• Journal of Korea Society of Industrial Information Systems
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• v.20 no.4
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• pp.25-37
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• 2015

The early studies indicated that the firm with monopoly power is likely to engage in X-inefficiency such as a managerial slack. The reflection of the X-inefficiency theory has led to the issue that the public sector may be more inefficient than the private sector. In Korea like other many countries the electricity gas water service which can be considered as natural monopoly have been provided mostly by the public sector. In order to provide the empirical evidence to the argument that the public sector may be more inefficient than the private sector this paper estimated the four types of Solow residual which is called the total factor productivity in the electricity gas water service industry with the associated empirical model and compared its productivity with one in the manufacturing industry. The empirical results do not support the argument that the public sector may be more inefficient or less productive than the private sector.

• Microbiology and Biotechnology Letters
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• v.24 no.5
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• pp.597-603
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• 1996

This study was carried out to examine degradation characteristics of microalgae Chlorella vulgaris in methane fermentation. We measured COD and VS reduction, gas and methane productivity, VFA (volatile fatty acid), respectively. Then we calculated material balance and hydrolysis rates in soluble and solid material. The substrate concentration was controlled from 14 gCOD$_{cr}$/l to 64 gCOD$_{cr}$/l in batch cultures, and HRT (hydraulic retention time) controlled from 2 days to 30 days in continuous experi- ments. The results were as follows. In batch culture, accumulated gas productivity increased with the increase of the substrate concentration. The SS and VSS was removed all about 30% increase of substrate concentration and the most of the degradable material removed during the first 10 days. The curve of gas and methane production rate straightly increased until substrate concentration is 26 gCOD$_{cr}$/l. In continuous culture experiments, the removal rates at HRT 10days were 20% for total COD and TOC, respectively. At longer HRT, there was no increase in the removal efficiency. At HRT 15 days, the removal rates were 30% for SS and VSS, respectively. Soluble organic materials were rapidly degraded, and so there was no accumulated. Soluble COD concentration was not increase regardless of HRT-increasing. That meaned the hydrolysis was one of the rate-limiting stage of methane fermentation. The first-order rate constants of hydrolysis were 0.23-0.28 day$^{-1}$ for VSS, and 0.07-0.08 day$^{-1}$ for COD.

• Journal of the Korea Organic Resources Recycling Association
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• v.10 no.1
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• pp.87-95
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• 2002

The slow degradation rate of sludge in anaerobic digestion is due to rate-limiting step of sludge hydrolysis. To upgrading of sludge hydrolysis and biodegradabiliry, the pre-treatment had been carried out using acidlc (pH 1.5, 3, 4, 5) and alkaline (pH 9, 10, 13), thermal (50, 100, 150, $200^{\circ}C$), and ultrasonic treatment (400W, 20kHz, 15, 20, 25, 30, 40, 50, 60, 90min). In the best conditions of each treatment, the Soluble SCOD Ratio(%)of treated/untreated sample were increased 102% in acid (pH5), 986% in alkali (pH 13), 595% in thermal ($200^{\circ}C$) and 1123% in ultrasonic (35min) treatment. As the result, the ultrasonic treatment was most effective, followed by alkali, thermal, acid treatment. In the effects of total gas productivity in vial test, the thermal ($200^{\circ}C$) pre-treatment was the highest, followed by thermal ($150^{\circ}C$), ultrasonic (90min), alkaline (pH 9), and ultrasonic (50min). We compared untreated samples and the most efficient pre-treatment samples(at $200^{\circ}C$, for 30min) on gas productivity with changes of HRT in continuous experiments IN thermal treated samples were 2.5 times in SCOD, 2 times in soluble protein and 3.3 times high in soluble carbohydrate than untreated ones. In gas productivity, the thermal treated samples were average 2 times high than untreated ones. And HRT 7 days was most effective. followed by HRT 10, HRT 15 days. But The gas productiviry of HRT 2.5 days was less than untreated, the reason of low gas productivity was come from high organic acids accumulation within reactor.

