• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.2
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• pp.72-78
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• 2006

Effect of organic loading rate on digester performance was evaluated under the conditions of same surface area/reactor volume ratio and different reactor diameter. At the low loading rate of $0.4\;kg\;COD/m^3{\cdot}d$, high rate of organic removal could be obtained regardless of reactor diameter. It can be estimated that reactor configuration can not affect reactor performance at the low loading rate. However, different performance depending on reactor diameter was observed at the organic loading rate of $6\;kg\;COD/m^3{\cdot}d$. That is, volatile acid accumulation and low COD removal efficiency was observed in reactor having 6.4 cm diameter, while volatile acid was not accumulated at all and high COD removal efficiency was observed in reactor having 3 cm diameter. Such a difference of reactor performance depending on reactor diameter can be explained that sludge bed can be fluidized by evolved gas bubble in narrow reactor while sludge bed can not be fluidized by evolved gas bubble only in wide reactor. At a high organic loading rate of $20\;kg\;COD/m^3{\cdot}d$, it can be judged that there is no relation between reactor configuration and reactor performance because all reactors showed very low COD removal efficiencies regardless of reactor diameter. Sludge bed fluidization is one of the most important factors in achieving efficient start-up of anaerobic digester. Narrow and tall type reactor is favorable condition for making sludge bed fluidization at a constant surface area/reactor volume ratio. Thus, it can be judged that reactor configuration and sludge bed fluidization have great influence to reactor performance.

• Journal of the Korea Organic Resources Recycling Association
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• v.11 no.3
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• pp.75-86
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• 2003

In the near future, the capacity of conventional anaerobic digester is thought to be insufficient because of the increase of the total solids from expansion of intercepting sewer, sewage quantity and direct input of night soil from near apartment districts. The objectives of this study was to investigate the improvement of digestion efficiency using microbial agent(Bio-dh). The system was a pilot-scale, two-staged, anaerobic sludge digestion system. The first-stage digester was heated and mixed. The agitation velocity of the first-stage digester was 120rpm. The second-stage digester was neither heated nor mixed. The Digestion temperature was kept at $35{\pm}1^{\circ}C$ The detention time of digester was 19 days. The dosage of sewage sludge and microbial agent were $0.65m^3/day$ and $0.5{\ell}/day$, respectively. The experiments was run for 25days. Three times a week, $COD_{Mn}$ and SS of effluent, TS, VS, and biogas production rate were measured. Temperature, pH, and alkalinity were measured daily. The results were as follows ; Without microbial agent, digestion efficiencies ranged 46.0%~50.9%(mean=48.6%), with microbial agent(Bio-dh), digestion efficiencies ranged 52.8%~57.3%(mean=54.2%). Consequently, microbial agent(Bio-dh) increased the sludge digestion efficiency about 12%. Also, Without microbial agent, the mean concentration of $COD_{Mn}$ and SS of second-stage digester effluent were 1,639mg/L, 4,888mg/L respectively. With microbial agent, the mean concentration of $COD_{Mn}$ and SS of second-stage digester effluent were 859mg/L, 2,405mg/L respectively. Consequently, microbial agent(Bio-dh) increased the removal efficiency of $COD_{Mn}$ and SS about 47.6% and 50.8%, respectively.

• Journal of Environmental Science International
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• v.20 no.10
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• pp.1233-1241
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• 2011

The main objective of this experimental investigation was $CH_4$ recovery from biogas generated in municipal and wastewater treatment plant. The polysulfone hollow fiber membrane was prepared in order to investigate the permeation properties of $CH_4$ and $CO_2$. Permeability of $CO_2$ in Polysulfone membrane was 11-fold higher than of $CH_4$ gas. A membrane pilot plant for upgrading biogas was constructed and operated at a municipal wastewater treatment plant. The raw biogas contained 66 ~ 68 Vol % $CH_4$, the balance being mainly $CO_2$. The effect of the operating pressure of feed and permeate side and feed flowrate on $CH_4$ recovery concentration and efficiency were investigated with double stage membrane pilot plant. The $CH_4$ concentration in the retentate stream was raised in these tests to 93 Vol % $CH_4$.

