Green fuels

Drilling and drilling, extracting until the last drops warn that no more money will possibly be gained from that same platform. Leaving it as it is, let’s go in search of a new spot full of this resource that humans aliment their vehicles with everyday – fuel. This is the routine that oil companies have been following since 1859, when Edwin Drake devised a method to drill an oil well.

However, as the deposits are getting exhausted, humans have come up with ways to produce and use a different type of fuels, called biofuels. These in fact, do not require the long geological processes to decompose plants and animals to carbon and hydrogen containing molecules. Instead, biofuels like biodiesel can be produced from used cooking oil, soybean, palm and rapeseed oils or microalgae.

Being the vegetable oils used for human purpose and the unsustainable crops cultivation, single-celled eukaryotic microalgae win them all. In fact, most microalgae have high growth rates, meaning that they reach their highest life stage within a few days, converting the sun energy into chemical energy through the absorption of CO2 from the atmosphere and storing it as biomass, and are relatively easy to cultivate. The only necessary points to be checked are light availability and simple nutrients.

But how can these tiny autotrophs make biodiesel? Some microalgal species more than others synthesize and store high concentrations of lipids per cell volume. When the highest lipid accumulation is reached, they are collected and go through different steps of processing through which lipids are separated from other parts of the cell. These long-chain fatty acids then undergo a transesterification process, which consists in an R group of an alcohol being replaced with an R group of an ester by an acidic/alkaline or enzymatic catalyst, with the production of biodiesel.

Transesterification of fatty acids into biodiesel.

The leftover biomass can be further processed into methane, ethanol, natural soil fertilizer high in nitrogen and phosphorus or even livestock feed. In addition, some species such as Dunaliella salina – a halophyte algae – not only accumulates high levels of fatty acids, but is also capable of accumulating highly valuable β-carotene molecules that are used in food, pharmaceutical and cosmetic industries.

When one would think that Dunaliella salina is the only superhero, one might be surprised to know that is not true. Scenedesmus abundans, for example, has been found to synthesize up to 90% of saturated and unsaturated fatty acids, like palmitic acid (C16:0) and oleic acid (C18:1) respectively, when grown in a medium with a pH of 8 and exposed to 16h light and 8h dark. These types of fatty acids have been appreciated for biodiesel production. One strain of Scenedesmus sp. has also been found to not only synthesize the desired fatty acids, but also to reduce heavy metals and contaminants, such as xenobiotics, when grown in a 100% wastewater medium. So apart from sequestering CO2 from the atmosphere and being used as biofuel, the Scenedesmus can be used for bioremediation.

Despite the many more microalgal species known to possess superpowers, research is yet to be deepened. Aside from the biological potentials, there are other factors that need to be included in the bigger picture of biofuel production. What does the set up of such facilities bring? Can we keep everything under control without intervening too much? Is it really that beneficial as it seems on paper?

Chen, J., Li, J., Dong, W., Zhang, X., Tyagi, R.D., Drogui, P. and Surampalli, R.Y., 2018. The potential of microalgae in biodiesel production. Renewable and Sustainable Energy Reviews, 90, pp.336-346.

Li, Y., Horsman, M., Wang, B. et al. Effects of nitrogen sources on cell growth and lipid accumulation of green alga Neochloris oleoabundans . Appl Microbiol Biotechnol 81, 629–636 (2008).

Mata, T.M., Martins, A.A. and Caetano, N.S., 2010. Microalgae for biodiesel production and other applications: a review. Renewable and sustainable energy reviews, 14(1), pp.217-232.

Rai, M.P. and Gupta, S., 2017. Effect of media composition and light supply on biomass, lipid content and FAME profile for quality biofuel production from Scenedesmus abundans. Energy Conversion and Management, 141, pp.85-92.

Tripathi, R., Gupta, A. and Thakur, I.S., 2019. An integrated approach for phycoremediation of wastewater and sustainable biodiesel production by green microalgae, Scenedesmus sp. ISTGA1. Renewable Energy, 135, pp.617-625.

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