossil fuels.

  All living cells, including prokaryotic and eukaryotic cells, have a plasma transmembrane that surrounds the cell contents and acts as a semi-porous barrier to the external environment. This transmembrane functions as a boundary that keeps cellular components together and prevents foreign substances from entering. According to the accepted current theory known as the fluid mosaic model (SJ Singer and G. Nicolson (1972), incorporated herein by reference), the plasma membrane is a double layer of lipids. (Double layer). Lipids are oily or waxy substances found in all cells. Most of the bilayer lipids can be described more precisely as phospholipids. A phospholipid is a lipid having a phosphate group at one end of each molecule.

  Many diverse useful proteins are embedded in the phospholipid bilayer of the plasma membrane, and other types of mineral proteins are simply attached to the surface of the bilayer. Some of these proteins, primarily those that are at least partially exposed outside the membrane, have carbohydrates attached and are therefore referred to as glycoproteins. The placement of proteins along the inner plasma membrane is in part related to the organization of the filaments that make up the cytoskeleton, which helps to fix them in place. This sequence of proteins is further involved in the hydrophobic and hydrophilic regions of the cell.

  Intracellular extraction methods vary greatly depending on the type of organisms involved, their desired internal components, and their purity levels. However, when the cells are destroyed, these useful components are released and usually suspended in the liquid medium used to contain live microbial biomass. This makes the harvesting of these useful substances difficult or energy intensive.

  In most current methods of harvesting intracellular products from algae, a dehydration process must be performed to separate and harvest useful components from liquid media or biomass waste (cell mass and cell debris) . Current processes are inefficient due to the time frame required for liquid evaporation or the input of energy required to dry the liquid medium or the input of chemicals required for material separation. In addition, such processes are generally limited to batch processing and are difficult to adapt to continuous processing systems.

  Therefore, microorganisms such as algae can be dehydrated, harvested such microorganisms, their intracellular products can be recovered, and they can be used in the price of chemical and chemical derivatives required for the manufacture of industrial products. There is a need for a simple and efficient procedure that allows it to be used as a competitive alternative.

  The present invention is generally directed to an apparatus for harvesting algae using a two-stage approach. This two-stage approach includes an aggregation stage and a dehydration stage. The flocculation stage is carried out in a first stage flocculation tank in which suspended algae in the growth medium are flocculated. The agglomerated algae is then fed to a second stage flotation separation tank where hydrogen and oxygen bubbles are generated using electrodes that adhere to the agglomerated algae and cause the agglomerated algae to float to the surface. . The floating algal mat can then be scooped from the surface of the growth medium.

  In one embodiment, the present invention is implemented as an apparatus for harvesting algae using a two-stage process. The apparatus includes a flocculation tank in which the first stage of the two stage process is performed. The agglomeration tank includes a reaction tube that generates an electric field in a growth medium containing suspended algae, and the electric field causes the algae to aggregate. The apparatus further includes a flotation separation tank in which the second stage of the two-stage process is performed. The floating separation tank includes a tank that includes a plurality of electrodes that adhere to the agglomerated algae and cause formation of bubbles that raise the agglomerated algae to the surface of the growth medium. The flotation separation tank is connected to the agglomeration tank to allow agglomerated algae to flow from the agglomeration tank into the flotation separation tank.

  In other embodiments, the invention is implemented as a method of harvesting algae using a two-stage process. A growth medium containing suspended algae is fed into the agglomeration tank. The agglomeration tank includes a reaction tube that generates an electric field in the growth medium, and this electric field agglomerates the algae. Transfer growth medium containing agglomerated algae into the flotation tank. The floating separation tank includes a tank that includes a plurality of electrodes that adhere to the agglomerated algae and cause formation of bubbles that raise the agglomerated algae to the surface of the growth medium. The floating algae are then removed from the surface of the growth medium.

