Thread Content
October 27, 2008 Source: Science and Technology Daily http://www.gov.cn/fwxx/kp/2008-10/27/content_1132010.htm To mitigate global warming, people need a new type of fuel source that does not compete with agriculture for land or water. At the “2008 Fisheries Science and Technology Forum” held in Shanghai recently, scientists introduced a new type of biofuel derived from the ocean. It has become a consensus that humanity must develop alternatives to oil. Food can be used to produce biofuels, but in 2007 the world produced only 7.5 billion gallons of alcohol from corn, and the prices of feed and corn have doubled compared to before. In the long run, alcohol production cannot reduce substantial greenhouse gas emissions. To mitigate global warming, people need a completely new source of fuel that does not compete with agriculture for land or water, requires no preparation for cultivation, and does not use harmful chemicals. As a result, more scientists turned their attention to the oceans, and aquaculture of aquatic microalgae is precisely such a source of fuel. At the \"2008 Fisheries Science and Technology Forum\" held in Shanghai at the end of September this year, Wang Zhao-kai, the first president of the Chinese Society of Aquaculture Engineering and a member of the ** Academy of Engineering in the United States, introduced a new type of biofuel derived from the ocean – diatoms. Cost is the most important factor. According to Wang Zhao Kai, among the candidate fuel sources that can replace oil, microalgae hold a leading position, especially diatoms. There are nearly 100,000 species of diatoms in the world. Diatoms contain various lipids, including compounds such as sterols, waxes, and acyl lipids; some diatoms have lipid contents as high as 70%–85%. By altering growth conditions, the lipid content of different diatom species can be increased. According to the Global Oil Club, 1 hectare of microalgae can produce 96,000 liters of biodiesel per year, while 1 hectare of oil palm can produce only 5,950 liters, and 1 hectare of soybeans can produce 446 liters. As early as 1978, the United States launched a research project called the \"Aquatic Species Program\" to demonstrate that biofuel produced from microalgae could be more than twice as effective as current petroleum and diesel fuels. Research in this area in Japan focuses on closed systems, which are very expensive, such as those that use fiber-optic vision light emitters. They achieved high productivity, but still could not meet the acceptable operating cost requirements. “What technology is most needed at the moment? ”Wang Zhao Kai said, “It is an open production system that operates economically and can maintain the dominance of certain microalgae.” We currently use the marine diatom Cosmarium as a research model. Of course, other species of diatoms and other types of microalgae can also be considered. From diatom cultivation and isolation to the extraction of oils and fatty acids, the entire process must be economically viable. The current production system is a biofuel production system based on an open microalgae cultivation system; it can capture carbon dioxide simultaneously and is also cost-competitive. ” Traditionally, aquaculture experts cultivate microalgae in closed systems to prevent the contamination that is inevitable in open systems, but this approach is difficult to manage and involves high costs and energy consumption. “Since the late 1990s, we have developed a small commercial system that operates successfully for cultivating marine diatoms—Cosmarium—in an open system, and filed for a patent in 2004. ”Wang Zhao Kai said that the existing open systems are still at the pilot-scale stage and are limited to a few types of marine diatoms; much work is still needed to extend these systems to freshwater microalgae species as well as to improve production efficiency. Fuel production requires key technologies. \"Harvesting microalgae, improving the efficiency of photobiological reactions, extracting oils, and producing fuel from diatom oils are among the key technologies involved.\" ”Wang Zhao Kai said. First, separating microalgae from their growth medium requires a large amount of energy. Conventional separation methods, such as centrifugation, filtration, or flocculation, are difficult to operate and require the addition of chemicals during the separation process. For example, Ceratium has an active substance on its surface that allows us to use a foaming separation method to concentrate the microalgae. By applying the foam separation method, 90% of Ceratium can be separated from its cultivation medium, after which Ceratium regenerates. To improve the efficiency of photobiological reactions, it is necessary to design a production system that maintains an optimal concentration of algal cells in the reactor at all times. Due to the silicate cell wall present in diatom frustules, which provides strong protection, oil extraction becomes difficult; conventional methods such as mechanical, chemical, or enzymatic treatment are not very effective. High-temperature decomposition technology requires a large amount of energy input, which reduces cost efficiency. There is now an HPQR alternative method that rapidly transfers diatoms from a high-pressure area to a low-pressure area, causing the cells to rupture, thereby eliminating the need for filtration during the separation of fatty acids. Research on HPQR and other oil extraction methods will further advance the commercialization of microalgae biodiesel. To convert diatom oils into biodiesel, it is necessary to understand the various components of microalgae and their oil content, as well as to develop appropriate fuel production methods in order to maximize yield. At the same time, it is also necessary to master reliable methods for testing the oil content in raw materials. Marine microalgae have clear production advantages. Wang Zhao-kai also told reporters that a recent research report indicates that using microalgae to produce biodiesel is now more cost-competitive than using mineral oil. In 10–20 years, as easily extractable oil approaches exhaustion and global warming intensifies, microalgae biodiesel will become more price-competitive compared to relatively expensive oil alternatives such as shale oil and tar sands oil. Furthermore, more biological products and by-products can be extracted from microalgae, further improving the economic viability of microalgae cultivation. Potential bioproducts include specialty organic substances such as food-grade beta-carotene, pharmaceuticals, and pigments, as well as various common compounds such as polysaccharides, carbohydrates, surfactants, and fermentation products like biogases. There are also high-value oils that can be used as animal feed. In addition, microalgae can also be used to treat agricultural or municipal wastewater, to extract potential value from the nutrients in it, and to help reduce greenhouse gas emissions. A research report by an American company indicates that by cultivating microalgae, it is possible to reduce CO2 emissions from diesel generator exhaust by up to 92%, as well as cut nitrogen oxide emissions. With high yields, low water requirements, and efficient fertilizer use, the potential yield of microalgae is more than 30 times that of terrestrial crops. The advantages of producing marine microalgae, coupled with ongoing advancements in fuel production technologies, are turning the vast oceans into a source of hope for new energy. (Reporters Fan Jian, Chang Lijun)