Energy from Microalgae

This chapter provides a brief overview of some of the major steps in the development of microalgae-based processes for renewable energy production. The chapter attempts to highlight the development and evolution of the key concepts and research in the field, preparing the reader for the following chapters, which will deepen the discussion on the subject.

The purpose of this chapter is to provide an overview of the main systems of microalgae production with highlights of biofuel production. The large-scale production systems (raceway ponds, horizontal tubular photobioreactors, and heterotrophic bioreactors) and small-scale photobioreactors (vertical and flat-plate photobioreactors) will be presented and discussed with a special emphasis on the main factors affecting its efficiency, biomass productivities reported in the literature, scaling-up, costs of construction and operation, and commercial applications. Besides this, the recent developments in microalgae cultivation systems will be reviewed in their main aspects. Finally, the criteria for selecting an appropriate bioreactor for microalgae cultivation will be presented, as well as the pros and cons of each system will be discussed in this chapter.

The rapid development of modern society has resulted in an increased demand for energy and, consequently, an increased use of fossil fuel reserves, compromising the energy sector sustainability. Moreover, the use of this source of energy led to the accumulation of greenhouse gases (GHGs) in atmosphere, which are associated with climate change. In this context, European Union has established new directives regarding GHG emissions and the renewable energy use. Microalgae may have an important role in the achievement of these goals. These photosynthetic microorganisms have a high growth rate, are able to capture CO₂, the biomass can be used to produce biofuels, constituting an undeniable economic potential. Microalgae may also be a source of low carbon fuel, being one of the most studied biofuels feedstock. They are considered a sustainable energy resource, able to reduce significantly the dependence on fossil fuel. They can grow on places that are unsuitable for agriculture, not competing with land for food production. The use of wastewater as microalgal culture medium will reduce the required amount of freshwater and nutrients, achieving simultaneously an effluent with low nutrient concentrations. An important step to increase the competitiveness (promoting simultaneously the environmental sustainability) of microalgal biofuels regarding fossil fuels is the optimization of culture parameters using wastewater as culture medium. Thus, this chapter aims to present the recent studies regarding the integration of wastewater treatment and microalgal cultivation for biomass/biofuel production.

A tremendous increase in population has also led to a significant increase in the demand for energy leading to search for alternatives which can match up with the current requirement quantitatively and also qualitatively as a green energy carrier. Fuels derived from algal biomass can be one of the potential alternatives, as microalgae possess higher nutrients, required lipids and CO₂ uptake capacity and can be grown quickly on nonarable land throughout the year without their interference in food supply chain. The quantum of biodiesel produced from microalgae can be about 10–20 times higher than that obtained from terrestrial plants. Microalgae also help in reducing global warming by capturing CO₂. The cost of production of biofuels from microalgae is the current setback which can be overcome by taking into consideration a biorefinery approach which can give multiple products with same expenditure as well as using some process intensification approaches. Process intensification plays a major role in reducing the cost and also can lead to use of less quantum of materials and lower operating temperatures. The present chapter will focus on analyzing the process intensification aspects applied to biofuels production from microalgae. The initial sections will cover the details of the types of microalgae and their harvesting techniques, followed by the discussion on the different approaches used to extract bio-oil from microalgae, and then the production of different biofuels. Intensification can be applied to both the extraction and the actual reaction for production of biofuels. The chapter will also focus on the mechanism of intensification using different approaches such as ultrasound, microwave, ultraviolet, and oscillatory baffled reactors. An overview of the literature will be presented so as to give guidelines about the possible reactor designs and operating parameters also highlighting the process intensification benefits that can be obtained. Overall, the work is expected to bring out critical analysis of the different approaches and the expected benefits due to the use of process intensification also enabling understanding of the reactor designs and operating parameters.

The 2015 Conference of the Parties (COP21) marked a turning point for global actions to mitigate atmospheric greenhouse gases, reduce the carbon dioxide emissions from fossil fuel combustion, and stabilize the global climate. On the other hand, the increase in energy demand asks for renewable sources and robust systems to supply energy and obtain product diversity like that obtained from a petroleum refinery. A biorefinery is the sustainable processing of biomass into a spectrum of profitable products and energy. Microalgal biomass is considered one of the most promising biorefinery feedstock providing alternatives for different areas, such as food, feed, cosmetics and health industries, fertilizers, plastics, and biofuels including biodiesel, methane, hydrogen, ethanol. Furthermore, microalgae can also be used for the treatment of wastewater and CO₂ capture. However, microalgal biofuels are not currently cost competitive at large scale and to develop a sustainable and economically feasible process, most of the biomass components should be valorized. High-value coproducts from microalgae include pigments, proteins, lipids, carbohydrates, vitamins, and antioxidants, and they can improve the process economics in the biorefinery concept. Therefore, mild and energy-efficient downstream processing techniques need to be chosen to maintain product properties and value. In this chapter, the existing products and microalgae biorefinery strategies will be presented, followed by new developments, sustainability assessments, and techno-economic evaluations. Finally, perspectives and challenges of microalgal biorefineries will be explored.

