METHODS FOR CONCENTRATING MICROALGAE

1 . A method of concentrating single cell microalgae in an aqueous environment, the method comprising:

a) contacting microalgae having an average single cell diameter of less than 20 μm in an aqueous environment with an inorganic flocculant present at a concentration that is less than 10% of the dry biomass of the microalgae, thereby yielding flocculated microalgae in flocs having an average diameter of at least 100 μm; and

b) separating the flocs of microalgae from the aqueous environment, thereby concentrating the microalgae into a slurry with a biomass density of at least 1%.

2 . The method of claim 1 , wherein the inorganic coagulant is present at a concentration of 100 mg/l or less.

3 . The method of claim 1 , wherein the flocculant is present at a concentration between 2 mg/l and 80 mg/l.

4 . The method of claim 1 , wherein the flocculant is present at a concentration between 2 mg/l and 10 mg/l.

5 . The method of claim 1 , wherein the flocculant is an iron flocculant or an aluminum flocculant.

6 . The method of claim 5 , wherein the flocculant is an aluminum flocculant selected from the group consisting of aluminum chloride, aluminum sulfate, polyaluminum chloride, aluminum chlorohydrate, and sodium aluminate.

7 . The method of claim 5 , wherein the flocculant is an iron flocculant selected from the group consisting of ferric chloride, ferric sulfate, and ferrous sulfate.

8 . The method of claim 1 , wherein the flocculant is not algicidal.

9 . The method of claim 1 , wherein the microalgae are in a non-natural body of water.

10 . The method of claim 1 , wherein the microalgae in the aqueous environment are essentially a monoculture.

11 . The method of claim 1 , wherein the flocs of microalgae are separated from the aqueous environment to produce a slurry with a biomass density of 1-10%.

12 . The method of claim 1 , wherein the separating step comprises subjecting the flocculated algae to air flotation.

13 . The method of claim 1 , wherein the separating step comprises subjecting the flocculated algae to sedimentation.

14 . The method of claim 1 , wherein the microalgae has an average single cell diameter of less than 10 μm.

15 . The method of claim 1 , wherein the microalgae has an average single cell diameter of less than 5 μm.

16 . The method of claim 1 , wherein the microalgae is from a microalgal strain selected from the group consisting of Dunaliella, Chlorella, Tetraselmis, Botryococcus, Haematococcus, Phaeodactylum, Skeletonema, Chaetoceros, Isochrysis, Nannochloropsis, Nannochloris, Pavlova, Nitzschia, Pleurochrysis, Chlamydomas and Synechocystis.

17 . The method of claim 16 , wherein the microalgae is Nannochloropsis.

18 . The method of claim 1 , further comprising contacting the microalgae with an organic polymer.

19 . The method of claim 18 , wherein the organic polymer is a cationic or a non-ionic polymer.

20 . The method of claim 18 , wherein the organic polymer is comprised of monomers selected from the group consisting of acrylamide, acrylate, amine or mixtures thereof.

21 . The method of claim 18 , wherein the organic polymer is from a naturally occurring source.

22 . The method of claim 21 , wherein the organic polymer is chitosan or a clay.

23 . The method of claim 18 , wherein the organic polymer is present in a concentration of less than 2% of the weight of the dry biomass.

24 . The method of claim 1 , wherein the aqueous environment is free of sewage.

25 . The method of claim 1 , wherein the aqueous environment is free of polybasic carboxylic acid.

26 . The method of claim 1 , wherein the aqueous environment contains only trace amounts of copper.

27 . The method of claim 1 , wherein the aqueous environment is less than pH 10.

28 . The method of claim 27 , wherein the aqueous environment is between pH 7-9.

29 . The method of claim 27 , wherein the aqueous environment is not externally pH adjusted.

30 . The method of claim 1 , wherein the aqueous environment has a salinity of at least 20 ppt.