WO2024141713A1 - Processes and systems for removing salt from a froth containing an algal biomass and a salt-containing solution - Google Patents

Abstract

A process, system and use of the system are disclosed for treating a froth or removal of salt from a froth, wherein the froth contains an algal biomass and a salt-containing solution. An exemplary process includes: (a) supplying a wash liquid to an interface between the froth and a liquid phase to generate a froth stream and a tails stream; and (b) recovering the froth stream from (a). The application also relates to an algal biomass or a froth stream produced by the process of the present disclosure.

Description

PROCESSES AND SYSTEMS FOR REMOVING SALT FROM A FROTH CONTAINING

AN ALGAL BIOMASS AND A SALT-CONTAINING SOLUTION

FIELD

[0001] The present application relates to a process for removal of salt from a froth, wherein the froth contains an algal biomass and a salt-containing solution, applications thereof, and products obtained by the process. Also, the present application is directed to a system for treating a froth containing an algal biomass and a salt-containing solution and use thereof for removal of salt from a froth including an algal biomass and a salt-containing solution.

BACKGROUND INFORMATION

[0002] Known algal biomass contains three main components in various percentages by weight: carbohydrates proteins, and lipids/natural oils, and includes mircroalgae, macroalgae and cyanobacteria. There is increasing interest in using algal biomass for a plethora of sustainable activities, such as a source of renewable energy, as a mode to safely and efficiently capture carbon dioxide from the atmosphere for carbon sequestration, and as a renewable source of chemical intermediates. Once the algae are grown and harvested to form an algal concentrate, subsequent processing can depend on a desired product or chosen product mixture. Appropriate selection of the product blend can maximize economic return. Often the algal concentrate that is produced by the harvester is passed through a unit operation to separate algal oil from the algal biomass. The algal oil can be a source of valuable products including carotenoids, fatty acids, and other lipids. The algal biomass can also be a source of valuable products, including human nutrition, animal feeds, soil builder, feed for fermentation, and fuel.

[0003] From a sustainability perspective, known algal strains of commercial interest do not utilize fresh water in their growth process, but use water derived from the ocean or saline aquifers to offset water losses due to evaporation from the open ponds. This constraint, based on sustainability, favors the use of halophilic algae that live in a saline growth medium. As a result, the salts in the saline growth medium will be present in the algal concentrate that are produced by the harvesting process. When the algal oil and algal biomass are separated, these residual salts will remain with the algal biomass to form a salt-laden algal biomass. It is desirable to remove these salts so that the algal biomass depleted of salt can be used for products, such as those listed above.

[0004] The separation of salts from the salt-laden algal biomass is difficult because this biomass can blind filtration equipment that is required in washing the salt-laden algal biomass.

[0005] Thus, there is a need in the art for an efficient system and process for removing salts from salt-laden algal biomass that improves upon known systems and processes as described herein.

[0006] For example, WO 2008/156795 A1 and US Patent Nos. 5,951 ,875, 5,776,349, and 5,910,254 disclose an adsorptive bubble separation process to harvest algae from an algal growth medium. The harvested biomass, termed the algal concentrate, contains salt concentrations similar to those found in the algal bioreactor, which can approach saturation. These three patents disclose that diafiltration of the algal concentrate can be used to reduce the salt concentration in the algal concentrate prior to extraction. Although this method may be effective at reducing salt levels in an algal concentrate, a high-pressure pump and a membrane system are involved to effect the separation. Where the high-pressure equipment is made of steel, the equipment is susceptible to corrosion by the salt water unless expensive alloys are used. Expensive ceramic membranes are also used to affect the separation. Thus, this diafiltration to remove salt from the algal concentrate has a high capital cost due to expensive equipment, and high operating costs due to energy requirements for pumping and for membrane replacements. In addition, these patents disclose removing salt prior to the liquid-extraction of lipids from the algae. [0007] Thus, there is a need in the art for a robust process to remove salts from saltladen algal biomass, optionally in the process of harvesting algae, and to provide an appropriate, efficient and simple desalting of an algal concentrate.

SUMMARY

[0008] The present application discloses an exemplary process for removal of salt from a froth containing an algal biomass and a salt-containing solution, the process comprising: (a) supplying a wash liquid to an interface between the froth and a liquid phase, to generate a froth stream, and a tails stream, wherein the froth stream contains the algal biomass and a reduced amount of salt relative to the froth; and (b) recovering the froth stream from (a). The froth stream is also termed an algal concentrate.

[0009] The present application also discloses an exemplary system for treating a froth containing an algal biomass and a salt-containing solution, the system comprising: a collection zone; a bubble generation zone; a separation zone; a froth zone; a wash interface zone between the separation zone and the froth zone; an optional launder; and an optional wash liquid supplying unit, optionally in communication with a wash liquid reservoir; the bubble generation zone being configured to interact with or being in communication with the collection zone, the collection zone being in communication with the separation zone, and optionally the wash liquid supplying unit being in communication with the wash interface zone.

[0010] The present disclosure is also directed to an exemplary algal biomass produced, obtained or obtainable by the process described in the present disclosure.

[0011] The present disclosure is also directed to an exemplary froth stream produced, obtained or obtainable by the process described in the present disclosure, wherein the amount of salt in the salt-containing solution of the froth is about 80% or less, about 70% or less, about 60% or less, about 50% or less, about 40% or less, about 30% or less, about 20% or less, about 15% or less, about 10% or less, about 5% or less, or about 1 % or less in relation to the amount of salt in the salt-containing solution of the algal biomass feed , or the amount of salt of the froth stream is below levels which may be detected by any analytical method.

[0012] The present disclosure is also directed to an exemplary use of the system described in the present disclosure for removal of salt from a froth containing an algal biomass and a salt-containing solution.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The scope of the present disclosure will be understood from the following detailed description and exemplary embodiments when read in conjunction with the accompanying drawings, wherein dashed lines in the drawings represent flows or operations that are optional, and wherein:

[0014] FIG. 1 shows an exemplary flow diagram of a process as disclosed herein for removal of salt from a froth containing an algal biomass and a salt-containing solution.

[0015] FIG. 2 shows an exemplary system for treating a froth including an algal biomass and a salt-containing solution, in accordance with the present disclosure.

DETAILED DESCRIPTION

[0016] FIG. 1 shows an exemplary flow diagram of a process for removal of salt from a froth containing an algal biomass and a salt-containing solution. In describing exemplary embodiments of the figures, various terms and phrases will be used to facilitate an understanding by those skilled in the art. A brief listing of those terms and phrases follows.

[0017] As referenced herein: “removal of salt” refers for example to reducing the salt concentration to any degree or percentage, e.g., 80%, 70%, 60%, 50%, 40%, 30%, 20%, 15%, 10%, 5%, 3%, 2%, or 1 %, and including degrees or percentages which are below degrees and percentages which may be detected by any analytical methods, and including eliminating salt entirely. [0018] “Salt-containing solution” or “salt-based solution” refers for example to a solution that contains a percentage of salt, wherein the salt-containing solution can combine with contaminants, such as dirt particles.

[0019] “Algal suspension”, includes algae such as microalgae, and refers for example to a mixture containing algal particles and/or algal biomass, optionally algal oil which may be a dispersion of algal oil wherein the dispersion is a second liquid phase, the solution including one or more of liquid, fluid and/or gas; an exemplary algal suspension can include bubbles in a salt-containing solution. An algal suspension refers to a single or multi-phase suspension.

[0020] “Algal biomass” refers for example to algae-based biomass or feedstock such as algae-based naturally grown feedstock, and can also include contaminants, other substances and gases; “alga(e)” or “algal biomass” can refer to any algal cells or any parts thereof such as ruptured algal cells; in an exemplary embodiment “algal biomass” can be an “algal concentrate” such as harvested algal biomass.

[0021] “Bubbles” or "adsorptive bubbles", when used in the present disclosure, refer for example to bubbles of, for example, gas, and containing algae or algal biomass adhered to the gas bubble surface, and/or the bubbles can comprise a salt-containing solution surface and algae or parts thereof adhered to said surface.

[0022] In an exemplary embodiment, a “froth” as disclosed herein includes a dispersion wherein algal content can adhere to a surface of the bubbles. The bubbles can include adsorptive air bubbles to which algae, other particles and a salt-containing solution, can adhere. Froth refers for example to a mass including gas-formed bubbles (e.g., gas such as air, carbon dioxide, oxygen, nitrogen, or any gas evolved during photosynthesis or combustion, and so forth) containing algal biomass for example adhered to the bubbles, to create a foam optionally at the top of an algal suspension. Presence of gas, such as air, leads to formation of the bubbles, generating a froth in the suspension. The suspension can include solid or otherwise suspended particles, algae, and/or algal biomass as described herein. After the froth has been through a washing process as disclosed herein, it can be referred to as a “froth stream”, the froth stream containing a reduced amount of salt relative to the initial (un-washed) froth. For example, water may be mixed with a coagulant that causes the algae to clump together, which are then brought to the surface by air bubbles, and optionally may be skimmed off into a launder. The algal biomass may subsequently be dewatered and dried.

[0023] "Interface" refers to a phase or zone where different phases connect or interact with each other. Said interface can be, e.g., between a gas phase, such as air bubbles, and a liquid phase. In an exemplary embodiment, an interface is between a froth and a liquid phase. In an exemplary embodiment, the interface between a froth and a liquid phase refers to a phase or zone, which is located immediately under the froth zone and is termed the separation zone in Figure 1.

[0024] “Solution” refers for example to a liquid mixture comprising one or more solutes dissolved in a liquid (such as water), for example, a minor component (a solute such as algal carbohydrates) is distributed within a major component of liquid, the liquid being or including one or more of water or other liquid.

[0025] “Aqueous” refers to something made from, with, or by water; “aqueous solution” refers for example to a solution which contains water as the major component.

[0026] “Liquid” refers for example to a substance that flows freely and has a consistency, such as water.

[0027] “Fluid” refers for example to medium which has no fixed shape and yields easily to external pressure, such as a gas or a liquid.

[0028] “Brine” or “brine liquid” refers for example to a salt-based liquid such as a solution of salt in water, which has a salt content that can vary, brine includes sodium chloride salt concentrations ranging from about 3.5 weight % (concentration in seawater) up to about 26.5 weight % (a saturated brine solution) at 25C. Saltwater solutions, in decreasing order of salt concentration are represented as: brine>seawater>brackish water>freshwater. [0029] “Freshwater” contains or consists of fresh water and refers, for example, to any pure water, naturally occurring liquid, or frozen water containing low or no concentrations of (dissolved) salts and optionally low or no concentrations of other total (dissolved) solids. Freshwater may be derived from glaciers, lakes, reservoirs, ponds, rivers, streams, wetlands, and even groundwater, but not the sea. Freshwater also includes non-salt containing mineral rich waters. In one aspect, brackish water contains a salt concentration selected from any one of: less than 3.5 weight %, and less than or about 3.0 weight %, 2.5 weight %, 2.0 weight %, 1 .5 weight %, 1 .0 weight %, and 0.5 weight %.

[0030] In exemplary embodiments disclosed herein, salt is removed from a froth containing an algal biomass and a salt-containing solution. In further exemplary embodiments, an algal suspension comprising the froth is obtained by generating froth in a mixture comprising an algal biomass (or algal concentrate) and a salt-containing solution.

[0031] A harvested biomass is an example of an “algal concentrate” and can contain salt concentrations similar to those found in the algal bioreactor, which can approach saturation.

