Future Prospects of Biodiesel Production by Microalgae: A Short Review

Future Prospects of Biodiesel Production by Microalgae: A Short Review

C H A P T E R 12 Future Prospects of Biodiesel Production by Microalgae: A Short Review Myla Sunil Kumar*,†, Viswanath Buddolla‡ ⁎ Department of Vir...

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C H A P T E R

12 Future Prospects of Biodiesel Production by Microalgae: A Short Review Myla Sunil Kumar*,†, Viswanath Buddolla‡ ⁎

Department of Virology, Sri Venkateswara University, Tirupati, India †NextBio Research Pvt., Ltd., Bengaluru, India ‡Department of Bionanotechnology, Gachon University, South Korea

O U T L I N E 12.1 Introduction

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12.2 Summary of Pathways for Microalgal Biodiesel/Fuel Production

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12.3 Recent Insights Into the Development of Biodiesel Production

From Microalgae and Future Prospects

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12.4 Conclusions

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Acknowledgments

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References

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12.1 INTRODUCTION Cultivation of microalgae is a promising long-term, sustainable candidate for lipid production, and the lipids from microalgae can be easily converted into biodiesel, a green and sustainable fuel, via transesterification process (Chen et al., 2018). These lipids are soluble in organic solvents, and the main constituents of lipids are neutral and polar lipid molecules of saturated and unsaturated types (Mubarak et al., 2015). Because of their relatively high lipid content, rapid growth properties, and high biomass production, microalgae are recognized as potentially good sources for biofuel production (Tan et al., 2018). The important advantages of microalgae over agricultural crops are the quick growth rate and no arable land necessity.

Recent Developments in Applied Microbiology and Biochemistry https://doi.org/10.1016/B978-0-12-816328-3.00012-X

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© 2019 Elsevier Inc. All rights reserved.

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12.  Future Prospects of Biodiesel Production by Microalgae: A Short Review

Additionally, carbon sequestration and burning clean (of microalgae biodiesel) are also the magnetizing aspects of exploitation microalgae for producing biodiesel (Chen et al., 2018). There is a plenty of literature on microalgae as feedstock of biodiesel production and the approaches of lipid extraction from microalgae, various transesterification processes, and advantages and limitations (Chisti, 2007; Rawat et al., 2013; Chen et al., 2018; Mata et al., 2010; Rawat et al., 2013; Sibi et al., 2016). This article presents the recent trends into the development of biodiesel production from microalgae along with future prospects.

12.2  SUMMARY OF PATHWAYS FOR MICROALGAL BIODIESEL/FUEL PRODUCTION Microalgae have been used for centuries to offer nourishment to humans and animals, but recently, they have become much more widely cultured and harvested at a large industrial scale (Garcia et al., 2017). The biology of microalgae has been studied for more than 50 years now and more intensely since the 1970s, when genetics and molecular biology approaches were integrated into the research programs. Recently, energy and resource creation using microalgae has established an immense deal of consideration. Microalgae grow quickly and contain high oil content compared with terrestrial crops, which take a season to grow and only contain a maximum of about 5% dry weight of oil (Chisti, 2007). Commonly, doubling time for microalgae is 24 h. During the peak growth phase, some microalgae can double every 3.5 h (Chisti, 2007). The oil content of microalgae is usually between 20% and 50% (dry weight, Table 12.1), while some strains can reach as high as 80%. The prospect of microalgal biotechnology depends on the progress of large-scale photobioreactors capable of operating under distinct optimal conditions with negligible contamination risk. Compared with open-air systems, closed systems can avoid most of their problems; however, development of more economical and efficient closed culturing systems is required (Garcia et al., 2017). The set of approaches that range from microalgae cultivation to collection and harvest and to fuel conversion is termed the pathway for microalgal biodiesel/biofuel TABLE 12.1  Percentage of Lipids in Dry Biomass of Various Easily Existing Microalgae Microalgae

% of Lipid (by Dry Mass)

Botryococcus braunii

25–75

Chlorella vulgaris

28–32

Crypthecodinium cohnii

20

Cylindrotheca sp.