  In other embodiments, the present invention is implemented as an apparatus for removing ammonia from a fluid. This apparatus includes a reaction tube that generates an electric field in a fluid containing ammonia. The reaction tube includes a cathode and an anode, and the anode includes a titanium ruthenium alloy. When an electric field is generated, the anode generates free chlorine in the fluid, which oxidizes ammonia to nitrite and nitrate. The apparatus further includes a flotation separation tank connected to the reaction tube. The floating separation tank includes a tank including a plurality of electrodes that cause formation of bubbles.

  This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description of the Invention section. This summary is not intended to identify key features or essential features of the claimed subject matter.

  Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. These features and advantages of the invention may be realized and attained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention described hereinafter.

  To describe the above and other advantages and features of the present invention and the manner in which the other advantages and features can be obtained, a brief description has been given above with reference to specific embodiments of the invention shown in the accompanying drawings. A more specific description of the invention is given. Under the assumption that these drawings depict only typical embodiments of the invention and are therefore not considered to limit the scope of the invention, by using the accompanying drawings, The invention will be described and explained with additional specificity and detail.

It is a figure which shows the two-stage algae harvesting apparatus which has a 1st stage aggregation tank and a 2nd stage floating separation tank. FIG. 4 is a side view of various possible configurations of electrodes in a second stage levitation separation tank. It is a side view of a 1st step aggregation tank. FIG. 5 shows the first stage flocculation tank when filled with a growth medium containing suspended algae. It is a figure which shows the 1st step flocculation tank when algae are flocculated in batch mode. It is a figure which shows the 1st step aggregation tank when algae are aggregated by the continuous flow mode. 3A-D are diagrams illustrating a process performed in a second stage flotation separation tank that dehydrates the agglomerated algae by levitating the agglomerated algae to the surface using hydrogen bubbles. FIG. 6 shows an example implementation of a two-stage algae harvesting apparatus according to one or more embodiments of the present invention.

Detailed Description of the Invention

  The present invention is generally directed to an apparatus for harvesting algae using a two-stage approach. This two-stage approach includes an aggregation stage and a dehydration stage. The flocculation stage is carried out in a first stage flocculation tank in which suspended algae in the growth medium are flocculated. The agglomerated algae is then fed to a second stage flotation separation tank where hydrogen and oxygen bubbles are generated using electrodes that adhere to the agglomerated algae and cause the agglomerated algae to float to the surface. . The floating algal mat can then be scooped from the surface of the growth medium.

  Algae harvested in this way are free of harmful substances that are often unavoidable with other algae harvesting methods. In addition, because no harmful substances are used in this two-step process, the nutrient rich growth medium can be reused in subsequent algal harvests.

  The device of the present invention can be configured in various sizes. However, in many embodiments, the device can be sized so that it is relatively portable that can be used in virtually any location. In this way, many business entities can use this equipment to produce algae biomass without the need for large land and / or large amounts of electricity often required by other harvesting approaches.

  FIG. 1A shows an example configuration of an apparatus 100 for harvesting algae using a two-stage approach. The apparatus 100 includes two main components, a first stage flocculation tank 101 and a second stage levitation separation tank 102.

  A growth medium containing suspended algae is introduced into the first stage flocculation tank 101. This growth medium can be obtained by virtually any method. For example, a dedicated unit for growing algae in water can be connected to the first stage flocculation tank 101, or growth media obtained by other methods can be fed directly to the first stage flocculation tank 101.

  In the first stage flocculation tank 101, suspended algae are flocculated (that is, agglomerates are formed). This agglomeration can be triggered using the current generated by the electrodes, as further described below. After the algae are aggregated to a desired degree, a growth medium containing the aggregated algae is supplied into the second stage floating separation tank 102.

  The second stage flotation separation tank 102 generates bubbles of gases (eg, hydrogen and oxygen) that rise in the growth medium. While rising, these bubbles attach to the agglomerated algae and raise the agglomerated algae to the surface. As a result of this process, an algal mat is formed on the surface of the growth medium. Finally, the algae can be collected using conveyors 115 and 116, described further below.