[0032] Salinity is a term that defines the total amount of dissolved inorganic solids (salts) in an aqueous solution. The typical salts found in natural waters may include sodium chloride, calcium and magnesium sulfates, bicarbonates, and carbonates. It is a standard practice to express salinity as parts per thousand (%o), which is the milligrams of salt per gram of water. In more general terms, salinity is indicated by the water source, such as a freshwater, a brackish water, a saline water, and a brine. Ranges of salinity are associated with these general terms and these ranges are defined as < 0.5 %o (< 0.05 %) for freshwater, 0.5 - 30 %o (0.05 - 3 %) for brackish water, 30 - 50 %o (3 - 5 %) for saline (seawater) water, and > 50 %o (> 5 %) for a brine.

[0033] As used herein, wt % refers to a dry mass of a component in a solution in grams divided by 100 grams of the solution. In addition, unless otherwise stated herein or clear from the context, any percentages referred to herein are understood to refer to wt %. [0034] In the FIG. 1 flow diagram of an exemplary process for removal of salt from a froth containing an algal biomass and a salt-containing solution as disclosed herein, an initial step is performed of supplying or providing a wash liquid. The wash liquid may be provided as a liquid stream entering at one or more inlet ports at one or more locations between the froth zone and the separation zone. In one embodiment, the liquid stream would be provided in laminar flow to reduce the hydraulic impact on the interfacial region between the froth zone and the separation zone. The wash liquid may comprise water, fresh water, brackish water, seawater, or brine so long as the salt content of the wash water is lower than the salt content of the salt containing solution.

[0035] As shown in FIG. 1 , the wash liquid 100 is supplied to the Wash Interface Zone 106 between the Froth Zone 104 and the liquid phase during the washing, e.g., through one or more inlets, after which the froth stream containing algal biomass 110 may be recovered. The froth is typically called the Froth Zone 104 in adsorptive bubble separation processes, and it is where froth dominates the volume of the zone. It is where bubbles that carry the algal biomass and salt-containing solution dominate the volume. Bubbles carrying algal biomass rise though the Separation Zone 108 and enter the Froth Zone 104. The salt-containing solution drains through the Froth Zone 104 and enters the Separation Zone 108. Thus, the bubbles carrying algal biomass and the salt-containing solution flow in counter-current mode through the Froth Zone 104 and through the Separation Zone 108. The liquid phase is commonly termed the Separation Zone, and this is where the gas bubbles that collected the algal biomass carry the biomass along with the salt-containing solution to the Froth Zone 104. Once the salt-containing solution drains through the Separation Zone 108, it exits as a tails stream 112. The tails stream may be returned to aquaculture ponds.

[0036] When wash water is added to form the Wash Interface Zone 106, the wash water has a lower density than the salt-containing solution so can remain at the interface between the Froth Zone 104 and the Separation Zone 108 to form the Wash Interface Zone 106. The bubbles carrying algal biomass pass through this Wash Interface Zone 106 and the salt-containing solution is partially replaced with the wash water that reduces the salinity of the salt-containing solution as the bubbles rise in the Froth Zone 104. At the top of the Froth Zone 104, the froth stream overflows the lip and the froth stream is collected in the launder (not shown).

[0037] The process described herein reduces the salt concentration in the froth which contains an algal biomass and a salt-containing solution.

[0038] An exemplary process as disclosed thus includes: (a) supplying a wash liquid to an interface between the froth and a liquid phase, to generate a froth stream and a tails stream; and (b) recovering the froth stream; wherein the froth stream contains algal biomass and a reduced amount of salt relative to the initial untreated froth. In a further exemplary embodiment, the salt concentration in the wash liquid divided by the salt concentration in the salt-containing solution and/or tails stream is less than unity. In a further exemplary embodiment, a ratio of densities of the wash liquid to the salt-containing solution is less than unity. In another further exemplary embodiment, the algal concentration in the froth stream divided by the algal concentration in the salt-containing solution and/or tails stream is greater than unity.

[0039] In an exemplary embodiment, the froth includes bubbles of the salt-containing solution, and algal cells or parts thereof (such as ruptured algal cells or parts thereof) of the algal biomass are adsorbed to surfaces of the bubbles.

[0040] In an exemplary embodiment, the process is a fractional flotation process or an adsorptive bubble separation process. In one embodiment, the fractional flotation process or the adsorptive bubble separation process includes two or more actual stages of flotation, and optionally the algal concentrate moves counter-currently to the flow of the wash liquid.

[0041] In an exemplary embodiment, the process steps (a) to (b) are repeated.

[0042] In an exemplary embodiment, the process further comprises recovering and/or recycling at least a portion of the tails stream from (a). In an exemplary embodiment, at least a portion of the tails stream is removed and/or recycled through an outlet. [0043] The wash liquid may be produced using a liquid alone or a gas and liquid together, and supplied to the interface optionally through one or more inlets. In an exemplary embodiment, the wash liquid is supplied by feeding a liquid, or liquid and gas, into a vessel or into an adsorptive bubble separation vessel, through one or more inlets. An advantage of multiple inlets is a resulting even distribution of the wash liquid being supplied, across the interface 106 between the froth and the liquid phase. The algal biomass body may additionally be rotated or mixed for an even distribution. This step can permit at least partial exchange of the salt-containing water/solution in the froth containing algae biomass, for a water/solution having lower salt concentration from the wash liquid being supplied, through exploiting the concentration gradient established via diffusion. The integrity of algal bubbles in the froth can be substantially retained through the process.

[0044] A wash liquid can be used for effectively and gently removing salt from a froth. It has been surprisingly found that the washing liquid when supplied to an interface between the froth and a liquid phase remains at the interface and allows the bubbles carrying algal biomass to retain the algal biomass on the surface but replace the saltcontaining solution with some portion of wash water.

[0045] In an exemplary embodiment, the process is a continuous process. In an exemplary embodiment in the continuous process, fresh algal biomass and salt-containing solution (such as a feed comprising an algal biomass and a salt-containing solution) is continuously supplied to the process or vessel, while at least a portion of the froth stream and/or tails stream is removed optionally so as to keep the total volume of the algal biomass and the salt-containing solution in the process or vessel substantially constant. In a further exemplary embodiment, the wash liquid is also continuously supplied.

[0046] For example, algae from the divisions Bacillariophyta, Chlorophycophyta, Chrysophycophyta, Cyanophycophyta, Cryptophycophyta, Phaeophycophyta, Pyrrhophycophyta, Rhodophycophyta or combinations thereof are suitable for use in the present disclosure. [0047] For example, algae from the divisions Chlorophycophyta, Phaeophycophyta, Chrysophycophyta, Cyanophycophyta, Cryptophycophyta, Pyrrhophycophyta and Rhodophycophyta, which are adaptable to saline water as an algal growth medium, are suitable for use in the present application.

[0048] Suitable algae or microalgae species that can be utilized with the instant application include, but are not limited to, at least one or more of Amphora sp., Anabaena sp., Anabaena flos-aquae, Ankistrodesmus falcatus, Arthrospira sp., Arthrospira (Spirulina) obliquus, Arthrospira (Spirulina) platensis, Botryococcus braunii, Ceramium sp., Chaetoceros gracilis, Chlamydomonas sp., Chlamydomonas mexicana, Chlamydomonas reinhardtii, Chlorella sp., Chlorella fusca, Chlorella protothecoides, Chlorella pyrenoidosa, Chlorella stigmataphora, Chlorella vulgaris, Chlorella zofingiensis, Chlorococcum citriforme, Chlorococcum littorale, Closterium sp., Coccolithus huxleyi, Cosmarium sp., Crypthecoddinium cohnii, Cryptomonas sp., Cyclotella cryptica, Cyclotella nana, Dunaliella sp., Dunaliella bardawil, Dunaliella salina, Dunaliella kone, Dunaliella tertiolecta, Dunaliella viridis, Euglena gracilis, Fragilaria, Fragilaria sublinearis, Gracilaria, Haematococcus pluvialis, Hantzschia, Isochrysis galbana, Microcystis sp., Monochrysis lutheri, Muriellopsis sp., Nannochloris sp., Nannochloropsis sp., Nannochloropsis salina, Navicula sp., Navicula saprophila, Neochloris oleoabundans, Neospongiococcum gelatinosum, Nitzschia laevis, Nitzschia alba, Nitzschia communis, Nitzschia paleacea, Nitzschia closterium, Nitzschia palea, Nostoc commune, Nostoc flagellaforme, Pavlova gyrens, Peridinium, Phaeodactylum tricornutum, Pleurochrysis carterae, Porphyra sp., Porphyridium aerugineum, Porphyridium cruentum, Prymnesium, Prymnesium paruum, Pseudochoricystis ellipsoidea, Rhodomonas sp., Scenedesmus sp., Scenedesmus braziliensis, Scenedesmus obliquus, Scenedesmus quadricauda, Scenedesmus acutus, Scenedesmus dimorphus, Schizochytrium sp., Scytonema, Skeletonema costatum, Spirogyra, Schiochytrium limacinum, Stichococcus bacillaris, Synechoccus, Tetraselmis sp., Tolypothrix sp., and genetically-engineered varieties and/or combinations (mixtures, or mixed cultures) of these algal or microalgal species.

[0049] The algae used can include, but are not limited to, one or more species from the following genera: Acutodesmus, Achnahtes, Amphipora, Amphora, Anabaena, Ankistrodesmus, Arthrospira (also known as Spirulina), Asteromonas, Asterionella, Boekelovia, Borodinella, Botryococcus, Bracteacoccus, Carteria, Chaetoceros, Chlamydomonas, Chlorella, Chlorococcum, Chlorogonium, Chloromonas, Chroomonas, Chrysophaera, Ceratium, Closterium, Coccolithus, Coelastrella, Coscinodiscus, Cosmarium, Cricosphaera, Crocosphaera, Crypthecodinium, Cryptomonas, Cyanocystis, Cyanospira, Cyclotella, Desmodesmus, Ditylum, Dunaliella, Ellipsoidon, Emiliania, Eremosphaera, Euglena, Fragilaria, Franceia, Galdieria, Gracilaria, Graesiella, Guinardia, Haematococcus, Halocafeteria, Halospirulina, Hantzschia, Hymenomonas, Isochrysis, Lepocinclis, Limnothrix, Micractinium, Microactinium, Microcystis, Monochrysis, Monodus, Monoraphidium, Muriellopsis, Nannochloris, Nannochloropsis, Navicula, Neochloris, Neospongiococcum, Nephrochloris, Nephroselmis, Nitzschia, Nodularia, Nostoc, Ochromonas, Oedogonium, Oocystis, Oscillatoria, Ostreococcus, Parachlorella, Pavlova, Peridinium, Phaeodactylum, Picochlorum, Platymonas, Pleurochrysis, Pleurococcus, Porphyra, Porphyridium, Prochlorococcus, Prototheca, Prymnesium, Pseudanabaena, Pseudochlorella, Pseudochoricystis, Pseudoneochloris, Pyramimonas, Pyrobotrys, Rhodomonas, Scenedesmus, Schizochytrium, Scytonema, Skeletonema, Spirogyra, Stichococcus, Synechococcus, Tetrachlorella, Tetradesmus, Tetraselmis, Thalassiosira, Tisochrysis, Tolypothrix, Tribonema, Trichodesmium, Ulothrix, Vaucheria, Viridiella, Volvox, and genetically-engineered varieties or combinations (mixtures, mixed cultures, cocultures or synthetic co-cultures) thereof.

