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 decreased 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.