Harvesting of algal biomass refers to the separation of algae from water for subsequent biofuel production. The process consists of two distinctive steps: (1) bulk harvesting, to separate algae from bulk suspension via gravity sedimentation, flocculation, and flotation, and (2) thickening, to concentrate the algal slurry after bulk harvesting using techniques such as centrifugation and filtration (Brennan and Owende, 2010; Chen et al., 2011). Harvesting of algal biomass is extremely challenging because of algae’s small cell size (gen­erally 1-20 pm) and suspension in water (Lam and Lee, 2012; Suali and Sarbatly, 2012). The mass ratio of algal biomass to water is considered very low, even if the algae are cultivated in a closed photobioreactor (Chen et al., 2011). For example, the mass ratio of algal biomass to wa­ter lies in the range of 0.00035-0.027 for algae cultivated in a closed photobioreactor, assuming a biomass productivity of 0.05-3.8 g/L/day and cultivated for seven days. When the algal cultivation system (typically a closed photobioreactor) is scaled up for mass production of algal biomass, an average of 73 tonnes of water need to be processed when harvesting 1 tonne of algal biomass. This amount of water is quite substantial; thus, developing effective algal harvesting methods is exceptionally important to strengthen the possibility of commercia­lizing algal biofuel production. Table 12.4 summarizes the current available algal biomass harvesting technologies.

A recent LCA study revealed that current technologies for harvesting and drying algal biomass consumed a significant amount of energy input to produce algal biodiesel (Sander and Murthy, 2010). The study assessed two types of algal thickening methods (without prior bulk harvesting), namely, filter press and centrifugation, and reported that each method contributed 88.6% and 92.7%, respectively, to the total energy input for the LCA. Thus,

harvesting algal biomass using solely centrifugation or filtration is still far from commercial application because of the high energy consumption and high operating cost.

On the other hand, bulk harvesting methods such as flocculation offer an alternative approach to harvesting algal biomass with lower energy input and at a reasonable cost. Conventional flocculants, such as ferric chloride (FeCl3), aluminium sulphate (Al2(SO4)3), and ferric sulphate (Fe2(SO4)3) (Brennan and Owende, 2010), which are widely used in waste­water treatment plants, can be used to agglomerate algal cells to become dense flocs (slurry) and subsequently settle out of the cultivation medium (de Godos et al., 2011). After the flocculation process, water that is still retained in the algal slurry can be concentrated further through centrifugation or filtration (Suali and Sarbatly, 2012).

Nevertheless, conventional flocculants that are always referred to as multivalent salts could contaminate the algal biomass and may affect the quality of the final product. Although no scientific work or assessment has been carried out to justify this claim, flocculant toxicity should not be ignored, especially if health-related products are to be extracted from algal biomass before the algal biomass is diverted to biofuel production. Other organic polymeric flocculants that are biodegradable and less toxic offer an alternative and environmentally friendly way to harvest algal biomass, but these organic polymeric flocculants require further development prior to application on the commercial scale.

After concentrating the algal slurry to 5-15% dry solid content through centrifugation or filtration, further dehydration or drying of the slurry is necessary to facilitate subsequent biofuel production (Brennan and Owende, 2010; Lam and Lee, 2012). The presence of water could severely inhibit the biofuel processing and conversion, including lipid extraction using

chemical solvents and biodiesel production through transesterification (Ehimen et al., 2010). The water would cause some difficulty in recovery of chemical solvents as well as biodiesel refining, requiring even higher energy input for subsequent water separation.