  FIG. 4 illustrates an example implementation of an apparatus according to one or more embodiments of the present invention.

First Stage Agglomeration Tank As shown in FIG. 1A, the agglomeration tank 101 has two main components: a cathode 105 formed by an outer cylinder (eg, an inserted pipe or tube), and an inner part of the outer cylinder. It includes an anode 106 formed by an included inner cylinder (eg, a pipe or other plugged cylinder). Thus, the growth medium flows between the cathode 105 and the anode 106, as indicated by the arrows in FIG. 1A. Other shapes other than the cylinder can be used as long as a fluid path is formed between these two components. Further, in some embodiments, multiple inner cylinders can be used for the anode 106. In some embodiments, the surfaces of the cathode 105 and the anode 106 that are in contact with the growth medium can include grooves (eg, swirls) that can reduce the generation of deposits on those surfaces.

  FIG. 1C shows a side cross-sectional view of the agglomeration tank 101. As shown, there is a space between the cathode 105 and anode 106 through which the growth medium flows. In some embodiments, the width of this space can be between 0.5 mm and 200 mm. A voltage is applied to each of the cathode 105 and the anode 106, whereby an electric current flows in the growth medium. This current causes the suspended algae in the growth medium to clump together (ie coalesce to form a clump). In some embodiments, as algae pass through the agglomeration tank 101, the cells are exposed to both a magnetic field that aligns the cells and an electric field that induces the current absorption of the cells. Cells can be aggregated by these effects.

  Figures 2A-2C show how this aggregation can occur. As shown, a growth medium source 210 containing suspended algae is connected to the agglomeration tank 101. Alternatively, the growth medium can be manually supplied to the aggregation tank 101. The shading in FIG. 2A initially shows that algae are suspended in the growth medium.

  FIG. 2B shows the case where the growth medium is processed in batch mode. In batch mode, the agglomeration tank 101 is first filled with a growth medium containing suspended algae. The growth medium is then exposed to the electric field generated by the cathode 105 and anode 106 until the desired level of aggregation occurs. In some embodiments, the size of the agglomerated algae can be between 1 and 4 mm. Next, the growth medium containing the agglomerated algae is transferred to the second stage floating separation tank 102. Thus, FIG. 2B shows that the growth medium in the flocculation tank 101 contains algae clumps ready to be transferred to the flotation separation tank 102.

  FIG. 2C, in contrast, shows the case where the growth medium is treated in continuous flow mode. In continuous flow mode, algae can be agglomerated in the same way as in batch mode (eg, by passing current through the growth medium). However, the growth medium can be continuously flowed into the flocculation tank at an appropriate flow rate such that the algae are sufficiently flocculated by the time the growth medium reaches the opposite end of the flocculation tank. This is illustrated in FIG. 2C where the leftmost growth medium has as much agglomeration as the growth medium in source 210 and the degree of aggregation increases toward the right end.

  Whatever mode is used to agglutinate the algae, the agglomeration tank has a control mechanism that automatically determines the appropriate settings to ensure that the algae are sufficiently agglomerated before leaving the agglomeration tank 101. 101 can be configured. For example, in batch mode, the flocculation tank 101 can automatically determine the appropriate duration of processing the growth medium or the appropriate voltage level to apply to the cathode 105 and anode 106. Similarly, in continuous flow mode, agglomeration tank 101 can automatically determine the proper flow rate and the appropriate voltage level to apply to cathode 105 and anode 106.

  In at least one embodiment, the flow rate in the flocculation tank 101 can be 0.1 ml / second per ml of volume. However, in other embodiments, the flow rate is at least 0.5 ml / sec per ml volume or at least 1.0 ml / sec per ml volume. In other embodiments, the flow rate in this volume is at least 1.5 ml / sec per ml of volume. In other embodiments, the flow rate in this volume is greater than 1.5 ml / sec per ml of volume. In at least one additional embodiment, this flow rate can be controlled by controlling the pressure using a pump or other suitable mechanical fluid flow device.