• Asian-Australasian Journal of Animal Sciences
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• v.13 no.8
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• pp.1113-1120
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• 2000

Productivity, nutrient contents, in vitro gas production and in sacco degradability of different fractions and whole OPF were determined to assess the feeding value of OPF as a ruminant feed. An in vivo digestibility trial was also carried out using goat. Freshly harvested OPF was randomly collected, partitioned and weighed. An OPF from 21 years older palm weighed 13.4 kg and the annual fresh matter yield of petiole, leaflet and midrib was 46.5, 11.8 and 3.4 ton/ha, respectively. Leaflet contained 439, 926, 698, 501, 168, 196, 748 and 52 (g/kg) of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), cellulose (CE), hemicellulose (HC), total carbohydrate (TC) and non fiber carbohydrate (NFC), respectively. Petiole contained lower (p<0.01) DM, CP and EE contents than leaflet. Organic matter, CE and TC contents were higher (p<0.01) in petiole compared to leaflet. Silica and lignin contents were highest (p<0.01) in midrib followed by leaflet, whole OPF and least in petiole. The Ca, P, Na, K and Mg contents (g/100 g DM) of leaflet were 0.529, 0.182, 0.039, 0.876, and 0.168, respectively. In vitro DM digestibility (g/100 g) at 48 h of leaflet, petiole and midrib was 32.7, 38.7 and 30.2, respectively. The in sacco DM degradation (g/100 g) at 48 h of leaflet was higher than that of whole OPF, petiole and midrib. The in vivo digestibility of DM, OM, CP and ADF of whole OPF was 52, 56, 43 and 26%, respectively. It can be concluded that leaflet is the most nutritious fraction of OPF and midrib is the least. The nutrient content and digestibility of the whole OPF showed that OPF could be an alternative roughage source for ruminant diets.

• Journal of Korean Society on Water Environment
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• v.26 no.5
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• pp.754-760
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• 2010

This study was carried out not only to evaluate optimal operating condition to increase biogas production, but also to estimate feasibility of renewable energy from anaerobic digester of sewage sludge. Semi- continuous Fed and Mixed Reactors (SCFMRs) were operated in various condition to quantify the reactor variables. The result of SCFMR operation showed that the biogas productivity and total volatile solids (TVS) removal of total solids (TS) 4% reactor at hydraulic retention time (HRT) 20 days with Organic Loading Rate (OLR) of $1.45kg/m^3-d$ were $0.39m^3/m^3-d$ and 26.7%, respectively which was two times higher than that of TS 2.5% reactor. Consequently the daily biogas production of $20,000m^3$ would be possible from the total volume of $52,000m^3$ of anaerobic digesters of the municipal wastewater treatment plant in D city. In feasibility study for the Biogas utilization, combined heat and power system (CHP) and CNG gasification were examined. In case of CHP, the withdrawal period of capital cost for gas-engine (GE) and micro gas-turbine (MGT) were 7.7 years and 9.1 years respectively. biogas utilization as Clean Natural Gas (CNG) shows lower capital cost and higher profit than that of CHP system. CNG gasificaion after biogas purification is likely the best alternative for Biogas utilization which have more economic potential than CHP system. The withdrawal period of capital cost appeared to be 2.3 years.

• Korean Journal of Environmental Agriculture
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• v.31 no.3
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• pp.205-211
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• 2012

BACKGROUND: Generally, nitrogen (N) fertilization higher than the recommended dose is applied during vegetable cultivation to increase productivity. But higher N fertilization also increases the concentrations of nitrate ions and nitrous oxide in soil. In this experiment, the impact of N fertilization was studied on nitrous oxide ($N_2O$) emission to standardize the optimum fertilization level for minimizing $N_2O$ emission as well as increasing crop productivity. Herein, we developed $N_2O$ emission inventory for upland soil region during red pepper and Chinese milk vetch cultivation. METHODS AND RESULTS: Nitrogen fertilizers were applied at different rates to study their effect on $N_2O$ emission during red pepper and Chinese milk vetch cultivation. The gas samples were collected by static closed chamber method and $N_2O$ concentration was measured by gas chromatography. The total $N_2O$ flux was steadily increased due to increasing N fertilization level, though the overall pattern of $N_2O$ emission dynamics was same. Application of N fertilization higher than the recommended dose increased the values of both seasonal $N_2O$ flux (94.5% for Chinese cabbage and 30.7% for red pepper) and $N_2O$ emission per unit crop yield (77.9% for Chinese cabbage and 23.2% for red pepper). Nitrous oxide inventory revealed that the $N_2O$ emission due to unit amount of N application from short-duration vegetable field in fall (autumn) season (6.36 kg/ha) was almost 70% higher than that during summer season. CONCLUSION: Application of excess N-fertilizers increased seasonal $N_2O$ flux especially the $N_2O$ flux per unit yield during both Chinese cabbage and red pepper cultivation. This suggested that the higher N fertilization than the recommended dose actually facilitates $N_2O$ emission than boosting plant productivity. The $N_2O$ inventory for upland farming in temperate region like Korea revealed that $N_2O$ flux due to unit amount of N-fertilizer application for Chinese cabbage in fall (autumn) season was comparatively higher than that of summer vegetables like red pepper. Therefore, the judicious N fertilization following recommended dose is required to suppress $N_2O$ emission with high vegetable productivity in upland soils.

