Continually rising energy needs in conjunction with negative externalities of fossil fuel use demand the diversification of energy resources. However, fossil hydrocarbons are also used as raw materials for a vast web of manufacturing of industrial and consumer goods. The use of plant based raw materials as substitutes for fossil materials in fuels and manufacturing has been demonstrated successfully, and microalgae are an extremely diverse and promising resource in this category. One of the chief challenges in the implementation of a bio-economy is efficient processing and conversion of biomass to platform chemicals. In order to maximize extraction efficiency, pretreatment is employed to effect cell rupture. Many pretreatment processes have been implemented using empirical operating curves, but the fundamental energy requirements of the cell disruption process have not been thoroughly explored. To fill this void, a constitutive model of cell rupture energy is derived here and implemented for low frequency power ultrasound processing of Chlorella vulgaris. A sensitivity analysis of the constitutive model is performed, identifying cell diameter as a high sensitivity input. Measured distribution of microalgae cell diameters is then used as a fixed input to Monte Carlo simulations of cell rupture energy from the constitutive model. The influence of growth media on microalgal growth rate is then investigated, and the resultant biomass subjected to power ultrasound processing to determine the effect of media choice on processing efficiency. The theoretical kinetics of cell rupture via power ultrasound induced cavitation is developed next. A reactor model is introduced to convert reactor kinetics to reaction zone kinetics. An elementary reaction model is then developed in the context of the constitutive model, leading to the introduction of an alternative reaction mechanism employing a critical distance parameter to capture the relative energies and proximity of cells and cavitation bubbles. This reaction mechanism is extended to generate an explicit expression for the cell disruption first order rate constant in terms of cell properties and power ultrasound operating parameters. This rate constant is mapped over the parameter space, then used to back-calculate cavitation rate, and finally extended to incorporate PDF parameter inputs.

Algal biofuel has a potential for reducing dependence on fossil fuel while curbing CO2 emissions. Despite these potential benefits, a scalable, sustainable, and commercially viable system has not yet been developed due to the high production cost. Currently harvesting and dewatering accounts for 30-50% of the total cost. In this study, a new harvesting method was proposed that uses a heat exchanger along with low grade waste heat in flue gas and heats the algal suspension and subsequently evaporates the water inside an evaporation tank. The CO2 contained in the flue gas stream after cooling can be used as feedstock for algae cultivation.To fully develop and demonstrate the proposed method, four major objectives were completed to evaluate the performances of heat exchanger and evaporation tank, their impact on the extracted lipid and the economy of the method. The proposed system was analyzed experimentally and computationally with Ansys Fluent to investigate the temperature rise in a heat exchanger and evaporation rate in the tank. Unlike the properties of algal suspension and heat exchanger tube walls, flue gas properties such as flowrate, temperature and thermal conductivity had the major impact on overall heat transfer coefficient. The overall heat transfer coefficient and evaporation rate estimated with different theoretical methods showed a relatively acceptable agreement with the computational results. The results showed an increase of about 100% and 85% in evaporation rate when the flue gas temperature and air speed increased from 175⁰C to 245⁰C and from zero to 3.5 m/s, respectively. The effects of experiment duration, storage volume and vacuum evaporation were also evaluated experimentally. Next, the yield and quality of lipid were investigated by comparing lipid and fatty acid methyl esters (FAMEs) concentrations in samples harvested by the proposed method and centrifugation. FAME extraction showed a 17% net increase in the sample harvested by the proposed method. The FAME components remained the same compared to the sample harvested by centrifugation. Finally, the cost of harvesting and biodiesel production with the proposed method was estimated to be about 44% and 22%, respectively, lower than their counterparts in algal biomass harvested by centrifugation.