(10f) An Integrated Approach for Bioenergy Production from Microalgae Using Solar Energy, CO2 and Wastewater

New biomass sources for alternative fuels has grown to be a subject of increasing importance as the world struggles to resolve the economic and strategic impacts of limited fossil fuel resources on environment and global climate. Microalgae are among the most promising non-food-crop-based biomass feedstocks. Microalgae are photosynthetic microorganisms with simple growing requirements (light, CO₂ and nutrients) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both bioenergy and valuable co-products. On the other hand, carbon dioxide (CO₂) is one of the most important contributors for the increase of the greenhouse effect. CO₂ concentrations are increasing in the last decades mainly due to the increase of emissions due to human activities. A promising technology is the biological capture of CO₂ using microalgae. These microorganisms can fix CO₂ using light with efficiency ten times greater than terrestrial plants.

To be economically competitive with carbon capture/sequestration methodologies, an intensive research is needed to integrate all microalgal culture benefits: flue gas and wastewater treatment and biomass production. In this research, an integrated process is introduced to produce bioenergy from microalgal biomass combined with simultaneous CO₂ capture/sequestration and bioremediation of wastewater nutrients. Also, this research investigates different processes and operations to optimize microalgal biomass production using open ponds or photobioreactors. Finally, this research focuses on the potential of producing biogas from microalgal biomass through anaerobic digestion and further upgrading of biogas into higher alkenes through catalytic processes

The main objective of this research is to investigate the growth kinetics of the appropriate microalgae species at different feed composition of CO₂ with air to optimize the growth rate of microalgae at maximum CO₂ consumption and in various wastewater media to reduce wastewater nutrients concentrations (COD, ammonia, nitrate and phosphate) to the potable clean water level. Also, this research aims to study the growth kinetics of the microalgae at other important parameters such as the effect of concentrated solar energy, pH, temperature, wastewater dilution and algae circulation rate. The anaerobic digestion of the harvested algae is investigated at different operating conditions such as liquid/solid ratio, temperature and pH. Methane concentration in the outlet stream will be optimized as function of these operating conditions.

There is a number of challenging issues in the realization of the proposed technology. One of the major challenges is to find appropriate microalgae species tolerant to high concentrations of CO₂. The flue gas of a power plant contains up to 500 times higher CO₂ content than that in the atmosphere. Therefore, different microalgae species will be studied under similar composition of CO₂ in the flue gas from a fossil fuel-based power generating station to find the proper type of microalgae adapting to higher CO₂ concentrations. Another major challenge is to find the proper technology for microalgal biomass production. There are two main technologies; open ponds and photobioreactors. Even that the open ponds are relatively cheap and easy to clean and maintain, they have poor biomass productivity, mixing, light and CO₂ utilization and they require large area of land. On the other hand, photobioreactors have different designs such as tubular, flat plate and column. Usually, the photobioreactors produce high microalgal biomass. Therefore, this research will explore different designs of open ponds and photobioreactors to optimize the growth of desired microalgae species. Finally, integrated processes propose different challenges that need to be faced. One of the powerful tools to meet these challenges is modelling and simulation software. For example, an essential part of any integrated process is heat and energy integration. Aspen simulation packages proved their capabilities to design and simulate such integration. In this research, modelling and simulation packages will be used to optimise the overall proposed integrated process along with analysing and modelling collected data from the experimental work.

It is expected that the innovation and implementation of the integrated approach for microalgal bioenergy production CO₂ will offer a solution of providing sustainable energy demand and addressing the global commitment to reduce greenhouse gases emissions by CO₂ capture/sequestration.