  In some embodiments, a voltage that is repeatedly turned on and off can be pulsed to cause algal cell stretching and relaxation. According to such an embodiment, the voltage can be higher, the peak amperage can be made smaller, and at the same time the average amperage can be kept relatively small. In such embodiments, this condition or controlled situation reduces the energy requirement to operate the device and reduces wear on one or more anode / cathode pairs. In at least one embodiment, the frequency of this pulse is at least about 500 Hz, at least about 1 kHz, at least about 2 kHz, or at least about 30 kHz. In other embodiments, this frequency is less than 200 kHz, less than 80 kHz, less than 50 kHz, less than 30 kHz, less than 5 kHz, or less than 2 kHz. The range of pulse frequencies can be any combination of the above highest and lowest frequencies according to various embodiments.

  In some embodiments, electrical pulses are frequently repeated to generate an electromagnetic field between the electrodes, resulting in electrical energy transfer between the electrodes. According to certain embodiments, an electromagnetic field is generated when this pulsed electromigration occurs, resulting in the algal cells being elongated due to the polarity of the algal cells. According to other embodiments, suspended algae absorb electrical input, thereby expanding the size of internal cellular components and their liquid mass. In such an embodiment, internal pressure is applied to the transmembrane due to expansion, but according to certain embodiments, this internal expansion is mitigated during the off-frequency phase of the pulsed electrical input, It is considered only momentary. As described above, in some embodiments, rapid repetition of on / off electrical frequencies rearranges components, creates polar regions within the algal cells, and / or increases polar regions within the algal cells. In some embodiments, the continuous frequency input further creates an internal pressure that results from the expansion of the expanded internal component, which ultimately creates a magnetic / electrostatic attraction, thereby coagulating the treated cell. ) / Flocculation.

  Although this specification primarily describes that the first stage leaves the algal cells intact during the aggregation process, it is also possible to lyse the algal cells during aggregation. For example, the algal cells can be lysed by changing the voltage level / frequency applied to the cathode 105 and the anode 106 and / or changing the time the algal cells are applied to the current formed between the cathode 105 and the anode 106. , Thereby releasing the contents in the algal cells. Thus, in some embodiments, the device 100 can be used to perform lysis, aggregation and dehydration of algal cells.

After agglutinating the algae in the second stage floating separation tank growth medium, the growth medium is transferred to the floating separation tank 102. Electrodes can be used to apply an electric field to the growth medium in the flotation separation tank 102. This electric field increases the interfacial potential between the solvent and the solute, generating hydrogen and oxygen gas micron-sized bubbles that raise the agglomerated algae to the surface. Algae form a mat on the surface, which makes it possible to easily remove algae. In addition, the algal mat contains significant amounts of hydrogen and oxygen gases. Algae can be used with this gas present, or another downstream process can be performed to recover this gas. For example, this gas can be recovered and used to power the device 100, thereby minimizing the energy requirements for using the device 100.

  Referring back to FIG. 1A, the flotation separation tank 102 includes a cathode plate 111 and a series of stacked anode and cathode bars 112 and 113. FIG. 1B shows a side view of another configuration of electrodes that can be used in the flotation separation tank 102. For example, the configuration shown in FIG. 1A is shown in the upper left corner of FIG. 1B. In some embodiments, a plate can be used instead of a bar.

  Various other configurations of electrodes can be used. For example, a single cathode and a single anode, two cathodes and a single anode, a single cathode and two anodes, two cathodes and two anodes, or other combinations can be one or more cathodes And one or more anodes.

  As shown in FIG. 1B, some embodiments provide a 2 × 3 electrode arrangement that includes two vertical columns of three electrodes. The top and bottom stages of the electrodes can be cathodes, and the middle stage can contain two anodes. Various other such anode-cathode configurations can be used in the embodiment of the flotation separation tank 102. In general, depending on the size of the flotation separation tank 102, a combination of between 1 and 20 anodes and between 1 and 20 cathodes can be used.

