| With the depletion of fossil fuels, the situation that modern society rely on fossil fuels relied modern society has been a serious challenge. Searching for a renewable energy is imminent. Biodiesel is considered to be the preferred renewable sources of energy which could substitute for fossil fuels. Due to the shortage of the traditional vegetable oil and animal fat, which can not supply the demand of biodiesel production, microalgae with its rapid growth rate, high oil production and wide growth space, is considered the most potential raw materials. This essay aims at screening microalgae with rapidly growth biomass, high oil content as raw materials of biodiesel, then searching for a high-density culture of microalgae, studying on its heterotrophic culture mechanism, researching its recovery technology, finally transesterification for the oil extracted from the microalgae to provide biodiesel, Analyzing whether they meet the requirements of an ideal substitute for the fossil fuels, providing a theoretical basis for the large-scale and industrialized microalgae biodiesel. The main results were as follows:(1) Among6strains of microalga, Scenedesmus obliqnus, Chlorella sp., Dunaliella sp, Dunaliella salina, Chlorella pyrenoidosa and Spirulina sp., Chlorella sp. got the highest oil content and the fastest growth rate. Its suitable growth temperature was30℃, the light intensity was6000lux, and pH was9.00-10.00.(2) The results showed that the optimum carbon source of Chlorella sp. growth was glucose, and suitable concentration of glucose was556mg/L (0.2g/L of carbon). Chlorella sp. could use glucose to grow under the tested modes, but the growth rate decreased in the order:mixotrophy＞photoheterotrophy＞light-activated heterotrophy＞chemoheterotrophy＞photoautotrophy. The maximum biomass and specific growth rate (SGR) of the tested algae in mixotrophy were8.6and3.4times as compared to those in photoautotrophy. The SGR of Chlorella sp. in mixotrophy was in close to the sum of SGRs in photoautotrophy and photoheterotrophy. Under mixotrophic and photoheterotrophic modes, glucose was mainly used as carbon source for the Chlorella sp. growth, whereas energy was from the light. Chlorella sp. had an oxidation respiratory chain metabolic pathway, and the succinic dehydrogenase and cytochrome oxidase were held in the cells.(3) Orthogonal experiment results showed that composite using of the polyaluminium chloride (PAC) and chitosan (CTS) gave a better chlorella recovery effect, and less dosing quantity. CTS had a coagulation on PAC, composite using of them can reduce residues of Al3+in the flocculation supernatant, with lower PAC toxicity to microalgae and Al3+harmful effects on the environment.The optimal combination for:PAC adding quantity is160mg/L, CTS adding quantity is20mg/L, pH value is5, rotational speed is150r/min, algal concentration OD690=0.450, the sedimentation time is20min. Under this condition the flocculation liquid Chlorella sp. gave the microalgae cell removal rate of99.83%, the algal concentration ratio of14.26.(4) GC-MS analysis for the Chlorella sp. biodiesel results showed that:the main ingredients were C16and C18, saturated fatty acid methyl ester (25.80%), unsaturated fatty acid methyl ester (47.09%). The molecular structure of the Chlorella sp. biodiesel are similar to Kevin’s ideal molecular structure for the fossil diesel substitute, so that the Chlorella sp.biodiesel can be used as an ideal renewable energy, the Chlorella sp. biodiesel gas phase-mass spectrometry (GC-MS) analysis:the main ingredients for C16and C18, and more than25.80%saturated fatty acid methyl ester, unsaturated fatty acid methyl ester (47.09%). Chlorella sp. the ideals of the molecular structure of the biodiesel and Kevin molecular structure similar to that of fossil diesel substitute can be used as an ideal renewable energy. |
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