Matching Items (4)
Description
Lipids and free fatty acids (FFA) from cyanobacterium Synechocystis can be used for biofuel (e.g. biodiesel or renewable diesel) production. In order to utilize and scale up this technique, downstream processes including culturing and harvest, cell disruption, and extraction were studied. Several solvents/solvent systems were screened for lipid extraction from Synechocystis. Chloroform + methanol-based Folch and Bligh & Dyer methods were proved to be "gold standard" for small-scale analysis due to their highest lipid recoveries that were confirmed by their penetration of the cell membranes, higher polarity, and stronger interaction with hydrogen bonds. Less toxic solvents, such as methanol and MTBE, or direct transesterification of biomass (without pre-extraction step) gave only slightly lower lipid-extraction yields and can be considered for large-scale application. Sustained exposure to high and low temperature extremes severely lowered the biomass and lipid productivity. Temperature stress also triggered changes of lipid quality such as the degree of unsaturation; thus, it affected the productivities and quality of Synechocystis-derived biofuel. Pulsed electric field (PEF) was evaluated for cell disruption prior to lipid extraction. A treatment intensity > 35 kWh/m3 caused significant damage to the plasma membrane, cell wall, and thylakoid membrane, and it even led to complete disruption of some cells into fragments. Treatment by PEF enhanced the potential for the low-toxicity solvent isopropanol to access lipid molecules during subsequent solvent extraction, leading to lower usage of isopropanol for the same extraction efficiency. Other cell-disruption methods also were tested. Distinct disruption effects to the cell envelope, plasma membrane, and thylakoid membranes were observed that were related to extraction efficiency. Microwave and ultrasound had significant enhancement of lipid extraction. Autoclaving, ultrasound, and French press caused significant release of lipid into the medium, which may increase solvent usage and make medium recycling difficult. Production of excreted FFA by mutant Synechocystis has the potential of reducing the complexity of downstream processing. Major problems, such as FFA precipitation and biodegradation by scavengers, account for FFA loss in operation. Even a low concentration of FFA scavengers could consume FFA at a high rate that outpaced FFA production rate. Potential strategies to overcome FFA loss include high pH, adsorptive resin, and sterilization techniques.
ContributorsSheng, Chieh (Author) / Rittmann, Bruce E. (Thesis advisor) / Westerhoff, Paul (Committee member) / Vermaas, Willem (Committee member) / Arizona State University (Publisher)
Created2011
Description
This research focused on how low-income communities in Ghana could convert Waste Vegetable Oil (WVO) into biodiesel to supplement their energy demands. The 2016 World Energy Outlook estimates that about 8 million Ghanaians do not have access to electricity while 82% of the population use biomass as cooking fuel. However, WVO is available in almost every home and is also largely produced by hotels and schools. There are over 2,700 registered hotels and more than 28,000 educational institutions from Basic to the Tertiary level. Currently, most WVOs are often discarded in open gutters or left to go rancid and later disposed of. Therefore, WVOs serve as cheap materials available in large quantities with a high potential for conversion into biodiesel and commercializing to support the economic needs of low-income communities. In 2013, a group of researchers at Kwame Nkrumah University of Science and Technology (KNUST) in Ghana estimated that the country could be producing between 82,361 and 85,904 tons of biodiesel from WVOs generated by hotels alone in 2015. Further analysis was also carried out to examine the Ghana National Biofuel Policy that was introduced in 2005 with support from the Ghana Energy Commission. Based on the information identified in the research, a set of recommendations were made to help the central government in promoting the biodiesel industry in Ghana, with a focus on low-income or farming communities. Lastly, a self-sustaining biodiesel production model with high potential for commercialization, was proposed to enable low-income communities to produce their own biodiesel from WVOs to meet their energy demands.
ContributorsAnnor-Wiafe, Stephen (Author) / Henderson, Mark (Thesis director) / Rogers, Bradley (Committee member) / Engineering Programs (Contributor) / Department of Management and Entrepreneurship (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
Over the past decade, there has been a revival in applied algal research and attempts at commercialization. However, the main limitation in algal commercialization is the process of cultivation, which is one of the main cost and energy burdens in producing biomass that is economically feasible for different products. There are several parameters that must be considered when growing algae, including the type of growth system and operating mode, preferred organism(s), and many other criteria that affect the process of algal cultivation. The purpose of this dissertation was to assess key variables that affect algal productivity and to improve outdoor algal cultivation procedures. The effect of reducing or eliminating aeration of algal cultures at night, in flat panel photobioreactors (panels), was investigated to assess the reduction of energy consumption at night. The lack of aeration at night resulted in anoxic conditions, which significantly reduced lipid accumulation and productivity, but did not affect log phase biomass productivity. In addition, the reduction in aeration resulted in lower pH values, which prevented ammonia volatility and toxicity. Raceways are operated at deeper cultivation depths, which limit culture density and light exposure. Experimentation was accomplished to determine the effects of decreasing cultivation depth, which resulted in increased lipid accumulation and lipid productivity, but did not significantly affect biomass productivity. A comparison of semi-continuous cultivation of algae in raceways and panels in side-by-side experiments showed that panels provided better temperature control and higher levels of mixing, which resulted in higher biomass productivity. In addition, sub-optimal morning temperatures in raceways compared to panels were a significant factor in reducing algae biomass productivity. The results from this research indicate that increasing lipid productivity and biomass productivity cannot be completed simultaneously. Therefore, the desired product will determine if lipid or biomass productivity is more crucial, which also dictates whether the system should be operated in batch mode to either allow lipid accumulation or in semi-continuous mode to allow high biomass productivity. This work is a critical step in improving algal cultivation by understanding key variables that limit biomass and lipid productivity.
ContributorsEustance, Everett (Author) / Sommerfeld, Milton R (Thesis advisor) / Fox, Peter (Committee member) / Westerhoff, Paul (Committee member) / Arizona State University (Publisher)
Created2015
Description
The need for clean fuel sources is greater than ever, as fossil fuel dependence has soared and harmful emissions are being released into the atmosphere at increasingly higher rates. A viable solution to this issue is the use of microalgae for the creation of biofuels, as it holds a high concentration of lipids without requiring arable land for growth. This experiment studies downstream applications of microalgae, including how the extraction efficiency can be improved for greater lipid yield. 3-dimethyldodecylammonium propanesulfonate, myristyltrimethylammonium bromide and sodium dodecyl sulfate were used as surfactants to break down the algae cell walls and improve lipid recovery. The incubation times of the biomass in the surfactant were also studied at 0, 4.5, 24, 48 and 72 hours to more fully examine how surfactants affect the extraction of lipids. Along with this, hexane and isopropanol were used as the main extraction solvent in this experiment, but testing was done to compare these lipid yields to when ethyl acetate was used as the solvent. It was found that the MTMAB surfactant led to the greatest cell disruption, as its lipid yields were consistently higher than those of the other surfactants. Also, longer incubation times did improve the amount of lipid extracted, showing that the surfactants do have a strong effect on the cell breakdown. Finally, it was found that the ethyl acetate was a slightly more effective solvent than hexane and isopropanol in the conditions of this experiment. Overall, a stronger understanding of the wet extraction process was gained from these tests, as well as more insight into how some of the variables interact and work together during extraction.
ContributorsMartarella, Rebecca Lynne (Author) / Rittmann, Bruce (Thesis director) / Lai, Sean Yen-Jung (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2015-12