  The flotation separation tank 102 further includes a conveyor 115 (with rakes 115a and 115b) and a conveyor 116, which further removes algal cells from the flotation separation tank 102, as further described below, and a collector. Used to enter 114. Other means known in the art that remove algae from the surface of the growth medium can also be used.

  To provide an example of how agglomerated algae can be levitated to the surface, FIGS. 3A-3D show a flotation separation tank 102. FIG. 3A shows the state of the floating separation tank 102 when the growth medium containing the agglomerated algae is sent into the floating separation tank 102. As mentioned above, prior art approaches to separating algae from growth media are difficult, expensive and often harmful to algae, which means that these approaches can be used for certain purposes. Make it unsuitable for the purpose of recovery. In contrast, the present invention provides a simple and safe process for recovering algal cells. This process involves applying an electric field to the growth medium using electrodes 111, 112, and optionally 113 further.

  FIG. 3C shows the state of the levitation separation tank 102 after the aggregated algal cells have surfaced to the surface. In order to show that this process is very effective in separating algae from the growth medium, FIG. 3C further shows that the remaining growth medium under the floating agglomerates is substantially clear. . This growth medium rich in nutrients can then be reused.

  Finally, FIG. 3D shows an example of how floating algal cells can be removed. As shown, this removal can be performed using rakes 115a, 115b. These rakes rotate across the surface of the growth medium and drive the algal cells toward the conveyor 116. The conveyor 116 is rotated to move the scraped algae cells into the collector 114 where they can be removed for further processing. This process thus provides a highly dehydrated biomass that can be easily transported and used.

  3A-3D generally represent a process that is being performed batch by batch (ie, fully aggregating the entire growth medium before adding new algal cells). However, in some embodiments, this process can also be performed continuously, such as by periodically adding fresh growth medium containing agglomerated algae.

  Bubble formation can be facilitated by strategically placing the electrodes close to each other. For example, in some embodiments, the cathode and anode are between about 0.1 inches and about 36 inches, between about 0.2 inches and about 24 inches, between about 0.5 inches and about 12 inches, Spacing between about 0.5 inches to about 6 inches, about 3 to about 8 inches, or about 1 inch to about 3 inches, or variations and combinations of these ranges or values within these ranges Can be arranged. The rate of dispersion can be varied depending on the conductivity of the growth medium and / or the power level applied to the electrodes. For example, the higher the salinity of the growth medium, or the greater the conductivity of the growth medium, the smaller the gap required to generate hydrogen and / or oxygen. In some configurations, placing two or more cathodes near a single anode can increase turbulence around the anode, thereby increasing the mixing effect, thereby increasing the algal cell Can aid in flocculation / aggregation and algal cell elevation.

  Applying an operating voltage between about 1 to about 30 volts, between about 1 to about 24 volts, between about 2 to about 18 volts, between about 2 to about 12 volts, or combinations within these ranges and intermediate ranges it can. For example, about 4 Volts, 6 Volts, 8 Volts, 10 Volts, 12 Volts, 14 Volts, 16 Volts, 18 Volts, 20 Volts, 22 Volts, 24 Volts, 26 Volts, 28 Volts, 30 Volts, and / or these A combination of voltages or a range of voltages encompassing these voltages can be applied. The amperage can be varied and can generally be between about 1A and about 20A, between about 2A and about 15A, or a combination or intermediate range within these ranges. The actual current can be reasonably varied depending on the density of the growth medium and the relative conductivity of the growth medium.

  In some configurations, it may be desirable to supply pulsed power to the electrodes. To supply pulsed power, the frequency of pulsing can be changed and the duty cycle can be changed. In this context, the term duty cycle refers to the relative length of the on and off portions of each power cycle, for example, the ratio of the duration of the on portion of the cycle to the total time of the cycle, or the on portion of the cycle. Expressed as the ratio of the duration to the duration of the off part of the cycle, or by indicating the duration of on and off, or by indicating the duration of on or off and the total cycle time it can. Unless stated otherwise, or where it is not apparent from the context, duty cycle is described herein as the ratio of cycle on duration to off duration.