Several dehydration methods are currently applicable to drying the algal slurry, including solar drying, spray drying, freeze drying, and fluidized bed drying (Brennan and Owende, 2010; Desmorieux and Decaen, 2005; Orset et al., 1999; Prakash et al., 1997). Solar drying is apparently the most inexpensive dehydration method because it is free, but a large drying surface is required, and it is time-consuming (Prakash et al., 1997). Nevertheless, solar drying is not feasible in temperate countries where sunlight is not always available throughout the year (Lam and Lee, 2012). Thus, the use of heat generated from fossil fuels cannot be avoided to ensure that the algal slurry is continuously dried for each cultivation cycle. Some LCA stud­ies have emphasized that a large amount of energy is consumed in drying the algal slurry, making commercial algal biofuel production even more challenging (Cooney et al., 2011; Lardon et al., 2009; Lohrey and Kochergin, 2012; Sander and Murthy, 2010; Xu et al., 2011). For example, Sander and Murthy (2010) revealed that using natural gas as the fuel to dry the algal slurry consumed nearly 69% of the overall energy input and consequently resulted in a negative energy balance for producing algal biofuels. Heavy dependence on fossil fuels to dry the algal slurry could reduce the market potential and feasibility for producing algal biofuels; thus, new development of an efficient drying method is required to ensure that the energy input in this step is minimized (Lohrey and Kochergin, 2012).

Experimental studies exploring new technologies to extract energy from algal biomass are often based on lyophilized algae or use solvents that are difficult to use at the industrial scale (e. g., chloroform). For instance, oil extraction performance and oil esterification yields are of primary importance to realize the LCA of algal biodiesel. Yet up to now LCA studies have demonstrated that dry extraction was too expensive in terms of energy, but at the same time there is a lack of reliable data to assess the wet extraction path.

Anaerobic digestion is mostly used to produce bioenergy from the obtained residues after lipid extraction. Energy consumption should be taken into account, and the potential meth­ane production must be more realistically assessed with existing data in order to avoid overestimation of the global energy balance. Operational parameters such as the organic load­ing rate or the hydraulic retention time should be specified, since they directly influence the energy consumption of the anaerobic process.

Electrophoresis is another potential method for separating the microalgae without the need for chemicals. In this method an electric field directs the microalgae to the external part of the solution. Electrolysis of water produces hydrogen, which adheres to the flakes of microalgae and carries them to the surface. There are several benefits to using this technique, including environmental compatibility, versatility, energy efficiency, safety, and selectivity (Mollah et al., 2004), but the high cost means that this method is rarely used on a large scale (Uduman et al., 2010).

According to Richmond (2004), one of the main criteria for selecting an appropriate pro­cedure to harvest the microalgal biomass depends on the type of bioproduct desired. In prod­ucts of low commercial value, sedimentation through gravity with the aid of flocculants can be applied. However, for high-value products such as human food, aquaculture, or drugs, the use of continuous operation centrifuges is recommended because they can process large vol­umes of biomass. Another criterion for selecting the method of harvesting is the humidity for the biomass (Grima et al., 2003). Gravity sedimentation is usually more diluted than the centrifugation method, influencing the downstream process (Mata et al., 2010).

Even though the optimistic outlook on microalgae-based biofuels has driven microalgal research forward, we are still far from understanding the molecular networks underlying the complex metabolic flexibility and physiological adaptations to environmental cues of photosynthetic microalgae. Elucidation of molecular mechanisms of favorable traits such as stress-induced oil accumulation and anaerobic fermentation capability is of fundamental importance to the basic biology and of practical importance to algal biotechnology. The recent efforts in sequencing algal genome sequences have facilitated isolation of genes involved in lipid biosynthesis, photosynthesis, anaerobic adaptation, and stress regulation. The utiliza­tion of reverse genetics techniques has allowed functional characterization of some of the isolated genes. Furthermore, integrated omics approaches have started to reveal novel insights into the gene regulatory networks and cellular responses associated with metabolic features for fuel production. The accumulated knowledge has generated testable hypotheses and provided strategies to increase biomass and improve fuel production. However, the mo­lecular toolbox required for reliable genetic manipulation of microalgae remains limited to only a few species (e. g., C. reinhardtii, Volvox carteri, Nannochloropsis sp., and the diatom Phaeodactylum tricornutum) (Kilian et al., 2011; Leon and Fernandez, 2007; Schiedlmeier et al., 1994; Schroda, 2006; Siaut et al., 2007). For other species, genetic transformations have been documented sporadically but have not been robustly applied to routine genetic modi­fications. Lack of a reliable toolkit makes hypothesis-driven functional studies and practical manipulation in oleaginous species impossible. Development of custom-made molecular toolkits for the chosen oleaginous algal species will be essential for metabolic engineering. Because genomic sequencing projects of various microalgae are in progress, the development of toolkits will accelerate in the coming years and shape the future of microalgal biotechnology.

