December, 2009 Int J Agric & Biol Eng Open Access at http://www.ijabe.org Vol. 2 No.4 1 Review of the biological and engineering aspects of algae to fuels approach Paul Chen1, Min Min1, Yifeng Chen1, Liang Wang1, Yecong Li1, Qin Chen1, Chenguang Wang1, Yiqin Wan1,2, Xiaoquan Wang1, Yanling Cheng1,3, Shaobo Deng1, Kevin Hennessy1, Xiangyang Lin1,4, Yuhuan Liu1, Yingkuan Wang1,5, Blanca Martinez1, Roger Ruan1,2 (1. Center for Biorefining, Department of Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Ave., St. Paul, MN 55108, USA; 2. State Key Laboratory of Food Science and Technology, Engineering Research Center for Biomass Conversion, Ministry of Education, Nanchang University, Nanchang 330047, China; 3. Biochemical Engineering College, Beijing Union University, Beijing, China; 4. College of Biological Science and Technology, Fuzhou University, Fuzhou 350108, China; 5. Chinese Academy of Agricultural Engineering, Beijing 100125, China) Abstract: Current biofuel production relies on limited arable lands on the earth, and is impossible to meet the biofuel demands. Oil producing algae are alternative biofuel feedstock with potential to meet the world’s ambitious goal to replace fossil fuels. This review provides an overview of the biological and engineering aspects in the production and processing technologies and recent advances in research and development in the algae to fuels approach. The article covers biology, selection and genetic modification of algae species and strains, production systems design, culture media and light management, harvest and dewatering, downstream processing, and environment and economic assessment. Despite the many advances made over several decades, commercialization of algal fuels remains challenging chiefly because of the techno-economic constraints. Technological breakthroughs in all major aspects must take place before commercial production of algal fuels becomes economically viable. Keywords: algae, microalgae, open pond, enclosed photobioreactor, light, harvest, dewatering, extraction, hydrothermal liquefaction, gasification, pyrolysis, fermentation DOI: 10.3965/j.issn.1934-6344.2009.04.001-030 Citation: Paul Chen, Min Min, Yifeng Chen, Liang Wang, Yecong Li, Qin Chen, et al. Review of the biological and engineering aspects of algae to fuels approach. Int J Agric & Biol Eng, 2009; 2(4): 1－30. investment in biofuels technology development as there is 1 Introduction now. Bioethanol and biodiesel are the two most There has never been so much interest, effort, and Received date: 2009-12-25 Accepted date: 2009-12-31 Chenguang Wang, Ph.D, Postdoc Research Associate, Research Biograpies: Paul Chen, PhD, Senior Research Associate, Program interest areas: Biomass to Liquid fuel process, Email: Director, Food Science and food engineering, renewable energy, [email protected]; Yiqin Wan, PhD Candidate, Research biorefining. Email: [email protected]; Min Min, Ph.D, Follow of UMN, Assistant Prof. of Nanchang University, majored Research Associate, research in algal mass production system in renewable energy, bioresource utilization and processing, food development, spectral based nutrients detection, system control. engineering; Email: [email protected]; Xiaoquan Wang, Email: [email protected]; Yifeng Chen, Ph.D, Research Ph.D, Postdoc Research Associate. Email: [email protected]; Associate, research interest areas Algal strain development, Algal Yanling Cheng, PhD, Associate Professor, research areas: design, biology, Email [email protected]; Liang Wang, Ph.D, synthesis, and applications of functional polymeric materials from Postdoc Research Associate, Research interest areas: Algae-based renewable resources. Email: [email protected]; biological wastewater treatment. Email: [email protected]; Shaobo Deng, PhD, Senior Research Associate, Email: Yecong Li, Ph.D student, Research Assistant, research interest [email protected]; Kevin Hennessy, Graduate Student, areas: Lipid extraction and biodiesel production from algae renewable energy, Email: [email protected]. edu; Xiangyang Lin, biomass. Email: [email protected]; Qin Chen, Ph.D, Postdoc PhD, associate professor, email: [email protected]; Yuhuan Liu, Research Associate, Research in renewable energy, value-added PhD, Assistant Professor, biomass refining, food science; Email: processing, and food engineering. Email: [email protected]; [email protected]; Yingkuan Wang, PhD, associate 2 December, 2009 Int J Agric & Biol Eng Open Access at http://www.ijabe.org Vol. 2 No.4 successful biofuels widely available in many parts of the It is under this context that a renewed interest in world. However, the pursuit for biofuel alternatives does algae has come into play in the biofuel sector. The April not stop there for a number of