Ji-Won Yang

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.

Carbon Dioxide Fixation by Algal Cultivation Using Wastewater Nutrients

Chlorella vulgaris was cultivated in wastewater discharged from a steel- making plant with the aim of developing an economically feasible system to remove ammonia from wastewater and from Nue gas simultaneously. Since CO 2 no phosphorus compounds existed in wastewater, external phosphate (15E3E 46E 0gm ~3) was added to the wastewater. After adaptation to 5% (v/v) the CO 2 , growth of C. vulgaris was signi-cantly improved at a typical concentration of in Nue gas of 15% (v/v). Growth of C. vulgaris in raw wastewater was better CO 2 than that in wastewater bu†ered with HEPES at 15% (v/v) -xation CO 2 .C O 2 and ammonia removal rates were estimated as 26E 0g m~3 h~1 and 0E92 g CO 2 m~3 h~1, respectively, when the alga was cultivated in wastewater supple- NH 3 mented with 46E 0g m~3 without pH control at 15% (v/v) PO 4 CO 2 .

Degradation of trichloroethylene (TCE) by nanoscale zero-valent iron (nZVI) immobilized in alginate bead.

Nowadays, many researchers have studied the environmental application of the nanoscale zero-valent iron (nZVI) and several field applications for the groundwater remediation have been reported. Still, there are many concerns on the fate and transport of the nZVI and the corresponding risks. To avoid such concerns, it was investigated to immobilize nZVI in a support and then it was applied to degrade trichloroethylene (TCE). The nZVI and palladium-doped nZVI (Fe(0)- and Fe/Pd-alginate) were immobilized in the alginate bead where ferric and barium ions are used as the cross-linking cations of the bead. According to TEM (transmission electron microscopy), the size of the immobilized ZVI was as small as a few nanometers. From the surface analysis of the Fe/Pd-alginate, it is found that the immobilized nZVI has the core-shell structure. The core is composed of single crystal Fe(0), while most of irons on the surface are oxidized to Fe(3+). When 50 g/L of Fe/Pd-alginate (3.7 g Fe/L) was introduced to the aqueous solution, >99.8% of TCE was removed and the release of metal from the support was <3% of the loaded iron. The removal of TCE by Fe/Pd-alginate followed pseudo-first-order kinetics. The observed pseudo-first-order reaction constant (k(obs)) of Fe/Pd-alginate was 6.11 h(-1) and the mass normalized rate constant (k(m)) was 1.6 L h(-1) g(-1). The k(m) is the same order of magnitude with that of iron nanoparticles. In conclusion, it is considered that Fe/Pd-alginate can be used efficiently in the treatment of chlorinated solvent.

Removal of heavy metals from aqueous solution by apple residues

Abstract The removal of copper, lead and cadmium by apple residues (AR) was investigated to evaluate cation exchange capacities. The effects of solution pH, ionic strength, ligands and co-ions were studied in batch experiments. Apple residues were modified with phosphorus (V) oxychloride to improve their physico-chemical properties and greatly enhance the capacity of metal removal. Adsorption equilibria were established rapidly initially and decreased markedly after 1 h. Column experiments were carried out in a glass column filled with AR and modified AR to evaluate the metal removal capacity. The influences of the feed concentration, chemical treatment and ligand were also studied. After exhaustion of the residues, the columns were regenerated successfully by a simple elution procedure.

Removal of Copper in Aqueous Solution by Apple Wastes

Abstract Removal of copper from a solution was investigated to evaluate the cation-exchange capacities of apple residues from agricultural wastes. The effects of solution pH, ionic strength, co-ion, ligands, initial metal concentrations, and particle size of apple residues were studied. The optimal pH range for copper removal by apple residues was shown to be from pH 5.5 to 7.0, and the maximum percentage of copper removal was 91.2%. Increasing ionic strength, up to 0.1 N, has little effect on metal uptake. The presence of co-ions such as lead decreases the removal capacity of copper as expected. The presence of ligands, such as EDTA and ammonia, also reduces metal removal efficiency due to the formation of a metal-ligand complexation in solution. Equilibrium of copper sorption was established very rapidly initially and decreased markedly after 1 hour. Equilibrium isotherms of copper fit the Langmuir equation adequately. Column experiments showed that the dynamic capacity of chemically modified apple resi...

