| In this paper 30 strains of oil-rich microalgae isolated from Hainan Island and three microalgae isolated from sewage water were tested for the purpose of using sewage treatment of microalgae. A dominant microalgae was obtained after screening these 30 strains. Meanwhile, the growth factors of the 30 strains like nutrient conditions,environmental conditions were systematically investigated. According to the optimized conditions and growth rules, the scale-up cultivation was available in artificial sewage. The antibacterial and antioxidant activities of different extracts and fatty acids compositions were analyzed and investigated. The main results were as follows,(1) The determination of sewage samples was carried out. The results showed that the contents of nitrogen and phosphorus in sewage were 29.66% and 3.8% respectively which was close to the water quality of secondary effluent treatment. There were four kinds of metal ions in the water sample that exceeded the drinking water standard. Three strains of microalgae were isolated from sewage samples and identified as Chlorella lewinii LX01,Chlorella vulgaris LX02, Desmodesmus sp. LX03, respectively, according to microscopic morphology, 18S rDNA or ITS sequence alignment and phylogenetic tree analysis.(2) Screening test results showed that there were 5 strains which biomass were more than 0.4g / L in 33 strains microalgae. The results showed that Desmodesmus sp.WC08 was superior to the other four dominant strains. When it was cultivated in sewage, the biomass was 0.64 g / L and the oil content was up to 40.50%, the removal rates of nitrogen and phosphorus were 78.11% and 89.48% respectively. Moreover, the removing effect of Desmodesmus sp. WC08 on the heavy metal ions in sewage was higher than 50%.Synthesizes each kind of situation, Desmodesmus sp. WC08 as the main study of this study.(3) Plackett-Burman factor screening test was carried out to screen the main factors affecting the growth of Desmodesmus sp.WC08 .Then, four significant factors were screened out. The results were analyzed by response surface method, indicating that the optimum parameters were 0.33 for the initial OD680, 10 mmol /L of nitrogen, 16 ‰ for salinity and 6.5 for the initial pH. The optimum medium is composed of 0.6 g of CO (NH2) ,20.087 g K2HPO4 ,0.0222 g MgS04·7H20, 0.00645 g CaCl2·H20, 0.006 g citric acid, 0.00976 mg ferric ammonium citrate ,0.0487 g Na2CO3 ,0.001 g EDTA · Na2 ,2.860 g H3BO3,0.220 g ZnSO4·7H2O,1.810 g MnCl2 · 4H20, 0.079 g CuSO4 · 5H20,0.049 g Co (N03) 2 ·6H2O ,0.390 g Na2MoO4 · 2H2O. The optimum inoculation amount was the initial OD680=0.33 and the optimum culture medium pH was 6.8. According to the optimal conditions and the principle of amplification, Desmodesmus sp.WC08 was cultivated successfully in an 800L pipeline bioreactor amplification with artificial sewage. The results showed that the biomass of the Desmodesmus sp. WC08 was up to 0.53 g / L, the oil content was 29.17%, the removal rates of nitrogen and phosphorus were 69.41% and 89.97% respectively.(4) The results showed that the crude protein,polysaccharide,oil,ash,crude fiber and pigment of Desmodesmus sp.WC08 accounted for 28.75%, 17.13%, 38.98%, 11.47%,14.68% and 4.79% of dry weight of algae, respectively. Amino acid content of 28.07%, of which the necessary amino acids for the 10.99%, accounting for 39.15% of the total amino acids. A total of 9 fatty acids were measured, and of which octane carbon within the short-chain fatty acids accounted for 86.27%, oleic acid content of 46.05%. Total unsaturated fatty acids accounted for 73.23% of total fatty acids. The antibacterial and antioxidant activities test showed that petroleum ether extract and n-butanol extract had strong antibacterial activity. The scavenging ability of the six extracts to DPPH radicals was n-butanol phase>ethyl acetate phase> ethanol extract> dichloromethane phase> water phase> petroleum ether phase. Among them n-butanol phase extract also has a high antibacterial antioxidant activity. |
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