Chul Woong Kim

Methods of downstream processing for the production of biodiesel from microalgae.

Despite receiving increasing attention during the last few decades, the production of microalgal biofuels is not yet sufficiently cost-effective to compete with that of petroleum-based conventional fuels. Among the steps required for the production of microalgal biofuels, the harvest of the microalgal biomass and the extraction of lipids from microalgae are two of the most expensive. In this review article, we surveyed a substantial amount of previous work in microalgal harvesting and lipid extraction to highlight recent progress in these areas. We also discuss new developments in the biodiesel conversion technology due to the importance of the connectivity of this step with the lipid extraction process. Furthermore, we propose possible future directions for technological or process improvements that will directly affect the final production costs of microalgal biomass-based biofuels.

Direct lipid extraction from wet Chlamydomonas reinhardtii biomass using osmotic shock.

High-cost downstream process is a major bottleneck for producing microalgal biodiesel at reasonable price. Conventional lipid extraction process necessitates biomass drying process, which requires substantial amount of energy. In this regard, lipid extraction from wet biomass must be an attractive solution. However, it is almost impossible to recover lipid directly from wet microalgae with current technology. In this study, we conceived osmotic shock treatment as a novel method to extract lipid efficiently. Osmotic shock treatment was applied directly to wet Chlamydomonas reinhardtii biomass with water content >99%, along with both polar and non-polar organic solvents. Our results demonstrated that osmotic shock could increase lipid recovery approximately 2 times. We also investigated whether the presence of cell wall or different cell stages could have any impact on lipid recovery. Cell wall-less mutant stains and senescent cell phase could display significantly increased lipid recovery. Taken together, our results suggested that osmotic shock is a promising technique for wet lipid extraction from microalgal biomass and successfully determined that specific manipulation of biomass in certain cell phase could enhance lipid recovery further.

Phytohormone Supplementation Significantly Increases Growth of Chlamydomonas reinhardtii Cultivated for Biodiesel Production

Cultivation is the most expensive step in the production of biodiesel from microalgae, and substantial research has been devoted to developing more cost-effective cultivation methods. Plant hormones (phytohormones) are chemical messengers that regulate various aspects of growth and development and are typically active at very low concentrations. In this study, we investigated the effect of different phytohormones on microalgal growth and biodiesel production in Chlamydomonas reinhardtii and their potential to lower the overall cost of commercial biofuel production. The results indicated that all five of the tested phytohormones (indole-3-acetic acid, gibberellic acid, kinetin, 1-triacontanol, and abscisic acid) promoted microalgal growth. In particular, hormone treatment increased biomass production by 54 to 69xa0% relative to the control growth medium (Tris–acetate–phosphate, TAP). Phytohormone treatments also affected microalgal cell morphology but had no effect on the yields of fatty acid methyl esters (FAMEs) as a percent of biomass. We also tested the effect of these phytohormones on microalgal growth in nitrogen-limited media by supplementation in the early stationary phase. Maximum cell densities after addition of phytohormones were higher than in TAP medium, even when the nitrogen source was reduced to 40xa0% of that in TAP medium. Taken together, our results indicate that phytohormones significantly increased microalgal growth, particularly in nitrogen-limited media, and have potential for use in the development of efficient microalgal cultivation for biofuel production.

Effect of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil.

Electrokinetic remediation has been successfully used to remove organic contaminants and heavy metals within soil. The electrokinetic process changes basic soil properties, but little is known about the impact of this remediation technology on indigenous soil microbial activities. This study reports on the effects of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil. The main removal mechanism of diesel was electroosmosis and most of the bacteria were transported by electroosmosis. After 25 days of electrokinetic remediation (0.63 mA cm(-2)), soil pH developed from pH 3.5 near the anode to pH 10.8 near the cathode. The soil pH change by electrokinetics reduced microbial cell number and microbial diversity. Especially the number of culturable bacteria decreased significantly and only Bacillus and strains in Bacillales were found as culturable bacteria. The use of EDTA as an electrolyte seemed to have detrimental effects on the soil microbial activity, particularly in the soil near the cathode. On the other hand, the soil dehydrogenase activity was enhanced close to the anode and the analysis of microbial community structure showed the increase of several microbial populations after electrokinetics. It is thought that the main causes of changes in microbial activities were soil pH and direct electric current. The results described here suggest that the application of electrokinetics can be a promising soil remediation technology if soil parameters, electric current, and electrolyte are suitably controlled based on the understanding of interaction between electrokinetics, contaminants, and indigenous microbial community.

Serial optimization of biomass production using microalga Nannochloris oculata and corresponding lipid biosynthesis

As energy and environment have become urgent issues, there has been increasing needs to develop alternative energy source, such as microalgal bio-fuel. In this study, we investigated the growth and lipid contents of microalgae Nannochloris oculata under various environmental conditions for biodiesel production. Our results indicated that biomass productivities of N. oculata were correlated with increasing nitrogen concentrations up to 37.5xa0ppm. High irradiance using 230–250xa0μmol/m2 led to higher biomass yields than low irradiance of 160–180xa0μmol/m2. Biomass productivities increased further by manipulating surface to volume ratio (S/V), which in turn enhanced light penetration. Finally, optimal biomass productivities (1.04xa0g/lxa0day) could be achieved by the supplementation of yeast extract. Lipid contents and fatty acid profiles of N. oculata were affected by the different growth conditions. Lipid contents of N. oculata decreased as nitrogen concentration increased. Lower temperature (15 °C) resulted in higher lipid content than higher temperature (25 °C). Fatty acid profiles of N. oculata indicated that palmitic acid (C16:0) and linoleic acid (C18:2) were the two most abundant fatty acids, but the supplementation of yeast extract increased linolenic acid (C18:3) content. Our results suggested the feasibility of N. oculata for the biodiesel production.

