Jae Hoon Hwang

Photoautotrophic hydrogen production by eukaryotic microalgae under aerobic conditions

Eukaryotic algae and cyanobacteria produce hydrogen under anaerobic and limited aerobic conditions. Here we show that novel microalgal strains (Chlorella vulgaris YSL01 and YSL16) upregulate the expression of the hydrogenase gene (HYDA) and simultaneously produce hydrogen through photosynthesis, using CO2 as the sole source of carbon under aerobic conditions with continuous illumination. We employ dissolved oxygen regimes that represent natural aquatic conditions for microalgae. The experimental expression of HYDA and the specific activity of hydrogenase demonstrate that C. vulgaris YSL01 and YSL16 enzymatically produce hydrogen, even under atmospheric conditions, which was previously considered infeasible. Photoautotrophic H2 production has important implications for assessing ecological and algae-based photolysis.

Feasibility of hydrogen production from ripened fruits by a combined two-stage (dark/dark) fermentation system

Anaerobic fermentation for hydrogen (H2) production was studied in a two-stage fermentation system fed with different ripened fruit feedstocks (apple, pear, and grape). Among the feedstocks, ripened apple was the most efficient substrate for cumulative H2 production (4463.7 mL-H2 L(-1)-culture) with a maximum H2 yield (2.2 mol H2 mol(-1) glucose) in the first stage at a hydraulic retention time (HRT) of 18 h. The additional cumulative biohydrogen (3337.4 mL-H2 L(-1)-culture) was produced in the second stage with the reused residual substrate from the first stage. The major byproducts in this study were butyrate, acetate, and ethanol, and butyrate was dominant among them in all test runs. During the two-stage system, the energy efficiency (H(2) conversion) obtained from mixed ripened fruits (RF) increased from 4.6% (in the first stage) to 15.5% (in the second stage), which indicated the energy efficiency can be improved by combined hydrogen production process. The RF could be used as substrates for biohydrogen fermentation in a two-stage (dark/dark) fermentation system.

MEMS Based Integrated Particle Detection Chip for Real Time Environmental Monitoring

In this paper, we report design, fabrication and characterization of a MEMS based integrated particle detection chip for real time environmental monitoring. The chip is designed on the basis of aerosol technology and is realized using micromachining processes. The complete device is composed of two parts, one is a micro virtual impactor for the classification of particles according to their sizes and the other is a micro corona discharger for measuring the particle concentration. The integrated chip is used for classifying bigger and smaller size particles and finally determining the number concentration by measuring the current carried by charged particles. In this experiment, the cut-off diameter of the particle was 550 nm. Since conventional particle detection equipments are relatively big in size and expensive as well, the proposed device will be the first step to the realization of low-cost and real-time environmental monitoring.

Effect of COD/SO42−ratio and Fe(II) under the variable hydraulic retention time (HRT) on fermentative hydrogen production

The effect of chemical oxygen demand/sulfate (COD/SO(4)(2-)) ratio on fermentative hydrogen production using enriched mixed microflora has been studied. The chemostat system maintained with a substrate (glucose) concentration of 15 g COD L(-1) exhibited stable H(2) production at inlet sulfate concentrations of 0-20 g L(-1) during 282 days. The tested COD/SO(4)(2-) ratios ranged from 150 to 0.75 (with control) at pH 5.5 with hydraulic retention time (HRT) of 24, 12 and 6h. The hydrogen production at HRT 6h and pH 5.5 was not influenced by decreasing the COD/SO(4)(2-) ratio from 150 to 15 (with control) followed by noticeable increase at COD/SO(4)(2-) ratios of 5 and 3, but it was slightly decreased when the COD/SO(4)(2-) ratio further decreased to 1.5 and 0.75. These results indicate that high sulfate concentrations (up to 20,000 mg L(-1)) would not interfere with hydrogen production under the investigated experimental conditions. Maximum hydrogen production was 2.95, 4.60 and 9.40 L day(-1) with hydrogen yields of 2.0, 1.8 and 1.6 mol H(2) mol(-1) glucose at HRTs of 24, 12 and 6h, respectively. The volatile fatty acid (VFA) fraction produced during the reaction was in the order of butyrate>acetate>ethanol>propionate in all experiments. Fluorescence In Situ Hybridization (FISH) analysis indicated the presence of Clostridium spp., Clostridium butyricum, Clostridium perfringens and Ruminococcus flavefaciens as hydrogen producing bacteria (HPB) and absence of sulfate reducing bacteria (SRB) in our study.

Influence of CO2 and light spectra on the enhancement of microalgal growth and lipid content

The effect of different light spectrum and CO2 concentrations on the growth and lipid content of Micractinium pusillum and Ourococcus multisporus was investigated. The highest biomass yields (2.9 and 2.6 g-dry cell weight l−1) were observed for M. pusillum and O. multisporus, respectively, at 5% CO2 with red light illumination. Red light spectrum with 5% CO2 supported the highest lipid contents (20% and 27%) and lipid productivity (32 and 36 mg l−1 d−1) for M. pusillum and O. multisporus, respectively. The highest fatty acid methyl esters content for both microalgal species was observed under red light spectrum and 5% CO2 conditions, with the oleic acid fraction ranging between 35% and 37%. This study showed that the red light spectrum and 5% CO2 were the optimum conditions for maximum growth, lipid content and lipid productivity of both microalgae species, which could be further exploited to establish a microalga-based biodiesel production strategy.

Electrically tunable airborne particle classifier using a virtual impactor

This paper reports an airborne particle classifier based on a virtual impactor (VI) which is capable of actively tuning a cut-off diameter by applying the electric potential. The VI aerodynamically classifies airborne particles according to their size. An electrode pair is integrated in the VI, which make possible to electrically control the cut-off diameter of the VI without additional fabrications. The VI with a cut-off diameter of 1 mum was designed, and its cut-off characteristics were examined. Thereafter, the cut-off diameter was successfully tuned to from 35 nm to 70 nm by applying electric potentials from 1 kV to 3 kV.

Enhancement of microalgal growth and biocomponent-based transformations for improved biofuel recovery: A review

Microalgal biomass has received much attention as feedstock for biofuel production due to its capacity to accumulate a substantial amount of biocomponents (including lipid, carbohydrate, and protein), high growth rate, and environmental benefit. However, commercial realization of microalgal biofuel is a challenge due to its low biomass production and insufficient technology for complete utilization of biomass. Recently, advanced strategies have been explored to overcome the challenges of conventional approaches and to achieve maximum possible outcomes in terms of growth. These strategies include a combination of stress factors; co-culturing with other microorganisms; and addition of salts, flue gases, and phytohormones. This review summarizes the recent progress in the application of single and combined abiotic stress conditions to stimulate microalgal growth and its biocomponents. An innovative schematic model is presented of the biomass-energy conversion pathway that proposes the transformation of all potential biocomponents of microalgae into biofuels.