Adsorptive bubble separation methods and systems for dewatering suspensions of microalgae and extracting components therefrom

A process for dewatering an aqueous suspension of microalgae comprising the steps of:

• a) obtaining an aqueous suspension of the algae from a source thereof;
• b) rupturing the algal cells sufficiently to promote adsorptive bubble separation of the cells from the aqueous suspension;
• c) dispersing a gas into fine bubbles for contact with the aqueous suspension;
• d) intimately contacting fine bubbles with the aqueous suspension;
• e) adsorbing the algae onto the surfaces of bubbles to form bubble and alga agglomerates having a different density from that of the aqueous suspension;
• and
• f) separating the bubble and alga agglomerates from the aqueous suspension to obtain a dewatered algal concentrate;
• and
• g) mechanically filtering the ruptured algal cells prior to dispersion step c) and/or after separation step f).

A process for dewatering an aqueous suspension of the alga Dunaliella salina in brine comprising the steps of:

• a) obtaining a suspension of D. salina cells from a source thereof;
• b) rupturing the D. salina cells sufficiently to promote adsorptive bubble separation of the algae from the brine;
• c) dispersing a gas into fine bubbles for contact with the brine;
• d) intimately contacting fine bubbles with the brine;
• e) adsorbing the algae onto the surfaces of bubbles to form bubble and alga agglomerates having a different density from that of the brine;
• and
• f) separating the bubble and alga agglomerates from the brine to obtain a dewatered D. salina concentrate;
• and
• g) mechanically filtering the ruptured algal cells prior to dispersion step c) and/or after separation step f).

A process for recovering mixed carotenoids from a suspension of the alga Dunaliella salina in brine comprising the steps of:

• a) obtaining a suspension of D. salina from a source thereof;
• b) rupturing at least a portion of the D. salina cells by circulating the brine through a constriction in a pump loop at a pressure drop of from about 50 to 200 psig and a percent recycle of from about 100 to 300 percent;
• c) treating the brine from step b) in a froth flotation circuit to produce an algal concentrate;
• d) passing the algal concentrate across a cross flow microfiltration membrane to produce a permeate stream of brine depleted in algae and a retentate stream having an extractable concentration of algae;
• e) contacting the extractable concentration of algae with a dense gas;
• f) extracting mixed carotenoids into the dense gas;
• and
• g) recovering the mixed carotenoids from the dense gas.