Harvesting Nannochloropsis oculata by Flocculation

Abstract

<abstract><title><italic>Abstract.</italic></title> Algal biomass harvesting from dilute suspensions of a culture is challenging. Although a flocculation process is commonly used to separate suspended solids from water, information on the flocculation characteristics of microalgae cells is limited. In this study, the flocculation characteristics of Nannochloropsis oculata (NO) were examined. Chitosan addition, adjustment of the pH of the growth medium, and electroflocculation techniques were examined. Adjustment of the algae growth medium pH to 11 resulted in over 99% flocculation efficiency. Although chitosan addition facilitated cell flocculation at a lower pH (pH 9), the high flocculant requirement is a disadvantage of this process. In general, the efficiency of electroflocculation improved with increasing current, operation time (OT), and settling time (ST), and 97.1% NO cell flocculation efficiency could be obtained at 0.3 A, 3 min OT, and 30 min ST. This study demonstrated that over 90% NO cell flocculation efficiency is achievable by adjusting the pH of the growth medium, chitosan addition, or electroflocculation. The process selection for commercial operations needs to be based on the characteristics of the harvested biomass required for a given application and the environmental impact and economic feasibility of the process.