ABSTRACT

A Study on the Cell disruption of Microalgae using Ultrasound sonication


Bae, Myeong Gwon
Advisor : Prof. Jeong, Sang-Hwa, Ph.D.
Department of Mechanical Engineering,
Graduate School of Chosun University

Recently, because of industry development, the consumption of fossil energy such as petroleum, coal, and natural gas has increased exponentially. Therefore, there is an issue with environmental pollution caused by greenhouse gases due to energy shortages. The increase in carbon dioxide emissions is getting serious. In order to solve these serious problems, many studies are being conducted on renewable energy sources and alternative bioenergy. Among them, the third generation bioenergy, microalgae, has recently emerged as a resource with infinite potential. Microalgae are photosynthetic and independent nutrient microorganisms, a sustainable source of bio-energy without environmental pollution because they produce useful substances by synthesizing the necessary nutrients using inorganic light. In addition, one efficient approach is the production of biodiesel based on biomass extracted from the useful materials from microalgae; this approach also has a carbon dioxide reduction effect that might reduce global warming. To extract lipids from microalgae, the cell membrane disruption process is essential during the harvesting process, and research is being conducted into various ways for efficient lipid extraction. Harvesting methods are largely divided into mechanical and non-mechanical methods. In general, the mechanical methods has the advantage of maintaining the protein structure of the microalgae well, but the processing is complicated, and the maintenance cost is high. Non-mechanical methods can harvest large quantities and are economical, but there are fatal disadvantages due to environmental pollution caused by chemical treatments. However, at present, the efficiency of extracting lipids from microalgae still requires research and development due to the lack of productivity and economy compared to existing bioenergy.
In this study, the efficiency of continuous and highly productive cell membrane crushing using an ultrasonic mechanical method, which causes not environmental pollution or has a not post-treatment cost due to the chemical process, was used for economic and efficient lipid extraction of microalgae. When microalgae are irradiated with ultrasonic waves according to type , the crushing efficiency of the microalgae varies greatly depending on the size and concentration of the cell and the thickness of the cell wall. This study was conducted to investigate the optimum crushing efficiency condition for the microalgae Chlorella sp. In addition, the necessary data was collected using various sensors to analyze the growth curves of cultured Chlorella sp. In order to measure the crystal coefficient of the growth curve, the growth curve was approximated using two types of mathematical equations: the Gompertz model and the Logistic model. In the low frequency experiment, four kinds of cell density, output power, initial capacity, and pH were designated as variables. Finally, in the continuous ultrasonic experiment, five kinds of optical density, output power, cell cycle flow rate, duty cycle, and pH were designated as variables, and the relationship between the variables was analyzed. Through the experiments, the effects of the interactions between the variables on the cell disruption efficiency and the optimum disruption conditions were studied. Experimental results showed that cell crushing efficiency was most affected by output power in all three types of ultrasonic devices. Moreover, the highest crushing efficiency result was obtained under all conditions when the pH was adjusted in parallel.