| The rapid development of the global economy necessitated the soaring demand for energy.There is an urgent need for a renewable,sustainable,and eco-friendly energy source to help reduce the disadvantages of traditional energy.At present,the development of renewable energy draws increasing attention,particularly microalgae bio-energy has received great attention in the past decade.Microalgae,which contain photosynthetic pigment in their bodies,are photosynthetic autotrophic microorganisms that can synthesize macromolecular organic matter by using light energy and inorganic nutrient,and the oil is regarded as an ideal raw material for biodiesel production.However,due to the high production cost,especially compared with traditional fossil energy,the price is still high.This disadvantage weighs heavily against the application at large scale.Improving the oil yield of microalgae is one of the effective ways to solve this problem.The increase of oil yield can be achieved by looking for high-yielding species of microalgae and promoting its growth by optimizing the culture conditions.However,during the rapid growth of microalgae,the synthesis of oil in alga cells will be negatively affected,resulting in a decrease in oil content.Therefore,the key to improving the final oil yield is how to realize the rapid accumulation of oil on the premise of ensuring microalgae to obtain a high biomass concentration.Therefore,based on the above points,the main conclusions of this study are as follows:Firstly,microalgae screening was carried out.Water samples were collected from local lakes in Jinan,Shandong province,and the algae strains were obtained for culture.Compared with other algae strains,it was found the following characteristics:(I)rapid growth and high lipid content(biomass concentration could be as high as 2.05 g/L,with lipid content of 30.43%respectively),(ii)good adaptability in campus domestic sewage(biomass concentration can be up to 1.90 g/L,with lipid content of 21.83%),(iii)large cell size(mean cell radius up to 3.5-9 ?m).Therefore,it may have better sedimentation and filtration performances and achieve lower cost microalgae harvest,(iv)the length of the fatty acid carbon chain is mainly 16 to 18 carbon atoms long,and the distribution of saturated fatty acids and unsaturated fatty acids is balanced,which can meet the biodiesel standards set by the United States and the European Union.The above results indicated that this green alga was a suitable alga strain for bioenergy.It was identified as polygonum by morphology and 18S rRNA sequencing and named Golenkinia SDEC-16.Relevant sequencing results have been submitted to GenBank(Accession No.:KT180320).Secondly,given the large cell radius of Golenkinia SDEC-16 and the characteristic of being surrounded by spines,the potential of Golenkinia SDEC-16 in sedimentation and filtration was explored.In the self-sedimentation experiment,the sedimentation efficiency reached 89.82%at 40 min.The method of gauze filtration was adopted for harvesting.When 16 layers of gauze were used,the harvesting efficiency of Golenkinia SDEC-16 reached 73.82%,and when the number of gauze layers increased to 32 layers,the harvesting efficiency of Golenkinia SDEC-16 reached 93.32%.This result was much higher than that of Chlorella and Scenedesmus in the same layer as the control group.When 16 and 32 layers of gauze were used,the harvest efficiency of Chlorella SDEC-11 was only 9.29%and 13.38%,respectively.The harvesting efficiency of Scenedesmus SDEC-13 was only 10.09%and 14.17%.The morphology of Golenkinia SDEC-16 will respond differently to the change of culture conditions.It was found that introduced NaCl to the culture medium of Golenkinia SDEC-16 caused the algal cells to become larger.In particular,when the initial NaCl concentration was 320 mM,the cell radius of Golenkinia SDEC-16 became the largest,with a median radius of 14.64 ?m,far greater than the reported radius range of 3.5 to 9 ?m.Meanwhile,the spines surrounding Golenkinia SDEC-16 cells were lost along with the outer cell wall.Besides,when the Golenkinia SDEC-16 multiplied,their progeny cells found no spines on the periphery.The changes in the morphology of Golenkinia SDEC-16 can help to understand the physiological response of Golenkinia SDEC-16 to the culture conditions and provide the morphological cognitive experience of Golenkinia SDEC-16 for the identification of microalgae.Thirdly,aiming at the problem that there are few physiological studies on Golenkinia SDEC-16,the culture conditions of physical properties(temperature,aeration,light intensity,and monochromic LEDs)were optimized to promote the accumulation of biomass and lipid of poly Golenkinia SDEC-16.The results showed that(1)the optimum growth temperature of Golenkinia SDEC-16 was 27.5±2.5 ?,and it was difficult to survive at 37.5±2.5?.The temperature increase was observed to be beneficial to the accumulation of oil content on day 8,but the regular change was not obvious on day 18.Considering the biomass concentration and lipid content,27.5±2.5? should be used as the temperature condition for cultivating Golenkinia SDEC-16.Low temperature is beneficial to the accumulation of unsaturated fatty acids in the lipid of Golenkinia SDEC-16,which can provide practical experience for the development of unsaturated fatty acids in Golenkinia SDEC-16 in the future.(2)under the monochromatic lights of red,green,and blue,the growth of Golenkinia SDEC-16 was ranked as red,blue,and green light.However,under the exposure of green light,the lipid content can reach 41.96%on day 8.However,considering the biomass concentration,the highest lipid yield was obtained under the condition of red light irradiation.Therefore,the green light strategy can be used as a strategy to stimulate lipid production in the two-stage culture method.Besides,under the exposure of green light,Golenkinia SDEC-16 can accumulate a large amount of unsaturated fatty acids On day 24,C 22:4 accounted for 25.15%of the fatty acids,and C 22:6 was also detected,with only 4.79%.(3)Golenkinia SDEC-16 can adapt to a strong aeration intensity.Under the aeration volume of 1.0 L/min,the maximum biomass concentration of 4.89 g/L with the lipid content of 41.09%can be obtained.(4)for light intensity,Golenkinia SDEC-16 could adapt to higher light intensity.Under the condition of 25,000 lux,the maximum biomass concentration and lipid content was 5.27 g/L and 23.07%,respectively.Fourth,the culture conditions by changing the medium chemical composition:the decrease in initial nitrogen concentration and introduced NaCl,were evaluated.The optimized parameters of the culture conditions were as follows:the initial nitrogen concentration of the medium of Golenkinia SDEC-16 can be reduced to 9 mM,and an introduced 20 mM NaCl.Under this culture condition,the results showed that the biomass accumulation of Golenkinia SDEC-16 could not be affected,and the lipid content was also increased compared with that of the experimental group without NaCl The biomass concentration and lipid content of Golenkinia SDEC-16 reach 6.65 g/L and 54.38%.Fifth,the feasibility of treating campus sewage with Golenkinia SDEC-16 was explored.The results showed that under the culture conditions of white light and 0.8 L/min aeration,the total nitrogen,ammonia nitrogen,and total phosphorus in the campus domestic sewage treated by Golenkinia SDEC-16 could meet the national standard of A discharge.Under the conditions of monochromatic light of different wavelengths and only red and blue light irradiation,the domestic sewage of the campus treated by Golenkinia SDEC-16 meets the national standard of sewage discharge of Class A.To sum up,the present work was carried out by screening,purification,and identification of a promising strain for bioenergy production.It also made clear the morphological changes of Golenkinia SDEC-16 in response to the different culture conditions and the growth periods.Golenkinia SDEC-16 is easily harvesting.This study can fill the gap in the application of Golenkinia sp.in the field of biomass production and sewage treatment,enrich the theoretical achievements of using microalgae to achieve bioenergy production and sewage treatment,and provide new algae strains and technological support for biomass production coupling biological method to treat domestic sewage. |
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