• Journal of Microbiology and Biotechnology
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• v.6 no.1
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• pp.30-35
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• 1996

Distillery wastewater was used in a thermophilic laboratory-scale two stage anaerobic digester to test the effects of the redox potential of the first acidogenic reactor on the performance of the system. The digester consisted of first a acidogenic reactor and the an upflow anaerobic sludge blanket (UASB) reactor. The digestor was operated at a hydraulic retention time (HRT) of 48 h. Under these conditions, about 90% of the chemical oxygen demand as measured by the chromate method ($COD_{cr}$) was removed with a gas production yield of 0.4 l/g-COD removed. The redox potential of the acidogenic reactor was increased when the reactor was purged with nitrogen gas or agitation speed was increased. The increase in reduction potential was accompanied by an increase in acetate production and a decrease in butyrate formation. A similar trend was observed when a small amount of air was introduced into the acidogenic reactor. It is believed that the hydrogen partial pressure in the acidogenic reactor was decreased by the above mentioned treatments. The possible failure of anaerobic digestion processes due to over-loading could be avoided by the above mentioned treatments.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1446-1451
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• 2008

The clay found in the river or in any waste water treatment plant usually have a very high content of water. A large amount of sediments hinder the navigation in river. In waste water treatment plant, there is requirement of settling the thick sludge. These problems are overcome by using rapid means of sedimentation and settling. This paper focus on how method of Electrokinetic sedimentation can be made faster. Sedimentation using Electrokinetic phenomenon has been discussed with varied voltage applied and effect and dose of coagulant in increasing the process. The experimental test has been carried out at water content that are generally present in the case of river and small canals carrying waste water. This paper also focus on different heavy metals concentration during the process and the power aspects of process. A series of experiment were done to support the proposed theory and how a bubble formation could hinder the purpose of experiment.

• Korean Journal of Metals and Materials
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• v.46 no.7
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• pp.437-442
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• 2008

The synthesis and hydration of Calcium Sulfo Aluminate[$3CaO{\cdot}3Al_2O_3{\cdot}CaSO_4(C_4A_3{\overline{S}})$, CSA cement utilizing secondary steelmaking refining slags is studied for recycling the discarded steel plant wastes to meet the environmental requrations imposed on the steel industry. Raw materials of secondary refining slag, lime sludge, gypsum and bauxite were prepared to be sintered at $1,250^{\circ}C$. The sintered samples were hydrated for 1, 3 and 7 days to evaluate the mineralogical and physico-mechanical properties. The hydration products evaluated with the aid of SEM and XRD analyses confirmed the formation and the continuing growth of ettringite phase with the further hydration times, which plays a role in developing the early strength and the expansion properties of cements. The physico-mechanical properties of hydrated CSA products employing the recycled steelmaking refining slags determined in terms of compressive strength and linear expansion of hydrated products are found to be superior to those of the Ordinary Portland Cement(OPC) or the other commercial CSA cements.

• Journal of Species Research
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• v.8 no.4
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• pp.351-364
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• 2019

Here we describe indigenous prokaryotic species in Korea, a total of 42 bacterial strains affiliated to the class Alphaproteobacteria isolated from various environmental samples: fermented vinegar, sea water, beach sand, fresh water, salt flats, moss, algae, activated sludge, and soil. From the high 16S rRNA gene sequence similarity (>98.7%) and formation of a robust phylogenetic clade with the closest species, it was determined that each strain belonged to predefined bacterial species. There is no official report that these 42 species included in Alphaproteobacteria in Korea: 15 species of 6 genera in the order Rhodospirillales, 12 species of 10 genera in the order Rhizobiales, 10 species of 8 genera in the order Rhodobacterales, 4 species of 4 genera in the order Sphingomonadales and 1 species of 1 genus in the order Caulobacterales. Gram reaction, colony and cell morphology, basic biochemical characteristics, isolation source, and strain IDs are also described in the species description section.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.11
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• pp.783-789
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• 2011