Recently, the use of mathematical tools, such as the life cycle assessment (LCA) methodology for ecologically sound processes, with the purpose of establishing a process designer involving the limits of “cradle to grave” in an efficient and flexible way with less subjectivity, has become an ambitious challenge to be won. Therefore, to generate biofuels with low atmospheric emissions and minimal energy requirements has become crucial to commercial competitiveness. Thus, the objective of this chapter is to approach the current situation of the different scenarios of microalgal biofuels production by an evaluation of them via a life cycle assessment. The chapter is based on three main topics: (1) fundamentals for structuring a life cycle assessment, (2) biofuels data set reported in the literature, and (3) application of LCA in microalgae biofuels.

Biofuels such as biodiesel and bioethanol, synthesized via microalgal bioprocess engineering, could be a major contributor to the purview of sustainable energy in the foreseeable future. In contrast to other biomass feedstocks like corn, sugar crops, and vegetable oil, microalgae display a number of significantly superior benefits as a raw material for biofuel manufacturing. This includes an enhanced metabolic rate of biomass production, subsistence of diverse microalgae species with sundry biochemical profiles, prospects for carbon dioxide sequestration, and either limited or near absolute monopoly from the perspective of food production modalities and logistics. However, attributing to a wide range of factors, for instance the insipid characteristic of microalgal cultures, and the fact that microalgae cells possess trivial sizes, the process of biomass production and subsequent conversion into biofuels become prohibitively expensive. As a consequence, from an economic outlook, the large-scale production of biofuels from microalgae achieves a somewhat less appealing status, compared to the other biomass types and sources. The current chapter delivers an outline of the bioeconomy analysis for microalgae-derived biofuels. In addition, case studies on microalgal biofuel production are presented along with cost estimations and the necessary strategies to augment its commercial viability.

It has been argued that the energy output from microalgal biofuel production should at least be 5–8 times the energy input, apart from solar irradiation driving algal photosynthesis. There is as yet no commercial production of microalgal biodiesel or large-scale demonstration project to check whether this criterion regarding the energy balance can be met in actual practice. There is, however, a set of relatively well-documented peer-reviewed scientific papers estimating energy inputs and outputs of future autotrophic microalgal biodiesel production. Energy balances for biodiesel from autotrophic microalgae grown in ponds tend to be better than for biodiesel from such microalgae grown in bioreactors. The studies regarding energy balances for biodiesel derived from microalgae grown in open ponds are considered here. None of these energy balances meets the criterion that the energy output should exceed the energy input by a factor 5–8. Estimated energy balances are variable due to divergent assumptions about microalgal varieties, applied algal and biodiesel production technologies, assumed parameters and yields and due to differences in system boundaries, allocation, and the use of credits. The studies considered here could have done better in handling uncertainties in estimated energy balances.

Nowadays, the microalgae have been gaining importance due to their different applications in the biofuel, food, and pharmaceutical industries. One of the applications that is commonly proposed for microalgae oil is the transformation into biodiesel through transesterification. This biodiesel is a biofuel that present energy yields similar to traditional diesel, generating an alternative to replace a fuel from petrochemical origin. The objective of this work is to analyze deeply a process for biodiesel production from microalgae oil. The process includes the cultivation, harvesting, and extraction stages for the oil. In this case, the software Aspen Plus is employed for simulation. From the results obtained (mass and energy balances), the energy, exergy, and economic and environmental analysis of the process are carried out through the development of different scenarios. Last allow to evaluate the energy, economic and environmental viability of this type of processes. As a result, this work shows the challenges to be overcome to make possible the real introduction of microalgae fuels.