16–37

Nitzschia sp.

45–47

Phaeodactylum tricornutum

20–30

Schizochytrium sp.

50–77

Tetraselmis suecia

15–23

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12.3  RECENT INSIGHTS INTO THE DEVELOPMENT OF BIODIESEL PRODUCTION FROM MICROALGAE

O O O O O

+

OH OH OH

O Triglycerides

3 Methanol

Catalyst e.g., NaOH

OH

163

O

OH + 3 O

Rx

OH Glycerol (by-product)

Biodiesel

FIG. 12.1  Base-catalyzed transesterification of a triglyceride with alcohol (Buddolla et al., 2010).

production. Chaudry et al. (2015) summarized the most promising conversion pathways of microalgae and compared based on significant assessment parameters of product quality and yield, nutrient recovery, GHG emissions, energy, and the cost connected with the production of fuel from microalgae, in order to understand the advantages and disadvantages of each method. In addition, an overview of the potential environmental impacts of large-scale microalgae cultivation for various applications was summarized by Usher et al. (2014) and Sutherland et al. (2017). As summarized by Hadrich et al. (2018), three stages are particularly considered in order to produce microalgal lipids for a variety of applications, that is, controlling the microalgae cultivation via experimental and modeling investigations, optimizing culture conditions to maximize lipid production and to determine the fatty acid profile the most suitable for biodiesel synthesis, and optimizing the extraction of the lipids accumulated in the microalgal cells. However, environmental factors and process conditions can vary the quality and the quantity of lipid produced by microalgae, which can be dangerous for the overall production of biodiesel and required proper attention (Shin et al., 2018). Biodiesel is produced through the transesterification of these microalgal lipids, which are subjected to a reaction with alcohol in the presence of a catalyst. The process removes roughly 10% of the original weight of the oil as glycerin, which is the backbone of the triglyceride molecule as summarized in Fig. 12.1.

12.3  RECENT INSIGHTS INTO THE DEVELOPMENT OF BIODIESEL PRODUCTION FROM MICROALGAE AND FUTURE PROSPECTS Recently, a research demonstrated that the oleaginous microalgae have the ability to purify biogas along with enhanced production of lipids. Here, the researchers have followed the approach of the stepwise increasing of significant growth factors, including, nitrogen source, light intensity, and CO2 supply to enhance the microalgae performance in the successful manner. This strategy helped not only in biomass and lipid production but also in the removal of CO2 (Srinuanpan et al., 2018). The combined processes and approaches applied in this research are very much helpful for the production of biogas and biodiesel along with the removal of CO2. In another study, researchers have focused on the biorefinery strategy for simultaneous production of biodiesel and bioethanol from microalgae feedstock (Sivaramakrishnan and Incharoensakdi, 2018a,b). In this study, different pretreatment techniques were employed to confirm the maximum recovery of sugars from Scenedesmus sp., and the total sugar yield of more than 90% was attained when the biomass was pretreated by acid hydrolysis. In addition, the hydrolysate produced 86% of ethanol after the fermentation

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12.  Future Prospects of Biodiesel Production by Microalgae: A Short Review