Recently, auto-thermal thermophilic aerobic digestion (ATAD) has a great attention for destruction of wasted sludge biomass in wastewater treatment plant. Reduction of sludge concentration has been successfully achieved with pilot scale ATAD and ceramic filtration process in field condition. However, high concentration of COD, total nitrogen (TN) and total phosphorus (TP) was observed in filtrate, which should be treated before recirculation of filtrate to biological wastewater treatment plant. This study was focused on removal of nitrogen and phosphorus contained in the filtrate of ATAD, using struvite crystallization method. The effect of operational and environmental parameters (such as, N, P and Mg ion concentration and molar ratio, pH, reaction time, agitation strength, seed dosage, and reaction temperature) on the treatment of TN and TP with struvite crystallization were evaluated. Magnesium (as $MgCl_26H_2O$) and phosphorus (as $K_2HPO_4$) ions were, if necessary, added to increase nitrogen removal efficiency by the crystal formation. Average concentration of $NH_4^+-N$ and $PO_4^{3-}-P$ of the filtrate were 1716.5 mg/L and 325.5 mg/L, respectively. Relationship between removal efficiencies of nitrogen and phosphorus and molar ratios of $Mg^{2+}$ and $PO_4^{3-}-P$ to $NH_4^+-N$ was examined. Crystal formation and nitrogen removal efficiencies were significantly increased as increasing molar ratios of magnesium and phosphorus to nitrogen. As molar ratio of $Mg^{2+}:PO_4^{3-}-P:NH_4^+-N$ were maintained to 2 : 1 : 1 and 2 : 2 : 1, removal efficiencies of nitrogen and phosphorus were 71.6% and 99.9%, and 93.8% and 98.6%, respectively. However, the effect of reaction time, mixing intensity, seed dose and temperature on the struvite crystallization reaction was not significant, comparing to those of molar ratios. Settled sludge volume after struvite crystallization was observed to be reduced with increase of seed dose and to be increased at high temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.105-114
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• 2018

Membrane fouling in EC-MBR (Electro-Coagulation aided Membrane Bio-Reactor) processes was evaluated according to the operating parameters, such as current density and contact time. In addition, the fouling mechanism was investigated. Compared to the control (i.e., no electro-coagulation), membrane fouling for filtration of the activated sludge suspension after electro-coagulation was reduced significantly. Membrane fouling was improved further when the contact time was doubled under a low current density of $2.5A/m^2$. On the other hand, membrane fouling was not mitigated further, as expected, even though the contact time was doubled from 12 to 24 hr. at a current density of $10A/m^2$. This indicates that the overall decrease in membrane fouling is a function of the product of the current density and contact time. The particle size of the activated sludge flocs after electro-coagulation was changed slightly, which means that the membrane fouling reduction was not attributed to a larger particle size resulting from electro-coagulation. The experimental confirmed that the dynamic membrane made from aluminum hydroxide, Al(OH)3, and/or aluminum phosphate, Al(PO4), which had been formed during the electro-coagulation, played a key role on the reduction of membrane fouling. The dynamic membrane prevents the particles in the feed solution from deposition to the membrane pores and cake layers. Dynamic membrane formation as a result of electro-coagulation plays a critical role in the mitigation of membrane fouling in EC-MBR.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.1
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• pp.87-96
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• 2010

The electrode material is one of the factors affecting the power production of microbial fuel cell. In this study, effects of carbon electrode material, thickness and configuration on the power density, biofilm formation and microbial community diversity of microbial fuel cell were investigated. To optimize the anode-cathode electrode assembly, seven lab-scale reactors which had various carbon electrode constructions were operated in continuous mode. Under the steady state condition, the electrode combination of graphite felt (6 mm) with hole showed the highest cell voltage of 238 mV and the coulombic efficiency of 37%. As a result of SEM analysis, the bacteria growing on surface of knitted type of carbon cloth and graphite felt electrode ncreased significantly. The change of dominant species between seeding sludge and biofilm on the surface of anode electrode, microbial analysis with PCR-DGGE showed that the dominant species of seeding sludge are quite different from those of biofilm on the surface of each anode electrode. Especially Geobacter sp., a well known electrochemical bacteria, was found as the dominant species of the electrode combination with graphite felt.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1170-1175
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• 1999

