Background: Mass cultivation of algae for biofuel production has focused on the use of open ponds or closed bioreactors. Both approaches depend upon routine liquid culturing of the algae and require the removal of large quantities of water at the time of cell harvesting and subsequent extraction of desired products. This invention proposes the use of porous inert membranes to support the growth and subsequent harvesting of the algae. Moisture and nutrients required for growth are provided by misting of the membrane from above or percolation of an aqueous nutrient medium through a semisolid basement layer in contact with the membrane. Algal cells can be harvested from the membrane surface by scraping or lifting the cells using an industrial sized \"squeegee\"". Technology Description: Oil accumulation in algae often is triggered by environmental stress e.g. high salinity or nitrogen starvation. In this invention the algal cells are grown to the desired cell density on the membrane surface by providing all essential nutrients in a misting or percolating medium. Environmental stress is then induced by moving the membrane with adherent cells to a new basement layer that induces the appropriate stress response or by changing the misting or percolating solution. After cell harvesting the membrane with residual cells can be moistened with complete medium (via misting or percolation) to induce a new round of growth and subsequent stress induction. Applications: Microalgae grown at commercial scale can provide commodity products inclluding bio-fuels through lipid esterification nutraceuticals such as beta carotene and astaxanthin and poly-unsaturated fatty acids including omega-3 and omega-6 dietary supplements."
Algal growth on membrane dramatically decreases water consumption and alleviates a dewatering step. This method makes it easier to induce stress on algae for lipid production. Removing culture from ponds decreases contamination while increasing control of nutrient feed. A \"squeegee\"" harvest method means thatere is no production-limiting step and the growth membrane can be re-seeded. This eco-friendly approach decreases water consumption."