A new method to control electrolytes pH by circulation system in electrokinetic soil remediation

To simultaneously avoid a decrease of electro-osmotic flow by hydrogen ions and to increase heavy metal precipitation due to hydroxide ions, simulated electrokinetic remediation was conducted in saturated kaolinite specimens loaded with lead(II) using an electrolyte circulation method to control electrolyte pH. At an electrolyte circulation rate of 1.1 ml/min, it was possible to increase the anolyte pH from 2 to 4 and decrease the catholyte pH from 12 to 8. Using electrolyte circulation, it was observed that the rate of decrease of clay pH due to the change of electrolyte pH was reduced. As a result, the operable period was extended and the removal efficiency for lead(II) was also increased. It was observed that most of the effluent lead(II) from the cathode compartment was electroplated onto the cathode and that residual effluent lead(II) did not precipitate onto, or adsorb to, the clay at the anode compartment during circulation. Therefore, there was no need to treat the electrolyte because there was virtually no effluent from the cathode compartment in the circulation system. It was also found that the electrolyte volume required to sustain the electrolytic reaction was sufficient for the whole electrokinetic remediation process.

Continuous production of galacto-oligosaccharides from lactose by Bullera singularis beta-galactosidase immobilized in chitosan beads

Abstract Galacto-oligosaccharides (GalOS) were continuously produced using lactose and immobilized β-galactosidase from Bullera singularis ATCC 24193 in a packed bed reactor. Partially purified β-galactosidase was immobilized in Chitopearl BCW 3510 bead (970 GU/g resin) by simple adsorption. 55% (w/w) oligosaccharides was obtained continuously with a productivity of 4·4 g/(litre-h) from 100 g/litre lactose solution during a 15-day operation. Batch productivity was 6·5 g GalOS/(litre-h) from 300 g/litre lactose.

Two-stage cultivation of two Chlorella sp. strains by simultaneous treatment of brewery wastewater and maximizing lipid productivity.

A cultivation system in the two-stage photoautotrophic-photoheterotrophic/mixotrophic mode was adapted to maximize lipid productivity of two freshwater strains of Chlorella sp. grown in brewery wastewater (BWW). The endogenous Chlorella sp. isolated from BWW had a higher growth rate than wild-type Chlorella vulgaris (UTEX-265) while C. vulgaris (UTEX-265) had a higher maximal biomass and lipid contents than that of endogenous Chlorella sp., resulting in more than 90% of the inorganic nutrients in both total nitrogen (TN) and phosphorus (TP) was removed during the first stage in the two-stage photoautotrophic-photoheterotrophic mode in each Chlorella sp. The maximal biomass and lipid contents of C. vulgaris (UTEX-265) for single stage photoautotrophic cultivation were 1.5 g/L and 18%, respectively. Importantly, during two-stage photoautotrophic-photoheterotrophic cultivation for C. vulgaris (UTEX-265), the biomass was increased to 3.5 g/L, and the lipid productivity was increased from 31.1 to 108.0mg/L day.

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.

Advances in direct transesterification of algal oils from wet biomass

An interest in biodiesel as an alternative fuel for diesel engines has been increasing because of the issue of petroleum depletion and environmental concerns related to massive carbon dioxide emissions. Researchers are strongly driven to pursue the next generation of vegetable oil-based biodiesel. Oleaginous microalgae are considered to be a promising alternative oil source. To commercialize microalgal biodiesel, cost reductions in oil extraction and downstream biodiesel conversion are stressed. Herein, starting from an investigation of oil extraction from wet microalgae, a review is conducted of transesterification using enzymes, homogeneous and heterogeneous catalysts, and yield enhancement by ultrasound, microwave, and supercritical process. In particular, there is a focus on direct transesterification as a simple and energy efficient process that omits a separate oil extraction step and utilizes wet microalgal biomass; however, it is still necessary to consider issues such as the purification of microalgal oils and upgrading of biodiesel properties.