High Biomass Accumulation And Pyrolysis Products Of Desmodesmus Sp. Cultivation In Anaerobic Digested Wastewater

Microalgae, which are known as the new source of biofuel production, have such features as extensive distribution, widely adaptability, rapid growth and high in lipid content, etc. By conducting anaerobic digested wastewater (ADW) to cultivate microalgae, not only it is beneficial to the wastewater disposal but also can lower the cost of the algae production effectively. During the process of biomass gasification, liquefaction and combustion, biomass pyrolysis technology is an indispensable procedure, which can convert the biomass to liquid fuel or other valuable chemical products. Current thesis primarily focus on the following four aspects:the optimization of biomass accumulation of Desmodesmus sp. cultivation in ADW; the yield and chemical composition of pyrolysis products of Desmodesmus sp. by Py-GC/MS; the analysis of pyrolysis process of Desmodesmus sp. based on life cycle assessment (LCA); potential energy application of lipid-extracted Desmodesmus sp.Response surface methodology (RSM) was applied to optimize the biomass accumulation of Desmodesmus sp. cultivation in ADW. The optimal biomass accumulation conditions were the additive volume of Ammonium ferric citrate (0.0348g/L), K2HPO4(0.1584g/L), and MgSO4·7H2O (0.489g/L). Under such conditions, the experimental biomass accumulation of Desmodesmus sp. was0.777g/L, which was close to the predicted value (0.782g/L).The pyrolysis-gas chromatographic mass spectrometry (Py-GC/MS) was investigated to determine yield and chemical composition of pyrolysis products of Desmodesmus sp. cultivation in BG11medium, ADW, and ADW-added nutrient elements, respectively (BG11/8-10, ZY/8-10and W/8-10). It was comcluded that the chemical compounds from pyrolysis products of Desmodesmus sp. cultivation in three conditions, which were mentioned above, mainly consisted of aliphatic hydrocarbons, aromatic hydrocarbons, acids, nitrogen compounds, phenols, polycyclic aromatic hydrocarbons (PAHs), alcohols, aldehydes, and furans. However, higher temperature would easily lead to mass generation of nitrogen compounds and PAHs. Therefore,700℃,600℃and300℃were found to be favorable for producing biofuel from BG11/8-10, ZY/8-10and W/8-10.The whole pyrolysis process of1kg BG11/8-10, ZY/8-10and W/8-10under the optimal temperature were evaluated by using the method of LCA, respectively. The environment emissions and energy efficiency were under considerable for the corresponding parametric study. The functional unit was1kg microalgae. It was concluded that the energy conversion efficiency for the three processes were larger than1, which indicated that all the three processes are profitable. In addition, the energy conversion efficiency, which was6.21, of W/8-10was found to be the largest. The environmental impact of the three processes were515.61,449.78and323.68mPET2ooo, among which the pyrolysis process of W/8-10has the lowest environmental impacts. Thus, the pyrolysis process of W/8-10was the optimal selection.It was found that, among the pyrolysis products of lipid-extracted Desmodesmus sp., aliphatic hydrocarbons, aromatic hydrocarbons, and acids can be used as in the potential energy materials; nitrogen compounds, chlorine-containing compounds, and PAHs, and small amount of sulfur-containing compounds functioned in pollutants. Pyrolysis of lipid-extracted Desmodesmus sp. at800℃produced36.61%(the maximum yield) of pyrolysis products, compared to that of29.34%at700℃, but more pollutants (21.42%) were produced in the meanwhile. Under such consideration, a reasonably high yield and minimum release of pollutants temperature (700℃) was found to be optimum for producing bio-oil from lipid-extracted Desmodesmus sp.