Biomedical subjects

Y K Chang

Publications and source records attributed to Y K Chang.

40 records · Page 3Linked to original sources

PubMedDate not supplied

Desulfurization of diesel oils by a newly isolated dibenzothiophene-degrading Nocardia sp. strain CYKS2.

A dibenzothiophene (DBT)-degrading bacterial strain was isolated from dyeing industry wastewater and identified as Nocardia sp. CYKS2. The newly isolated bacterial strain Nocardia sp. CYKS2 was able to convert DBT to 2-hydroxybiphenyl (2-HBP) as the dead-end metabolite through a sulfur-specific pathway. Other organic sulfur compounds, such as thiophene derivatives, thiazole derivatives, sulfides, and disulfides were also desulfurized by Nocardia sp. CYKS2. In batch culture, 0.2 mM DBT was completely desulfurized in 60 h. After DBT was depleted, neither cell growth nor 2-HBP production was observed. When a model oil which DBT was dissolved in hexadecane was treated with growing cells, DBT was desulfurized from 10 mM to about 2 mM in 80 h. In this case, desulfurization rate was 0.279 mg-sulfur/(L-dispersion.h), which was about 2.5 times higher than that in the previous case of batch culture. When diesel oil was treated, the sulfur content decreased from 0.3 to 0.24 wt % in 48 h. A volumetric phase ratio of oil to water was 1/10 in this case. The sulfur decreased from 0.3 to 0.2 wt % in 48 h, when the volumetric phase ratio was 1/20. The desulfurization rates were 0.909 and 0.992 mg-sulfur/(L-dispersion.h), respectively.

Biodegradation, Environmental↗

PubMedDate not supplied

Development of a cell-loaded biosupport separator for continuous immobilized-cell perfusion culture.

An efficient cell-loaded biosupport separator of the decantor type was developed and applied for a continuous perfusion culture to produce cyclosporin A (CyA), in which fungal cells were immobilized on Celite beads. In the preliminary experiments employing highly viscous polymer (carboxymethyl cellulose) solutions, the decantor showed good separation performances at high solution viscosites and dilution rates. Two concentric cylindrical tubes installed inside the decantor turned out to play key roles in the efficient separation of the immobilized cells. By installing the decantor on an immobilized-cell perfusion bioprocess system, a stable continuous operation was possible even at a high dilution rate for an extended period, leading to high productivities of free cells and CyA. Almost no immobilized biomass existed in the effluent stream from the bioreactor, demonstrating the effectiveness of the decantor system. It is noteworthy that we could obtain these results despite unfavorable fermentation conditions, i.e., reduced apparent density of cell-loaded beads and increased drag force on the bead particles caused by overgrowth of cells on the bead surface, tubulence caused by large air bubbles, and the existence of a high density of suspended fungal cells (10 g/L) in the fermentation broth.

Carboxymethylcellulose Sodium↗

PubMedDate not supplied

Continuous ethanol production from concentrated wood hydrolysates in an internal membrane-filtration bioreactor.

Continuous culture for the production of ethanol from wood hydrolysate was carried out in an internal membrane-filtration bioreactor. The hydrolysate medium was sterilized at a relatively low temperature of 60 degrees C with the intention of reducing the formation of inhibitory compounds during the sterilization. The maximum ethanol concentration and productivity obtained in this study were 76.9 g/L and 16.9 g/L-h, respectively, which were much higher than those (57.2-67 g/L and 0.3-1.0 g/L-h) obtained in batch cultures using hydrolysate media sterilized at 60 degrees C. The productivity was also found to be much higher than that (6.7 g/L-h) obtained in a continuous cell retention culture using a wood hydrolysate sterilized at 121 degrees C. These results show that the internal membrane-filtration bioreactor in combination with low-temperature sterilization could be very effective for ethanol production from wood hydrolysate.

Bioreactors↗

PubMedDate not supplied

Separation of Alcaligenes eutrophus cells containing Poly(3-hydroxybutyrate) from fermentation broth with pretreatment using Al- and Fe-based coagulants.

Alcaligenes eutrophus containing intracellular poly(3-hydroxybutyrate) was recovered from fermentation broth by centrifugation and filtration after pretreatment with Al- and Fe-based coagulants. Coagulation efficiency was largely affected by pH, and the optimum pH's for cell recovery were about 4.6-5.6 for the Al-based coagulants and about 5-8 for the Fe-based coagulants. Ammonium ions that combined with metals to form complex compounds increased the coagulant requirement, and the additional requirement of coagulant was found to be proportional to the ammonium concentration. In addition, various ligands in addition to ammonium ions contained in the culture medium interfered with the coagulation reaction and increased the coagulant requirement also. The coagulant requirement increased with the cell concentration regardless of coagulant type. The polymeric coagulants such as PACS, Hi-PAX, and Ferix-3 were more effective than nonpolymeric coagulants of aluminum sulfate and ferrous sulfate. The optimum dosages of the coagulants tested were determined over a broad range of cell concentration of 20.5-210 g/L. It was observed that the energy requirement for centrifugation could be greatly reduced with cell coagulation.

Alcaligenes↗