Method for dewatering microalgae with a bubble column
First Claim
1. A process for dewatering an aqueous suspension of microalgae comprising the steps of:
- (a) obtaining an aqueous suspension of algae from a source thereof;
(b) rupturing the algal cells;
(c) introducing the aqueous suspension into a froth flotation column selected from the group consisting of a Jameson cell and a multi-stage loop flow froth floatation column for downward gravity flow therein;
(d) generating fine bubbles of a gas for establishing a net countercurrent flow through the aqueous suspension in intimate contact with the aqueous suspension;
(e) adsorbing algal cells onto the bubbles to form bubble and alga agglomerates; and
(f) forming a froth of bubble and alga agglomerates.
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Accused Products
Abstract
A process for dewatering an aqueous suspension of microalgae is disclosed in which the aqueous suspension of the algae is introduced into a bubble column or a modified bubble column for generating a froth of bubbles and adsorbed algal cells that can be separated from the aqueous suspension. In one advantageous embodiment, the bubble column is a multi-stage loop-flow flotation column that has three loop-flow zones, each of which is defined by a draft tube concentrically mounted in the column to divide each loop-flow zone into a riser and the downcomer. Fine bubbles of gas and brine are in cocurrent upward flow in the riser and in cocurrent downward flow the downcomer. A higher gas holdup is promoted in the riser than in the downcomer, thereby circulating the brine in loop-flow upwardly through the riser and downwardly through the downcomer. Liquid communication between adjacent loop-flow zones is substantially eliminated. A froth enriched in algae is generated that can be separated from the aqueous suspension. The process has application in the recovery of mixed carotenoids from Dunaliella salina.
86 Citations
34 Claims
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1. A process for dewatering an aqueous suspension of microalgae comprising the steps of:
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(a) obtaining an aqueous suspension of algae from a source thereof; (b) rupturing the algal cells; (c) introducing the aqueous suspension into a froth flotation column selected from the group consisting of a Jameson cell and a multi-stage loop flow froth floatation column for downward gravity flow therein; (d) generating fine bubbles of a gas for establishing a net countercurrent flow through the aqueous suspension in intimate contact with the aqueous suspension; (e) adsorbing algal cells onto the bubbles to form bubble and alga agglomerates; and (f) forming a froth of bubble and alga agglomerates. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A process for dewatering the algal Dunaliella salina in brine comprising the steps of:
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(a) obtaining an aqueous suspension of algae from a source thereof; (b) rupturing the algal cells; (c) introducing the aqueous suspension into a froth flotation column selected from the group consisting of a Jameson cell and a multi-stage loop flow froth floatation column for downward gravity flow therein; (d) generating fine bubbles of a gas for establishing a net countercurrent flow through the aqueous suspension in intimate contact with the aqueous suspension; (e) circulating the suspension in a loop-flow within the column to promote intimate contact of fine bubbles and algal cells; (f) adsorbing algal cells onto the bubbles to form bubble and alga agglomerates; and (g) forming a froth of bubble and alga agglomerates. - View Dependent Claims (20, 21, 22, 23)
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24. A process for separating the alga Dunaliella salina from brine for the subsequent recovery of mixed carotenoids from the alga, the process comprising the steps of:
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a) obtaining a suspension of D. salina in brine from a source thereof; b) rupturing the algal cells; c) introducing the brine into a multi-stage loop-flow flotation column for net downward gravity flow therein, the column including at least two loop-flow zones defined by a vertical baffle to divide the column into a riser and a downcomer, wherein the gas and brine are in cocurrent upward flow in the riser and cocurrent downward flow in the downcomer; d) dispersing the gas into fine bubbles by sparging the gas into the riser of the lowermost loop-flow zone for countercurrent flow through the brine; e) promoting a higher gas holdup in the riser than in the downcomer, thereby circulating the brine in loop-flow upwardly through the riser and downwardly through the downcomer; f) diverting gas flow from the riser upwardly, thereby minimizing gas bypass into the downcomer; g) diverting liquid flow from the riser downwardly into downcomer, whereby liquid communication between adjacent loop flow zones is substantially eliminated, whereby the fine bubbles and algal cells are intimately contacted to adsorb the algae onto the surfaces of the bubbles; and h) generating a froth enriched in algae, whereby the algae are separated from the brine. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A process for extracting mixed carotenoids from the alga Dunaliella salina, the process comprising the steps of:
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a) obtaining a suspension of D. salina in brine from a source thereof; b) rupturing the algal cells; c) introducing a feed of the algal suspension into a multi-stage loop-flow flotation column for net downward gravity flow therein, the column including at least two loop-flow zones, each defining a radially inward region and a radially outward annular region; d) sparging a gas in the absence of oxygen into the radially inward region of the lowermost loop-flow zone for net countercurrent flow through the algal suspension at a superficial gas velocity, Jg, of from about 0.1 to 1.0 cm/s and at a gas to feed ratio of from about 0.1 to 1.5; e) promoting a higher gas holdup in the radially inward region than in the annular region, thereby circulating the algal suspension in a loop-flow upwardly through the radially inward region and downwardly through the annular region; f) diverting gas flow from the radially inward region upwardly and radially inwardly, thereby minimizing gas bypass into the annular region; g) diverting liquid flow downwardly and radially outwardly into the annular region, whereby backmixing is substantially eliminated, and the fine bubbles and algal suspension are intimately contacted to adsorb the algae onto the surfaces of the bubbles; h) generating a froth enriched in algae, whereby the algae are separated from the brine; i) collapsing the froth to obtain an algal concentrate; and j) repeating steps c) through i) to provide a concentration of mixed carotenoids having a solids fraction in the froth on a gas-free basis of from about 1 to 17 percent by weight of the gas-free froth.
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Specification