Research On The Retrieval Of Optical Properties And Hydrogen Production Kinetics Of Microalgaes

Energy shortage is the important crisis facing humanity in the 21 st century. With the increasing of population and rapid development of the industrialization, the consumption of the traditional energy sources increases and the dependence on energy is also more serious. However, the traditional energy sources are usually non-renewable energy and limited. Moreover, these energy sources are usually harmful to the environment, which makes human turn their attention to a clean and renewable new energy. Compared with solar energy, nuclear energy, wind energy etc., the microalgae energy has several advantages, e.g. abundant raw materials, safe operation production, low energy production process and zero-emission, which make microalgae energy obtain widespread attention at home and abroad. Currently, microalgae photosynthetic H2 and oil productions has become a global hot spot. The United States and other developed countries have been the first to achieve the industrial production from microalgae cultivation to the production of biofuels. There are many factors that affect the production of H2 and oil by micoralgae, and the most important one is the solar energy. Thus, it is especially important to accurately analyze the absorption and scattering properties of the microalgae and the radiation transfer in photobioreactors. In the background of microalgae photobiological H2 production, the microalage cells radidative properties, the radaitive transfer in photobioreactors and photobiological H 2 production kinetics are all studied theoretically and experimentally. The specific work of this thesis includes the following several aspects:First, several radiative properties models of single microalgae are introduced, the differences between the radiative properties of spheroidal Chlamydomonas reinhardtii(C. reinhardtii) and those of its corresponding equivalent-sphere radiative models are studied. Moreover, the radiative properties model based on the fractal theory and GMM theory for studying the microalgae aggregates is established, and the effects of fractal dimension, monomer radius and the number of monomers on the radiative properties of cells aggregates are investigated. The results show that the equivalent-sphere radiative models can be used to predict the radiative properties of spheroidal C. reinhardtii approximately. The scattering properties of the aggregates with smaller radius and larger number of monomers become smaller when the fractal parameters become larger, while the changing of the absorption properties of the aggregates is not obvious.On the basis of cells radiative properties models and inverse radiation problem solving techniques, the radiative properties of microalgae are studied. To retrieve the spectral complex refractive indices of microalgae dispersio n medium, the inversion model based on the time-domain or frequency-domain laser transmission-reflection measurement technique and the particle swarm intelligence optimization algorithms is established. Besides, to retrieve the cells size distribution of microalgae dispersion system, the inversion model based on the spectral extinction technique and the ant colony intelligence optimization algorithms is established. The results show that the retrieval results of spectral complex refractive indices by time-domain pulse laser show satisfactory robustness, high accuracy and slow convergence speed. The measurement technique based on the multi-layers model and the transmission-reflection signals is a kind of effective methods to retrieve the spectral complex refractive indices of C. reinhardtii GY-D55. The J-SB and M-? functions can be used as the general functions to study the parametric estimation of microalgae cells size distribution, when there is no prior information about the size distribution. The detective laser wavelengths selection method based on wavelengths sensitivity analysis and matrix condition number analysis is proved to be a kind of potential techniques to promote the non-parametric estimation accuracy of microalgae cells size distribution.Finally, based on the cells radiative properties and the Michaelis-Menten kinetic model, the investigations about the radiative transfer and photobiological H 2 production in photobioreactors are carried out. The effects of light intensities at different times in different regions, bubble concentration, algae cell concentration and cells aggregation on the radiation transfer and H2 production rate in photobioreactors are studied. Moreover, a flat-plate airlift photobioreactor experimental platform for studying photobiological H2 production is established, the H2 production rates of C. reinhardtii GY-D55 cultivated under the LED lamps with different wavelengths and light intensities are measured, and the corresponding H2 production characteristic parameters are retrieved. The results show that the light intensity and the H2 production rate in the summer solstice are high, but the light to H2 energy conversion efficiency is low. When increasing the bubble concentration, the maximum photosynthetic effective H2 production regions in photobioreactors will become smaller and away from the illuminating surfaces of photobioreactors. When increasing the microalgae concentration, the total H2 production rates in photobioreactors will increase first and then decrease. The spectral absorption index of microalgae is one of the key factors that affect the microalgae p hotosynthetic kinetics. The larger growth rate and larger H2 production rate can be obtained, when the microalgae is cultivated under the wavelengths in which the microalgae shows larger spectral absorption index.