(443b) Membrane Filtration of Algae

Microalgae are unicellular organisms that offer a promising source of sustainable energy and specialty products. Hundreds of thousands of diverse species exist, but only a few are produced commercially today, primarily for high-value products. Today, algae are increasingly investigated for their ability to locally produce non-fossil-derived liquid fuels, without impinging on food supplies. However, algae cultures are quite dilute (<1 g/L), and energy-intensive processing methods—for instance, centrifugation—create a major bottleneck to sustainable algae production.

Conventional routes may need to be re-envisioned to sustainably replace a significant portion of our current fossil fuel usage with fuels from algae. One alternative is to continuously “milk” cells that produce extracellular fuel precursors. This approach could lower process energy (since cell disruption and drying are bypassed) and decrease fertilizer inputs (since cells are kept alive). The separation scheme for the proposed process incorporates submerged microfiltration membranes to selectively remove product-containing growth media from the algae cells.

Membrane filtration of algae could provide a lower-energy solution to the dewatering challenge, but has largely been avoided due to a high propensity for cells and secreted material to “foul” the membrane. The present work investigates the properties of thin layers of algae cells deposited on the membrane, and the factors that control the variable cake resistance for different species. Specifically, we are interested in how the suspension composition—including cells and secreted material—controls the rate and reversibility of membrane fouling. Improved understanding of the effect of algae suspension composition on membrane fouling will guide the system design in terms of local hydrodynamics and sub-critical flux operation, with the goals of reducing flux decline and minimizing the energetic burden of algae dewatering.