Abstract
In recent decades and to deal with the scarcity of fossil fuels, many studies have been developed in order to set up a sustainable biofuel production sector. This new sector must be efficient (high productivity), economically profitable (low production costs and therefore acceptable fuel prices), and ethical (low carbon balance, no competition with food resources). The production of bioethanol is based on the fermentation of reserve sugars, accumulated in the form of starch in microalgae and glycogen in cyanobacteria. The advantage of this bioenergy production route lies in the fact that the post-crop fermentation process is at the industrial stage since it has already been tested for many years for the production of bioethanol from agricultural resources. One of the most cultivated cyanobacteria is Arthrospira (“Spirulina”) and its production is also already at industrial scale. Depending on the cultivation conditions, this cyanobacteria is able to accumulate up to 65% DW (dry weight) of glycogen, making it a feasible feedstock for bioethanol production. The aim of this review is to provide a clear overview of these operating conditions for glycogen accumulation.
Highlights
Feasible Feedstock for BioethanolFaced with the decrease in available fossil fuel resources, their substitution with biofuels like bioethanol or biodiesel could be a sustainable alternative [1]
The glycogen synthesis in Arthrospira platensis is strictly regulated by the amount of phosphorous in the cell, and the enzyme ADP-glucose pyrophosphorylase is responsible for producing ADP-Glc, which is the glucosyl donor for the elongation of the α-1,4-glucosidic chain to synthesize glycogen [71]
The biomass production was not compromised. Another interesting result was obtained by El-Shouny et al [66], who increased the total carbohydrates of Arthrospira platensis by 300%, when the phosphate concentration was half-reduced during the culture
Summary
Faced with the decrease in available fossil fuel resources, their substitution with biofuels like bioethanol or biodiesel could be a sustainable alternative [1]. 4th G are based on low-input autotrophic microbial feedstock, especially microalgae and cyanobacteria (i.e., Chlorella, Arthrospira, Dunaliella, Botryococcus, or Haematococcus) [4,5] Innovative development of these processes can allow for the production of sustainable amounts of biofuel without competing for arable lands while fixing CO2 via photosynthesis [6]. Attention has to be paid to the chelating properties of Spirulina species, which can lead to the fixation of heavy metals such as Al, Pb, Ba, Ni, Cd [17] or fluoride [18] This microorganism is suitable for biofuel production (3rd generation) due to its fast growth, all year cultivation, and chemical composition (44.4% carbohydrates, 45% proteins, and 10% lipids and ashes) [19,20,21].
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