• Journal of Electrochemical Science and Technology
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• v.1 no.2
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• pp.102-111
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• 2010

Molten carbonate fuel cell (MCFC) power plants are one of most attractive electricity generation systems for the use of biogas to generate high-efficiency ultra-clean power. However, MCFCs are considerably more expensive than comparable conventional electricity generation systems. The commercialization of MCFCs has been delayed more than expected. After being effective in the Kyoto protocol and considerably increasing the fossil price, the attention focused on $CO_2$ regression and renewable energy sources has increased dramatically. In particular, the commercialization and application of MCFC systems fed with biogas have been revived because of the characteristics of $CO_2$ collection and fuel variety of MCFCs. Better economic results of MCFC systems fed with biogas are expected because biogas is a relatively inexpensive fuel compared to liquefied natural gas (LNG). However, the pretreatment cost is added when using anaerobic digester gas (ADG), one of the biogases, as a fuel of MCFC systems because it contains high $H_2S$ and other contaminants, which are harmful sources to the MCFC stack in ADG. Thus, an accurate economic analysis and comparison between MCFCs fed with biogas and LNG are very necessary before the installation of an MCFC system fed with biogas in a plant. In this paper, the economic analysis of an MCFC fed with ADG was carried out for various conditions of electricity and fuel price and compared with the case of an MCFC fed with LNG.

• Journal of Korean Society on Water Environment
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• v.16 no.4
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• pp.541-554
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• 2000

Experimental study of anaerobic digestion process combined with and without the submerged separation membrane was investigated by using laboratory-scale reactor at the hydraulic retention time of 0.5 day and 1.0 day. The removal efficiencies of carbohydrate at the digester without and with membrane were 84.4 to 86.8 % and 99.6 to 99.7 %, respectively, and the methane gas recovery efficiencies were 0.4 to 1.2 % and 12.3 to 28.7 %. According to the measurement by the most probable numbers method. the numbers of various groups of bacteria in the digesters with membrane were enumerated in the following ranges ; acidogens : $1.7{\times}10^9$ to $5.0{\times}10^9MPN/m{\ell}$, homoacetogens : $5.0{\times}10^7$ to $2.4{\times}10^8MPN/m{\ell}$, $H_2$-utilizing methanogens : $1.3{\times}10^7$ to $9.2{\times}10^8MPN/m{\ell}$, and acetate-utilizing methanogens : $2.3{\times}10^6$ to $2.0{\times}10^8MPN/m{\ell}$. The number of methanogens at the digester with membrane increased by approximately $10^2$ to $10^4$ times in comparison with that of the digester without membrane.

• Journal of Environmental Health Sciences
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• v.25 no.3
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• pp.29-35
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• 1999

Quantity and composition of biogas from semi-continuous anaerobic digestion of straw were obtained experimentally in laboratory scale digesters fed with 1 liter of 5% straw-water mixture and maintained at 35$^{\circ}C$. Experiments were carried out for hydraulic retention time(HRT) of 8, 10 and 15days, respectively. The amount and composition of biogas produced were measured until steady-state was achieved for each run. The amount of biogas and methane percent go through a maximum and decrease continuously towards the steady-state after three times operation of hydraulic retention time(HRT). Methane gas production rates at steady-state increase with the increasing of HRT. Biogas production of 0.45 liter/day with 25% methane, 0.42 liter/day with 33.7% methane and 0.492 liter/day with 31.7% methane were obtained for 8, 10 and 15days of HRT, respectively. The high proportion of soluble carbohydrates present in straw makes the volatile fatty acids to build up within the digester causing a drop in pH that inhibits digestion. Regular control of pH is therefore necessary by adding alkalinity. Reductions in COD increase with increase in HRT. The stratification of plant material within the digester is different from that of manure, and modifications in design and operation of digesters may be necessary if they are fed with plant matter.

• Journal of Environmental Science International
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• v.1 no.2
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• pp.125-136
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• 1992

