Production

Man Kee Lam, Keat Teong Lee

School of Chemical Engineering, Universiti Sains Malaysia, Pulau Pinang, Malaysia

12.1 INTRODUCTION

Increasing energy demand coupled with serious environmental concerns over the last 10 years have made the search for renewable and sustainable energy a key challenge of this century (Singh and Gu, 2010). To date, many countries are still heavily dependent on crude petroleum as a source of transportation fuel, and the price of petroleum has always fluctuated in the global fuel market. In addition, 57.7% of the primary energy consumed has been used in the transportation sector, where the consumption rate of fossil diesel fuel was estimated to be 934 million tonnes per year (Kulkarni and Dalai, 2006; Lam et al., 2010). Nevertheless, fossil fuels are nonrenewable resources that are limited in supply and will one day be exhausted (Sharma and Singh, 2009). The concern regarding limited energy resources is caused by the rapid growth in human population and industrialization (Pimentel and Pimentel,

2006) . Due to our knowledge of the impending shortage of energy resources, the era of inex­pensive fossil fuel no longer exists. Instead, the world is facing a shortage in the fossil fuel supply, bitter conflicts, and an increasing number of undernourished people, especially in the undeveloped countries (Lam et al., 2010).

Lately, much attention has been devoted to the cultivation of algae for biofuel production. Algae are desirable for biofuel production compared to land-based plants because (1) algae are fast-growing microorganisms, with reproducibility 100 times faster than land-based plants and able to double their biomass in less than one day; (2) some algal strains can accu­mulate significant amounts of lipids within their cells (as high as 75% of their weight), and the lipids can be converted to biodiesel; (3) algal-based biofuels do not interfere with food secu­rity concerns; (4) fertile land is not required to cultivate algae and thus their cultivation does not compete with agricultural land, and (5) cultivation of algae could be coupled with waste­water treatment and biological CO2 mitigation that enhances the sustainability of algal-based biofuels (Chisti, 2007; Mata et al., 2010; Mutanda et al., 2011; Pittman et al., 2011). The residue of algal biomass after lipid extraction could be further converted to produce different types of biofuels such as bioethanol, biomethane, and biohydrogen (Harun et al., 2010). Examples of algal strains that have been widely evaluated for biofuel production include Botryococcus braunii, Neochloris oleoabundans, Nannochloropsis sp., Chlorella vulgaris, Dunaliella salina, and Haematococcus pluvialis (Chisti, 2007; Harun et al., 2010; Mata et al., 2010; Singh and Gu, 2010).

To date, large-scale algal cultivation still faces several technical challenges that hinder the commercialization potential of algal biomass as a renewable feedstock for biofuel production. The challenges can be divided into two categories: (1) upstream processes: algal selection and cultivation method, energy input for operating closed photobioreactors, nutrient sources, water reusability and footprint, and sensitivity of algae to surrounding environment; and (2) downstream processes: harvesting and drying techniques for algal cells, effective algal lipid extraction methods, algal biodiesel conversion technologies, and biodiesel quality and potential to diversify biofuel production from algal residue after the lipid-extraction process. Beyond the technical challenges, the economic feasibility of commercial algal biofuel produc­tion is still questionable because algal cultivation and associated biofuel production technol­ogies are still under development. As such, an in-depth understanding of these technical and economically related problems should be able to help identify possible solutions to enhance the commercial potential of algal biofuels (Bull and Collins, 2012). In this chapter, several im­portant technical problems surrounding the entire algal biofuels supply chain are discussed, especially from a thermodynamic (energy-balance) perspective. In addition, techno-economic assessments of algal biofuel production are included at the end of this chapter to benchmark the current status of algal biofuels compared to fossil fuels and other renewable fuels.