Which Flocculant/Coagulant is ideal for harvesting Algae?

While dealing with Algae fit for human consumption (as protein supplements), which is the most suitable coagulant/Flocculant available? 


Factors to consider:


1) Cost Effectiveness (for instance poly glu cost is prohibitive for commercial scale)


2) pH range (If growth medium of algae is alkaline, many coagulants don't work)


3) Suitable for Vegans (Since food grade Algae is often marketed as Vegan food, using Chitosan is not an option)


4) Metallic salts are needed in high doses and are not preferred in general


With these factors in mind, which coagulant/flocculant would be best for harvesting Algae?


