Chlorella sp. coagulation‐flocculation by inducing a modification on the pH broth medium

Abstract

Harvesting algae from the culture medium is a major area of R&D as it is one of the greater obstacles for marketing microalgal oil for biodiesel production at competitive costs when compared to vegetable oils. Former investigations of large scale algae harvesting especially examine the removal of freshwater algal populations from wastewater treatment processes using metal salts like ferric chloride or aluminum sulfate were used.These are effective coagulation-­flocculation agents, but, besides of being expensive, their application can be unacceptable if the oil will be used for biodiesel production and the biomass for animal feeding, since the contamination of such products with metals will occur. Indeed, methods based on autoflocculation, biofloculation or even new technologies like electrolytic flotation are promising and could be of very low cost. However, for the moment they require very specific situations and provide significant operating limitations. Chlorella characteristics shown to impact on aggregation and flocculation like size, surface functional groups and surface charge were analyzed. Effectiveness of microalgae flocculation by pH manipulation and ionic strength effects were investigated using the Jar-­test procedure. A relationship between cell surface at different incubation stages and negative zeta potential for a wide range of pH was checked and it was found that algae removal was not significantly affected by ionic strength.