Treatment updates of microalgae biomass for bioethanol production: A comparative study

Microalgae is a third-generation biomass source that can potentially be used as a raw material for bioethanol production. Microalgae is a viable alternative energy source to substitute or complement fossil fuels based on the disadvantages related to first- and second-generation biofuels. Bioethanol from microalgae sources does not compete with food needs. In addition, third-generation biomass can be grown in aquatic environments and has large-scale CO2 requirements. This review article compiles literature focusing on the production of microalgal bioethanol and summarises the advantages, disadvantages, main features and key aspects for each process. The production of bioethanol is achieved through pretreatment to break down the cell wall, which is followed by saccharification of carbohydrates and fermentation of suitable sugars. An effective pretreatment should be simple, have less chemical consumption, and have low energy demand so that production costs can be reduced. Producing bioethanol by fermentation can be performed in many ways, such as separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). The SSF process is more economical, because the combination of hydrolysis and fermentation reduces production costs. The results of the comparison of hydrolysis methods show that enzymatic hydrolysis can potentially be applied to the production of bioethanol because of its affordable economic cost and less negative impact on the environment. Economic reasons, such as the final yield of ethanol products using this method, are higher than other pretreatments. Moreover, this method requires low energy, lack of chemicals and mild environmental conditions.