Abstract
Biofuels derived from microalgae biomass have received a great deal of attention owing to their high potentials as sustainable alternatives to fossil fuels. Microalgae have a high capacity of CO2 fixation and depending on their growth conditions, they can accumulate different quantities of lipids, proteins, and carbohydrates. Microalgal biomass can, therefore, represent a rich source of fermentable sugars for third generation bioethanol production. The utilization of microalgal carbohydrates for bioethanol production follows three main stages: i) pretreatment, ii) saccharification, and iii) fermentation. One of the most important stages is the pretreatment, which is carried out to increase the accessibility to intracellular sugars, and thus plays an important role in improving the overall efficiency of the bioethanol production process. Diverse types of pretreatments are currently used including chemical, thermal, mechanical, biological, and their combinations, which can promote cell disruption, facilitate extraction, and result in the modification the structure of carbohydrates as well as the production of fermentable sugars. In this review, the different pretreatments used on microalgae biomass for bioethanol production are presented and discussed. Moreover, the methods used for starch and total carbohydrates quantification in microalgae biomass are also briefly presented and compared.
Highlights
Microalgae biomass pretreatmentIn the production of bioenergy from aquatic biomass, as in any types of biorefineries, a very important step is the pretreatment of the raw materials, where the objective is to make available the intracellular compounds such as carbohydrates, proteins, lipids, and added-value compounds such as short chain oligosaccharides, antioxidants, pigments, etc. (Harun et al, 2014; Demuez et al, 2015)
Biofuels derived from microalgae biomass have received a great deal of attention owing to their high potentials as sustainable alternatives to fossil fuels
This pretreatment method is an alternative for cell disruption where water, acid, or alkalis could be used as catalysts for cell wall disruption of microalgal biomass
Summary
In the production of bioenergy from aquatic biomass, as in any types of biorefineries, a very important step is the pretreatment of the raw materials, where the objective is to make available the intracellular compounds such as carbohydrates, proteins, lipids, and added-value compounds such as short chain oligosaccharides, antioxidants, pigments, etc. (Harun et al, 2014; Demuez et al, 2015). The carbohydrate from microalgae can be found in the cell wall in the form of cellulose and in the plastids in the form of starch as the major sugar reserve (Fig. 1) Such information is relevant to select the biomass with the highest sugars content for bioethanol production (Chen et al, 2013). Cell wall is composed of cellulose, pectin (polygalacturonic acid), and sulfated polysaccharides, that can be impregnated with inorganic substances such as calcium carbonate, silica, and magnesium (Castrillón et al, 2013; Chen et al, 2013) It is composed of two layers, i.e., external and internal cell walls (Fig. 2).
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