Agent based modeling and experimental studies on a 3rd generation closed cycle for improved biogas Production

Abstract

Continued use of fossil fuels is now widely recognized as unsustainable because of di minishing supplies and the contribution of these fuels to the increased carbon dioxide concentration in the environment. Microalgae are considered as a most capable feedstock for the generation of biofuels due to its several advantages, compared to the feedstock of first- (food feedstock) and second- (non-food feedstock) generation biofuels. It is a photosynthetic organisms that convert carbon dioxide to potential biofuels, foods, feeds and high-values bioactives. When comparing microalgae as feedstock for biofuel pro duction with conventional raw materials, several advantages are observed: much faster growth rate (doubling time of hours), greenhouse gas fixation ability (net zero emission balance), higher area yields (potentially 15- 300 times more), possibility of growing in non arable land, no competition with food crops, less land requirement, cheaper raw materials, lower water consumption, possibility to grow in saline water and non-potable water, etc. However, one major challenge of microalgal biofuels lies in algal biomass harvesting and nutritional cost for production. Therefore, work described in thesis was designed, devel opment an integrated process of microalgal production using anaerobic digestion under outdoor conditions. This decreases the production cost of microalgae as well as biofuel. The main objective of this thesis was to develop a closed loop for biological wastewater treatment system of AD slurry that could be utilized for algal growth and simultaneously produce the renewable energy in the form of biomethane and remove polluting nutrients as well as reduce the greenhouse gases. The integration of microalgae growth with anaerobic digestion could significantly improve the economics and energy balance of biofuels produc tion. Nutrient removal, in particular nitrogen and phosphorus; and COD reduction from wastewater is a developing regulatory need and the use of algae cultivation could create a unique integration between waste treatment and biofuel production. Both the quanti tative and qualitative aspect of the mass (substrate and biomass) and biogas production was studied and modelled. This integrated process of Chlorella pyrenoidosa cultivation coupled with anaerobic digestion (under outdoor conditions) in order to properly design a microalgae growth-anaerobic digestion process to minimize the overall biofuel production costs. The process also reduces the need for fresh water by reusing AD slurry water.