Dong Sup Kim

Production and characterization of cellobiose dehydrogenase from Phanerochaete chrysosporium KCCM 60256 and its application for an enzymatic fuel cell

The enzyme cellobiose dehydrogenase (CDH), with high ability of electron transport, has been widely used in enzymatic fuel cells or biosensors. In this study, the cellobiose dehydrogenase gene from Phanerochaete chrysosporium KCCM 60256 was amplified and expressed in the methylotrophic yeast Pichia pastoris X-33. The recombinant enzyme (PcCDH) was purified using a metal affinity chromatography under non-denaturing conditions. The purified enzyme was analyzed by SDS-PAGE, confirming a corresponding band about 100 kDa. The enzyme activity of this purified PcCDH was determined as 1,845U/L (65mg/L protein). The enzyme showed the maximum activity at pH 4.5 and high activity in broad ranges of temperature from 30°C to 60°C. Moreover, the application of PcCDH to enzymatic fuel cell (EFC) was demonstrated. Lactose was used as the substrate in the EFC system; anode and cathode were immobilized with PcCDH and laccase, respectively. The cell’s open circuit voltage and maximum power density of the EFC system were, respectively, determined as 0.435 V and 314 μW/cm2 (at 0.247 V) with 10 mM lactose.

Evaluation of the overall process on bioethanol production from miscanthus hydrolysates obtained by dilute acid pretreatment

In this study, dilute sulfuric acid pretreatment was performed to improve the sugars recovery from Korean Miscanthus straw. The effect of pretreatment conditions on solubilized xylose was fundamentally investigated for the efficient removal of xylan. The optimal conditions were determined using a statistical method, and were shown to be a temperature of 121.6°C, an acid concentration of 1.1%, and a reaction time of 12.8 min. The combined severity factor was shown to be 1.1 under the optimum conditions. Following the pretreatment, the solubilized xylose in liquid fraction was found to be 71.2%, and about 72.6% of the solid was recovered. After enzymatic hydrolysis, about 86.4% glucose conversion was achieved when the pretreated biomass was used as a substrate, with the conversion being improved 4-fold compared with the control (untreated). The hydrolysates, approximately 10 g/L glucose, were applied to the fermentation of Saccharomyces cerevisiae K35, and the ethanol yield was about 96%. The overall process was evaluated based on the material balance, and the results show that approximately 172 g bioethanol can be produced when 1,000 g Miscanthus straw is loaded into the process.

Utilization of hydrolysate from lignocellulosic biomass pretreatment to generate electricity by enzymatic fuel cell system.

The waste hydrolysate after dilute acid pretreatment (DAP) of lignocellulosic biomass was utilized to generate electricity using an enzymatic fuel cell (EFC) system. During DAP, the components of biomass containing hemicellulose and other compounds are hydrolyzed, and glucose is solubilized into the dilute acid solution, called as the hydrolysate liquid. Glucose oxidase (GOD) and laccase (Lac) were assembled on the electrode of the anode and cathode, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were measured, and the maximum power density was found to be 1.254×10(3) μW/cm(2). The results indicate that the hydrolysate from DAP is a reliable electrolyte containing the fuel of EFC. Moreover, the impurities in the hydrolysate such as phenols and furans slightly affected the charge transfer on the surface of the electrode, but did not affect the power generation of the EFC system in principal.

Enhanced electron transfer mediator based on biochar from microalgal sludge for application to bioelectrochemical systems

This study is focused on the utilization of waste microalgal sludge (MS) from microalgal extraction and its potential as an electrode material. The MS was activated under N2 at high temperature for conversion to biochar (MSB). In addition, cobalt (Co; metal hydroxide) and chitosan were used as a mediator for electron transfer by immobilization on MSB (MSB/Co/chitosan). Through analysis of the surface and components of the MSB/Co/chitosan, it was shown that Co and chitosan were properly synthesized with MSB. The enzymatic fuel cell (EFC) system successfully obtained a power density of 3.1 mW cm-2 and a current density of 9.7 mA cm-2. In addition, the glucose biosensors applied with the developed electron transfer mediator showed a sensitivity of 0.488 mA mM-1 cm-2.