Methods for harvesting microalgae

Abstract

Methods for harvesting microalgae, comprise providing water containing microalgae, providing flocculant in an amount to form flocs of microalgae when mixed with the water, generating a mixture of the water and the flocculant and separating the flocs from the mixture.

1 . A method for harvesting microalgae, the method comprising
 providing water comprising microalgae,   wherein the water has a pH between about 6.0 and about 10.0 and has a salinity between about 0.01% and about 5%;   providing flocculant in an amount sufficient to form flocs of microalgae when mixed with the water;   generating a mixture of the water and the flocculant, wherein the mixture is acidic; and   separating the flocs from the mixture, thereby harvesting the microalgae.   
     
     
         2 . The method of  claim 1 , wherein the water has a pH between about 8.0 and about 9.0. 
     
     
         3 . The method of  claim 1 , wherein the water has a salinity of about 2.2%. 
     
     
         4 . The method of  claim 1 , wherein the water comprises sodium hydrogen carbonate at a concentration between about 0.01 g/L and about 0.5 g/L. 
     
     
         5 . The method of  claim 4 , wherein the water comprises sodium hydrogen carbonate at a concentration between about 0.1 g/L and about 0.2 g/L. 
     
     
         6 . The method of  claim 1 , wherein the water is at a temperature between about 10° C. and about 38° C. 
     
     
         7 . The method of  claim 1 , wherein the flocculant is chitosan. 
     
     
         8 . The method of  claim 1 , wherein the flocculant is a polysaccharide that forms cationic polyelectrolytes to precipitate the microalgae. 
     
     
         9 . The method of  claim 7 , wherein the chitosan is provided at a concentration between about 0.08% and about 3.5% of the weight of the microalgae in the mixture. 
     
     
         10 . The method of  claim 7 , wherein the chitosan is provided at about 2% of the weight of the microalgae in the mixture. 
     
     
         11 . The method of  claim 1 , wherein the method comprises adding flue gas or wherein the water is mixed with flue gas. 
     
     
         12 . The method of  claim 11 , wherein the flue gas comprises carbon dioxide. 
     
     
         13 . The method of  claim 11 , wherein the flue gas has less than 5 ppm of sulfur oxide. 
     
     
         14 . The method of  claim 11 , wherein the flue gas comprises carbon dioxide at a concentration between about 4% and about 20%. 
     
     
         15 . The method of  claim 11 , wherein the flue gas comprises carbon dioxide at a concentration between about 10% and about 14%. 
     
     
         16 . The method of  claim 1 , wherein the mixture has a pH between about 4.5 and about 6.5. 
     
     
         17 . The method of  claim 16 , wherein the mixture has a pH of about 5.5. 
     
     
         18 . The method of  claim 1 , wherein the microalgae can produce eicosapentaenoic acid (EPA) at temperatures above 32° C. 
     
     
         19 . The method of  claim 1 , wherein the microalgae is Nannochloropsis. 
     
     
         20 . A method for preparing a crude microalgal extract, the method comprising
 providing water comprising microalgae,   wherein the water has a pH between about 6.0 and about 10.0 and has a salinity between about 0.01% and about 5%;   providing flocculant in an amount sufficient to form flocs of microalgae when mixed with the water;   generating a mixture of the water and the flocculant, wherein the mixture is acidic; and   separating the flocs from the mixture, thereby preparing a crude microalgal extract.   
     
     
         21 . A method for preparing a microalgal lipid extract, the method comprising
 providing water comprising microalgae,   wherein the water has a pH between about 6.0 and about 10.0 and has a salinity between about 0.01% and about 5%;   providing flocculant in an amount sufficient to form flocs of microalgae when mixed with the water;   generating a mixture of the water and the flocculant, wherein the mixture is acidic;   separating the flocs from the mixture, thereby harvesting the microalgae; and   extracting lipid from the microalgae, thereby preparing a microalgal lipid extract.