[0050] Even more specifically, the algal biomass can include any algal or microalgal species (including diatoms, coccolithophorids and dinoflagellates) and including but not limited to the at least one or more of following: Amphora sp., Ankistrodesmus, Arthrospira (Spirulina) plantesis, Botryococcus braunii, Chlamydomonas sp., Chlamydomonas reinhardtii, Chlorella protothecoides, Chlorella sp., Closterium sp., Cosmarium sp., Crypthecoddinium cohnii, Cyclotella sp., Dunaliella salina, Dunaliella tertiolecta, Haematococcus pluvialis, Hantzschia sp., Nannochloris sp., Nannochloropsis sp., Navicula sp., Neochloris oleoabundans, Nitzschia sp., Phaeodactylum tricornutum, Scenedesmus sp., Schiochytrium limacinum, Stichococcus sp., Tetraselmis suecica, and Thalassiosira pseudonana, and/or genetically-engineered varieties and/or combinations (mixtures, or mixed cultures) of these algal or microalgal species.

[0051] In an exemplary embodiment the algae or microalgae is selected from the group including or consisting of Dunaliella sp., Dunaliella bardawil, Dunaliella kone, Dunaliella salina, Dunaliella bioculata, Dunaliella granulata, Dunaliella maritima, Dunaliella minuta, Dunaliella parva, Dunaliella peircei, Dunaliella polymorpha, Dunaliella primolecta, Dunaliella pseudosalina, Dunaliella quartolecta, Dunaliella terricola, Dunaliella tertiolecta, and Dunaliella viridis.

[0052] In an exemplary embodiment, the algal biomass can comprise an algal biomass derived from algae capable of phototaxis; and/or an algal biomass derived from Dunaliella.

[0053] In an exemplary embodiment, the algae is microalgae. In one exemplary embodiment, the algae or microalgae have not been genetically modified or do not originate from genetically engineered algae or microalgae. In a specific embodiment, the algae or microalgae is selected from the group comprising or consisting of Dunaliella sp., Dunaliella bardawil, Dunaliella salina, Dunaliella kone, Dunaliella tertiolecta, Dunaliella parva and Dunaliella viridis, and any combination thereof. In a specific embodiment, the algae or microalgae is Dunaliella salina.

[0054] A group of algae are those with flagella, cilia and/or eyespots. Flagella are a tail-like projection that protrudes from the cell body of certain algae and functions in locomotion. Cilia are an adaptation that allows independent cellular creatures, like algae, to move around in search of food. Photosensitive eyespots are found in some free-swimming unicellular algae. Photosensitive eyespots are sensitive to light. They enable the algae to move in relation to a light source. Such algae have the capability of independent motion, phototaxis, and can move towards the surface during daylight. Phototaxis is the movement of microalgae in response to light. For example, certain algae (e.g., Dunaliella) can perceive light by means of a sensitive eyespot and move to regions of higher light concentration to enhance photosynthesis. [0055] Prior to deploying in accordance with the instant application, the microalgae can be harvested by harvesting means in order to increase the concentration of algae fed into the process. Suitable harvesting means include known harvesting technologies. For example, a harvesting technology that can optionally be used prior to fractional flotation includes, but is not limited to, systems which provide skimming, sedimentation, adsorption, dissolved air flotation, centrifugation, deep bed filtration, cross flow filtration, membrane processes, adsorptive bubble separation processes, and combinations thereof. In all of these harvesting technology methods, a stream is produced that is depleted in algal biomass, and this stream is termed the "spent washing stream". A second stream that is enriched in algal biomass is termed the "algal concentrate". The algal concentrate can range in consistency from an inviscid liquid to a thick paste. The consistency, or the amount of residual algal growth medium in the algal concentrate, will depend on the desired downstream processes. However, the instant application can be used with algal concentrate derived from any of the harvesting methods known in the art or combinations thereof.

[0056] Skimming can be used as a harvesting technology (as a harvester) in the instant application, as some algae exhibit phototaxis. For example, Dunaliella salina swim to the gas-liquid interface at the top of the pond surface as disclosed in US Patent No. 4,958,460, the contents of which are incorporated herein by reference in their entirety. This accumulation of algae at the gas-liquid interface facilitates their concentration by skimming.

[0057] Sedimentation can be used as a harvesting technology in the instant application, as some algae can be flocculated or separated by placing the microalgae in a quiescent zone. Some algae, for example Haematococcus pluvialis can be separated from the algal growth medium by sedimentation resulting from the addition of alum or the lack of agitation of the algal growth medium. For example, US Patent No. 5,541 ,056, the contents of which are incorporated herein by reference in their entirety, discloses a method of concentrating Haematococcus pluvialis by sedimentation. Other algae, such as Dunaliella salina can be flocculated and then separated by sedimentation. In this case, the addition of ferric chloride causes the flocculation. Any polymer or ions that cause flocculation can be used in this step. Cyclones can also be used to accelerate the rate of sedimentation. Any sedimentation equipment known in the art can be used to separate the flocculated algae from the algal growth medium in order to harvest the algae.

[0058] Adsorption can be used as a harvesting technology for algae in order to reduce the volumetric flow to downstream processes. Some algae, for example Dunaliella salina, can be concentrated by adsorbing the algae onto a hydrophobic surface, and then desorbing the algae with another fluid, as disclosed in US Patent No. 4,554,390, the contents of which are incorporated herein by reference in their entirety. Thus, adsorption can be used to pre-concentrate the algae.

[0059] Dissolved air flotation is another suitable harvesting technology for algae in the instant application, and it can be used without or with the addition of flocculating agents. The floatation gas may include air, carbon dioxide, nitrogen, helium, argon, steam, an exhaust from combustion of carboneous fuel or a combination of two or more of the above. A process using this technique is disclosed in US Patent No. 4,680,314, the contents of which are incorporated herein by reference in their entirety. This disclosure teaches how Dunaliella or Chlorella can be concentrated with dissolved air flotation after the addition of a flocculating agent such as alum or ferric chloride. A weakness with this pre-concentration step is associated with the flocculating agents, specifically their cost, impact on recycle streams, and permitting.

[0060] Centrifugation is another suitable harvesting technology for algae in the instant application, and it can be combined with other concentration methods, such as sedimentation as taught in US Patent No. 4,115,949, the contents of which are incorporated herein by reference in their entirety. Sedimentation and centrifugation can be used either individually or in combination in order to generate an algal biomass paste. Centrifuges known in the art can be used to affect algal pre-concentration, as long as they can readily handle solids. Suitable centrifugation equipment must also be constructed from acceptable materials of construction in order to handle the ions present in the algal aquaculture media. When the algal culture media includes sodium chloride, stainless steel or more exotic metals and/or plastic wetted parts on the centrifuge are used for robust operations. Suitable centrifuges known in the art include, but are not limited to, those produced by Westfalia and Alfa Laval. Disc-stack centrifuges produced by Westfalia and Alfa Laval are used. Weaknesses with this method of concentration are the use of rotating equipment, the relative high cost of centrifugal separations, and the necessity of using proper materials of construction - especially if halotolerant algae are being used.

[0061] Deep bed filtration is another suitable harvesting technology for algae in the instant application, as disclosed in US Patent No. 5,951 ,875, the contents of which are included herein by reference in their entirety. Deep bed filtration can be useful to preconcentrate the algal suspension prior to adsorptive bubble separation. Deep bed filtration relies upon a bed of granular media, usually sand, through which the algal growth medium containing algae flows downward under gravity. The algae are deposited in the pores of the granular media and in the interstitial spaces between the grains of media. Deep bed filtration should not be confused with straining filtration. Straining takes place on the surface of a mesh or fabric, and is only suitable to pre-concentrate algae that will not blind the filtration equipment. However, deep bed filters retain particles throughout their volume, with each pore and void space having a probability of retaining algal cells from the suspension that is flowing through. Suitable deep bed filtration media include those used in commercial processes, such as quartz sand, garnet sand, anthracite, fiberglass, and mixtures thereof.

[0062] Membrane systems and processes can be used to harvest the algae. Suitable membranes include, but are not limited to, those constructed from plastic, ceramic, metal, or combinations of these materials. Suitable types of membranes include those capable of particle filtration or microfiltration. Examples of membrane algae harvesting equipment include that which is produced by Pall, Koch, or LycOflux.

[0063] Another suitable concentration unit technology for harvesting algae in the instant application is a technology developed by Algaeventure technology, termed the AlgaeVS Harvester. It is essentially a belt filter on which the algal growth medium is placed. The water portion of the algal growth medium passes through the filter, and additional water is removed by contacting the underside of the belt with a super-absorbent belt. The super-absorbent belt pulls additional water from the algal biomass further dewatering the algal material to form a paste. This paste continues on the belt, optionally through a drying unit, and then on to a knife, which cuts the dried algal flakes from the belt.

[0064] Adsorptive bubble separation is another suitable harvesting technology for the instant application, and it is based on the selective adsorption of algal cell material to the surfaces of gas bubbles passing through the algal suspension. Bubbles rise to form a froth that carries the algal material off, typically overhead. Adsorptive bubble separation methods are suitable for removing a small mass of algae from a large volume of brine. Since adsorptive bubble separation processes are an efficient method to concentrate algae, they will be discussed in more detail below. There are a variety of adsorptive bubble separation techniques, in some of which a froth is generated and in some of which no froth is generated. One useful adsorptive bubble separation technique for dewatering algae is a dispersed gas flotation technique termed "froth flotation."

[0065] In an exemplary embodiment, a salt concentration (i.e., salinity) in the algal growth medium, algal suspension, a salt concentration of the salt-containing solution of the froth and/or a salt concentration of the liquid phase is at least about 5 wt%, at least about 6 wt%, at least about 7 wt%, at least about 8 wt%, at least about 9 wt%, at least about 10 wt%, at least about 11 wt%, at least about 12 wt%, at least about 13 wt%, at least about 14 wt%, at least about 15 wt%, at least about 16 wt%, at least about 17 wt%, at least about 18 wt%, at least about 19 wt%, at least about 20 wt%, at least about 21 wt%, at least about 22 wt%, at least about 23 wt%, at least about 24 wt%, or at least about 25 wt%; and/or the ratio of the salt concentration in the algal suspension or salt-containing solution of the froth stream to the salt concentration of the tails stream is less than 1.0, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, less than 0.1 , or less than 0.05.

[0066] In a specific embodiment, the algal suspension or the salt-containing solution of the froth is saturated with salt. In particular embodiments, the algal suspension or the salt-containing solution of the froth is from about 5 wt% to about saturation, from about 10 wt% to saturation, from about 20 wt% to saturation, from about 5 wt% to about 20 wt%, from about 10 wt% to about 20 wt%, from about 5 wt% to about 15 wt%, from about 10 wt% to about 15 wt%, or from about 5 wt% to about 10 wt%.

[0067] The exemplary algal suspension, algal biomass or salt-containing solution of the froth and/or of the liquid phase may contain a salt concentration of about 18 to 27 percent by weight per unit weight of the algal suspension, algal biomass or salt-containing solution.

[0068] In an exemplary embodiment, the process of the present disclosure comprises feeding an algal biomass feed containing an algal biomass and a salt-containing solution to the process.

[0069] In an exemplary process, the algal biomass feed contains an algal cell concentration of about 2,000 to millions of cells per milliliter or about 20,000 to millions of cells per milliliter of the algal biomass feed.

[0070] In an exemplary process, the algal biomass feed contains carotenoids in a concentration of less than about 10,000 ppm.

[0071] In an exemplary process, the salt in the salt-containing solution contains sodium chloride, sodium carbonate, magnesium chloride or a combination of two or more of the above.

[0072] In an exemplary process, the salt-containing solution is a brine solution.

