Surface modification of Chlorella vulgaris cells using magnetite particles

Expensive cell concentration procedures represent one of the bottlenecks of large-scale microalgal biotechnological processes as many industrially attractive species have a small cell size and sustain in suspension. An economically effective solution is to alter the process conditions for the cells to form aggregates, which sediment faster. The use of magnetic agents binding to the cell surface and forming larger complexes, that sediment very fast upon application of an external magnetic field, is a rarely explored possibility in this area. We used commercially available, finely pulverized magnetite (Sigma Aldrich) as a potential harvesting agent and studied its surface interactions with an industrially important microalgal strain (Chlorella vulgaris). Firstly, we characterized the interacting surfaces in model environments by zeta potential and contact angle measurements, which were followed by particle size determination. Secondly, we applied the XDLVO theory to predict favorable experimental conditions for a successful magnetic cell modification, which would lead to an effective biomass separation. The hypotheses were then tested by using various ratios of magnetic agent and microalgal biomass under different environmental conditions. Obtained results were in good accordance with the predictions and we achieved an excellent separation efficiency of over 90% within a few minutes at a ratio of microalgae to magnetite 1: 26 (w/w). We can conclude that magnetite successfully modifies the microalgal surface under certain conditions and is a promising agent for harvesting C. vulgaris, enabling high separation efficiencies in a very short period of time, but further research is necessary to optimize the process. (C) 2012 Published by Elsevier Ltd.