The recent advances in developing innovative technologies are aimed at improving the economics of microalgae-based biofuels. However, the practical application of the current technology is still in its infancy, and most of the work has only been demonstrated at the laboratory scale level. For instance, the proposed metabolic engineering strategies to improve biodiesel production are designed to increase oil content at the per-cell level. Crucial to overall yield relies on oil content at the per-culture basis. It is not clear whether small-scale experimental concepts can be directly translated into large-scale industrial setups. If not, what factors need to be considered and modified to allow laboratory oil producers to scale up to industrial-level production? Until now, accurate assessment of energy balance and carbon reduction potential based on industrial-scale data spanning continuous seasons remains lim­ited. It is therefore difficult to assess the overall yield, energy balance, carbon mitigation, and environmental impacts of the yet-to-be-refined technology. Moreover, other interference factors such as parasite contamination, temperature fluctuation, weather influence, and light penetration that can potentially affect the productivity of the energy crop also need to be con­sidered during such an assessment. To make microalgae-based fuels a realistic industrial commodity, multidisciplinary principles need to be integrated into current research strategies to establish production platforms. In particular, integration of engineering and biology, followed by life-cycle-based long-term feedback evaluation/adjustment analyses of produc­tion pipelines, will be crucial to establishing solutions and optimizing protocols for energy production from microalgae.

Currently, the algal products (mostly food supplements and cosmetics products) on the market cost approximately two orders of magnitude more than the current cost for biodiesel production derived from oleaginous crops (Wijffels and Barbosa, 2010; Wijffels et al., 2010). Therefore, the practicality of producing microalgae-based fuels using the current technology is still questionable (Chisti, 2008; Reijnders, 2008). Before the microalgae-to-fuels technology is in place, incorporating the existing high-valued commodities into fuel production pipelines may provide a sustainable business model for microalgal biotechnology.

Acknowledgment

I am grateful to Dr. Lu-Shiun Her for his valuable comments on and suggestions regarding this chapter.

Microalgae are more efficient than higher plants with respect to photosynthesis, through which light, together with CO2, is converted to chemical energy. Aside from photo­autotrophy, some microalgae are capable of growing heterotrophically as well as mixotro — phically. Heterotrophy refers to the fact that microalgae utilize organic carbon as the solo carbon and energy source for their reproduction in the absence of light; mixotrophy is indic­ative of microalgae performing growth in the presence of light through use of both CO2

(photosynthesis) and organic carbon sources. A number of microalgae have been reported for heterotrophic growth, among which green algae, in particular, Chlorella, are the most studied (Table 6.1). Microalgae are capable of utilizing a wide range of organic carbon sources, includ­ing sugars, hydrolyzed carbohydrates, waste molasses, acetate, and glycerol, as well as or­ganic carbons from wastewater (Table 6.1). Regardless of the microalgal species and strains, sugar—in particular, glucose—is the most commonly used organic carbon for boosting heterotrophic growth of microalgae (Table 6.1).