[0073] In an exemplary process, the wash liquid is supplied using substantially horizontal dispensing means such as a nozzle that discharges parallel to the interface or a slotted tube that discharges parallel to the interface between the froth zone and the separation zone.

[0074] In an exemplary process, the wash liquid is supplied to the wash interface zone in laminar flow so the algae biomass that is adsorbed to the bubbles are not dislodged by turbulent forces. [0075] In an exemplary process, the wash liquid is supplied to the wash interface zone at a temperature close to that of the algal suspension, which is typically at a temperature of - 0.15 - 99.85 °C (273-373 Kelvin (K)), for example, at temperatures of 24.85-59.85 °C (298- 333 K), 24.85 °C (298 K), 26.85 °C (300 K), 41.85 °C (315 K), 56.85 °C (330 K), or 59.85 °C (333 K).

[0076] In an exemplary process, the wash liquid has a lower density than the saltcontaining solution of the froth, or the wash liquid contains salt in a lower concentration than the salt-containing solution of the froth. In a further exemplary process, the wash liquid is freshwater which preferably contains substantially no salt.

[0077] In an exemplary embodiment, a ratio of densities of the wash liquid to the salt-containing solution is less than unity. Thus, the wash liquid stays in the wash interface zone because its density is greater than the fluid in the froth zone, but less than the density of the liquid in the separation zone.

[0078] In an exemplary process, a ratio of the algal biomass feed to the wash liquid is at least about 1 by volume. In a further exemplary process, the ratio of the algal biomass feed to the wash liquid is at least about 3, 5, 10, 20, 50 or 100 by volume.

[0079] In an exemplary embodiment, the algal biomass is separated from the froth stream or recovered from the froth stream using a method known in the art. Suitable methods for separating the algal biomass include but are not limited to centrifugation, cross-flow microfiltration, sedimentation, and/or combinations thereof. In an exemplary embodiment, the algal biomass is extracted from the froth stream using an extraction solvent. Extraction solvents suitable for use include, e.g., edible oils, flavorants, petrochemical solvents, and dense gases, although not necessarily with equivalent results. Any extraction solvents that are immiscible with water should be useful for extraction of carotenoids and lipids from a suspension of algae in water or Dunaliella salina in brine. The extraction solvent could be one that at least does not adversely change the physical and chemical characteristics of algal oils or carotenoids. Solvents can be selected, e.g., from synthetic and natural flavorants, edible oils, petrochemicals, dense gases, and combinations of these, e.g., so long as a system results having two or more immiscible phases. However, some of these extraction solvents are more desirable than others for various reasons as discussed below and the results obtained are not necessarily equivalent.

[0080] Petrochemical solvents typically are of low viscosity, and the solute molecular diffusivity is favorable. Algal oils and carotenoids typically are highly soluble in petrochemical solvents and concentrated extracts are possible. Petrochemical solvents include: the aliphatic hydrocarbons, such as hexane, pentane, octane, petroleum ether, cyclohexane, methylene chloride, methanol, ethanol, and other low boiling alcohols; aromatics including benzene and toluene; and numerous other petrochemicals not listed. Combinations of petrochemical solvents may be used if desired.

[0081] However, it should be recognized that petrochemical solvents generally are not considered desirable as extraction solvents for extraction of carotenoids and lipids for the preparation of nutritional supplements. Solvent residues are normally removable at least to some extent by chromatography. Nevertheless, the use of compounds derived from petroleum to process nutritional supplements and the presence of any petroleum residue in a nutritional supplement is objectionable to many people.

[0082] Edible oils are preferred to petrochemical solvents from a nutritional standpoint. Edible oils may be obtained from plant or animal sources, including fish oils. Edible vegetable oil solvents include corn, olive, soybean, safflower, sunflower, and numerous other oils. Combinations of edible oils may be used, if desired.

[0083] However, compared to petrochemical solvents, edible oils typically are more viscous, and the solute molecular diffusivity is lower. Carotenoids normally have limited solubility in edible oils and concentrated extracts are difficult to obtain without steps that could change the chemical and physical characteristics of the carotenoids, including applying excessive heat.

[0084] Synthetic and natural flavorants typically are more desirable than petrochemical solvents and edible oils. Naturally derived flavorants have appeal in nutritional supplements. Flavorants classified by the Flavor and Extract Manufacturers Association, or FEMA, as Generally Recognized As Safe, or GRAS, do not have the drawbacks of petrochemical solvents in association with nutritional supplements. The presence of residual flavorant solvents in nutritional supplements is generally acceptable in comparison with petrochemical solvents, which reduces downstream purification and recovery costs. Flavorants can be selected to have boiling points, viscosities, and molecular diffusivity properties comparable to petrochemical solvents.

[0085] Examples of flavorants that are suitable for this invention include methyl-, ethyl-, propyl-, butyl-, isobutyl-, benzyl-, and/or octyl-esters with the carboxylic acid component of the ester including acetate, ethanoate, propionate, butyrate, hexanoate, caproate, heptanoate, octanoate, decanoate, cinnamate, and/or isovalerate. Other examples of flavorants include, but are not limited to, benzaldehyde, other aldehydes, limonene, and/or other terpenes. Combinations of flavorants may be used, if desired.

[0086] In an exemplary embodiment, at least part of lipids have been extracted from the algal biomass before removal of salt from the froth.

[0087] In an exemplary embodiment, the process of the present disclosure comprises: extracting at least part of lipids from the algal biomass after removal of salt from the froth.

[0088] In an exemplary embodiment, the process of the present disclosure comprises harvesting the algal biomass, optionally the harvesting being selected from one or more of the group comprising sedimentation, centrifugation, adsorption, adsorptive bubble separation processes, froth flotation, and dissolved air flotation, and any combination thereof.

[0089] In an exemplary embodiment, the process of the present disclosure comprises one adsorptive bubble separation process, which is for both harvesting and desalting. [0090] In an exemplary embodiment, the process of the present disclosure comprises filtration after removal of salt from the froth.

[0091] In an exemplary embodiment, after recovering the froth stream, the method further comprises one or more selected from the group comprising drying, extraction, washing, filtration, and dewatering the froth stream; or any combination thereof.

[0092] In an exemplary embodiment, a system such as a continuous system is disclosed for treating a froth including an algal biomass and a salt-containing solution or for removal of salt from a froth including an algal biomass and a salt-containing solution. An exemplary system includes a bubble generation zone; a collection zone; a separation zone; a froth zone; a wash interface zone between the separation zone and the froth zone; a launder; and a wash liquid supplying unit, optionally in communication with a wash liquid reservoir; the bubble generation zone being configured to interact with or being in communication with the collection zone, the collection zone being in communication with the separation zone, and the wash liquid supplying unit being in communication with the wash interface zone.

[0093] In an exemplary embodiment, the wash liquid supplying unit is in communication with the wash interface zone.

[0094] In an exemplary embodiment, the separation zone is in communication with an exit for a tails stream. For example, the tails stream exit can be located at a bottom of the separation zone.

[0095] In an exemplary embodiment, the froth zone is in communication with an exit for a froth stream and/or with the launder. The launder is designed to receive froth in an adsorptive bubble separation unit. There may be one or more launders in a single flotation cell. The launder may be centrally located in a flotation cell or located at the periphery of the flotation cell. Optional locations for the launder are provided in AU 2013206418 B2, the contents of which are included herein by reference. [0096] In an exemplary embodiment, the wash liquid supplying unit is for supplying the wash liquid to an interface between the froth and a liquid phase.

[0097] In an exemplary embodiment, the system comprises a vessel. Typically a vessel can comprise, e.g., a launder, a froth zone, a separation zone and a tails stream exit.

[0098] In one embodiment, the system is for a fractional flotation process, an adsorptive bubble separation process or for the process described herein.

[0099] In an exemplary embodiment, the system comprises a froth containing an algal biomass and a salt-containing solution.

[00100] In an exemplary embodiment, the system is for removal of salt from a froth containing an algal biomass and a salt-containing solution; or the system comprises a froth including an algal biomass and a salt-containing solution.

[00101] The present disclosure includes exemplary applications and use of the disclosed processes and systems to produce a froth stream containing algal biomass and a reduced amount of salt relative to that in the froth.

[00102] The foregoing process can be implemented using the exemplary system shown in Fig. 2 for treating a froth containing an algal biomass and a salt-containing solution or for removal of salt from a froth. In the system or process of the present disclosure, the wash liquid can be added in one or more stages of a multi-stage adsorptive bubble separation process. For example, wash liquid can be added to different stages of the adsorptive bubble separation process, and the salinity of the wash liquid can be different from stage to stage in order to minimize the amount or salinity of wash water needed.

[00103] FIG. 2 shows an exemplary froth flotation system for treating a froth or removal of salt from a froth containing an algal biomass and a salt-containing solution. In FIG. 2, the exemplary system includes: a collection zone 202; a bubble generation zone 214; a froth zone 204 located next to a separation zone 208, and an exit for the tails stream from the separation zone 208, and a wash interface zone 206 between the separation zone 208 and the froth zone 204; optionally a launder 216 for the froth; and a wash liquid supplying unit, optionally in communication with a wash liquid reservoir; the bubble generation zone 214 being configured to interact with or in communication with the collection zone 202, the collection zone 202 being in communication with the separation zone 208, the froth zone 204 optionally being in communication with the launder 216, and the wash liquid supplying unit being in communication with the wash interface zone 206. Some or all of these Zones may or may not occupy the same vessel.

[00104] The feed stream enters the froth flotation device at either the collection zone 202 or the bubble generation zone 214, depending on the equipment chosen. In either event, a gas is dispersed through the bubble generation zone 214 in the algal suspension in the collection zone 202 to produce a two phase dispersion of gas in liquid. It is desirable to produce a large number of small bubbles to maximize the surface area of gas available for collision with algal biomass in a given volume of the collection zone. In the collection zone 202, the algal suspension is contacted with fine bubbles under conditions that promote intimate contact. The bubbles collide with the algal biomass and form bubble and algal agglomerates. It is desirable to generate intense mixing in the collection zone to provide a high frequency of collisions between bubbles and the algal biomass. The bubbles and the algal biomass feed enter the collection zone where bubble and algae collisions occur to form bubbles and algal biomass agglomerates. Bubbles and algae collisions can be achieved, e.g., by countercurrent or co-current flow of the flotation gas and liquid phases, or by pneumatic mixing.

[00105] After the bubbles and algal agglomerates are formed in the collection zone 202, they are then separated from the brine depleted in algae in the separation zone 208, typically by gravity. The density of the gas is two to three orders of magnitude less than that of the brine. The density difference promotes floating of the bubbles and algal agglomerates to the interface between the separation zone 208 and the froth zone 204.

[00106] The wash interface zone 206 is created by the addition of wash water at a location between the separation zone 208 and the froth zone 204. The wash interface zone 206 is a region where the wash water concentration is elevated above that of the salt containing solution. Since the wash water has a lower salt concentration than the salt containing solution, it floats on the surface of the salt containing solution in the separation zone 208. As the bubbles rise through the separation zone 208 they enter the wash interface zone 206 where the salt containing solution is partially displaced by the wash water. It is critical for the algal biomass to remain on the surface of the bubbles in this zone and not be washed off. In order to achieve this goal, it was found to be necessary to add the wash water gently to the zone. Typically, the wash water is fed to the wash interface zone 206 by a tube or pipe that discharges at the wash interface zone 206, or by a slotted pipe wherein the discharge is parallel to the interface between the froth zone 204 and the separation zone 208.