Digestion of a municipal wastewater sludge by the anaerobic sequencing batch reactor (ASBR) was investigated to evaluate the performance of the ASBR process at a critical condition of high-solids-content fined. The reactors were operated at an HRT of 10 days with an equivalent loading rate of 0.8-1.5 gVS/L/d at 35$^{\circ}C$ The main conclusions drawn from this study were as follows: 1. Digestion of a municipal wastewater sludge was possible using the ASBR in spite of high concentration of settleable solids in the sludge. The ASBRS with 3- and 4-day cycle period showed almost identical high digestion performances. 2. No adverse effect on digestion stability was observed In the ASBRS in spite of withdrawal and replenishment of 30% or 40% of liquid contents. A conventional anaerobic digester could be easily converted to the ASBR without any stability problem. 3. Flotation thickening occurred in thicken step of the ASBRS throughout steady state, and floating bed volume at the end of thicken period occupied about 70% of the working volume of the reactor Efficiency of flotation thickening in the ASBRS could be comparable to that of additional gravity thickening of a completely mixed digester. 4. Solids were accumulated rapidly in the ASBR during start-up period. Solids concentrations in the ASBRS were 2.6 times higher than that in the completely mixed control reactor at steady state. Dehydrogenase activity had a strong correlation with the solids concentration. Dehydrogenase activity of the digested flu형e in the ASBR was 2.9 times higher than that of the flu형e in the control reactor, and about 25 times higher than that of the subnatant in the ASBR. 5. Remarkable increase in equivalent gas production of 52% was observed at the ASBRS compared with the control reactor in spite of similar quality of clarified effluent from the ASBRS and control reactor. The increase in gas production from the ASBRS was believed to be combined results of accumulation of microorganisms, higher driving force applied, and additional long-term degradation of organics continuously accumulated.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.7
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• pp.516-522
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• 2011

The largest problem of domestic anaerobic digestion is low digestion efficiency. Reasons of the problem would be low organic matters input, low mixing efficiency in digestion tank, refractory excess sludge etc.. In this study, screw attached disk-type concentration system and a mechanical mixing system, solubilization facility improvements were performed to solve problems. Through these improvements, the sludge conc. of the concentrator increased 2.6-fold and the volume reduction efficiency was increased 3.0-fold. In addition, the dead-space is reduced by mechanical agitation. Anaerobic digester gas production in the digestion tank is increased from $193.8m^3$ to $386.0m^3$ per day. Digestion efficiency is improved to 54.6% from 47.6%. Digestion gas production is increased from $0.30Nm^3/kg$ VS to $0.42Nm^3/kg$ VS.

• Microbiology and Biotechnology Letters
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• v.9 no.4
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• pp.219-223
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• 1981

Experiments on methane gas digestion were conducted to prevent livestock pollution and develop substitute energy. When about 30(w/w)% of sludge was added to cow feces, pig feces, and poultry feces and digested at 37$^{\circ}C$ for 20 days, methane gas produced per Kg of organic matter for cow feces, pig feces, poultry feces was 131, 248 and 235 l, respectively. pH decreased slightly at first but increased gradually afterwards during digestion period. When 20, 30, and 40(w/w)% of sludge were added to the mixture of cow feces (300g) and water (200g), the volumes of gas produced were 6.1, 14.5 and 13.4 l, respectively. Volume of methane gas produced from the mixture of cow feces and saw dust was much more than that from the mixture of cow feces and rice polishings. The contents of N, K, P for digestion residues were sufficient to be utilized as a fertilizer. When methane gas digestion was carried out with cow feces in a submersible pump digester the volume of methane gas produced per Kg of organic matter was 188 l. The price of total methane gas produced at this digestion was similar to that of the electric power consumed.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.5
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• pp.554-561
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• 2016

Depending on the Bio-gas sources, main component gases of $CH_4$ and $CO_2$ are shown to be variously present in amounts. For the anaerobic digester, The concentration of $CH_4$ and $CO_2$ in the gases are 60~70 and 30~35 vol%. For the landfill gas, $CH_4$ and $CO_2$ are 40~60 and 40~60 vol%. For the food wastes, $CH_4$ and $CO_2$ are 60~80 and 20~40 vol%, respectively. In this study, maximum conversion rates of $CO_2$ were obtained from the variety of concentrations of $CH_4$ and $CO_2$ by the catalysts of reforming reactions. Moreover, in order to get maximum producing amount of synthetic gas, experimental studies were performed to optimize the reaction variables. On the basis of $CH_4$, 243 ml, R [$CH_4/(O2+CO_2)$] value were varied from 0.8 to 1.35, in the study of $CH_4$ and $CO_2$ reforming reactions. It was shown that the optimal results were obtained for 1.35 of R value. And also, at $850^{\circ}C$ and 1 atm, the production rate of synthetic gas was 90% and the conversion rates of $CH_4$ and $CO_2$ were higher than 99% and 90%, respectively.