Improving electrocoagulation floatation for harvesting microalgae

Abstract

Electro-coagulation floatation (ECF) is a foam-floatation dewatering method that has been shown to be a highly effective, rapid, and scalable separation methodology. In this manuscript, an in-depth analysis of the gas and flocculant levels observed during the process is provided, with microbubbles observed in the 5–80 μm size range at a concentration of 10 2 –10 3 bubbles mL −1 . Electrolysis of microalgae culture was then observed, demonstrating both effective separation using aluminium electrodes (nine microalgal species tested, 1–40 μm size range, motile and non-motile, marine and freshwater), and sterilisation of culture through bleaching with inert titanium electrodes. Atomic force microscopy was used to visualise floc formation in the presence and absence of algae, showing nanoscale structures on the magnitude of 40–400 nm and entrapped microalgal cells. Improvements to aid industrial biotechnology processing were investigated: protein-doping was found to improve foam stability without inducing cell lysis, and an oxalate buffer wash regime was found to dissolve the flocculant whilst producing no observable difference in the final algal lipid or pigment profiles, leaving the cells viable at the end of the process. ECF separated microalgal culture had an algal biomass loading of 13% and as such was ideal for direct down-stream processing through hydrothermal liquefaction. High bio-crude yields were achieved, though this was reduced slightly on addition of the Al(OH) 3 after ECF, with carbon being distributed away to the aqueous and solid residue phases. The amenability and compatibility of ECF to integration with, or replacement of, existing centrifugation and settling processes suggests this process may be of significant interest to the biotechnology industry.

Biodiesel Production through Acid Catalyst In Situ Reactive Extraction of Chlorella vulgaris Foamate

“…Physical deformation of the microalgae cells was observed under the microscope to continue after treatment with the foam column. Treatment of microalgae with CTAB has previously been observed to significantly enhance cell disruption [40]. Figure 3 shows the effect of methanol/oil mole ratio on reaction temperatures in the range of 30-70 °C on the yield of the FAME.…”

Biological-Based Produced Water Treatment Using Microalgae: Challenges and Efficiency

“…Depending on the extent of the angular velocity, denser suspended solids (i.e., algae) move to the edge while the lighter water moves in the other direction, achieving separation. In the flotation method, air bubbles are introduced into the tank from below, moving upwards and lifting more of the algae with them to the surface to be collected and skimmed [158]. However, sometimes the algae cells are too small to be separated by physical methods, which can be solved by using chemical harvesting methods.…”

The contribution of Atomic Force Microscopy (AFM) in microalgae studies: A review

“…For instance, Landels and co-workers used AFM to image Chlorella sorokiniana cells after harvesting by electro-coagulation flotation with Al(OH)3 used as a metal flocculant. Their results showed cells that were embedded into the Al(OH)3 hydrogel, which allows understanding how cells interact with the flocculant [41].…”