The uptake of external glucose relies on a hexose/H+ symport system that has been char­acterized in Chlorella (Hallmann and Sumper, 1996). In the presence of glucose, the hexose/H+ symport system is activated and transports glucose and H+ (1:1) into cytosol at the cost of equal ATP molecules (Tanner, 2000). The catabolism of transported glucose starts with a phos­phorylation of the hexose to form glucose-6-phosphate, an important intermediate product for respiration, storage, and biomass synthesis. Two pathways that share the initially formed glucose-6-phosphate are proposed to be involved in the aerobic glycolysis in algae—namely, the Embden-Meyerhof-Parnas (EMP) pathway and the pentose phosphate (PP) pathway (Figure 6.1; Neilson and Lewin, 1974). Both pathways are present in cytosol and contribute to the glucose metabolism in algae of autotrophy, mixotrophy, and heterotrophy, though their contributions may vary largely (Yang et al., 2000, 2002; Hong and Lee, 2007). For instance, glucose is mainly metabolized via a PP pathway in heterotrophic Chlorella pyrenoidosa, which accounts for 90% of total glucose metabolic flux distribution (Yang et al., 2000). The dominant role of a PP pathway was also demonstrated in the heterotrophic culture of the cyanobacterium Synechocystis sp. PCC6803 (Yang et al., 2002). In contrast, the EMP pathway serves as the major flux of glucose metabolism in algae in the presence of light (Yang et al., 2000,2002), suggesting the regulation of light on glycolysis. Table 6.2 shows the central metabolic network of glucose in heterotrophic algae with stoichiometric reactions.

As we mentioned, closed cultivation systems that house the growth of algae under con­trolled conditions are referred as photobioreactors (PBRs). Photobioreactors provide a more controlled environment than open ponds because these systems are closed and everything that the algae need to grow (carbon dioxide, water, and light) can be supplied with in the system (Weissman, 1987; Pulz, 2001). There are different types of PBRs reported for algae cultivation. PBRs facilitate better control of culture environment, such as carbon dioxide sup­ply, water supply, optimal temperature, efficient exposure to light, culture density, pH levels, gas supply rate, mixing regime, and so on (Mata et al., 2010). High mass transfer is one of the important criteria for PBR design, especially for CO2 sequestration (Ugwu et al., 2008). Ag­itations in PBR are done either mechanically or nonmechanically. Non-mechanical agitation can be observed airlift, bubble column, tubular reactor, and flat panel operations. PBRs spe­cifically designed for CO2 sequestration have the flexibility of using CO2-rich gas as a means of mixing as well as providing nutrients for the growth of algae (Hu et al., 1996). PBRs can be operated in both batch and continuous modes. In comparison with open culture systems, a closed photobioreactor is easy to control with regard to environmental parameters and can achieve high growth rates (Pulz, 2001; Sierra et al., 2008). Higher biomass of microalgae pro­ductivity is obtained in closed cultivation systems where contamination can also be prevented (Ramanathan et al., 2011). Fully closed photobioreactors provide opportunities for monoseptic culture of a greater variety of algae than open cultivation systems (Borowitzka, 1999). Various types of closed cultivation systems are studied to a great extent.

Chlamydomonas reinhardtii has been comprehensively investigated in terms of potential hydrogen photoproduction; in addition to hydrogen, a variable amount of byproducts are generated as part of the microalgal biomass. Its volatile nature permits the biomass to remain essentially intact (Kruse, Rupprecht et al., 2005).

To obtain further energy, the biomass can itself be processed via extraction and transester­ification of the remaining lipids to produce biodiesel. For example, the total lipid content of the biomass of the C. reinhardtii strain D1 after photobiological hydrogen production is 15 ± 2% on a dry-weight basis; oil may then be extracted, being composed of 3.3% w/woii phytols, 21% w/woii triglycerides, 39% w/woii polar lipids, and 37% w/woii highly polar lipids, to eventually biodiesel composed of 41% saturated fatty esters, 53% mono unsaturated fatty esters, and 7.2% polyunsaturated fatty esters (mainly linoleic acid) (Torri, Samori et al., 2011). This mix of methyl esters adheres to European Union (EU) standard EN 14214 pertaining to biodiesel specifications.