reasons. First, current 2009 GreenTech Innovations report published by [4] production of biofuels cannot meet the existing and future GreenTechMedia listed more than 50 algae related demands. Many countries have set ambitious targets companies in the United States alone, most of which are replacing fossil fuels with alternatives including biofuels start-up companies formed in recent years. Hundreds of within 15 to 20 years. Aside from the limited higher education and research institutes worldwide are production capacity, production of grains and oil crops conducting research on algae. The efforts span over based biofuels is also limited by the available arable lands many areas of “algae to fuels” technologies including on the earth. The United States roughly uses 60 billion production system development, algae harvest, algae gallons (1gallon = 4.5461L) diesel and 120 billion gallons strain development and genetic modification, algae gasoline per year[1]. The 120 billion gallons of gasoline products development, etc. is equivalent to 78 billion gallons of diesel (Gasoline Algae offer many potential advantages: contains about 65% of the energy of diesel). Therefore ● algae can potentially produce 1 000-4 000 gallon/ the total transportation fuels need is translated to 138 acre/yr significantly higher than soybeans and other oil billion gallons of diesel, equivalent to 140.8 billion crops (Table 1) gallons biodiesel (Biodiesel is 2% less than petrol diesel ● they do not compete with traditional agriculture in terms of fuel efficiency). If the entire arable land of the because they are not traditional foods and feeds and they United States (roughly 435 million acres, 1 acre = can be cultivated in large open ponds or in closed 4046.86 m2= 4.047×10-3 km2) were used to grow soybean photobioreactors located on non-arable land for oil, it would produce about 21 billion gallons of ● they can grow in a wide variety of climate and water biodiesel per year (based on 48 gallon/acre/yr), only conditions; they can utilize and sequester CO2 from many about 15% of the total US biodiesel need. Secondly, sources current production of biofuels especially bioethanol and ● finally, they can be processed into a broad spectrum biodiesel displaces croplands currently for food and feed of products including biodiesel via trans-esterification, production, and has been blamed for food price hike, green diesel and gasoline replacements via direct catalytic threatening food security and putting tremendous burden hydrothermal conversion, and catalytic upgrading, and on the poor[2,3]. Thirdly, there are tremendous business bioethanol via fermentation, methane via anaerobic opportunities in the biofuel sector, which attract interests digestion, heat via combustion, bio-oil and biochar via and investments from large and small entrepreneurs and thermochemical conversion, and high protein animal investors. feed. Table 1 Comparison of oil yields from biomass feedstocks (Modified from DOE[5]) professor of editorship, visiting scholar at UMN, majoring in Oil Yield Land needed to produce 140.8 gallons agricultural machinery, renewable energy, editing and publishing. Crop (gallon/acre/yr) biodiesel (million acre) Email: [email protected]. Blanca Martinez, PhD, Email: Soybean 48 2 933 [email protected]; Roger Ruan, PhD, Yangtze Scholar Camelina 62 2 270 Distinguished Guest Professor at Nanchang University, Director at Sunflower 102 1 380 Center for Biorefining, and Professor at University of Minnesota. Jatropha 202 697 Food science and nutrition, food engineering, renewable energy, Oil palm 635 2 217 biorefining, bioprocessing, and value-added process development. Algae 1 000-4 000 140.8-35.5 Corresponding author: Roger Ruan, PhD, Professor. Dept. of BioProducts & BioSystems Engineering, University of Minnesota, Above all, the huge productivity potential of algae is 1390 Eckles Ave. St Paul, MN55108,USA. Tel: 612-625-1710; the most important driving force behind the algae fever. Fax: 612-624-3005. Email: [email protected] To put it in perspective, to produce 140.9 billion gallons December, 2009 Review of the biological and engineering aspects of algae to fuels approach Vol. 2 No.4 3 biodiesel from algae would require a total area of 35- stems, and leaves of higher plants. In contrast, 140 million acres marginal or non-arable land, which is microalgae are a large group of microscopic about 60%-250% of the size of the State of Minnesota, photosynthetic organisms, many of which are present in a based the conservative oil yields of 1 000-4 000 unicellular manner and found in diverse environments. gallon/acre/yr. Microalgae are the subject of this review. The terms The concept of using algae as energy feedstock dates “microalgae” and “algae” will