Characterization of microalgal species isolated from fresh water bodies as a potential source for biodiesel production
Introduction
Current energy demand is mostly fulfilled by conventional energy resources, such as coal, petroleum, and natural gas. Petroleum-based fuels have limited reserves and are concentrated in certain regions of the world. According to many analysts, at the present staggering rates of consumption, the world fossil oil reserves will be exhausted in less than 50 years. The scarcity of known petroleum reserves makes renewable energy resources more attractive [1]. The most feasible way to meet the growing demand for energy is by utilizing alternative fuels. An alternative fuel to petrodiesel must be technically feasible, economically competitive, environmentally acceptable, and easily available [2]. One such fuel that exhibits great potential is biofuel, in particular, biodiesel [3]. Biofuels are generally considered to have many benefits, including sustainability, reduction of greenhouse gas emissions, regional development, social structure, agriculture and security of supply [4]. Usage of biodiesel will allow for a balance to be achieved between agriculture, economic development and the environment [5].
Extensive studies have been conducted on using vegetable oils as diesel fuel. The focus has mainly been on oils, like soybean, rapeseed, sunflower and safflower oils [2], which are essentially edible in nature. Most recently, research efforts have been aimed at identifying suitable biomass species which can provide high-energy outputs to replace conventional fossil fuels [6]. However, few attempts have been made to produce biodiesel from non-edible sources, like used frying oil, greases, tallow, lard, jatropha, and mahua oils [7], [8], [9], [10]. Nevertheless, the cost of biodiesel production is still a major obstacle for large-scale commercial exploitation, mainly due to the high feed cost of vegetable oils [2].
Microalgae have been suggested as a potential feedstock for fuel production because of the number of advantages, including higher photosynthetic efficiency, higher biomass production, and higher growth rates, as compared to other energy crops [11]. Microalgae represent an exceptionally diverse but highly specialized group of microorganisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g., 20–50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Microalgae with high oil productivities are desired for producing biodiesel. Depending on the species, microalgae produce many different kinds of lipids, hydrocarbons, and other complex oils [12], [13]. Not all algal oils are adequate for making biodiesel, but suitable oils commonly occur. In this study, the algal growth rate, biomass production, lipid content, and productivity of microalgal cultures isolated from livestock wastewater and a river were determined. Furthermore, the fatty acid composition of these isolates was investigated. In addition, the identification of the microalgal species was confirmed by investigating the partial sequence of the (LSU) rDNA (D1-D2) and ITS genes.
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Isolation and identification of microalgae
Water samples for microalgae isolation were collected aseptically from sites that appeared to contain algal growth in a fresh water river (YSR) and livestock wastewater treatment plant (YSW) at Wonju, South Korea. The physicochemical characteristics of the livestock wastewater were as follows (units in mg·L−1): chemical oxygen demand (COD) 845, total nitrogen (TN) 1180, total phosphorus (TP) 4, chloride (Cl−) 593, sulfate () 86, nitrate () 2.6, and nitrite () 174. The pH of the
Isolation and identification of the microalgae
Microalgae are present in all existing earth ecosystems, not just aquatic, but also terrestrial, representing a large variety of species living in a wide range of environmental conditions [25]. It is estimated that more than 50,000 species exist, but only a limited number, of around 30,000, have been studied and analyzed [26]. In this study, a total of 33 microalgal cultures were isolated, 18 from the river nearest to Yonsei University Campus, Wonju, South Korea, and 15 from a livestock
Conclusions
To find microalgae with high biomass and lipid productivity, eight microalgal cultures were selected based on easy cultivation and growth rate. The highest growth rates (2.35 ± 0.55 and 1.68 ± 0.28 day−1) were found for M. pusillum YSW07 and S. obliquus YSR01, respectively. The highest total fatty acid and lipid contents (4.7 mg g−1 dwt, and 58 ± 1.5%) were found in S. obliquus YSR01. The composition of fatty acids in the studied species was mainly C14:0, C16:0, C18:1n9c, C18:2n6c, C18:3n6 and C18:3n3.
Acknowledgements
This work was supported by the 21st Frontier research project (Sustainable Water Resources Research Center 3-4-3), the Global Research Laboratory project (Korea Institute of Geosciences and Mineral Resources NP2008-019), the Senior Researchers (National Research Foundation of Korea, 2010-0026904), and the Brain Korea-21 (BK-21) program of the Ministry of Education, Republic of Korea.
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