Development of An Extractive Membrane System to Harvest Secreted Fuel Precursors From Algae

Microalgae are often cited as a sustainable source of energy and specialty products due to their ability to fix CO₂ as biomass through photosynthesis. At present, however, the large material and energy inputs required to grow and process the cells using conventional methods make these processes infeasible from both an economic and environmental perspective. In recent years, algal “milking” has been investigated as a more sustainable method to produce fuels and high-value products. Rather than dewater and then break open the cells, these processes continuously harvest secreted products from the cell culture. This approach has the potential to reduce the inputs for nitrogen and phosphorus fertilizers, solvents, and energy to lyse the cells, which are major components of the material and energy inputs to conventional systems.

Our work addresses the separations challenge presented by this complex biological suspension, including: 1) prevention of undesirable colloidal species from accumulating in the growth medium, 2) isolation of the secreted product, and 3) recycle of electrolyte to the growth reactor. In this presentation, we will discuss our progress in developing a membrane-based separation scheme to efficiently address these three challenges, while also improving fundamental understanding of the mechanisms that control transport of the suspension components through various membrane materials. The research has yielded a novel method to reduce bacterial contamination in the growth medium using microfiltration membranes. In addition, we have characterized the transport figures-of-merit of a range of commercial and novel membrane materials for fractionation of small, reduced-carbon fuel precursors from electrolyte. The permeance of water relative to solute is also examined, and we use experimental results to explore possible transport mechanisms that could account account for variation between materials.