Myunggu Lee

Effects of various pretreatments for enhanced anaerobic digestion with waste activated sludge.

The purpose of this study was to enhance the efficiency of anaerobic digestion with waste activated sludge (WAS) by batch experiments. We studied the effects of various pretreatment methods (thermal, chemical, ultrasonic and thermochemical pretreatments) on the biogas production and pollutants reduction owing to solubilization enhancement, particle size reduction, increased soluble protein, and increased soluble COD. The thermochemical pretreatment gave the best results, i.e., the production of methane increased by more than 34.3% and soluble COD (SCOD) removal also increased by more than 67.8% over the control. In this case, the biogas production, methane production and the SCOD removal efficiency were about 5037 l biogas/m3 WAS, 3367 l methane/m3 WAS and 61.4%, respectively. Therefore, it is recognized that higher digestion efficiencies of the WAS were obtained through thermochemical pretreatment of the sludge.

Enzymatic coproduction of biodiesel and glycerol carbonate from soybean oil and dimethyl carbonate.

The enzymatic coproduction of biodiesel and glycerol carbonate by the transesterification of soybean oil was studied using lipase as catalyst in organic solvent. To produce biodiesel and glycerol carbonate simultaneously, experiments were designed sequentially. Enzyme screening, the molar ratio of dimethyl carbonate (DMC) to soybean oil, reaction temperature and solvent effects were investigated. The results of enzyme screening, at 100 g/L Novozym 435 (immobilized Candida antarctica lipase B), biodiesel and glycerol carbonate showed conversions of 58.7% and 50.7%, respectively. The optimal conditions were 60 °C, 100 g/L Novozym 435, 6.0:1 molar ratio with tert-butanol as solvent: 84.9% biodiesel and 92.0% glycerol carbonate production was achieved.

Improvement of enzymatic biodiesel production by controlled substrate feeding using silica gel in solvent free system

A silica gel-based substrate feeding system was developed to prevent methanol inhibiting the catalyst during enzymatic biodiesel synthesis. In the system, silica gel swelled upon methanol addition and subsequently released it in a controlled manner to prevent excess methanol affecting the enzyme. Biodiesel was synthesized by the enzymatic transesterification of canola oil with methanol. For this reaction, enzyme loading, methanol/oil molar ratio, silica gel dosage, glycerol content, and methanol feeding method were tested using commercial immobilized enzymes (Novozym 435 and Lipozyme RM IM from Novozymes). The results showed that conversion was highest with controlled substrate feeding rather than direct methanol addition, suggesting that the method developed here can easily prevent enzyme inhibition by limiting methanol concentration to an acceptable level.

The nucleation of highly oriented diamond on silicon using a negative bias

The highly oriented diamond films are deposited on the mirror-polished Si(001) substrate by the cyclic hydrogen etching treatment during bias enhanced nucleation (BEN) process using a microwave plasma deposition system. The number of oriented diamond grains treated by the hydrogen etching during the BEN process are about two-times higher than that treated by normal BEN processes. The (111) X-ray pole figure of the oriented diamond film is clearly dominated by the four (100) peaks of diamond. The full width at half maximum of X-ray (111) poles and X-ray (004) peak rocking curves of diamond deposited by the cyclic hydrogen etching treatment during the BEN process is smaller than that by normal BEN treatment. From the results and our previously suggested model, we discuss the roles of hydrogen to nucleate the oriented diamond on Si by the BEN process.