The microstructures and mechanical properties of $Si_3N_4$ ceramics produced by nitridation and post-sintering using semiconductor-waste-Si sludge were investigated. Lots of microcracks were observed in the waste-Si powders which contained some amounts of amorphous $SiO_2$. The nitridation rate of waste-Si compacts showed lower value than that of commercial Si powder compacts. The nitridation rate was increased with increasing nitridation temperature and then the percent of nitridation at 1470$^{\circ}C$ showed 98%. The phases of $Si_3N_4$ in the reaction-bonded bodies were mixed with ${\alpha}$ and ${\beta}$-type, and small amounts of $Si_2N_2O$ phase while those after post-sintering were ${\beta}$-$Si_3N_4$ and ${\alpha}$-Sialon. The sample post-sintered at 1950$^{\circ}C$ showed the fracture toughness of 5.6 $^MPa{\cdot}m^{1/2}$ and the fracture strength of 497 MPa which were lower than those of sintered body using commercial Si powder possibly due to the formation of ${\alpha}$-Sialon phase.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.357-364
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• 2021

The present study investigated the hydration properties and NO_x-removal performances of the cement pastes containing three different types of TiO₂. Two commercially available TiO₂ (P-25 and NP-400) and refined TiO₂ (GST) obtained from waste sludge were incorporated to cement paste at levels of 0, 5, 10, and 20 wt%. Isothermal calorimetry test results indicated that the TiO₂ incorporation induced a notable influence on the reaction kinetics of cement paste, showing the highest cumulative heat release in the samples containing P-25, followed by NP-400 and GST. Quantitative X-ray diffractometry as calculated by the Rietveld method identified that the incorporated TiO₂ promoted the formation of C-S-H, ultimately leading to the enhancement in the 28 day-compressive strength of cement pastes. As revealed by SEM/EDS analysis, the content of distributed Ti elements on the surface of the samples was in the order of P-25, GST, and NP-400. Regardless, the NO_x-removal performance was the highest in the sample containing P-25, followed by NP-400 and GST.

• Journal of the Korea Organic Resources Recycling Association
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• v.11 no.3
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• pp.87-95
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• 2003

Although extensive studies were conduced on hydrogen fermentation of organic wastewaters, little is known about biohydrogen production from organic solid wastes. The leaching-bed reactor treating food waste by heat-shocked anaerobic sludge was, therefore, operated at D of 2.1, 3.6, 4.5 and $5.5d^{-1}$ to find optimal D for hydrogen production. Successful operation of a reactor can be accomplished when it is operated at proper dilution rate (D). Operation at high D leads to the washout of biomass in the reactor while operation at low D leads to product inhibition due to the accumulation of excess VFA. These appear to limit the production of hydrogen to reach a higher level. All the reactors showed that, on day 1-3, hydrogen production was dominant and VFA concentration was higher than ethanol. Butyrate and acetate were major components of VFAs over the whole operation, though lactate was very high on day 1-2. Compared with other D values, D of $4.5d^{-1}$, resulted in higher butyrate/acetae (B/A) ratios during the fermentation. The trend of B/A ratios was similar to the hydrogen production, suggesting that butyrate formation favored hydrogen production. Ethanol increased significantly from day 4 when hydrogen Production stopped. It indicated that heat-shocked sludge was able to induce a metabolic flow from hydrogen-and acid-producing pathway to solvent-producing pathway. Operation at D of $4.5d^{-1}$ led to higher fermentation efficiency (58%) than those (51.5, 55.3 and 53.7%) at 2.1, 3.6 and $5.5d^{-1}$. The COD removed was convened to hydrogen (10.1%), VFA (30.9%), and ethanol (17.0%).