Kyochan 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.

High-cell-density cultivation of oleaginous yeast Cryptococcus curvatus for biodiesel production using organic waste from the brewery industry.

Waste spent yeast from brewery industry was used as a sole growth substrate to grow an oleaginous yeast Cryptococcus curvatus for the purpose of biodiesel production. Approximately 7 g/l/d of biomass productivity was obtained using only spent yeast (30 g/l) without additional nutrients and pretreatment of any kind. To make best use of available nutrients in the spent yeast, stepwise cultivation was carried out in a batch culture mode and the highest biomass and lipid content, which were 50.4 g/l and 37.7%, respectively, were obtained at 35:1 of C/N ratio. Lipid from C. curvatus was found to be a quality-sufficient source of oil as a transportation fuel in terms of cetane, iodine values, and oxidation stability, although the values of cold filter plugging point were less desirable. Economic evaluation revealed that the use of the spent yeast could significantly reduce the unit cost of yeast-based biodiesel production.

Use of organic waste from the brewery industry for high-density cultivation of the docosahexaenoic acid-rich microalga, Aurantiochytrium sp. KRS101

In the present study, spent yeast from a brewery was used as the growth substrate for the docosahexaenoic acid (DHA)-rich microalga, Aurantiochytrium sp. KRS101. A significant biomass yield (6.69 g/l/d) was obtained using only spent yeast as the growth substrate, with simple stirring as pretreatment. Maximization of nutrient utilization through the use of stepwise cultivation increased the yield to 31.8 g/l of biomass. DHA constituted 38.2% (w/w) of the total fatty acids, and the highest DHA productivity was observed when the C/N ratio was 20:1 (w/w). Spent yeast thus served as a good growth substrate for the production of DHA. Economic assessment revealed that stepwise cultivation using spent yeast as either the sole growth substrate or as a nutrient source could substantially reduce the production cost of microalgal DHA.

Continuous microalgae recovery using electrolysis: Effect of different electrode pairs and timing of polarity exchange

Microalgae have great potential as a feedstock for biofuel production. Continuous operation is an important benefit of the continuous electrolytic microalgae (CEM) harvest system, but it is necessary to optimize cultivability and recovery efficiency in order to improve overall performance. Two pairs of best-candidate electrodes for polarity exchange (PE) were examined to improve these two key factors: (i) aluminum and dimensionally stable anode (Al-DSA), and (ii) Al-platinum (Al-Pt). Al-DSA was better than Al-Pt because it led to less cell damage and was less expensive. Moreover, cell viability and recovery were improved by optimizing the timing of PE. A P1:P2 ratio of 1:1.5 at 5min and 1:1.2 at 10min yielded the best results, with greatly reduced electricity consumption and enhanced cell viability and recovery. The CEM harvest system appears to be a well-suited option for the harvest of microalgae for biofuel production.

A novel fed-batch process based on the biology of Aurantiochytrium sp. KRS101 for the production of biodiesel and docosahexaenoic acid

The biology of Aurantiochytrium sp. KRS101 was thoroughly investigated to enhance its production of biodiesel and docosahexaenoic acid (DHA). Nutrients and salinity were optimized to prevent biomass loss due to cell rupture. Calculation of yield coefficients showed that nitrogen was mostly responsible for the early stage of cell growth or division, whereas carbon was necessary for the entire process of cell development, particularly cell enlargement during late stages. Using these distinctive yield coefficients, a modified fed-batch cultivation method was designed, resulting in increases in palmitic acid (PA) and DHA production of up to 137% and 29%, respectively. This modified fed-batch cultivation method, using appropriate supplies of nitrogen and carbon, may improve the yields of PA and DHA, thus expanding the biotechnological applications of Aurantiochytrium sp. KRS101.

Evaluation of various harvesting methods for high-density microalgae, Aurantiochytrium sp. KRS101.

Five technologies, coagulation, electro-flotation (EF), electro-coagulation-flotation (ECF), centrifugation, and membrane filtration, were systematically assessed for their adequacy of harvesting Aurantiochytrium sp. KRS101, a heterotrophic microalgal species that has much higher biomass concentration than photoautotrophic species. Coagulation, EF, and ECF were found to have limited efficiency. Centrifugation was overly powerful to susceptible cells like Aurantiochytrium sp. KRS101, inducing cell rupture and consequently biomass loss of over 13%. Membrane filtration, in particular equipped with an anti-fouling turbulence generator, turned out to be best suited: nearly 100% of harvesting efficiency and low water content in harvested biomass were achieved. With rotation rate increased, high permeate fluxes could be attained even with extremely concentrated biomass: e.g., 219.0 and 135.0 L/m(2)/h at 150.0 and 203.0 g/L, respectively. Dynamic filtration appears to be indeed a suitable means especially to obtain highly concentrated biomass that have no need of dewatering and can be directly processed.

Acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. KRS101.

In this study, acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. was performed, and its yield-enhancing effects were investigated. The total fatty acid content of the Aurantiochytrium sp. was 482.5mg/g cell, of which 141.7mg/g cell (29.4% of total fatty acids) was DHA. The lipid-extraction yield by acid-catalyzed hot-water treatment was compared with those by organic solvents. Among the various acid-catalyzed hot-water treatment conditions, the most optimal were 1.00% H2SO4 concentration, 100°C, 30min, under which the lipid-extraction yield was 472.4mg/g cell, and most of the DHA was extracted (29.2% of total fatty acids). Acid-catalyzed hot-water extraction treatment markedly improved the lipid-extraction yield of Aurantiochytrium sp.

Recovery of anionic surfactant by RO process.: Part I. Preparation of polyelectrolyte-complex anionic membrane

Abstract Crosslinked sodium alginate (SA) membranes which have a protective polyelectrolyte complex layer at a membrane surface were prepared by a simple technique for the reverse osmosis separation of an anionic surfactant that has been used as an emulsifier in PTFE emulsion polymerization. With this technique, when a nascent SA film cast onto a glass plate was dipped in the reaction solution that contained both CaCl 2 , a crosslinking agent, and chitosan, a cationic polymer, the stable SA membrane with double layer structure was fabricated by crosslinking with the divalent ion Ca 2+ inside the membrane and the simultaneous polyelectrolyte complexation of anionic SA with cationic chitosan at the membrane surface. The effects of the fabrication parameters on the characteristics of the resulting membrane were investigated. The complex membrane gave excellent membrane performance with rejections higher than 99% due to electrostatic repulsion between anionic solute molecules and the anionic membrane. Also, a comparison of membrane performance between crosslinked SA membranes with and without the protective complex layer was made at different operating conditions in the reverse osmosis separation of the anionic surfactant from waste fluids. The role of the protective polyelectrolyte complexes formed at the membrane surface is discussed in terms of membrane stability.

Recovery of anionic surfactant by RO process. Part II. Fabrication of thin film composite membranes by interfacial reaction

Abstract A new technique has been established to fabricate thin film composite membranes, by which a hydrophilic polymer could be coated in thin film on a hydrophobic support membrane. The new technique was composed of two steps: dispersion of a reactant to the hydrophilic polymer in the hydrophobic support membrane and interfacial reaction between the reactant and the hydrophilic polymer to produce thin film of the hydrophilic polymer on the support membrane. Composite membranes in which a thin film of sodium alginate is coated on a polysulfone support membrane were prepared by the new technique for the reverse osmosis separation of anionic surfactant–water mixture. Two methods were employed to fabricate a thin film of sodium alginate on the support membrane: (1) dispersion of the crosslinking agent, CaCl 2 alone in the support membrane and (2) dispersion of CaCl 2 in the support membrane with help of PVA which adheres fast to the support membrane. The formation mechanism of the thin layer was suggested schematically on each method. Both the methods could produce successively a thin layer of SA on the support membrane. Especially, method (2) gave a strong bonding of the thin layer on the support because of the large contact area with the support through the PVA layer which sticks fast to the SA layer. From the SEM pictures and permeation experiments, the method (2) was confirmed to be better to produce a defect-free thin film of SA on the support membrane.

Harvesting of Scenedesmus obliquus cultivated in seawater using electro-flotation

Seawater, when supplemented to a growth medium, appears to stimulate auto-flocculation of a certain microalgae species like Scenedesmus obliquus and thus renders its harvesting easy. To make use of this unique response for the purpose of biomass harvesting, S. obliquus was grown in a seawater-added medium and then collected in electrochemically- mediated ways. Significantly higher harvesting efficiency and energy saving were observed with electroflotation (EF) than with electro-coagulation-flotation (ECF) and the standard BG11 medium. An optimal EF condition, the highest recovery rate with least energy use, was found with a supply of 0.5 A. Seawater amendment was most beneficial in a level of 10%. All this clearly showed that applying EF to cells cultivated in the seawater-supplemented medium is a promising harvesting means that enables one to obtain algae biomass without interfering with the downstream process of biodiesel production.