Effect of monochromatic illumination on lipid accumulation of Nannochloropsis gaditana under continuous cultivation.

Although nitrogen starvation is frequently used to increase lipid contents in microalgae, it has a negative effect on cellular growth. Since light supply is essential for photosynthetic organisms, the effects of cultivation under monochromatic illumination on the growth and lipid contents of Nannochloropsis gaditana were assessed. Continuous cultivation under blue and red light conditions improved the productivity and physical properties for biodiesel from this microalga. FAME yield was twofold higher under red light than under normal white light (21.12% vs 11.35%), with no significant difference in growth rates. Blue and red light increased photosynthetic oxygen evolution, carbon fixation and nutrient uptake. In total, more significant physiological changes were observed under red than under blue light. These results show that red light illumination may be useful for enhancing lipid production by N. gaditana, with the increased photosynthetic reducing equivalents induced by red light which could be deposited as lipids and carbohydrates.

An integrated microfluidic device for the high-throughput screening of microalgal cell culture conditions that induce high growth rate and lipid content

AbstractThis study describes the development of a microfluidic device for the high-throughput screening of culture conditions, such as the optimum sodium acetate concentration for promoting rapid growth and high lipid accumulation of Chlamydomonas reinhardtii. An analysis of the microalgal growth on the microfluidic device revealed an optimum sodium acetate concentration of 5.72xa0gxa0L−1. The lipid content, determined by the 4,4-Difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY® 505/515) staining method, increased with the sodium acetate concentration. The results were found to be statistically reproducible with respect to cell growth and lipid production. Other nutrient conditions, including the nitrogen and phosphorus concentrations, can also be optimized on the same microfluidic platform. The microfluidic device performance results agreed well with the results obtained from the flask-scale experiments, validating that the culture conditions were scalable. Finally, we, for the first time, established a method for the absolute quantification of the microalgal lipid content in the picoliter culture volumes by comparing the on-chip and off-chip data. In conclusion, we successfully demonstrated the high-throughput screening of sodium acetate concentrations that induced high growth rates and high lipid contents in C. reinhardtii cells on the microfluidic device.n FigureWe have developed a microfluidic device for the high-throughput screening of culture conditions for promoting rapid growth and high lipid accumulation of Chlamydomonas reinhardtii

Utilization of lipid extracted algal biomass and sugar factory wastewater for algal growth and lipid enhancement of Ettlia sp.

The present study assessed the use of hydrolysate of lipid extracted algal biomass (LEA) combined with the sugar factory wastewater (SFW) as a low cost nutrient and a carbon source, respectively for microalgal cultivation. Microalgal strain Ettlia sp. was both mixotrophically and heterotrophically cultivated using various amounts of hydrolysate and SFW. The culture which was grown in medium containing 50% LEA hydrolysate showed highest growth, achieving 5.26 ± 0.14 gL(-1) after 12 days of cultivation. The addition of SFW increased the lipid productivity substantially from 5.8 to 95.5 mg L(-1)d(-1) when the culture medium was fortified with 20% SFW. Gas chromatography analysis indicated a noticeable increase of 20% in C16 and C18 fraction in FAME distribution under above condition. Therefore, it can be concluded that the combination of LEA hydrolysate and sugar factory waste water can be a powerful growth medium for economical algal cultivation.

Isolation and characterization of thermostable phycocyanin from Galdieria sulphuraria

Phycocyanin is a highly valuable pigmented protein synthesized by several species of cyanobacteria and red alga. In this study we demonstrate the production of thermostable phycocyanin from the unicellular red alga Galdieria sulphuraria. Phycocyanin was extracted by repeated freeze-thaw cycles and purified in a two-step process using ammonium sulfate fractionation, at 25% and 50% concentrations. Purified phycocyanin exhibited maximum absorbance at 620 nm, and the purity ratio (A620/A280) was found to be greater than 4. The recovery efficiency of phycocyanin from the crude extract was above 80%. In total, approximately 19 milligram pure phycocyanin was obtained from 3 g of wet cell mass of Galdieria sp. Subunits α and β of the protein were separated by SDS-PAGE and analyzed by MALDITOF mass spectrometry for identification, which confirmed that the isolated protein is phycocyanin. The molecular weight of α and β subunits of phycocyanin was found to be 17.6 and 18.4 kDa, respectively.

Energy-efficient cultivation of Chlamydomonas reinhardtii for lipid accumulation under flashing illumination conditions

Microalgal cultivation has been limited by the efficiency and costs associated with providing light energy, the most expensive and essential element needed for microalgal growth to a culture, particularly to cultures grown in a photo bioreactor (PBR). This study examined the economic benefits of using flashing illumination conditions in the context of microalgal cultivation. Chlamydomonas reinhardtii was cultivated under various conditions, including various inoculum sizes, light intensities, and durations of the light and dark periods. Our results showed that the highest microalgal growth efficiencies could be obtained using a large inoculum size under high intensity illumination accompanied by a 1:1 ratio of light and dark periods. The duration of the flashing light period was further optimized; permitting light energy savings of 62.5% of the light energy expended under continuous illumination conditions without reducing the biomass or lipid productivity. This study provides a more economical approach to cultivating C. reinhardtii via optimized flashing illumination without sacrificing microalgal growth or lipid content.