A critical review on production of bioethanol from macroalgal biomass

In order to combat emerging concerns due to global climate change and increasing conventional fuel prices, bioethanol appears to be a sustainable green resource as co-fuel to meet the future energy demand for transportation. As per the present scenario, bioenergy research emphasizes on bioethanol production from alternate non-terrestrial substrates, like microalgae and macroalgae. Among them, macroalgae represent a rich source of carbohydrates for bioethanol production. The production of bioethanol from macroalgal biomass mainly involves three steps namely mechanical pre-processing, pretreatment and microbial fermentation. Of these, the pretreatment step is the most crucial that tends to improve the saccharification efficiency for efficient bioethanol production. Currently, there are three main types of pretreatment methods used for macroalgae viz., physical/physicochemical, chemical and biological. In addition, the two-step saccharification or combinational pretreatment approach is also utilized to enhance the yield of reducing sugars, which can be fermented to bioethanol using suitable microbial strain(s) under restrained conditions. The current review provides a critical assessment and detailed overview about the sequential process for bioethanol production from macroalgal biomass. Additionally, this paper gives an insight on various statistical optimization approaches using response surface methodology for the biomass pretreatment step and provides a viewpoint about the technical advances in third-generation bioethanol production.