Shear-enhanced membrane filtration of model and real microalgae extracts for lipids recovery in biorefinery context

Lipids and Proteins Differentiation in Membrane Fouling Using Heavy Metal Staining and Electron Microscopy at Cryogenic Temperatures

The detailed characterization of fouling in membranes is essential to understand any observed improvement or reduction on filtration performance. Electron microscopy allows detailed structural characterization, and its combination with labeling techniques, using electron-dense probes, typically allows for the differentiation of biomolecules. Developing specific protocols that allow for differentiation of biomolecules in membrane fouling by electron microscopy is a major challenge due to both as follows: the necessity to preserve the native state of fouled membranes upon real filtration conditions as well as the inability of the electron-dense probes to penetrate the membranes once they have been fouled. In this study, we present the development of a heavy metal staining technique for identification and differentiation of biomolecules in membrane fouling, which is compatible with cryofixation methods. A general contrast enhancement of biomolecules and fouling is achieved. Our observations indicate a strong interaction between biomolecules: A tendency of proteins, both in solution as well as in the fouling, to surround the lipids is observed. Using transmission electron microscopy and scanning electron microscopy at cryogenic conditions, cryo-SEM, in combination with energy-dispersive X-ray spectroscopy, the spatial distribution of proteins and lipids within fouling is shown and the role of proteins in fouling discussed.

Membrane-Based Harvesting Processes for Microalgae and Their Valuable-Related Molecules: A Review

The interest in microalgae production deals with its role as the third generation of feedstock to recover renewable energy. Today, there is a need to analyze the ultimate research and advances in recovering the microalgae biomass from the culture medium. Therefore, this review brings the current research developments (over the last three years) in the field of harvesting microalgae using membrane-based technologies (including microfiltration, ultrafiltration and forward osmosis). Initially, the principles of membrane technologies are given to outline the main parameters influencing their operation. The main strategies adopted by the research community for the harvesting of microalgae using membranes are subsequently addressed, paying particular attention to the novel achievements made for improving filtration performance and alleviating fouling. Moreover, this contribution also gives an overview of the advantages of applying membrane technologies for the efficient extraction of the high added-value compounds in microalgae cells, such as lipids, proteins and carbohydrates, which together with the production of renewable biofuels could boost the development of more sustainable and cost-effective microalgae biorefineries.

The effect on single and combined stresses for biomass and lipid production from Nannochloris atomus using two phase culture system

The optimal conditions for high biomass and lipid production from Nannochloris atomus were evaluated. The parameters used in this study were light emitting diode (LED) wavelength mixing ratio, the photoperiod, salinity tolerance, and single and combined stresses. Biomass production was monitored in the first phase using red LED (625 nm), followed by lipid production by green LED (520 nm) in the second phase. The optimal conditions were obtained using a single red LED with light:dark durations of 20:4 h and two days of exposure in combined stresses of 1.06 M NaCl and green LED. Under these conditions, 68.6 % (w/w) lipid content were obtained. Compared to the non-stress control, the lipid content was increased by 31.9 %. Linolenic acid (C18:3) the omega-3 fatty acid was produced up to 52.4 % in 1.06 M NaCl as a single stress.