[00107] As the bubbles and algal agglomerates pass through the wash interface zone 206 they enter the froth zone 204, where the bubbles dominate the volume and the salt containing solution drains so that an increasingly dry froth is formed as the bubbles move up in the froth zone 204.

[00108] In an exemplary embodiment, the system such as a continuous system as disclosed herein is configured for removal of salt from a froth which contains an algal biomass and a salt-containing solution. An exemplary system includes a collection zone; a bubble generation zone; a froth zone located next to a separation zone, and an exit for the tails stream from the separation zone, and a wash interface zone between the separation zone and the froth zone; optionally a launder for the froth; and a wash liquid supplying unit, optionally in communication with a wash liquid reservoir; the bubble generation zone being configured to interact with or in communication with the collection zone, the collection zone being in communication with the separation zone, the froth zone optionally being in communication with the launder, and the wash liquid supplying unit being in communication with the wash interface zone.

[00109] In a further exemplary system, the wash liquid supply unit is in communication with the separation and/or wash interface zone. In an exemplary process, the wash liquid is supplied using substantially horizontal dispensing means, e.g., at a low velocity so the interfacial region is not disturbed. Suitable discharge velocities are typically less than 30 centimeters per second.

[00110] Physically, the wash water or liquid can be added to the flotation cell in one or more locations. In an exemplary embodiment, the wash liquid is added to or just below the liquid-froth interface. In an exemplary embodiment, this mode can be used when the density of the liquid phase density is greater than the density of the wash liquid. The wash liquid can be introduced by a disperser ring or other method known in the art. Baffles can also be used in the flotation cell in order to minimize mixing of the wash liquid into the bulk of the liquid phase in the flotation cell.

[00111] Suitable froth flotation devices include the commercially available equipment used for gas and liquid contact. These devices, which are also called "cells", can be classified into two broad groups, mechanical and pneumatic flotation cells. The mechanical flotation cells can include a rotor and stator mechanism for dispersing the gas and providing efficient bubble and algae contact.

[00112] Pneumatic flotation cells can be most easily distinguished from mechanical flotation cells by the absence of a rotating impeller in the flotation device. In pneumatic flotation cells, bubble and algae collisions are produced by addition of gas only, without any moving parts. Pneumatic flotation cells can operate as roughers, cleaners, and scavengers and the operating conditions for each service will require slightly different operating parameters in order to optimize the flotation circuit.

[00113] Pneumatic and mechanical flotation cells can be used at any or all of the locations in a froth flotation circuit, depending on equipment performance and separation objectives. However, the pneumatic flotation cells can have advantages over mechanical cells. Higher recovery and throughput can be attained in a pneumatic device as compared to a mechanical device for a given equipment volume and energy input, which can result in reduced capital and operating costs. Pneumatic devices can be produced from light weight, inexpensive plastics for further cost savings and to promote mobility. These advantages and others are discussed herein. [00114] The mechanical and pneumatic flotation cells described herein can have several operating parameters in common, including the gas phase superficial velocity, J_g; the gas to feed ratio; the liquid residence time in the flotation device; flotation aid dosage; and the nature of the flotation gas. Several design parameters are also common to various froth flotation devices, including the aspect ratio of the collection zone; the aspect ratio of the separation zone; the method of phase contact, including co-current flow, countercurrent flow, crossflow, and mechanical mixing; the method of separating the bubble and algal agglomerates from the pulp; and the method of bubble generation.

[00115] Performance of the froth flotation device can be quantified in terms of the algal biomass recovery, and the concentration of salts in the clean algal biomass. There are several geometrical and operating parameters that are specific to each type of froth flotation device, but the major parameters named above are common to the entire field of flotation processes described herein.

[00116] Mechanical flotation cells typically employ a rotor and stator mechanism for flotation gas induction, bubble generation, and liquid circulation providing for bubble and algal biomass collision. The ratio of vessel height to diameter, termed the "aspect ratio", usually varies from about 0.7 to 2. For example, four or more cells, each having a centrally mounted rotor and stator mechanism, are arranged in series to approach substantially perfect mixing and thereby to minimize liquid phase short circuiting. An auxiliary blower can be installed to provide sufficient gas flow to the cell. Mechanical cells can be sealed if desired to facilitate operation to control the flow of the flotation gas.

[00117] The flotation gas can be dispersed into fine bubbles by a rotating impeller, which serves as the bubble generator. The rotating impeller creates a low pressure zone that induces gas to flow through an aspiration tube into the collection zone where it is dispersed into fine bubbles and mixed with the algal biomass as it is circulated from the bottom of the cell. The algal biomass enters the mechanical cell as a feed stream through a feed box. Bubble and algal biomass collisions result from turbulence generated by the rotating impeller. As mentioned herein, the bubble and algal biomass agglomerates pass out of the collection zone into the separation zone, which is relatively quiescent, where they float to the surface and separate from the liquid phase.

[00118] The bubble and algal biomass agglomerates can be separated from the liquid phase by gravity and collect as froth concentrated in algal biomass at the top of the cell in froth zone. Froth concentrated in algal biomass is withdrawn as an algal concentrate stream. The froth normally overflows the cell into a collection launder. Alternatively, the froth can be withdrawn by mechanical means such as a froth paddle. The liquid phase is recirculated to the collection zone and eventually exits the cell as a tails stream of brine depleted in algal biomass.

[00119] The properly designed rotor and stator mechanism entrains the proper amount of flotation gas, disperses it into fine bubbles, and mixes the flotation gas with liquid to accomplish sufficient contact between the algal biomass and the bubbles. Good mixing and sufficient liquid residence time are desirable in the two phase mixing region to provide high bubble and algae collision efficiency, and good flotation performance.

[00120] J_g is defined in a mechanical flotation cell as the volumetric gas flow rate divided by the cell cross sectional area parallel to the froth and liquid interface. As the value of J_g increases, the gas holdup increases in the liquid phase and decreases in the froth, resulting in potentially faster flotation kinetics but reduced algal biomass concentration in the froth on a flotation gas free basis. In an exemplary embodiment, the values of J_g range from about 0.1 to 5 cm/s for recovery of algal biomass e.g. from Dunaliella salina. Values of from about 2 cm/s to 4 cm/s are somewhat more typical.

[00121] The liquid residence time is defined as the volume of the dispersion in the mechanical cell divided by the volumetric liquid flow rate. Longer residence times enable higher recovery of algal biomass in the froth. The residence time can range from, for example, about 3 to 12 minutes for continuous operation for the recovery of algal biomass e.g. from Dunaliella salina. Residence times greater than 5 minutes can be desirable.

[00122] An exemplary reason for a low flotation gas to feed ratio includes reduced equipment volume and blower costs in the mechanical cell. The flotation gas to feed ratio can range from about 5 to 20 for the recovery of algal biomass e.g. from Dunaliella salina. Flotation gas to feed ratios of from about 5 to 15 can be somewhat desirable.

[00123] Impeller tip speed influences the bubble size and the recirculation rate through the collection zone. The bubble size decreases and the recirculation rate through the collection zone increases as the tip speed increases. However, higher tip speeds result in greater mechanical wear and power requirements for the impeller drives. The bubble and algal agglomerates can be broken at high tip speeds. Tip speeds can range from about 900 to 2500 feet per minute for the recovery of algal biomass e.g. from Dunaliella salina. Tip speeds of from about 1500 to 1800 feet per minute can be somewhat desirable.

[00124] There are four exemplary, primary geometrical parameters for mechanical flotation cells. These geometrical parameters are 1 ) the ratio of rotor submergence to liquid depth, 2) the ratio of tank diameter to impeller diameter, 3) the ratio of liquid depth to tank diameter, and 4) the design of the rotor and stator mechanism. The ratio of rotor submergence to liquid depth can range from about 0.7 and 0.75 for the recovery of algal biomass e.g. from Dunaliella salina. The ratio of tank diameter to impeller diameter can range from about 1.5 to 5.5. A tank diameter to impeller diameter ratio of about 2 is somewhat more frequently used. The ratio of liquid depth to tank diameter can range from about 0.6 to 0.9. A ratio of liquid depth to tank diameter of from about 0.8 to 0.9 can be somewhat desirable.

[00125] Rotor and stator mechanisms include those produced by FLSmidth of Copenhagen, Denmark, which includes flotation cells historically provided by Dorr-Oliver Incorporated of Millford, Conn and Wemco Products of Salt Lake City as well as new flotation cell designs such as the FEFLUX™ flotation cell. They also include those produced by Metso:Outotec of Helsinki, Finland, which acquired the flotation technology of Denver and Sala Equipment Companies. Their flotation technologies include the cPIant Flotation, Metso RCSTM flotation machines, Metso DR flotation machines, and SkimAir flash flotation machines. [00126] Pneumatic flotation cells differ from mechanically agitated cells in several respects. Bubbles are generated by any non-mechanical means known to the art in a pneumatic cell. Bubbles can be produced by a perforated pipe sparger, an orifice plate, a venturi, or a static mixer. A frother solution can be mixed with the gas when a static mixer is used.

[00127] Some pneumatic cells generate finer bubbles than do mechanical cells. Therefore, the collision frequency is potentially higher, and the residence time required for the flotation is generally shorter in a pneumatic cell.

[00128] Pneumatic flotation cells, especially columns, can have a higher aspect ratio than mechanical cells. The ratio of vessel height to diameter typically is greater in the pneumatic cell. It is possible to operate a pneumatic device with a deeper froth bed, allowing for increased drainage time and a drier, more concentrated froth. Wash liquid can be added to the froth to improve product purity because the vessel height is usually somewhat greater than the vessel diameter. This use of wash liquid can optionally be used in the instant application to improve the removal of salt from the algal biomass.

[00129] An exemplary advantage of a pneumatic flotation cell over a mechanical cell is the potential to use lighter weight and lower costs of materials and construction. The pneumatic flotation vessel can be constructed of inexpensive light weight plastics, and weight and cost are further reduced by the absence of an impeller and drive. Capital and operating costs for the pneumatic flotation cell can be significantly lower than those for the mechanical cells because no mechanical rotor and stator assembly is required for bubble generation and gas and liquid contacting.

[00130] Generally speaking, pneumatic flotation cells serving as cleaners can be operated in either the collection limited regime or in the carrying capacity limited regime. In the collection limited regime, the particle collection rate is limited by the number of collisions between bubbles and the algal biomass. In the carrying capacity limited regime the bubble surfaces are saturated with algal material. Therefore, the particle collection rate is limited by the rate at which bubble surface area is added to the column. It can be advantageous to produce a froth whose surface approaches saturation with algal material because it is desirable to minimize the volume of water sent to the downstream process, which can be a drying step.

[00131] The flotation gas can be dispersed as fine bubbles by means of a bubble generator in a bubble generation zone. The bubble generator can be either internal or external to the froth flotation device. An example of an internal bubble generator is the perforated pipe sparger. An example of an external bubble generator is a static mixer where the gas is mixed with a frother solution. The froth can be contacted with wash liquid or wash liquid mist to separate entrained hydrophilic particles such as salt from the algal biomass in the froth. The froth leaves the device enriched in biomass. The liquid can pass through the base of the device as a tails stream depleted of biomass.

[00132] Air or an acceptable flotation gas with recycle can be easily used in pneumatic flotation devices. The flotation gas can be recycled by covering the collection launder. Acceptable flotation gases include, but is not limited to air, carbon dioxide, nitrogen, argon, steam, and combinations thereof. Frother can be added either to the liquid phase or to the gas phase to generate small bubbles.

