Utilizing CO2 from flue gas emitted by coal fired power plants
for microalgae cultivation may also be beneficial for reducing greenhouse gas.
Moreover, microalgae can be cultivated using valuable nutrients contained in wastewater
while simultaneously providing bio-treatment of that same wastewater.
Microalgae offers to be a viable alternative feedstock for biofuel production due to its high productivity
while requiring less arable land and water as opposed to conventional terrestrial crops.
In addition, their high lipid content makes them further more appealing for biodiesel production.
Microalgae are usually cultivated in large open ponds,
or in closed photo-bioreactors,
using enriched CO2 and nutrients.
Microalgae-based CO2 utilization technology
Cultivation of microalgae in wastewater
Fossil fuel has been widely used as the main source of energy and due to its shortage, the study of renewable energy continues to grow. Microalgae, in particular, is receiving great attention due to its high potential of lipid to biodiesel conversion. However, harvesting/dewatering of microalgae is a foremost impediment to large scale processing. The dilute nature of microalgae leads to high operational costs questioning its economical validity. Significant advances for dewatering microalgae have been made. Among many, drying via maximization of microalgae contact surface area to rotating discs is a relatively novel yet effective and economical approach. This method utilizes the evaporation principle; dry air is guided to a basin filled with microalgae which comes in contact to rotating discs for rapid drying. Such method can be further optimized by enlarging the rotating discs to increase the surface contact area between the dry air and microalgae while an increase of the inlet temperature will also critically decrease the operation time. Implementation of this method will prove to be a cost-effective dewatering system.
The concentration of microalgae right after cultivation is usually very low, which is not economically feasible for biofuel extraction. In order to increase efficiency and reduce the cost of biofuel production, incrementing microalgae concentration is essential. Such process is commonly known as harvesting. Among numerous harvesting techniques, membrane technology is a good candidate for enriching microalgae owing to its high separation efficiency and reliability. Membrane filtration must be meticulously controlled due to fouling from deposited and adsorbed particles on the surface and within the membrane leading to a drop in efficiency. Our group is trying to mitigate membrane fouling using various methods including membrane surface modification, cavitation, and electro-filtration. These novel membrane technologies are expected to effectively provide high concentrated microalgae with low cost.
The high harvesting cost is an aftermath of the low microalgae concentration acquired during cultivation, bringing about a difficulty to lipid extraction. Therefore, an effective dewatering process is required for efficient lipid extraction and biodiesel production from microalgae. Among several processes, forward osmosis (FO) is noted as one of the better dewatering process and is thus studied in our laboratory; it has the ability to lower energy use with a high rejection rate coupled with less fouling compared to other membrane processes. The greatest challenge in FO is achieving high flux with low back-diffused salts. In addition, draw salt recovery is also another issue to tackle. Hence, our research regarding microalgae dewatering primarily focuses on FO membranes and draw solutions.
The production of the aimed products requires many steps, i.e., cultivation, harvesting, oil extraction, and conversion, and it is costly. Though literally all the steps are challenging in terms of economics, downstream processes, from harvesting to conversion, are estimated to account for 60 % total production cost. To reduce cost and, at the same time, simplify the overall fuel production, direct extraction of lipids from wet microalgae has been proposed. Intracellular lipids have been shown to be hardly extractable from wet microalgae, unless the extraction is preceded by cell disruption. Microalgal lipids, particularly neutral lipids (triglyceride), are contained within the cellular matrix. These lipids are released and retrieved at a satisfactory level if the physical barrier is at least partially removed. Therefore, in recent years, mechanical (or physical) means of extraction, such as autoclaving, high-pressure homogenization, and sonication have been intensely investigated. Catalyst-mediated cell disruption, typically accompanied by heat (and thus termed hydrothermal catalytic treatment), is one possible alternative to mechanical extraction methods. In fact, hydrothermal catalytic treatment is one of the most common pretreatment methods for cellulosic biomass. The strong catalyst catalyzes the hydrolysis of bio-components, but this occurs almost exclusively when the temperature is increased about a certain value. In our laboratory, the combination of various mechanical and chemical means have been studied and improved.
Courtesy of Swineburne University
Bioethanol from cellulosic biomass – Rice straw, Reed, Sugar cane, and waste – is one of the most promising renewable alternatives that could significantly reduce national energy dependence on fossil fuels and decrease the environmental impacts of energy use. Cellulosic bioethanol production process is consisting of pretreatment, enzymatic hydrolysis (from cellulose to glucose) and fermentation (from glucose to ethanol).
Due to the structural complexity of components constituting the cellulosic biomass – Cellulose, Hemicellulose, and Lignin – enzymatic and microbial attack has been a bottleneck of the commercialization of biomass-based fuel. Pretreatment step has been regarded as one of the most expensive process and it has also great potential for improving total bioethanol production efficiency.
Therefore, we will develop novel pretreatment method to lower the cost of overall process and reduce the enzyme/chemical dosage on hydrolysis step. Also, the isolated potent microbes or microbial consortia will be manipulated to optimize cellulose depolymerization in the whole-cell level.
Develop the effective pretreatment process (mechanical, chemical)
Make promising integrated process of pretreatment and hydrolysis step
Isolate potential cellulose-eating microbes from various sources