using yeast. Moreover, this approach of bioethanol and biodiesel production was optimally attained when direct transesterification was completed first, followed by ethanol fermentation, yielding 92% and 93% of methyl ester and ethanol, correspondingly. A novel direct saponification-esterification conversion strategy was developed for biodiesel production from wet microalgae with a water content higher than 90 wt% by Fang et al. (2018). This approach is very simple and can replace conventional feedstock drying and lipid extraction methods for enhanced biodiesel production at low cost. Moreover, the proposed kinetic model with the trial results specified that the system is mainly by means of saponification/esterification conversion, which principally converted lipid released from microalgae cell into soap in the saponification step followed by the esterification into biodiesel in the next step. Similarly, Sandmann et al. (2018) applied a novel single-cell analytic technology to study a well-established model experiment and to understand the single-cell dynamics during lipid production in microalgae, and these studies are helpful for deeper investigation of the microalgal lipid accumulation process. In another study by Jiang et al. (2018), struvite precipitation was selected as a digestate pretreatment technique to verify the optimal combination of chemical additives and reaction conditions and to examine appropriate microalgal species. This provides a novel approach for combining liquid digestate treatment and microalgal cultivation for enhanced biodiesel production. Mureed et al. (2018) conducted to optimize the growth of microalgal strains and to evaluate biodiesel production potential of algae using untreated food industry wastewater as a source of nutrients. From the experimental results, it was confirmed that microalgae have an abundant potential to produce biodiesel from spent wash of the food industry. Additionally, this approach is cheaper and presents an environmentally friendly way to handle food industry wastewater along with biodiesel. In a study, a two-step processing approach, that is, hydrothermal liquefaction followed by catalytic upgrading was employed to produce upgraded bio-oil in a successful manner from microalgae. In addition, the extracted upgraded bio-oils have similar properties to those of naphtha and jet fuel (Xu et al., 2018). The application of ultrasound in biodiesel production from microalgae has freshly appeared as an innovative technology. In general, ultrasound treatment augments the mass-transfer characteristics leading to the increased reaction rate with short reaction time and potentially reduces the production cost. However, it requires further examination particularly in the area of technoeconomic feasibility (Sivaramakrishnan and Incharoensakdi, 2018b). Zhou et  al. (2017) conducted a study for continuous production of biodiesel from two kinds of microalgae Chrysophyta and Chlorella sp. In this study, coupling with the supercritical carbon dioxide extraction, the lipids of microalgae were extracted initially and then transferred to the downstream production of biodiesel. The residue after decompression can be reused as the material for pharmaceuticals and nutraceuticals. The observations of these experiments proved that the particle size of microalgae, temperature, pressure, molar ratio of methanol to oil, and flow of CO2 and n-hexane all have an influence on the biodiesel production. In another study, a combinatorial strategy integrating toxic and carcinogenic heavymetal arsenic alleviation coupled to biodiesel production using oleaginous microalgae grown in synthetic soft water (SSW) was undertaken, and this integrative technology has a strong potential path for verdurous environment and renewable fuels resulting in socioeconomic welfare (Arora et  al., 2017). In a study, Wang et  al. (2016) designed an approach based on using formic acid aided with minute amounts of hydrochloric acid, to treat water-containing

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REFERENCES 165

microalgae and extract lipid consequently. The results of this study confirmed that the dosage of formic acid and hydrochloric acid, liquid/solid (l/s) ratio, and temperature had a considerable influence on lipid extraction from water-containing microalgae. Gupta et  al. (2016) developed a superstructure-based optimization model to optimize the microalgae for biodiesel production. This model contains the key processing steps of converting microalgae into biodiesel, especially, their growth, harvesting, lipid extraction, and transesterification of lipid. Here, various options to execute these steps are considered, and the mass and volumetric balance for each procedure and equipment and the equipment capacity limitations comprise the significant model constraints. Moreover, the decision variables include growth duration, medium, and techniques and specifications to be followed in each of the downstream steps. Shin et al. (2018) summarized the strategies for increasing overall economic viability of lipid production and confirmed that the microalgal bioprocess of microalgal strain with desirable characteristics is essential for decreasing the overall cost of biodiesel production. In general, biodiesel from microalgae is the present research role that addresses the concerns of energy and environmental sustainability. Developing a large-scale microalgae cultivation system is necessary without delay to explore the economic feasibility of this new feedstock for alternative energy and valuable by-product production (Tan et al., 2018).

12.4 CONCLUSIONS The lipid, an energy reserve in the microalgal cell, is a promising feedstock for biodiesel production; therefore, these organisms have been rising as a feedstock for biofuel in response to the energy crisis. But it was observed that there were still several obstacles to make biodiesel production from commercialized microalgae, and constructive research is essential to overcome these obstacles, particularly, to get biodiesel in low cost with environmental sustainability.

Acknowledgments The authors are indebted to all the researchers whom we cited in this review for their significant and valuable research. No funding was received to perform this review.

Conflict of Interest The authors declare no relevant competing financial interests to disclose.

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