[00133] There are several pneumatic flotation devices available that can be used in accordance with the instant application to separate salt from algal biomass. Some of these devices include columns having an aspect ratio greater than one, which provide many of the benefits of the pneumatic devices discussed above.

[00134] Suitable pneumatic flotation cells for concentrating algal biomass include, but are not limited to: the air-sparged hydrocyclone, as described in US Patent No. 4,397,741 ; the Jameson cell described in US Patent No. 4,938,865, US Patent No. 5,188,726, and US Patent No. 5,332,100; the Canadian column and similar devices with various draft tube designs; the Renewable Algal Energy (RAE) Cell described in US Patent No. 5,776,349, US Patent No. 5,910,254, US Patent No. 5,951 ,875, US Patent No. 8,196,750, and US Patent No. 8,251 ,228; and the Microcel™ as defined in US Patent Nos. 4,981 ,582 and 5,167,798, the contents of which are incorporated herein by reference in their entireties.

For example, pneumatic flotation cells include the Jameson cell and the RAE cell.

[00135] Other adsorptive bubble separation techniques that can be useful in the practice of the current application are electrolytic flotation and dissolved gas flotation. However, it should be recognized that there are practical limits on these processes and that they are not necessarily equivalent to dispersed gas flotation. In electrolytic flotation, bubbles are generated by passing an electric current through the aqueous medium that is to be separated from the algal biomass. If the aqueous medium is concentrated brine, then a relatively larger current can be needed to generate the bubbles. In dissolved gas flotation, the gas is dissolved in a portion of the feed stream, under pressure in a separate vessel, and the resulting mixture is then introduced into the flotation vessel. The sudden drop in pressure causes the dissolved gas to nucleate and form small bubbles. The solubility of air in brine is somewhat limited and so another, more soluble gas that does not adversely affect the lipids or carotenoids can be selected, including, for example, carbon dioxide, nitrogen, or argon.

[00136] Obtaining the salt-laden algal biomass directly as the algal growth medium is specifically possible when closed photobioreactors are used to produce algal biomass in a relatively concentrated form. Suitable photobioreactors to produce a concentrated algal biomass include but are not limited to tubular reactors, enclosed raceways, covered ponds, covered raceways, ponds in greenhouses, clear plastic bags hung either indoors or outdoors, fermentors, and combinations thereof. In some cases, the photobioreactors rely on solar radiation for light, while others utilize lights or solar collectors that channel solar radiation to the photobioreactor. In yet other cases, the algal biomass can be derived from fermentors where the algae are grown on sugars, cellulose, and/or other biomass.

[00137] Suitable tubular photobioreactors include those constructed from glass; or from plastics, including, but not limited to polyethylene, polypropylene, polycarbonate, acrylic, polyesters, specialty polyesters such as CHDM modified polyesters and Tritan® from Eastman Chemical Company, and combinations thereof. The tubular photobioreactors can be constructed so that they are rigid in nature, such as those constructed from glass, polyester, or polycarbonate.

[00138] Fermentors can be those used for production of non-photosynthetic organisms, and are especially useful for growing genetically modified algae that must be contained. Other algae that are grown to relatively high concentration in fermentors are those that require sugars or a carbon source such as sugar that is not directly carbon dioxide. Specifically, fermentors can be used when heterotrophic algae are used.

[00139] Another suitable source of algal biomass is enclosed raceways, which are racetrack ponds with the ability to control the degree of agitation via a mixing device that is covered to protect the algae from inclement weather. These enclosed raceways are similar to a greenhouse. This type of aquaculture is expensive, but can be used at latitudes greater than about 35 degrees where the winter temperatures are too low to support efficient algal growth.

[00140] Algal biomass obtained from any bioreactor can be used for this application. In one embodiment, algal biomass is obtained from an open pond system or bioreactor that is not covered or enclosed. Furthermore, a combination of algal bioreactors of different types can offer improved performance.

[00141] Enclosed photobioreactors that are transparent so that the algae they contain can utilize the sunlight have also been proposed for the production of biofuels. These enclosed photobioreactors can include plastic bags, glass and plastic tubes, ponds in green-house structures, and the like. Tubular reactors were popularized by GreenFuel Technologies Corporation of Cambridge, Massachusetts for the production of biofuels, but the technology was economically unsuccessful. Plastic bag bioreactors can be those utilized by Algenol Biofuels of Bonita Springs, Florida. Although the capital cost of constructing a bioreactor from plastic instead of steel is substantially reduced, this type of bioreactor is still so expensive that the commercial use is for the production of astaxanthin, a carotenoid, which is a high-value product. Thus, the use of enclosed photobioreactors is only of commercial interest for the production of high- value products. [00142] Open-pond bioreactors are generally classified as natural, intensive, and extensive, and this type of bioreactor is for use with the instant application. The natural open-pond bioreactors are defined as those naturally occurring ponds where the conditions are right to grow algae. These ponds can contain either fresh or saline water, and they are unmanaged in terms that they lack controlled fertilizer addition and mechanical agitation. Natural open ponds that contain algae are common along the shores of the Great Salt Lake in Utah.

[00143] Both the intensive and extensive modes of aquaculture involve controlled addition of fertilizers to the medium in order to supply the desired and/or necessary nutrients, such as phosphorus, nitrogen, iron, and trace metals, that are necessary for biomass production through photosynthesis. The primary difference between the two modes of production is mixing of the algal growth medium. Intensive ponds employ mechanical mixing devices while extensive ponds rely on happenstance mixing. Therefore, factors that affect algae growth can be more accurately controlled in intensive aquaculture.

[00144] Intensive aquaculture ponds are frequently constructed of concrete block and are lined with plastic. Brine depth generally is controlled at about 20 centimeters, which has been considered to be the optimum depth for producing algal biomass. A number of configurations of these ponds have been proposed. However, the open-air raceway ponds are typically the most important commercially. Raceway ponds employ paddle wheels to provide mixing. Chemical and biological parameters are carefully controlled, including salt and fertilizer concentrations, pH of the brine, and purity of the culture.

[00145] Extensive aquaculture has been practiced in the hot and arid regions of Australia for the production of beta-carotene. Outdoor ponds for extensive aquaculture generally are larger than those for intensive aquaculture and normally are constructed in lake beds. The open-air ponds are typically bounded by earthen dikes. In one embodiment, no mechanical mixing devices are employed.

[00146] Algae bioreactors that utilize these types of aquaculture systems, others know in the art, and combinations thereof, can be used with the instant application. [00147] Other adsorptive bubble separation techniques that can be useful in the practice of the harvesting technology for the instant application are electrolytic flotation and dissolved gas flotation. However, it should be recognized that there are practical limits on these processes and that they are not necessarily equivalent to dispersed gas flotation. In electrolytic flotation, bubbles are generated by passing an electric current through the aqueous medium that is to be separated from the algae. If the aqueous medium is concentrated brine, then a relatively larger current can be needed to generate the bubbles. In dissolved gas flotation, the gas is dissolved in a portion of the feed stream, under pressure in a separate vessel, and the resulting mixture is then introduced into the flotation vessel. The sudden drop in pressure causes the dissolved gas to nucleate and form small bubbles. The solubility of air in brine is somewhat limited and so another, more soluble gas that does not adversely affect biomass can be selected, including, for example, helium.

[00148] Suitable gases for use in an adsorptive bubble separation device used for harvesting in the instant application are preferably non-toxic and non-hazardous, including air, nitrogen, carbon dioxide, helium, steam, argon and other noble gases, which are generally considered chemically inert, and mixtures thereof. An inert gas that does not contain oxygen or oxidizing agents is used to avoid oxidation of the lipids and carotenoids present in the cell mass.

[00149] The froth flotation devices used for harvesting in the instant application can be used in a flotation circuit to maximize recovery and concentration of the valuable components present in the algae. The energy costs for the flotation process are compensated for by the high recovery and concentration factors that can be achieved by using a flotation circuit. Froth flotation devices operate continuously, and that is preferable over batch or semi-batch processes.

[00150] A froth flotation circuit is described in US Patent No. 5,951 ,875 for froth flotation columns connected in series of the type that can be used in connection with pneumatic froth flotation. However, it should be understood that the principles represented apply to froth flotation circuits generally, including mechanical and pneumatic froth flotation equipment. [00151] The algal concentrate produced from the harvesting step can be processed by a multiplicity of unit operations, the exact sequence of which will depend on the desired product(s). Suitable unit operations include, but are not limited to drying, extraction, washing, filtration, further dewatering, or combinations thereof. However, for the production of low-value products, such as biofuels, the algal concentrate will typically be dried for direct use, or subjected to an extraction step to remove the lipid content prior to the biomass being dried.

[00152] The algal concentrate can include the algal biomass that is recovered in the harvesting step, some residual algal growth medium, halotolerant bacteria, and any compounds that were added during the harvesting or conditioning steps. The algal biomass can include either whole or ruptured algal cells. If the algal concentrate is to be subjected to the extraction step, it is preferable to have the algal cell ruptured prior to the extraction, but it is not essential since some extraction solvents will cause cell rupture. If this is not the condition of the algal cells derived from the harvester, the algal cells in the algal concentrate can be disrupted by any process known in the art, such as that disclosed in US Patent No. 6,000,551 or in WO 2008/156819. Depending on the dewatering efficiency of the harvesting process, the algal concentrate can have a consistency between that of water and of a paste. For example, the algal growth medium will include salts, and it is preferable to remove the unwanted salts prior to drying the algal biomass.

[00153] The algae concentrate can also include halotolerant bacteria, such as those reported to be found in the Great Salt Lake by Oren, A., Salts and Brines, Chapter 10 in The Ecology of Cyanobacteria Their Diversity in Time and Space, B.A. Whitton and M. Potts (eds.) pp. 281 -306 (2000) that include Aphanothece halophytica, species of Phormidium or Oscillatoria, Microcoleus lyngbyaceus, and Nodularia spumigena. Other halotolerant bacteria that can be present in the algae concentrate are discussed by Oren (2000), and those species are included herein by reference in their entireties.

[00154] In one embodiment, the salts in the algal concentrate are those found in the algal growth medium for the algae. For example, these salts are sodium chloride and the salts that would be encountered via the evaporation of seawater. However, the algal concentrate can include salts like sodium carbonate, magnesium chloride, and combinations thereof that are associated with certain saline aquifers and terminal lakes. Herein, salt is defined as any combinations of ions found in ocean water.

[00155] In general, fractional flotation is the step where algal concentrate is intimately contacted with wash liquid in one or more stages of an adsorptive bubble separation process to produce a salt-depleted algal biomass with a salt concentration that is diminished with respect to the algal concentrate fed to the adsorptive bubble separation process and a spent washing stream that includes some of the salt initially contained in the algal concentrate. In one embodiment, a ratio of the floatation gas to the algal concentrate is about 5 to 20 by volume. A spent washing stream will also be removed from the adsorptive bubble separation process which includes salt initially contained in the algal concentrate. In yet another embodiment, fractional flotation can be used to separate the salt from the algal biomass from harvesting and extraction processes by intimately contacting the algal concentrate, which includes salt with washing water and a flotation gas in one or more stages of an adsorptive bubble separation process to produce a salt- depleted algal biomass with a salt concentration that are both diminished with respect to the algal concentrate fed to the adsorptive bubble separation process. A spent washing stream which includes salt derived from the algal concentrate will also be removed from the adsorptive bubble separation process.