Rapid industrialization and urbanization are mainly responsible for the energy crisis, environmental pollution and climate change. In addition, depletion of the fossil fuels is a major concern now. To confront these problems, it is essential to produce energy from sustainable and renewable energy sources. Hydrogen is widely considered as a clean and efficient energy carrier for the future because it does not produce carbon-based emission and has the highest energy density among any other known fuels. Due to the environmental and socioeconomic limitation associated with conventional processes for the hydrogen production, new approaches of producing hydrogen from biological sources have been greatly encouraged. From the perspective of sustainability, microalgae offer a promising source and have several advantages for the biohydrogen production. Microalgae are characterized as high rate of cell growth with superior photosynthetic efficiency and can be grown in brackish or wastewater on non-arable land. In recent years, biohydrogen production from microalgae via photolysis or being used as substrate in dark fermentation is gaining considerable interest. The present chapter describes the different methods involved in hydrogen production from microalgae. Suitability of the microalgae as a feedstock for the dark fermentation is discussed. This review also includes the challenges faced in hydrogen production from microalgae as well as the genetic and metabolic engineering approaches for the enhancement of biohydrogen production.

The industrial potential of ethanol has been tested early in 1800 to be used as an engine fuel after the invention of an internal combustion engine. Currently, there are three generations of bioethanol that have been flourished based on different feedstocks. The first-generation bioethanol is derived from fermentation of glucose contained in starch and/or sugar crops. USA and Brazil are the main producers of bioethanol worldwide utilizing corn and sugarcane, while potato, wheat, and sugar beet are the common feedstocks for bioethanol in Europe. The term “second-generation bioethanol” emerged as a boon to overcome the “food versus fuel” that occurs by the first-generation bioethanol. The second generation also referred to as “advanced biofuels” is produced by innovative processes mainly using lignocellulosic feedstock and agricultural forest residues. The emergence of the third-generation bioethanol provides more benefits as compared to the first and second generations and is focused on the use of microalgae and cyanobacteria. These organisms represent as a promising alternative feedstock due to its high lipid and carbohydrate contents, easy cultivation in a wide variety of water environment, relatively low land usage and carbon dioxide absorption. This chapter will discuss the use of microalgae for the ethanol production and the main technological routes, i.e., enzymatic hydrolysis and yeast fermentation of microalgal biomass, metabolic pathways in dark conditions, and “photofermentation.”

The high cost of axenic microalgae cultivation in photobioreactors limits nowadays the potential uses of microalgal biomass as a feedstock for the production of biodiesel or bioethanol. In this context, microalgae-based wastewater treatment (WWT) has emerged as the leading method of cultivation for supplying microalgae at low cost and low environmental impacts, while achieving sewage treatment. Nonetheless, the year-round dynamics in microalgae population and cell composition when grown in WWTPs restrict the use of this low-quality biomass to biogas production via anaerobic digestion. Although the macromolecular composition of the microalgae produced during wastewater treatment is similar to that of sewage sludge, the recalcitrant nature of microalgae cell walls requires an optimisation of pretreatment technologies for enhancing microalgae biodegradability. In addition, the low C/N ratio, the high water content and the suspended nature of microalgae suggest that microalgal biomass will also benefit from anaerobic co-digestion with carbon-rich substrates, which constitutes a field for further research. Photosynthetic microalgae growth can also support an effective CO₂ capture and H₂S oxidation from biogas, which would generate a high-quality biomethane complying with most international regulations for injection into natural gas grids or use as autogas. This book chapter will critically review the most recent advances in biogas production from microalgae, with a special focus on pretreatment technologies, co-digestion opportunities, modelling strategies, biogas upgrading and process microbiology.

The aim of this chapter is to present a comprehensive overview of integrated bio-oxycombustion systems with photobioreactors. Divided into seven distinct topics, the chapter discusses issues related to fundamentals of oxycombustion, the operational implications for oxycombustion-enhanced performance, oxygen produced by photosynthesis, volatile organic compounds as energy source, photobioreactors design, the process integration in bio-oxycombustion systems, and the hurdles of bio-oxycombustion technology, summarizing a range of useful strategies directed to the sustainable development of industrial combustion systems.

To reduce greenhouse gas emissions and to prevent their devastative impacts of human health and the environment, bioenergy carriers have been at center of attention to supply global energy demand. Microalgae as solar energy-driven factories could efficiently convert carbon dioxide to a variety of hydrocarbons that can be used as biofuels. With the aim of realizing the current status of algal biofuels, respective patents were surveyed in this chapter using various databases, i.e., World Intellectual Property Organization, United States Patent and Trademark Office, and European Patent Office database. Information derived from the aforementioned databases was categorized into three: upstream, mainstream, and downstream strategies. The upstream strategies included patents on selection of algal strain and genetic engineering approaches while the mainstream strategies reviewed and discussed innovations pertaining to improving algal cultivation systems, production media and nutrients supply, and CO₂ supply. Finally, in the downstream strategies section, the inventions aimed at enhancing harvesting and dewatering of microalgae cells and lipid extraction were presented.