Following biodiesel production from the spent biomass, the lipid-free residue can still be used for animal feed or be anaerobically digested into biogas (Sialve, Bernet et al., 2009) as discussed in further detail in the following paragraph. Moreover, pyrolysis of the residue left after extraction may represent another pathway to produce extra energy (Mohan et al., 2006). Pyrolysis of the microalgal extraction residue may lead to oil with a quality lying between pe­troleum tar and bio-oil from lignocellulosic biomass (Miao et al., 2004); the mass yields of biochar, oil, and gas are 44 ± 1%, 28 ± 2%, and 28 ± 1%, respectively. The ash content of said biochar, obtained via combustion at 700 °C, was 45 ± 5%. On an ash-free basis, the mass yields of biochar, oil, and gas were 24 ± 5%, 38 ± 9%, and 36 ± 1%, respectively (Torri, Samori et al., 2011). Since a major portion of ashes, phosphorus, and nitrogen are retained in biochar, it may be used as fertilizer to improve the productivity of soil, thus contributing to abatement of greenhouse gases while making it possible to convert carbon-neutral energy into carbon­negative bio-energy (Kruse and Hankamer, 2010).

Additionally, production of biogas via fermentation of the microalgal biomass offers the possibility to recycle a large proportion of the original nutrients. Although this option is not economically feasible at low throughput rates, it will become a more interesting possi­bility as medium costs become a larger fraction of the final cost, coupled with consideration of phosphorous limitations (Cordell, Drangert et al., 2009).

Pyrolysis forms the base of thermochemical conversion in most cases. The products of con­version include biocrude, tars, charcoal (carbonaceous solid), and permanent gases, including methane, hydrogen, carbon monoxide, and carbon dioxide. The products and ratios in which they are formed vary depending on the reaction parameters, such as environment, reactors used, final temperature, rate of heating, and source of heat. Pyrolysis is the fundamental chem­ical reaction process and is simply defined as the chemical change that occurs when heat is applied to a material in the absence of oxygen. Hydrothermal upgradation (HTU) is one of the processes of a general term of thermochemical conversion (TCC), which includes gasification, liquefaction, and pyrolysis. Various conversion processes for the production of a wide range of products from algal biomass are provided in Figure 11.2.

The hydrothermal upgradation process is a promising liquefaction process because it can be used for the conversion of a broad range of biomass feedstock. The process is especially best suited to wet materials; the drying of feedstock is not necessary because the water is used as one of the reactants. This thermochemical means of reforming biomass may have energetic advantages since, when water is heated at high pressures, a phase change to steam is avoided, which in turn avoids large enthalpic energy penalties. Superior to pyrolysis technology, high — pressure direct liquefaction technology has the potential for producing liquid oils with much higher caloric values and a range of chemicals, including vanillin, phenols, aldehydes, and organic acids (Appell et al., 1971). The advantage of liquefaction is that the bio-oil produced is not miscible with water and has a lower oxygen content, and therefore higher energy con­tent, than pyrolysis-derived oils (Goudriaan et al., 2001; Huber et al., 2006). Oxygen hetero­atom removal occurs most readily by dehydration, which removes oxygen in the form of water, and by decarboxylation, which removes oxygen in the form of carbon dioxide (Peterson et al., 2008). The changes and optimization of reaction parameters and catalysts can produce the functional hydrocarbons/specialty chemicals in a single step. In the follow­ing sections the process of hydrothermal upgradation is explained in detail and its use for the valorization of algae is discussed.

FIGURE 11.2 Product profile from algae by various processes.

The main selection criterion has been a clear definition of a functional unit. The concept of

functional unit (FU) is the main characteristic of the LCA (Udo de Haes et al., 2006) and allows

relevant and fair comparisons between studies or between different technological options.

Here the studies are briefly described:

• Kadam (2002) (Kad). Comparative LCA of electricity production from coal only or from coal and microalgal biomass. Half of the CO2 emitted from the power plant is assumed to be captured by a monoethanolamine (MEA) process.

