[China Journal of Science] Microalgae Biodiesel： Innovate in Being Original.

Microalgae culture tank

Microalgae Image Source: Baidu Image
　　As a strategic technology involving bioenergy, carbon and alkali emission and agricultural production, microalgae biodiesel has attracted many research institutions, universities and enterprises all over the world to participate in research and development. However, the existing microalgae biodiesel technology is still uneconomical, with large investment, high cost and large land occupation, which are problems to be solved.
　　Extracting oil from microalgae sounds ridiculous, but many scientists are thinking about it at present.
　　As a strategic technology involving bioenergy, carbon and alkali emission and agricultural production, microalgae biodiesel has attracted many research institutions, universities and enterprises all over the world to participate in research and development. It has been regarded as one of the main technical routes for the development of advanced biofuels in the world.
　　As Cao Xianghong, an academician of China Academy of Engineering, said: "With the technological progress and the improvement of environmental requirements, microalgae biodiesel technology will show its competitiveness."
　　The protagonist of oil substitution technology
　　The three oil crises from 1970s to 1990s prompted the United States and other western developed countries, which are highly dependent on oil resources, to pay attention to the research of sustainable oil alternative energy technologies.
　　"Microalgae bioenergy technology has become the protagonist of this technology development." Liu Tianzhong, a researcher at Qingdao Institute of Bioenergy and Process, Chinese Academy of Sciences, said that microalgae, as a kind of single-celled low-grade plants, has a theoretical yield of 250 tons per hectare per year, which is much higher than any land plants. Moreover, algae cells accumulate as much as 50%~70% oil, which is very easy to be converted into biodiesel and even aviation fuel by catalysis.
　　In 1976, the U.S. Department of Energy began a 20-year "Aquatic Species Plan", the important goal of which was to solve the large-scale production technology of oil-producing microalgae. Japan, Canada, Britain and so on have also included microalgae biodiesel technology in major research plans. After 2000, the concerted action of global carbon emission reduction once again ignited the upsurge of microalgae biodiesel technology research.
　　"China has started relatively concentrated research since the end of the Eleventh Five-Year Plan, especially in the Twelfth Five-Year Plan." Researcher Lu Xuefeng, deputy director of Qingdao Institute of Bioenergy and Process, Chinese Academy of Sciences, said that the Ministry of Science and Technology has deployed a number of project support, including Chinese Academy of Sciences, China Ocean University, East China University of Science and Technology, etc. to vigorously carry out related technical research. Among them, Qingdao Institute of Energy, Chinese Academy of Sciences has systematically established a research and development team for the whole technology chain of microalgae energy such as algae seed selection, scale cultivation, processing and utilization, and carried out systematic research on basic research, common key technologies and pilot scale-up of microalgae bioenergy.
　　Liu Tianzhong said that in recent years, China has made great progress in genetic breeding, functional genes and metabonomics, genetic engineering transformation, scale cultivation and equipment technology, and the transformation of biodiesel and aviation biofuels. The overall level is comparable to that of foreign countries, and some technologies are even leading.
　　Breeding filamentous oil-producing algae to fight against "eating goods"
　　However, Min Enze, an academician of the two academies, bluntly said that it is still very difficult to develop microalgae biodiesel, and there is still a long and difficult way to go for large-scale industrial production.
　　"Microalgae culture pollution caused by microbial infection and explosive protozoan bite is a common story in oil-producing microalgae culture." Liu Tianzhong told reporters that microalgae cultivation is the basis for the development of microalgae biodiesel, but when they try to carry out large-scale high-density cultivation, all kinds of "foodies" will flock to them.
　　As a matter of fact, the research of American Aquatic Species Program failed to establish a commercial microalgae bioenergy system, one of the most important reasons is that it failed to solve the pollution problem in microalgae scale culture.
　　Liu Tianzhong led the team to adjust acid, alkali and pesticides … All the methods that could be thought of were used, and it didn’t work.
　　Suddenly, one day, Liu Tianzhong was inspired by fish farming: young fry must be fed with bait with high nutrition and small particles. The so-called "ants can’t swallow elephants". At the same time, he noticed that at present, only spirulina has formed a real large-scale commercial culture, and serious pollution rarely occurs in the culture process. One of the most likely reasons is that filamentous spirulina, which is much larger than rotifer size, is not conducive to the phagocytosis of protozoa.
　　Therefore, Liu Tianzhong’s team screened five strains of Chrysophyta for cultivation and oil evaluation in the laboratory. The results showed that the total lipid content could reach 51%~63% after 12-day culture, and the neutral lipid which can be used as biodiesel accounted for more than 80% of the total lipid. The total lipid and neutral lipid were even higher than those of the traditional single-cell oleaginous algae, and they grew quite fast. More importantly, it has been cultivated in dozens of batches a year in the pilot-scale amplification system in an open pool, and no protozoan pollution such as rotifers has occurred.
　　At present, they have obtained many strains of filamentous algae with high yield from many habitats in China, and have carried out the cultivation evaluation of other filamentous algae including fresh water and seawater. This provides a new way to solve the problem of pollution and collection of energy microalgae in large-scale culture.
　　Scale and cost are still bottlenecks.
　　"The existing microalgae biodiesel technology is still uneconomical, with large investment, high cost and large land occupation." Min Enze gave an example: the reactor of a 30,000-ton/year tubular photoreactor industrial demonstration device is 106,000 meters long and covers an area of 170,000 square meters. The demand for nitrogen, potassium and calcium and the power consumption are amazing.
　　This has also become the main obstacle to the industrialization of microalgae energy technology.
　　"For many years, researchers have tried to improve the cultivation technology and equipment structure, but the improvement effect is very limited." In this regard, Liu Tianzhong put forward the concept of microalgae "biofilm monolayer culture", that is, algae cells were inoculated on the surface of artificial media to form a growth membrane, and a small amount of culture medium was provided to keep the membrane surface moist, and then cultured in light and carbon dioxide environment. In this way, the light can directly shine on the cell surface, unlike the attenuation in water during traditional suspension culture, and the algae mud can be scraped directly, and the collection cost is greatly reduced.
　　At the same time, Liu Tianzhong got inspiration from the three-dimensional planting of vegetables in greenhouse: arranging these microalgae biomembrane in a certain way and diluting the excessive sunlight to a larger culture area can solve the photoinhibition of algae by strong light on the one hand, and improve the utilization rate of solar energy on the other hand, thus increasing the yield of culture area.
　　"This is 3 to 5 times higher than the traditional microalgae liquid culture mode, which is the highest level reported in the literature at present." Liu Tianzhong said that they have completed the pilot scale-up of 200 square meters, and this brand-new culture mode has also become a research hotspot of microalgae culture technology.
　　"From a global perspective, microalgae energy is still in the stage of research and development demonstration." Lv Xuefeng believes that to realize the industrialization of microalgae biodiesel, scale and cost are still bottlenecks that need to be solved vigorously.
　　Liu Tianzhong said that the future research and development goal is to strengthen the research on the basic theory of microalgae biology, strengthen the breeding and transformation of characteristic microalgae species with industrial application characteristics, and on the other hand, strengthen the research and development of innovative methods and equipment technologies for microalgae scale culture to solve the problems of efficiency, cost and scale amplification.
　　"While continuing to devote ourselves to the research on key technologies and equipment of microalgae energy, we will adopt the research and development idea of’ combining basic research with application development, and paralleling high-value chemicals with energy products’ to promote the formation and development of microalgae industry." Lu Xuefeng said.
　　(Originally published in China Science Journal, 6th Edition, December 30th, 2014)