The subject technology relates generally to devices and methods for isolating microorganisms.
Microorganisms have many commercial applications. Bacteria, fungi, and algae may be used in various applications for the production of pharmaceuticals, food, supplements, and even fuel. For example, algae have applications in pharmaceutical, food, and biofuel production.
Microalgae is a term that may be used to distinguish single-celled, generally microscopic algae from multicellular algae. Algae may be found in fresh as well as salt water environments.
Use of microalgae in commercial applications may depend in part on understanding the biochemical and genetic makeup of microalgae. In addition, commercial application may also require cost-effective methods for handling microalgae. For example, at present microalgae harvesting techniques may limit their successful commercialization in the production of microalgae-based biofuels.
Some characteristics of microalgae may present challenges for their efficient harvest. For example, microalgae are generally small (a few to a few hundred micrometers), with low specific gravity, and a generally negative overall surface charge. In addition, microalgae may grow at low cell densities in water.
Current techniques used in harvesting microalgae may include centrifugation, filtration, flotation, flocculation, and ultrasound sedimentation etc. Each of the present harvesting techniques may have limitations. For example, centrifugation and ultrasound sedimentation may be slow processes with concomitantly high operation costs; filtration may be subject to clogging and shortened run times; flotation may require use of surfactants that may hamper downstream processes; and flocculation may require various chemical additives such as pro-oxidants (to induce liberation of extracellular organic matter), electrolytes (e.g. chitosan), or Al- and Fe-based compounds (to neutralize the surface charge and aid cell-to-cell adhesion). In addition, some of these techniques must be combined for efficient microalgae processing, for example flocculation may also require centrifugation in order to collect slowly-settled microalgae. Chemicals used in some of these (such as flocculation or flotation) may inhibit microalgae growth and may be detrimental for continuous growth-harvest cycled operation.
In some cases, microalgae flocculation has been modeled using theories of colloidal stability. For example, the use of polyelectrolyte-induced flocculation for microalgae harvesting can be understood by DLVO theory of colloidal stability (DLVO stands for Derjaguin, Landau, Verwey and Overbeek who made seminar contribution to the theory. See: R J Hunter, Foundations of Colloid Science, Clarendon Press, Oxford). DLVO theory models flocculation in terms of the interplay between electronic double layer repulsion, van der Waals attraction and entropic depletion interactions.
What is needed is an efficient method of harvesting microorganisms like microalgae, that has little or no adverse impact on downstream processes, and that is low-cost.