  Thus, in embodiments that repeatedly turn the electromagnetic field on and off, the duty cycle is about 1: 1, about 1: 1.1, about 1: 1.2, about 1: 1.3, about 1: 1.4, About 1: 1.5, about 1: 1.6, about 1: 1.7, about 1: 1.8, about 1: 1.9, about 1: 2, about 1: 2.5, about 1: 3, about 1: 4, about 1: 5, about 1: 6, about 1: 7, about 1: 8, about 1: 9, or about 1:10. In addition, the duty cycle duration can be varied based on the flow rate, volume and / or characteristics of the growth medium.

Additional features or variations These electrodes include, but are not limited to, silver, copper, gold, aluminum, zinc, nickel, brass, copper, iron, lead, platinum group metals, steel, stainless steel, carbon allotropes and / or They can be made from metals, composites or other materials known to provide electrical conductivity, such as combinations thereof. Non-limiting examples of conductive carbon allotropes are graphite, graphene, synthetic graphite, carbon fibers (reinforced with iron), nanocarbon structures, and other forms of carbon deposited on silicon substrates, etc. . In some configurations, the anode and / or cathode can serve as a sacrificial electrode used in agglomeration and / or bubble generation processes. As such, the electrode can include a consumable conductive metal such as iron or aluminum.

  In some embodiments, the electrodes (eg, cathodes 105, 111, 113 and anodes 106, 112) can be composed of a metal coated with a catalyst, such as titanium coated with iridium oxide. Such metals can increase the efficiency of the process. For example, the use of titanium coated with iridium oxide on the anode can facilitate the generation of bubbles.

  Also, in some embodiments, one or more of the electrodes in the flotation tank 102 can include a number of perforations or surface textures that allow the growth medium to pass therethrough. Such perforations and textures increase the number of edges of the electrode, and this increased number of edges can promote bubble formation. For example, the one or more anodes can be formed as a mesh, grid, or other porous structure. The mesh may include relatively large openings that are larger than typical algae clumps or precipitate particulates in the growth medium. This configuration can advantageously allow for higher flow rates because it allows greater interfacial contact between the growth medium and the hydrogen generated by the anode. This configuration may be advantageous when faster flow through is desired or when the growth medium conductivity is low. Further, in some embodiments, a growth medium can be introduced at the center of the anode in the flotation separation tank 102. In this way, the growth medium flows out of one or more holes in the anode and is exposed to bubbles.

  Although the apparatus 100 described above has shown the flotation separation tank 102 as a separate tank placed higher, it is also possible to form the flotation separation tank as a groove (eg dug in the ground). is there. The use of trenches can allow the processing of larger amounts of growth media.

  In some embodiments, the efficiency of aggregating and / or floating algae can be increased by adding a protic solvent to the growth medium. For example, a dilute solution such as about 0.05% by volume of a protic solvent such as formic acid, n-butanol, isopropanol, n-propanol, ethanol, methanol, acetic acid can be injected into the growth medium. This solution can be mixed into the growth medium at various times. However, in some cases it is beneficial to add a protic solvent when the electric field of the aggregation process is generated or just before the batch process is performed.

  The apparatus described above can also be used to remove ammonia from wastewater or other fluids present in hydroponic environments. To achieve ammonia removal, one or more anodes of the agglomeration tank 101 can be made of a titanium ruthenium alloy. By using a titanium ruthenium alloy, free chlorine is produced in the growth medium when voltage is applied to the cathode and anode. This free chlorine oxidizes ammonia, so that ammonia is eventually converted to nitrate, nitrite and some nitrogen gas.