• Lardon et al. (2009) (Lar). LCA of biodiesel production in open raceways with or without nitrogen stress and with wet or dry extraction of the lipids.

• Baliga and Powers (2010) (Bal). LCA of biodiesel production in photobioreactors located in cold climates. Cultivation is realized under greenhouses; heat losses from a local power plant are used as the heat source.

• Batan et al. (2010) (Bat). LCA of biodiesel production in photobioreactors based on the Greenhouse Gases, Regulated Emissions, and Energy use in Transportation (GREET) model.

• Clarens et al. (2010) (Cla10). Comparative LCA of the energy content of microalgae with terrestrial crops used as biofuel feedstock. Microalgae are cultivated in open raceways using chemical fertilizers.

• Jorquera et al. (2010) (Jor). Comparative LCA of microalgal biomass production in open raceways, tubular photobioreactors, and flat plate photobioreactors.

• Sander and Murthy (2010) (San). LCA of biodiesel production in open raceways based on the GREET model with a culture in two stages (first photobioreactors, then open raceways).

• Stephenson et al. (2010) (Ste). Comparative LCA of biodiesel production in open raceways and photobioreactors. Oil extraction residues are treated by anaerobic digestion; the digestates are used as fertilizers.

• Brentner et al. (2011) (Bre). Combinatorial LCA of industrial production of microalgal biodiesel. The base configuration consists of cultivation in open raceways, hexane extraction of dry algae, and methanol transesterification. Oilcakes are considered as a waste; the optimized configuration is composed of cultivation in PBR, extraction with in situ esterification by supercritical methanol, anaerobic digestion of oilcakes, and use of the digestates as fertilizers.

• Campbell et al. (2011) (Cam). LCA and economic analysis of biodiesel production in open ponds. Pure CO2 produced during the synthesis of nitrogen fertilizer is used as a source of carbon.

• Clarens et al. (2011) (Cla11). LCA of algae-derived biodiesel and bioelectricity for transportation. Four types of bioenergy production are compared: (1) anaerobic digestion of bulk microalgae for bioelectricity production, (2) biodiesel production with anaerobic digestion of oilcakes to produce bioelectricity, (3) biodiesel production with combustion of oilcakes to produce bioelectricity, and (4) direct combustion of microalgae biomass to produce bioelectricity. Four ways to supply nutrients are compared: (1) pure CO2, (2) CO2 captured from a local coal power plant, (3) CO2 in flue gas, (4) CO2 in flue gas and nutrients in wastewater.

• Collet et al. (2011) (Col). LCA of biogas production from anaerobic digestion of bulk microalgae. Biomass is grown in open raceways; digestates are used as fertilizers.

• Hou et al. (2011) (Hou). LCA of biodiesel from microalgae and comparison with soybean and jatropha.

• Khoo et al. (2011) (Kho). LCA of biodiesel from microalgae. Cultivation is carried out in two phases: first in photobioreactors, then in open raceway.

• Yang et al. (2011) (Yan). LCA of biodiesel production limited to water and nutrient consumption.

Among the 15 selected papers, two functions are assessed: either biomass production (two publications) or bioenergy production (14 publications). Three final vectors for the bioenergy are considered: methylester (11 publications), methane (2 publications), and electricity (2 publications). It is worth noting that these different energy carriers have different charac­teristics. Methane and methylester are easily storable, unlike electricity. There is also an im­portant diversity of FUs. Most of the studies focus on the production of biodiesel as the main energy output from microalgae. The amount of biodiesel produced is described in different units: volume (Baliga and Powers, 2010), mass (Stephenson et al., 2010), or energy content (Lardon et al., 2009). Unfortunately, there is no consensus on the values of energy content or on the mass density of algal oil and algal methylester; in addition, the description of the energy content is not harmonized and can be based either on the lower heating value (LHV) or the high heating value (HHV). Finally, among the studies dedicated to biodiesel production, six are well-to-pump studies, which means that the use of the fuel is not included in the perimeter (Baliga et Powers, 2010; Batan et al., 2010; Sander and Murthy, 2010; Brentner et al., 2011; Khoo et al., 2011; Yang et al., 2011), and five are well-to-wheel studies, where the use of the fuel is included (Lardon et al., 2009; Stephenson et al., 2010; Campbell et al., 2011; Clarens et al., 2011; 2011; Hou et al., 2011).

