Method for flocculating algae using polymers including tannin

1. A method for pretreating water comprising dispersed algae in an algae biofuel production system, the method comprising:

adding to the water from about 50 ppm to about 100 ppm of a polymer including tannin;

mixing the water at 30 rpm to promote complexing between the polymer including tannin and the dispersed algae within a plurality of dispersed algae cells to form flocculated aggregates for harvesting, wherein the polymer including tannin comprises a copolymer of tannin and a cationic monomer; and

separating the flocculated aggregates from the water.

2. The method of claim 1 , wherein the cationic monomer is selected from the group consisting of diallyldimethyl ammonium chloride, diallyldiethyl ammonium chloride, methyl chloride or dimethyl sulfate quaternary salt of diethylaminoethyl acrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, and mixtures thereof.

3. The method of claim 1 , wherein the polymer including tannin further comprises at least one monomer selected from the group consisting of an anionic monomer and a nonionic monomer, and mixtures thereof.

4. The method of claim 3 , wherein the polymer including tannin further comprises a nonionic monomer, wherein the nonionic monomer is selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide, N,N-dimethyl-acrylamide; vinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, allyl glycidyl ether, ethoxylated allyl ether of polyethylene glycol, and polypropylene glycol, and mixtures thereof.

5. The method of claim 3 , wherein the polymer including tannin further comprises an anionic monomer, wherein the anionic monomer is selected from the group consisting of acrylic acid, methacrylic acid, vinyl acetic acid, itaconic acid, maleic acid, allylacetic acid, styrene sulfonic acid, 2-acrylamido-2-methyl propane sulfonic acid and 3-allyloxy-2-hydroxypropane sulfonic acid, and mixtures thereof.

6. The method of claim 1 , wherein the weight percent of the tannin is from about 20% to about 80% and the weight percent of the cationic monomer is from about 80% to about 20% of the polymer including tannin.

7. The method of claim 1 , wherein the weight percent of the tannin is from about 30% to about 50% and the weight percent of the cationic monomer is from about 70% to about 50% of the polymer including tannin.

8. The method of claim 1 , wherein separating the flocculated aggregates from the water comprises performing filtration.

9. The method of claim 1 , wherein separating the flocculated aggregates from the water comprises performing gravity sedimentation.

10. The method of claim 1 , wherein said complexing reduces said dispersed algae by at least 95%.

11. A method for pretreating water comprising dispersed algae in an algae biofuel production system, the method comprising:

adding to the water from about 50 ppm to about 100 ppm of a polymer including tannin, wherein said polymer including tannin comprises 50% tannin and 50% acryloyloxyethyltrimethyl ammonium chloride (AETAC);

mixing the water to promote complexing between the polymer including tannin and the dispersed algae within a plurality of dispersed algae cells to form flocculated aggregates for harvesting, wherein said complexing reduces said dispersed algae by at least 95%; and

separating the flocculated aggregates from the water, wherein said separating the flocculated aggregates from the water comprises performing filtration or gravity sedimentation.

12. A method for pretreating water comprising dispersed algae in an algae biofuel production system, the method comprising:

adding to the water from about 50 ppm to about 100 ppm of a polymer including tannin, wherein said polymer including tannin comprises 30% tannin and 70% acryloyloxyethyltrimethyl ammonium chloride (AETAC);

mixing the water to promote complexing between the polymer including tannin and the dispersed algae within a plurality of dispersed algae cells to form flocculated aggregates for harvesting, wherein said complexing reduces said dispersed algae by at least 95%; and

separating the flocculated aggregates from the water, wherein said separating the flocculated aggregates from the water comprises performing filtration or gravity sedimentation.