• Journal of the Korean Applied Science and Technology
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• v.21 no.3
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• pp.225-230
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• 2004

Synthesis gas is a high valued compound as a basic chemicals at various chemical processes. Synthesis gas is mainly produced commercially by a steam reforming process. However, the process is highly endothermic so that the process is very energy-consuming process. Thus, this study was carried out to produce synthesis gas by the partial oxidation of methane to decrease the energy cost. The effects of reaction temperature and flow rate of reactants on the methane conversion, product selectivity, product ratio, and carbon deposition were investigated with 13wt% Ni/MgO catalyst in a fluidized bed reactor. With the fluidized bed reactor, $CH_4$ conversion was 91%, and Hz and CO selectivities were both 98% at 850$^{\circ}C$ and total flow rate of 100 mL/min. These values were higher than those of fixed bed reactor. From this result, we found that with the use of the fluidized bed reactor it was possible to avoid the disadvantage of fixed bed reactor (explosion) and increase the productivity of synthesis gas.

• Korean Journal of Agricultural Science
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• v.46 no.4
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• pp.931-939
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• 2019

Biochar is a solid carbon material made by pyrolyzing a biomass under limited oxygen conditions. Biochar has been reported to confer various benefits, such as increased soil productivity, pollutant absorption, and reduced greenhouse gas. In this study, oak pyrolyzed at 600℃ for 3 hours was either powdered or pelleted. Each of the biochar types was added to the soil at a rate of 2%. The control did not receive any biochar while a combination of the biochar and NPK treatment (biochar 2% + NPK) was also included. The cherry tomatoes were grown in greenhouse pots for 50 days to compare the growth characteristics of the different treatments. The cherry tomato with the powdered biochar 2% + NPK treatment had the heaviest plant fresh shoot weight of 276.4 g and the highest chlorophyll content of 59.3 SPAD. The control had the lightest plant fresh shoot weight of 44.2 g and a chlorophyll content of 26.5 SPAD. Both forms of biochar affected the chemical properties of the soil, increased the pH, electrical conductivity, available phosphate, total carbon and total nitrogen and positively influenced the cherry tomato growth and productivity. From the above results, therefore, both biochar forms are suited for use as soil amendments.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.1
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• pp.99-110
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• 2004

In order to investigate the performance of carbon dioxide PSA over zeolite adsorbent, the present study showed results of isotherm measurement, cyclic operation of 3-bed apparatus, and the corresponding numerical simulation. The experiment data of bed temperature, purity, recovery were matched well with that of numerical simulation. Purity of both gas and adsorbent phase increased rapidly with rinse rate but the degree of increase was retarded for large rinse rate The total amount of adsorbed increased only 10% even if rinse rate was enlarged to 4 times. Optimal rinse rate was 7N㎥/hr in this study. The heating rinse led to augments in recovery and productivity, possibly thanks to ease of description resulting from increased volumetric rinse rate and temperature rise in the column.

• Korean Journal of Agricultural Science
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• v.46 no.1
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• pp.125-135
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• 2019

Late-maturing Dark Horse, and early-maturing High Speed oat varieties were seeded on March 3, 2016 and harvested on three periods: May 31, June 10, and June 20 coded as early, mid, and late-harvest, respectively. Dried and ground samples were subjected to chemical analysis to determine nutritional values such as crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract (EE), organic matter (OM), and total digestible nutrient (TDN). Effective degradability (ED) of nutrients and fermentation characteristics including volatile fatty acid (VFA) composition, pH, gas production, and ammonia-N concentration were evaluated through an in vitro digestion method. Varieties of oat hays showed significant difference in terms of nutritional value, ED, and fermentation characteristics. Dark Horse showed higher CP and OM, and lower EE contents than High Speed. Dark Horse also showed higher EDDM (dry matter), NDF, ADF, and OM than High Speed, and although High Speed showed higher pH and ammonia-N, it had lower gas and total VFA production than Dark Horse. However, in terms of harvest period, significant difference was only observed in Dark Horse where early-harvest increased the CP, and late-harvest increased the NDF and OM contents. In addition, early-harvest of Dark Horse increased the EDDM and EDNDF of the forage. Therefore, early-harvest of late-maturing Dark Horse would give better nutrient efficiency than High Speed. Allowing Dark Horse to advance in maturity would decrease its nutrient productivity and efficiency.