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| Screening of Oil-rich Microalgae Grown Rapidly in Swine Farm Wastewater |
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Abstract Production of biofuel and mass cultivation of microalgae mainly depends on the nature of microalgae strain. The aim of this study was to screen microalgae strains for swine manure wastewater treatment and lipid production from natural water area. Through multi-step screening, three experimental protocols including streak plate method, single-cell isolated offspring and capillary theory of separation, were used for separating and purifying the algal strains from 51 sites. As a result, 118 microalgaes were obtained, among which 71 facultative heterotrophic microalgae strains were screened including 33 strains which were proved to be tolerant to swine manure wastewater, among which 17 strains were adapted well in swine manure wastewater without further acclimation. Some algae strains were preliminarily identified by morphological observation as Chlorella sp. and Scenedesmus sp.. All candidate strains were grown in swine manure wastewater for 7 days to evaluate their specific growth rate and lipid content. The 13-6, 19-4, 20-6 and 34-2 strains showed faster specific growth rates than other candidate strains during 7 days with the average specific growth rates of 0.147, 0.162, 0.177 and 0.154 d-1, respectively. The total lipid content of the candidate algae which grew in swine manure wastewater ranged from 7.4% to 29.2%. Among them, the 19-4, 24-1 and 34-2 strains showed higher lipid content for 19.7%, 22.9% and 28.8%, respectively, which suggested that these candidates could accumulate higher lipid content than other strains. Two strains (C. sorokinlana 19-4 (GenBank No. KU948990) and Chlorella sp. 34-2 (GenBank No. KU948991)) were chosen for other studies because of their ability to adapt to swine manure wastewater for high growth rates (0.162 and 0.154 d-1) and high lipid content (19.7% and 28.8%). The maximal biomass concentrations of C. sorokinlana 19-4 and Chlorella sp. 34-2 in swine manure wastewater in 30 L photobioreactor reached 0.78 and 1.12 g/L, and algal growth rate reached 0.153 and 0.149 d-1, and lipid content reached 18.73% and 29.27%, respectively. Total nitrogen and total phosphorus were reduced during the cultivation period of the inoculation treatments, whereas no obvious variation was observed in the corresponding negative control. Total nitrogen was reduced 60.24% from 90.81 to 36.11 mg/L for Chlorella sp. 34-2, and 70.56% from 90.81 to 26.73 mg/L for C. sorokinlana 19-4. Total phosphorus was reduced 85.07% from 4.02 to 0.60 mg/L for Chlorella sp. 34-2, 90.98% from 4.02 to 0.36 for C. sorokinlana 19-4 during the 7 days. The production of biodiesel made from microalgae mainly influence by the fatty acid component. The fatty acid compositions of Chlorella sp. 34-2 cultured in swine manure wastewater and BG11 medium were investigated. It was found that C16:0, C18:2n6c and C18:3n3 were the major fatty acids, which accounted for more than 83.97% of the total fatty acids. Their fatty acid composition met the requirements of standards of the raw materials for biodiesel production. This species has great potential for use in the treatment of swine manure wastewater and biodiesel production.
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Received: 28 December 2015
Published: 20 May 2016
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