[00156] Suitable flotation gases for fractional flotation include, but are not limited to air, nitrogen, carbon dioxide, the exhaust from the combustion of carbonaceous fuels, other inert gases, steam, and combinations thereof. The flotation gas should be chosen so that it will separate the extraction liquid from the algal biomass so that the resulting clean algal biomass has an extraction liquid composition which is tolerable in the desired downstream process, such as spray drying. Different flotation gasses can be used at different stages of the flotation process in order to minimize the amount of flotation gas needed to achieve the desired salt in the clean algal biomass. Suitable washing water in the fractional flotation includes water compositions that have sufficiently low salt concentrations that a clean algal biomass can be produced for its desired use. Uses for the clean algal biomass include, but are not limited to: use as a soil builder; use in animal feeds including for poultry, fish, shrimp, livestock; use in human nutrition; use for carbon capture and storage; use in combustion, including direct combustion, gasification, and torification; use for fermentation, either aerobic or anaerobic; and combinations thereof. It can be appreciated that the acceptable residual salt level in the clean algal biomass will depend on the ultimate use of the material. Different washing water compositions can be added to different stages of the flotation process to minimize the amount of washing water necessary to achieve the desired salt concentration in the clean algal biomass. The wash liquid can be derived from a freshwater source, or it could be derived via evaporation of water from seawater or brines. The wash liquid can also be derived from seawater via reverse osmosis, distillation, or other methods known in the art, or combinations thereof. Generally, the availability of freshwater is limited in locations where algal aquaculture would be practiced. Therefore, it is preferable to minimize the amount of fresh water required in the fractional flotation process by using seawater and other water sources.

[00157] Adsorptive bubble separation is based on the selective adsorption of algal biomass to the surfaces of gas bubbles passing through the suspension of algal biomass. Bubbles rise to form a froth that carries the algal biomass off, typically overhead.

[00158] Suitable drying equipment for the algal biomass includes, but is not limited to, dryers of the type termed direct dryers, drum dryers, spray dryers, infrared or radiant- heat dryers or dielectric-heat dryers, and indirect heat dryers, or combinations thereof. These

XI- types of dryers are defined in Gas-Solid Systems, Chemical Engineers' Handbook, 5ⁱⁿ

Edition, Eds. R. H. Perry and C. H. Chilton, pages 20-1 to 20-74, the contents of which are included herein by reference. Either batch or continuous dryers can be used, but continuous drying of the algal biomass is used. Examples of suitable direct dryers include, but are not limited to belt dryers, vibrating tray dryers, pneumatic conveying dryers, rotary dryers, spray dryers, tunnel dryers, fluidized bed dryers, and combinations thereof. Examples of suitable indirect dryers include, but are not limited to cylinder dryers, drum dryers, screw-conveyor dryers, steam-tube dryers, vibrating tray dryers, and combinations thereof. Examples of suitable radiant type dryers are solar dryers such as belt, tray or sheet dryers that utilize solar radiation for drying. Other suitable types of dryers include that disclosed by Algaeventure of Marysville, Ohio, which is a type of belt dryer.

[00159] Any of a variety of products can be made from the algal biomass that is salt removal process described in the instant application, and they include, but are not limited to biofuels, nutraceuticals, cosmaceuticals, wastewater treatment processes, spa products, animal feeds, human feeds, soil builders, chemical intermediates, specialty lipids, solar salt, and combinations thereof.

[00160] Biofuels that can be produced from high temperature processing of the algal biomass described in the instant application include, but are not limited to, biodiesel, green diesel, renewable diesel, methane, alcohols, and dried algal biomass. Algal biodiesel is produced via any transesterification process known in the art, including those which utilize two immiscible liquid phases, and those that utilize a solid acid catalyst. Green diesel can be produced by hydrogenation, cracking, or a combination thereof of the algal oil in order to produce hydrocarbons that can be used directly in the existing diesel distribution system. Renewable diesel can be produced by cracking and treatment with hydrogen - such as in Neste's NEXBTL process. Methane and/or hydrogen can be produced from the algal biomass by any anaerobic process known in the art. Fermentation of the algal biomass by any process known in the art can be used to produce methanol, ethanol, butanol, n- butanol, i-butanol, other alcohols, and combinations thereof. The algal biomass can be torrified for the production of a soil builder or for use in combination with coal for power or steam generation. The algal biomass can be dried and then combined with coal or biomass and combusted in a boiler or gasification unit.

[00161] The algal biomass can be extracted from the froth stream to recover the lipids that can be used as a nutraceutical, cosmaceutical, soap or components of a soap or detergent composition, and cosmetic ingredients, including, but not limited to, carotenoids, omega fatty acids, and other lipids. For the production of solar salt, the algal biomass can be removed from solar salt works in order to improve the salt quality. The quality of sodium chloride, sodium carbonate, and other salts can be improved by this method. Algal biomass stabilized with the high temperature treatment process can also be used in animal nutrition, especially for shrimp and fish aquaculture diets. Algal biomass can also be treated with the high temperature process in order to stabilize it against degradation during transportation. Alternatively, high temperature processing could be used to stabilize the algal biomass prior to its storage for carbon sequestration purposes. The algal biomass can be used to derive valuable chemical intermediates such as fatty acids for the production of polyurethanes.

[00162] Suitable animal feeds include, but are not limited to feeds for shrimp, fish, shellfish, brine shrimp, chickens, poultry, cows, ducks, dogs, pigs, sheep, goats, and combinations thereof. The animal feeds can require the stabilized algal biomass to be dried, but in some cases, for example for use in shrimp and fish aquaculture diets, complete drying cannot be necessary as long as stabilization from the instant application is sufficient.

[00163] Suitable dietary supplements include, but are not limited to alpha carotene, beta-carotene, lutein, zeaxanthin, cryptoxanthin, phytoene, phytofluene, and the various cis- and trans-isomers and the various alpha, beta, gamma, delta isomers of the various carotenoids, and/or combinations thereof.

[00164] Suitable methods of carbon storage include, but are not limited to burying the algal biomass, sinking the algal biomass, torifying the algal biomass and using it as a soil builder, and/or combinations thereof.

[00165] Suitable methods for water and wastewater treatment include, but are not limited to, removal of BOD (biological oxygen demand), and or TOC (total organic carbon) from a water stream. This can be useful for municipal wastewater treatment processes, and it can be important for the treatment of brines being used for the production of sodium chloride salt and other salts via evaporation.

[00166] Suitable methods to process of the algal biomass into useful compounds include, but are not limited to torification, gasification, liquefaction, fermentation, drying, combustion, burial, and combinations thereof. Suitable applications of the torified algal biomass includes, but is not limited to, a soil builder and a material to be combined with coal, wood, or other combustible material for power generation. Suitable applications of gasified algal biomass include, but is not limited to, the production of the entire suite of products that can be produced via syngas chemistry, as described by the Gasification Technologies Council.

[00167] Suitable products from syngas include, but are not limited to chemicals, fertilizers, power generation, substitute natural gas, hydrogen, and transportation fuels. Suitable chemicals include, but are not limited to hydrogen, carbon monoxide, methanol, dimethyl ether, acetic acid, propionic acid, butyric acid, acetic anhydride, methyl acetate, ethylene, propylene, olefins, and combinations thereof. Suitable fertilizers that can be produced from the syngas include, but are not limited to, ammonia, ammonium nitrate, urea, and others known in the art. Suitable substitute natural gas can be generated from the syngas produced by gasifying algal biomass, and this includes methane. Suitable liquid fuels include gasoline, diesel fuel, jet fuels, and combinations thereof.

[00168] All of the chemicals that are produced by Eastman Chemicals and by Sasol via their gasification processes can also be produced by the gasification of algal biomass. Products produced by the utilization of syngas can also be produced by gasification of algal biomass. Illustrative processes are described in US Patent. No. 6,310,260, the contents of which are incorporated herein by reference in their entirety, include, for example, hydroformylation, hydroacylation (intramolecular and intermolecular), hydrocyanation, hydroamidation, hydroesterification, aminolysis, alcoholysis, hydrocarbonylation, reductive hydroformylation, hydrogenation, olefin oligomerization, hydroxycarbonylation, carbonylation, olefin isomerization, transfer hydrogenation and the like. For example, processes involve the reaction of organic compounds with carbon monoxide, or with carbon monoxide and a third reactant, e.g., hydrogen, or with hydrogen cyanide, in the presence of a catalytic amount of a metal-organophosphorus ligand complex catalyst.

[00169] For example, the processes include hydroformylation, hydrocyanation, hydrocarbonylation, hydroxycarbonylation and carbonylation. [00170] Thus, it has now been discovered how salt can be efficiently removed from salt-laden algal biomass. By the practice of exemplary embodiments disclosed herein, it is now possible to remove salt from a salt-laden algal biomass so that it can be used in a number of applications including but not limited to shrimp food, fish food, poultry food, animal feeds, human nutrition, gasification, and other applications described in the present disclosure.

EXAMPLES

Example 1

[00171] Dunaliella salina algae are grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide is transported directly from the atmosphere into the ponds. The algae are harvested by an adsorptive bubble separation process, specifically froth flotation involving Denver mechanical flotation cells. The algal biomass is fed to a flotation unit. Ocean water is fed to the interface between the separation zone and the froth zone by a disperser ring with discharge ports that are aligned with the interface between the separation and froth zones. Nitrogen is used as the flotation gas. The salt concentration in the froth was reduced by 76% relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 153 and the mass ratio of salt to algae in the froth was 1 .

Example 2

[00172] Dunaliella salina algae were grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide was transported directly from the atmosphere into the ponds. The algae were harvested by an adsorptive bubble separation process, specifically froth flotation involving column flotation cells. The algal concentrate derived from the column flotation cells was fed directly to a flotation unit with one stage of flotation. The flotation included a single stage of a Jameson column flotation cell with the following design parameters: 25 mm diameter downcomer with a length of 2400 mm, 152 mm diameter cell, 1200 mm cell length, external launder with a width of about 50 mm to receive the froth, a swing-arm was used to control the liquid-froth interface, and a distributor ring was used to introduce the wash water 300 mm below the lip of the launder near the interface between the separation and froth zones. Air was used as the flotation gas. The feed to wash water ratio was 1 .75, the feed to gas ratio was 3.5, and the froth depth was 432 mm. The concentration of algae in the feed was 0.1 wt%, the concentration of algae in the froth was 0.9 wt%, and no algae was detected in the tails. The salt concentration in the froth was reduced by 35% relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 158 and the mass ratio of salt to algae in the froth was 11 .

Example 3

[00173] Dunaliella salina algae were grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide was transported directly from the atmosphere into the ponds. The algae were harvested by an adsorptive bubble separation process, specifically froth flotation involving column flotation cells. The algal concentrate derived from the column flotation cells was fed directly to a fractional flotation unit including one stage of flotation. The fractional flotation included a single stage of a Jameson column flotation cell with the following design parameters: 25 mm diameter downcomer with a length of 2400 mm, 152 mm diameter cell, 1200 mm cell length, external launder with a width of about 50 mm to receive the froth, a swing-arm was used to control the liquid-froth interface, and a distributor ring was used to introduce the freshwater 300 mm below the lip of the launder. Air was used as the flotation gas. The feed to wash water ratio was 3.5, the feed to gas ratio was 3.5, and the froth depth was 397 mm. The concentration of algae in the feed was 0.1 wt%, the concentration of algae in the froth was 1.7 wt%, and no algae was detected in the tails. The salt concentration in the froth was reduced by 29% relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 155 and the mass ratio of salt to algae in the froth was 7.

