Bioethanol production from microalgae biomass has been proposed as an innovative alternative to substitute fossil fuel sources. Unlike other renewable sources (e.g., lignocellulosicmaterials), microalgae biomass has no lignin, which makes the carbohydrate extraction process easier and eventually it should help to develop cleaner and safer bioethanol production processes. Carbohydrates in microalgae can be present in a variety of forms (cellulose, starch, and/or glycogen) and located in different regions of the cells (inner, inside, outside). Carbohydrate type, location, and concentration will strongly depend on cultivation and operation conditions with concentrations ranging from 15% to 50%. Several steps must be applied to obtain bioethanol from this biomass. First, different methods can be employed to disrupt the cell wall and release the carbohydrates such as physical-mechanicals, chemicals, and/or a combination of them. After that, enzymatic hydrolysis could be required to convert the carbohydrates into simple sugars. Finally, a yeast or bacteria fermentation stage is performed to transform these sugars into ethanol. However, it is imperative that the principal parameters of these different steps should be optimized during the bioethanol production before industrial implementation, and more research on economic and life cycle analysis is needed to ensure the economic feasibility of the process.
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