Biomass from microalgae could play a key role in relieving climate warming – microalgae are fast-growing, photosynthetic microorganisms that convert light and carbon dioxide into energy-rich biomolecules with minimal nutrient requirements. When microalgae are grown and harvested on an industrial scale, they can be converted into a wide array of products for food, feed, fuel, organic pigments, pharmaceuticals and chemical applications. This approach is analogous to the refinery of crude oil, where a range of products is manufactured from a single feedstock to optimise value. Despite their potential, the large-volume production and commercial viability of algae-derived products are currently limited by the high cost of harvesting, extraction and purification. Step changes in the processing of algal biomass are therefore essential in developing the full potential of algae.
Combining multiple unit operations into a single process
The EU-funded CMHAlgae project set out to overcome these hurdles by “developing multifunctional nanomaterials that combine multiple unit operations in downstream processing into a single technology,” notes project coordinator Praveen Ramasamy. These operations include harvesting, dewatering and cell disruption. Harvesting and dewatering of biomass is challenging because of the small size of microalgal cells (around 5 µm), and the stable suspension and relatively low biomass concentration in the culture medium (around 0.5 g/L). Furthermore, the presence of a rigid cell-wall surrounding microalgae complicates cell disruption. Over the past decade, nanomaterials have been introduced to solve these problems in microalgae downstream processing. However, as Praveen explains, “the majority of them focus on improving a single unit operation comparing to a benchmark, which would result in a more complex and costly overall process.” In this context, multifunctional nanomaterials could make a real impact – they could reduce the cost and environmental burden of microalgae downstream processing in microalgae biorefineries.
Novel hybrid nanomaterials based on cellulose
The project integrated several promising recent breakthroughs in nanotechnology to produce cellulosic magnetic hybrid nanomaterials. These nanomaterials can be used to harvest and disrupt the cells of microalgae in a single step, and to rapidly separate cells from the culture medium using an external magnetic field. First, researchers functionalised cellulose nanocrystals with imidazolium and pyridinium that combine flocculating and cell-disrupting activities. Flocculation is the process by which fine particulates aggregate together, while cell disruption is the process of breaking the cell wall to aid releasing biological molecules from inside a cell. The functionalised cellulose nanocrystals were then linked to iron oxide nanoparticles that allowed rapid separation of the biomass from the culture medium. Ultimately, researchers demonstrated the harvesting and cell disruption efficiencies of the hybrid nanomaterials in both freshwater and marine microalgal model systems.
Seeking to share its results, the project has been presented at several research meetings and conferences. The project was also presented to the Leuven Children's University in Belgium in 2017. The two research articles that were published online can be found in Algal Research and also in the same journal. Furthermore, a manuscript is under review for publication in Chemical Engineering Journal.
CMHAlgae, microalgae, biomass, harvesting, cell disruption, multifunctional nanomaterials, dewatering, hybrid nanomaterials, cellulose nanocrystals