Example 4

[00174] Dunaliella salina algae were grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide was transported directly from the atmosphere into the ponds. The algae were harvested by an adsorptive bubble separation process, specifically froth flotation involving column flotation cells. The algal concentrate derived from the column flotation cells was fed directly to a fractional flotation unit including one stage of flotation. The fractional flotation included a single stage of a Jameson column flotation cell with the following design parameters: 25 mm diameter downcomer with a length of 2400 mm, 152 mm diameter cell, 1200 mm cell length, external launder with a width of about 50 mm to receive the froth, a swing-arm was used to control the liquid-froth interface, and a distributor ring was used to introduce the freshwater 300 mm below the lip of the launder. Air was used as the flotation gas. The feed to wash water ratio was 3.5, the feed to gas ratio was 3.3, and the froth depth was 356 mm. The concentration of algae in the feed was 0.1 wt%, the concentration of algae in the froth was 2.3 wt%, and no algae was detected in the tails. The salt concentration in the froth was reduced by 31 % relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 153 and the mass ratio of salt to algae in the froth was 5.

Example 5

[00175] Dunaliella salina algae were grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide was transported directly from the atmosphere into the ponds. The algae were harvested by an adsorptive bubble separation process, specifically froth flotation involving column flotation cells. The algal concentrate derived from the column flotation cells was fed directly to a fractional flotation unit including one stage of flotation. The fractional flotation included a single stage of a Jameson column flotation cell with the following design parameters: 25 mm diameter downcomer with a length of 2400 mm, 152 mm diameter cell, 1200 mm cell length, external launder with a width of about 50 mm to receive the froth, a swing-arm was used to control the liquid-froth interface, and a distributer ring was used to introduce the fresh water 300 mm below the lip of the launder. Air was used as the flotation gas. The feed to wash water ratio was 7.0, the feed to gas ratio was 3.3, and the froth depth was 356 mm. The concentration of algae in the feed was 0.1 wt%, the concentration of algae in the froth was 2.1 wt%, and no algae was detected in the tails. The salt concentration in the froth was reduced by 24% relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 153 and the mass ratio of salt to algae in the froth was 6. Example 6

[00176] Dunaliella salina algae were grown in open ponds with nitrogen and phosphorus fertilizers added. Carbon dioxide was transported directly from the atmosphere into the ponds. The algae were harvested by an adsorptive bubble separation process, specifically froth flotation involving column flotation cells. The algal concentrate derived from the column flotation cells was fed directly to a fractional flotation unit including one stage of flotation. The fractional flotation included a single stage of a Jameson column flotation cell with the following design parameters: 25 mm diameter downcomer with a length of 2400 mm, 152 mm diameter cell, 1200 mm cell length, external launder with a width of about 50 mm to receive the froth, a swing-arm was used to control the liquid-froth interface, and a distributor ring was used to introduce the fresh water 300 mm below the lip of the launder. Air was used as the flotation gas. The feed to wash water ratio was 1 .9, the feed to gas ratio was 1 .87, and the froth depth was 432 mm. The concentration of algae in the feed was 0.1 wt%, the concentration of algae in the froth was 2.0 wt%, and no algae was detected in the tails. The salt concentration in the froth was reduced by 50% relative to the salt concentration in the feed. The mass ratio of salt to algae in the feed was 151 and the mass ratio of salt to algae in the froth was 4.

[00177] All references cited herein are hereby incorporated by reference in their entireties.

[00178] It will be appreciated by those of ordinary skill in the art that the present disclosure can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The spirit and scope of the disclosure is set forth in the appended claims, and all changes that come within the meaning, range, and equivalence thereof are intended to be embraced therein.

Claims

1. A process for removal of salt from a froth, wherein the froth contains an algal biomass and a salt-containing solution, the process comprising:

(a) supplying a wash liquid to an interface between the froth and a liquid phase to generate a froth stream and a tails stream, wherein the froth stream contains the algal biomass and a reduced amount of salt relative to the froth, and

(b) recovering the froth stream from (a).

2. The process of claim 1 , wherein a ratio of densities of the wash liquid to the saltcontaining solution is less than unity.

3. The process of claim 1 or 2, wherein the froth comprises bubbles with the salt-containing solution, and algal cells or parts thereof are adsorbed to surfaces of the bubbles.

4. The process of any of the previous claims, wherein the process is an adsorptive bubble separation process.

5. The process of any of the previous claims, wherein (a) to (b) are repeated.

6. The process of any of the previous claims, wherein the process further comprises recycling at least a portion of the tails stream from (a).

7. The process of any of the previous claims, wherein the process is a continuous process, and the process comprises continuously supplying fresh algal biomass and salt-containing solution, such as a feed comprising an algal biomass and a salt-containing solution, while removing at least a portion of the froth stream and/or tails stream optionally so as to keep a total volume of the algal biomass and the salt-containing solution substantially constant.

8. The process of any of the previous claims, wherein the algal biomass comprises:

(i) an algal biomass derived from one or more of Amphora sp., Anabaena sp., Anabaena flos-aquae, Ankistrodesmus falcatus, Arthrospira sp., Arthrospira (Spirulina) obliquus, Arthrospira (Spirulina) platensis, Botryococcus braunii, Ceramium sp., Chaetoceros gracilis, Chlamydomonas sp., Chlamydomonas Mexicana, Chlamydomonas reinhardtii, Chlorella sp., Chlorella fuscam, Chlorella protothecoides, Chlorella pyrenoidosa, Chlorella stigmataphora, Chlorella vulgaris, Chlorella zofingiensis, Chlorococcum citriforme, Chlorococcum littorale, Closterium sp., Coccolithus huxleyi, Cosmarium sp., Crypthecoddinium cohnii, Cryptomonas sp., Cyclotella cryptica, Cyclotella nana, Dunaliella sp., Dunaliella bardawil, Dunaliella salina, Dunaliella kone, Dunaliella tertiolecta, Dunaliella, viridis, Euglena gracilis, Fragilaria, Fragilaria sublinearis, Gracilaria, Haematococcus pluvialis, Hantzschia, Isochrysis galbana, Microcystis sp., Monochrysis lutheri, Muriellopsis sp., Nannochloris sp., Nannochloropsis sp., Nannochloropsis salina, Navicula sp., Navicula saprophila, Neochloris oleoabundans, Neospongiococcum gelatinosum, Nitzschia laevis, Nitzschia alba, Nitzschia ommunis, Nitzschia paleacea, Nitzschia closterium, Nitzschia palea, Nostoc commune, Nostoc flagellaforme, Pavlova gyrens, Peridinium, Phaeodactylum tricornutum, Pleurochrysis carterae, Porphyra sp., Porphyridium aerugineum, Porphyridium cruentum, Prymnesium, Prymnesium paruum, Pseudochoricystis ellipsoidea, Rhodomonas sp., Scenedesmus sp., Scenedesmus braziliensis, Scenedesmus obliquus, Scenedesmus quadricauda, Scenedesmus acutus, Scenedesmus dimorphus, Schizochytrium sp., Scytonema, Skeletonema costatum, Spirogyra, Schiochytrium limacinum, Stichococcus bacillaris, Synechoccus, Tetraselmis sp., Tolypothrix sp., a genetically-engineered variety of any of the above, and/or a combination of two or more of the above species;

(ii) a microalgal species of Amphora sp., Ankistrodesmus, Arthrospira (Spirulina) plantesis, Botryococcus braunii, Chlamydomonas sp., Chlamydomonas reinhardtii, Chlorella protothecoides, Chlorella sp., Closterium sp., Cosmarium sp., Crypthecoddinium cohnii, Cyclotella sp., Dunaliella salina, Dunaliella tertiolecta, Haematococcus pluvialis, Hantzschia sp., Nannochloris sp., Nannochloropsis sp., Navicula sp., Neochloris oleoabundans, Nitzschia sp., Phaeodactylum tricornutum, Scenedesmus sp., Schiochytrium limacinum, Stichococcus sp., Tetraselmis suecica, Thalassiosira pseudonana, a genetically-engineered variety of any of the above, and/or a combination of two or more of the above species; (iii) an algal biomass derived from algae capable of phototaxis; and/or

(iv) an algal biomass derived from Dunaliella.

9. The process of any of the previous claims, comprising:

- recovering the tails stream, and/or

- removing the tails stream through an outlet or by recycling.

10. The process of any of the previous claims, comprising separating the algal biomass from the froth stream or extracting the algal biomass from the froth stream using a liquid or an extraction solvent.

11 . The process of any of the previous claims, comprising extracting at least part of lipids from the algal biomass after removal of salt from the froth.

12. The process of any of the previous claims, wherein

- a salt concentration of the salt-containing solution of the froth and/or a salt concentration of the liquid phase is at least about 5 wt%, at least about 6 wt%, at least about 7 wt%, at least about 8 wt%, at least about 9 wt%, at least about 10 wt%, at least about 11 wt%, at least about 12 wt%, at least about 13 wt%, at least about 14 wt%, at least about 15 wt%, at least about 16 wt%, at least about 17 wt%, at least about 18 wt%, at least about 19 wt%, at least about 20 wt%, at least about 21 wt%, at least about 22 wt%, at least about 23 wt%, at least about 24 wt%, or at least about 25 wt%; and/or

- the ratio of the salt concentration in the salt-containing solution of the froth stream to the salt concentration of the tails stream is less than 1.0, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, less than 0.2, less than 0.1 , or less than 0.05.

13. The process of any of the previous claims, wherein the process comprises feeding an algal biomass feed containing an algal biomass and a salt-containing solution to the process.

14. The process of claim 13, wherein the algal biomass feed comprises an algal cell concentration of about 2,000 to millions of cells per milliliter of the algal biomass feed.

15. The process of claim 13 or 14, wherein the algal biomass feed comprises carotenoids in a concentration of less than about 10,000 ppm.

16. The process of any of the previous claims, wherein the salt in the salt-containing solution comprises sodium chloride, sodium carbonate, magnesium chloride or a combination of two or more of the above.

17. The process of any of the previous claims, wherein the salt-containing solution is a brine solution.

18. The process of any of the previous claims, wherein the wash liquid is fresh water.

19. The process of any of claims 13-18, wherein a ratio of the algal biomass feed to the wash liquid is at least about 1 by volume.

20. A system for treating a froth containing an algal biomass and a salt-containing solution, the system comprising:

- a collection zone;

- a bubble generation zone;

- a separation zone;

- a froth zone;

- a wash interface zone between the separation zone and the froth zone;

- an optional launder; and

- an optional wash liquid supplying unit, optionally in communication with a wash liquid reservoir;

- the bubble generation zone being configured to interact with or being in communication with the collection zone,

- the collection zone being in communication with the separation zone, and

- optionally the wash liquid supplying unit being in communication with the wash interface zone.

21. The system of claim 20, wherein the wash liquid supplying unit is in communication with the wash interface zone.

22. The system of claim 20 or 21 , wherein the separation zone is in communication with an exit for a tails stream.

23. The system of any of claims 20-22, wherein the froth zone is in communication with an exit for a froth stream and/or with the launder.

24. The system of any of claims 20-23, wherein the system is a continuous system.

25. The system of any of claims 20-24, wherein the system is for an adsorptive bubble separation process or for the process of any of claims 1-19.

26. The system of any of claims 20-25, wherein the system is for removal of salt from a froth containing an algal biomass and a salt-containing solution; or the system comprises a froth including an algal biomass and a salt-containing solution.

27. The system of any of claims 20-26, wherein the wash liquid supplying unit is configured for supplying the wash liquid to an interface zone between a froth and a liquid phase.

28. Use of the system of any of claims 20-27 for removal of salt from a froth containing an algal biomass and a salt-containing solution.