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Microalgal carbohydrate is considered one of the potential feedstock for biofuel produced via the bioconversion process. However, the current cultivation process using commercial medium exhibited low biomass production and its carbohydrate productivity which become a bottleneck for sustainable microalgal-carbohydrate-based biofuel production. Thus, the objective of this study is to assess the utilization of industrial waste including molasses and glycerol on the Halochlorella rubescens and Tetraselmis suecica growth as well as its carbohydrate content under different cultivation modes such as autotrophic, heterotrophic and photoheterotrophic conditions. From this study, the highest maximum biomass of H. rubenscens and T. suecica of 0.653 ± 0.009 and 0.669 ± 0.01gL−1 were obtained when the cultivation was performed under photoheterotrophic using molasses. High carbohydrate content of H. rubescens and T. seucica of 56.81 ± 0.39% and 71.52 ± 0.03% with glucose represent the dominant sugar was observed under this condition. The growth kinetic model of the analysis indicated that Huang and Gompertz Models described well the growth of H. rubescens and T. suecica under photoheteroptroph condition with a high significant R2 of 0.99. The information generated could be beneficial for the future development of low-cost microalgal cultivation media formulation for future microalgal carbohydrate-based products such as bioethanol.

Bioethanol production from renewable biomass has gained considerable attention as one of the alternative biofuels to partially replace conventional fuel from fossil fuel feedstock. In recent years, the production of bioethanol from renewable biomass is far yet to be commercialized due to several limitations at upstream and downstream stages during bioethanol production process. Several problems including energy intensive pretreatment, low sugar yield during hydrolysis, and low conversion efficiency of fermentation of sugar are among the major limitations that affect final bioethanol yield. Development of bioprocess operational modes and strain improvement are crucial to ensure the feasibility of future bioethanol production from different renewable biomass feedstocks. Thus, this chapter provides a review on bioethanol production from various types of biomass feedstocks including local food crops, agro-industry wastes residues, and microalgae biomass. In addition, variations in cost-effective hydrolysis and fermentation separate-hydrolysis-fermentation, simultaneous-hydrolysis-fermentation, and consolidated bioprocessing are discussed. The chapter reviews the factors that influence hydrolysis and bioethanol production as well as strain improvement for better sugar metabolisms.

A two-part study on pretreatment and fed-batch enzymatic hydrolysis of pretreated Tetraselmis suecica using a high initial biomass concentration was conducted. First, the effect of different pretreatment processes, i.e. microwave (MC), dilute alkaline (AK), and microwave-alkaline assisted (MAK) pretreatment, on enzymatic hydrolysis of T. suecica biomass was evaluated. Furthermore, high initial biomass concentration enzymatic hydrolysis improvement via a fed-batch strategy was performed. Among the pretreatments tested, the MAK pretreatment produced the highest sugar concentration at 9.83 ± 0.24 mg/mL, corresponding to a conversion yield of up to 85.58% of carbohydrate content available in the pretreated biomass. The solid fraction generated after pretreatment was characterized using Fourier transform infrared (FTIR) spectroscopy. The FTIR analysis revealed a significant change in the functional hydroxyl and acetyl groups of the biomass, which is favorable for enzymatic hydrolysis. Introducing an initial microalgal biomass concentration beyond 15% (w/v) exhibited a low enzymatic hydrolysis yield. The fed-batch enzymatic hydrolysis strategy of the MAK pretreated T. suecica was further investigated by adding the substrate at different time intervals. The findings indicate that the fed-batch operation system could enhance sugar production and enzymatic hydrolysis yield one-fold.

Cultivation of microalgal is one of the important processes in biofuel production from microalgal biomass. In this process, different cultivation approaches are analyzed to ensure the most suitable condition for maximum biomass production prior to subsequent processes. To date, several approaches such as autotrophic, heterotrophic, and mixotrophic cultivation modes have been introduced to be applied for microalgal biomass production. Mixotrophic cultivation has gained great attention because this approach exhibits more advantages over other cultivation systems. In the mixotrophic condition, inorganic and organic carbons have simultaneously been utilized by microalgal for biomass and biochemical production. Utilization of both inorganic and organic carbon together in the cultivation process, in turn, could significantly reduce carbon and material cost. In this chapter, mixotrophic cultivation for biofuel production is reviewed. The advantages of mixotrophic cultivation for biomass and biochemical synthesis are discussed. Influence of cultivation parameters during mixotrophic cultivation toward microalgal biomass and biochemical synthesis is also presented. Also, the cultivation modes such as fed-batch and two-stage system to enhance biomass production in mixotrophic microalgal cultivation are discussed at the end of this chapter.