In general, it has been found that the anode current density is preferably between 30 and 50 mA / cm ² in order to maximize the oxidation of ammonia to nitrate and nitrite. However, other current densities can be used and the ideal density depends on various characteristics such as the temperature of the wastewater.

  Although the removal of ammonia from the wastewater is performed primarily in the flocculation tank 101, in such an embodiment, the flotation tank 102 is further used to remove other undesirable materials such as organic compounds from the wastewater. be able to.

  The present invention can be embodied in various other forms without departing from the spirit or essential characteristics of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive of the invention. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (20)

An apparatus for harvesting algae using a two-stage process,
A flocculation tank in which the first stage of the two-stage process is carried out, comprising a reaction tube for generating an electric field in a growth medium containing suspended algae, wherein the electric field flocculates the algae;
A flotation separation tank in which the second stage of the two-stage process is performed, the tank comprising a plurality of electrodes that adhere to the agglomerated algae and cause formation of bubbles that raise the agglomerated algae to the surface of the growth medium And a flotation separation tank connected to the agglomeration tank to allow the agglomerated algae to flow from the agglomeration tank into the flotation separation tank.   The apparatus according to claim 1, wherein the agglomeration tank includes an outer cylinder forming a cathode and an inner cylinder included in the other cylinder, and the inner cylinder includes an anode.   The apparatus of claim 2, wherein a pulse voltage is applied to the cathode and the anode to agglutinate algal cells in the growth medium.   The apparatus of claim 2, wherein the growth medium is pumped through the agglomeration tank at a specified flow rate.   The electrode of the levitation separation tank includes a first cathode layer, a second cathode layer, and an anode layer disposed between the first cathode layer and the second cathode layer. The device described.   6. The apparatus of claim 5, wherein the anode layer is spaced between 1 inch and 10 inches from each cathode layer.   The apparatus of claim 5, wherein the first cathode layer comprises a cathode plate.   The apparatus of claim 5, wherein the anode layer comprises a plurality of spaced apart bars.   The apparatus of claim 5, wherein the second cathode layer comprises a plurality of spaced apart bars.   The apparatus of claim 5, wherein the first cathode layer comprises a plurality of spaced apart bars.   The apparatus of claim 8, wherein each rod of the anode layer comprises titanium coated with iridium oxide.   The apparatus of claim 8, wherein each rod of the anode layer includes one or more openings.   The apparatus of claim 8, wherein each bar comprises a mesh.   The apparatus of claim 1, wherein the bubbles comprise hydrogen and oxygen.   The apparatus of claim 1, wherein the flotation separation tank includes a conveyor having one or more lakes that scrape the algae on the surface of the growth medium.   The apparatus of claim 15, wherein the flotation tank includes a second conveyor to which the algae are attracted, and the second conveyor carries the algae from the flotation tank to a collector. A method of harvesting algae using a two-stage process,
Supplying a growth medium containing suspended algae into a flocculation tank, wherein the flocculation tank comprises a reaction tube for generating an electric field for aggregating the algae in the growth medium;
Transferring the growth medium containing agglomerated algae into a flotation separation tank, wherein the flotation separation tank attaches to the agglomerated algae and raises bubbles that raise the agglomerated algae to the surface of the growth medium. Comprising a tank containing a plurality of electrodes that cause formation;
Removing the floating algae from the surface of the growth medium.   18. The method of claim 17, wherein the algae that have emerged are removed using one or more lakes.   18. The method of claim 17, further comprising extracting gas from the removed algae. An apparatus for removing ammonia from a fluid,
A reaction tube for generating an electric field in a fluid containing ammonia, wherein the reaction tube includes a cathode and an anode, the anode includes a titanium ruthenium alloy, and when the electric field is generated, the anode is the fluid A reaction tube in which free chlorine is generated, whereby the ammonia is oxidized to nitrite and nitrate;
An levitation separation tank connected to the reaction tube, the levitation separation tank comprising a tank including a plurality of electrodes that cause bubble formation.