This diversity of FUs leads to a diversity of perimeters for the inventory. Table 13.1 sum­marizes the assessed systems. The different steps potentially included in the perimeter of the study can be classified among five categories: production of the inputs required for the cul­tivation (I), cultivation (C), harvesting and conditioning of microalgae (H), transformation into different types of energy carrier (T), and, eventually, use of the produced energy (U).

Figures 13.1 and 13.2 illustrate the various options met in the selected LCAs. The culture phase is the more consensual, with two options: open raceways or photobioreactors. The transformation phase is the one with the largest number of alternatives, including the final energy carrier or the fate of the coproducts.

This book is about biofuels from microalgae. Microalgae have been used com­mercially for decades, but not for producing biofuels. Interest in algal fuels has seen a spectacular reawakening within the last 10-years. Several factors are driving the renewed quest for algal fuels: Concern about depletion of petroleum; the desire for energy independence; the need for carbon neutral renewable fuels that can be produced with­out compromising the supply of food and freshwater; and the need to prevent further deforestation. Algal fuels are not yet com­mercial and may not reach the market for long time or near-future. Nevertheless, they represent a strategic opportunity that must be persistently developed into a renewable and environmentally sustainable source of high-energy density liquid fuels.

The present book, which is the third book in the series on BIOMASS beingpublished by us, presents up-to-date state-of-art informa­tion and knowledge by the internationally recognized experts and subject peers in var­ious areas of algal biofuels. The 14 chapters of the book attempt to address many of the key issues relating to algal biofuels. Algal culture systems — open ponds as well as the closed photobioreactors — are discussed. Genetic and metabolic engineering of algae for enhanced capabilities in production of fuels are examined. Aspects of carbon fixation in industrially important microalgae are discussed. Technologies for recovering the biomass from the culture broth are assessed.

A chapter is devoted to heterotrophic produc­tion of algal oils as potential fuels. Production of fuels via fast pyrolysis of algal biomass is treated in some detail. An overview is provided of algal oils as fuels in one chapter. A chapter considers production of biohydro­gen from microalgae. Any production of algal fuels must consider the fate of the spent biomass. This is discussed in one chapter. A chapter is focused on the hydrothermal treatment of algal biomass to produce hydro­carbon fuels. Scale-up of production and com­mercialization aspects of algal fuels are examined in one chapter. A chapter discusses the life-cycle assessment of algal fuels. Changes in technology in this rapidly develop­ing field are bound to greatly diminish the environmental impact of future algal fuel production. Finally, a chapter assesses in some depth the economics of microalgal biomass production. Continuing developments will surely reduce the cost of producing algal fuels in the future.

The book would be of special interest to the post-graduate students and researchers of applied biology, biotechnology, microbiol­ogy, biochemical and chemical engineers working on algal biofuels. It is expected that the current discourse on biofuels R&D would go a long way in bringing out the exciting technological possibilities and ush­ering the readers towards the frontiers of knowledge in the area of biofuels and this book will be helpful in achieving this dis­course for algal biofuels.

We thank authors of all the articles for their cooperation and also for their prepared­ness in revising the manuscripts in a time­framed manner. We also acknowledge the help from the reviewers, who in spite of their busy professional activities, helped us by evaluating the manuscripts and gave their critical inputs to refine and improve the arti­cles. We warmly thank Dr Marinakis Kostas and Dr Anita Koch and the team of Elsevier for their cooperation and efforts in produc­ing this book.

Ashok Pandey Duu-Jong Lee Yusuf Chisti Carlos Ricardo Soccol Editors