Fast, low energy, and continuous biofuel extraction from microalgae

April 28, 2017
a) This is a colony full of cells (red) with polysaccharides (yellow) and hydrocarbons (green) leaving the colony (x20); b) parts of colony tightly packed together (x60); c) colony full of cells (red) with dichotomial ramification of polysaccharides (yellow) and hydrocarbons leaving the colony (green) (x100); d) Single cell (x100 and numerically magnified).(Adapted from Guionet, A., Hosseini, B., Teissie, J., Akiyama, H., & Hosseini, H. (2017). A new mechanism for efficient hydrocarbon electro-extraction from Botryococcus braunii. Biotechnology for Biofuels, 10(1), 39. DOI: 10.1186/s13068-017-0724-1) Credit: Professor Hamid Hosseini

As an alternative to liquid fossil fuels, biodiesel extracted from microalgae is an increasingly important part of the bioenergy field. While it releases a similar amount of CO2 as petroleum when burned, the CO2 released from biodiesel is that which has recently been removed from the atmosphere via photosynthesis meaning that it does not contribute to an increase of the greenhouse gas. Furthermore, research has shown that microalgae produces a much higher percentage of their biomass to usable oil in a significantly smaller land mass than terrestrial crops. Currently, one of the largest obstacles in replacing diesel with biodiesel is the cost of production. Fossil fuels are still cheaper than biofuels so improvements in production efficiency are highly sought-after.

Recently, efforts have been made by researchers in Japan to reduce the cost of biodiesel production by using pulsed electric fields (PEF) to extract hydrocarbons from . A milli- or microsecond PEF is typically used to weaken cell walls and increase permeability allowing for extraction of elements inside the cell. Kumamoto University researchers, on the other hand, used a nanosecond PEF (nsPEF) to focus on the microalgae matrix instead of the cells. A nsPEF generally uses less energy than the μs/msPEFs even at high voltages, and is not as destructive or costly as the traditional drying method of oil extraction.

The researchers performed several tests with the nsPEF on the microalgae Botryococcus braunii (Bb) to determine the optimal electric field, energy, and pulse repetition frequency for extraction. Interestingly, it was found that doubling the energy only resulted in a 10% increase in . At 10 Hz, the optimal field and energy conditions were determined to be approximately 50 kV/cm and 55.6 J/ml respectively per volume of algae. Further, the researchers found that pulse frequency had little to no effect on extraction percentage, meaning that a large amount of hydrocarbons may be extracted quickly for large/industrial systems.

"The advantage with this extraction mechanism is that it separates hydrocarbons from a matrix, rather than extracts them from cells. Other microalgae do not secrete a matrix so the cell membranes must be damaged or destroyed to get at the hydrocarbons, which both takes more energy and is less efficient than our method," said lead researcher, Professor Hamid Hosseini of the Institute of Pulsed Power Science at Kumamoto University. "On top of that, many extraction processes practiced today use a drying method to extract oil which ends in the destruction of the algae. Our method is relatively non-destructive and the microalgae are able to rebuild their colonies after extraction has finished."

One minor drawback is the impurity of the matrix; polysaccharides must be purified from the extracted hydrocarbon solution. Fortunately, these molecules may be used in the creation of bioethanol but their concentration is low.

It is hoped that this technology will improve biofuel production as an appropriate green source.

This work may be found in the online BioMed Central journal, Biotechnology for Biofuels.

Explore further: Microalgae have great potential as fish feed ingredient

More information: Alexis Guionet et al, A new mechanism for efficient hydrocarbon electro-extraction from Botryococcus braunii, Biotechnology for Biofuels (2017). DOI: 10.1186/s13068-017-0724-1

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Dug
1 / 5 (2) Apr 28, 2017
The unfortunate self-annihilating economics of biofuels is that any at scale - they compete with food production. While using wastes to generate biofuels seems like a good idea, the logistical costs of getting the wastes and the biofuels in useful proximity have been economic non-starters to date. Additionally, production costs aren't the major hurdles in biofuels and as the article only hints at - its the processing of raw biofuel crop yields into usable, storable, stable fuels that are the big energy/economic hurdle. From an alternative energy standpoint the continued development of biofuel technology is a waste of research money in that basic biology and physics hurdles (if not the Laws of Thermodynamics) - their EROIs are going to be extremely expensive and difficult/improbable to change. We should focus research on energy sources with potential of filling with both the economic and capacity (EROI) of our future needs - i.e. fusion.

dnatwork
5 / 5 (3) Apr 28, 2017
If you are producing waste anyway, and you have to process that or store it anyway, then extracting energy from it comes at very little extra cost. Also, the areas where you would put a waste processing plant, if your model is aqueous processing with algae, would not compete with those for food production.
EyeNStein
not rated yet Apr 28, 2017
Taking CO₂ from the atmosphere to make fuel for the remaining gas guzzling vehicles, and produced by algae powered by sunlight has to be an important transitional technology.

Turning Diesel vehicles into renewable fuelled vehicles, in the medium term future, is a great win if they can scale this process without competing with food growing land or solar power sites.
EmceeSquared
5 / 5 (1) Apr 29, 2017
How does culivating biofuel algae in large shallow lakes where there's bad soil compete with food production? Any more than any investment or activity competes with food production?

Dug:
The unfortunate

EyeNStein
not rated yet Apr 30, 2017
We are talking very large scale farming of the algae for this to be an effective supplement to bio-diesel. I must admit I was envisaging stirred ponds with solar concentrator mirrors, not natural lakes deliberately fed with algae nutrients.
I doubt that natural lakes could be constrained to the monoculture of a specific algae to keep the yield up and protein sludge content down.

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