Harvesting of freshwater and marine microalgae by common flocculants and magnetic microparticles

Abstract

The aim of this study was to investigate the harvesting of freshwater (Scenedesmus rubescens) and marine microalgae (Dunaliella tertiolecta) using common flocculants and iron oxide magnetic microparticles. Aluminum sulfate, aluminum chloride, and iron (III) chloride were tested as flocculants, while iron oxide magnetic microparticles were prepared by microwave treatment. The algal separation efficiency was evaluated, in the presence of aluminum and iron salts, under various operating conditions (stirring time and intensity, coagulant dose). Aluminum salts, and especially aluminum sulfate, were more efficient than iron chloride on algal removal. Turbidity removal was 99 % at a concentration of aluminum sulfate 1.26 mg Al3+ L−1. FeCl3·6H2O was not effective for freshwater microalgae, and the turbidity removal was 20 and 93 % for S. rubescens and D. tertiolecta, respectively. The algal separation efficiency in the presence of the magnetic microparticles depended on the initial algal and magnetic material concentration. The removal efficiency was ranged between 75 and 91 % for 6.2 and 62 mg L−1 magnetic particles, respectively.