• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.4
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• pp.5-13
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• 2022

The current environmental problem is that environmental pollution is accelerating due to the generation of large amounts of waste and indiscriminate consumption of energy. Fossil fuels, a representative energy production fuel, are burned in the process of producing energy, generating a large amount of greenhouse gases and eventually causing climate change. In addition, the amount of waste generated worldwide is continuously increasing, and environmental pollution is occurring in the process of waste treatment. One of the methods for simultaneously solving these problems is the energy recovery from and reduction of organic wastes. Sewage sludge generated in sewage treatment plants has been treated in various ways since ocean disposal was completely prohibited, but the amount generated has been continuously increasing. Since the sewage sludge contains a large amount of organic materials, it is desirable to recover energy from the sewage sludge and reduce the final discharged waste through anaerobic digestion. However, most of the excess sludge is a mass of microorganisms used in sewage treatment, and in order for the excess sludge to be anaerobically digested, the cell walls of the microorganisms must be destroyed first, but it takes a lot of time to destroy the cell walls, so high rates of biogas production and waste reduction cannot be achieved only by anaerobic digestion. Therefore, the pre-treatment process of solubilizing excess sludge is required, and the thermal solubilization process is verified to be the most efficient among various solubilization methods, and high rates of biogas production and waste reduction can be achieved by anaerobic digestion after destroying cell walls the thermal solubilization process. In this study, when pretreating TS 10% thickened excess sludge through a thermal solubilization system, a study was conducted on solubilization characteristics according to retention time and operating temperature variables. The experimental variables for the retention time of the thermal solubilization system were 30 minutes, 60 minutes, 90 minutes, and 120 minutes, respectively, while the operating temperature was fixed at 160℃. The soulbilization rates calculated through TCOD and SCOD derived from the experimental results increased in the order of 12.11%, 20.52%, 28.62%, and 31.40%, respectively. And the variables according to operating temperature were 120℃, 140℃, 160℃, 180℃, and 200℃, respectively, while the operating retention time was fixed at 60 minutes. And the solubilization rates increased in the order of 7.14%, 14.52%, 20.52%, 40.72%, and 57.85%, respectively. In addition, TS, VS, T-N, T-P, NH₄⁺-N, and VFAs were analyzed to evaluate thermal solubilization characteristics of thickened excess sludge. As a result, in order to obtain 30% or more solubilization rate through thermal solubilization of TS 10% thickened excess sludge, 120 minutes of retention time is required when the operating temperature is fixed to 160℃, and 170℃ or more of operating temperature is needed when the operating time is fixed to 60 minutes.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.189-196
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• 1998

Swage sludge cakes produced from domestic wastewater treatment plants were collected from 21 different sites throughout Korea, and chemical properties of the sludge samples were determined. Inorganic nutrient contents did not indicate great differences among swage sludges from each sites, whereas the toxic heavy metal contents differed greatly. T-N, $NH_4{^+}-N$ and $NO_3{^-}-N$ contents from 21 sites sludges ranged 2.3-6.0, 291-4284, $1.4-58.8mg\;kg^{-1}$, respectively. Heavy metal (Cd, Cu, Pb and Zn) contents ranged 2.86-58.22, 144.0-5417.3, N.D.-943.5, and $N.D.-8,083mg\;kg^{-1}$, respectively. One of the sludges was treated to soils at rates of 12.5, 25, 50. and 100, $Mg\;ha^{-1}$ and incubated for 12 weeks to determine nitrogen materialization rate. Ammoniun nitrogen content decreased sharply at higher rates of sludge treatment up to 8 weeks after treatment and did not change much, while $NO_3{^-}$ increased at all treatment levels. The net amount of mineralized N of sludge treatment rates (12.5, 25, 50, and $100Mg\;ha^{-1}$) during 12weeks incubation were 189.0, 277.2, 303.8 and $376.6mg\;kg^{-1}$.

• Journal of Life Science
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• v.21 no.10
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• pp.1473-1480
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• 2011

Perchlorate ($ClO_4^-$) is a contaminant found in surface water and soil/ground water. Microbial removal of perchlorate is the method of choice since microorganisms can reduce perchlorate into harmless end-products. Such microorganisms require an electron donor to reduce perchlorate. Conventional perchlorate-removal techniques employ heterotrophic perchlorate-reducing bacteria that use organic compounds as electron donors to reduce perchlorate. Since continuous removal of perchlorate requires a continuous supply of organic compounds, heterotrophic perchlorate removal is an expensive process. Feasibility of autotrophic perchlorate-removal using elemental sulfur granules and activated sludge was examined in this study. Granular sulfur is relatively inexpensive and activated sludge is easily available from wastewater treatment plants. Batch tests showed that activated sludge microorganisms could successfully degrade perchlorate in the presence of granular sulfur as an electron donor. Perchlorate biodegradation was confirmed by molar yield of $Cl^-$ as the perchlorate was degraded. Scanning electron microscope revealed that rod-shaped microorganisms on the surface of sulfur particles were used for the autotrophic perchlorate-removal, suggesting that sulfur particles could serve as supporting media for the formation of biofilm as well. DGGE analyses revealed that microbial profile of the inoculum (activated sludge) was different from that of the biofilm sample obtained from enrichment culture that used sulfur particles for $ClO_4^-$-degradation.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.67-74
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• 2005

Toxicity tests were performed to evaluate the feasibility of application with prediction models to 10 mixture chemicals (chloroneb, butylbenzylphthalate, pendimethaline, di-n-butylphthalate, di-iso-butylphthalate, diazinon, isofenphos, 2-chlorophenol, 2,4,6-trichlorophenol and p-octylphenol) detected in effluents from wastewater treatment plants (WWTPs). Ten chemicals were selected in the basis of their toxicities to Daphnia magna and the concentrations in effluents measured by GC/MS. Three models including concentration addition (CA), independent action (IA) and effect summation (ES) were employed for the comparison of the predicted and the observed mortality of D. magna exposed to 10 mixture chemicals for 48 hours. With a comparative study it was ineffective to predict the mortality through the CA and the ES prediction model, while the IA prediction model showed a high correlation($r^2\;=\;0.85$). Moreover, the ES model over-estimated the toxicity observed by bioassay experiments about five-fold. Consequently, IA model is a reasonable tool to predict the mixture toxicity of the discharging water from WWTPs.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.3
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• pp.162-166
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• 2011

Phosphorous contaminated in the effluent from sewage treatment plants can cause the eutrophication in surface water bodies. In this study, a powder of titanium oxysulfate-sulfuric acid made of ion-exchange materials was immobilized in an alginate gel and this material was examined to evaluate its phosphorous removal efficiency. Equilibrium and kinetic studies were carried out to quantify the adsorption capacity and time dependent removal rate of phosphorous. Adsorption isotherms and kinetic parameters were obtained for the entrapped titanium beads with three different methods. Equilibrium data were analyzed using Langmuir adsorption isotherm model and found to be well fitted to the model. The maximum adsorption capacity for phosphorous by the titanium bead synthesized with the solution method was 92.26 mg/g. Kinetic data followed a pseudo-second-order kinetic model. Due to the low production cost and high adsorption capacity, the titanium bead synthesized by the solution method has a potential to be utilized for the cost-effective removal of phosphorous from wastewater.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.3
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• pp.77-84
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• 2006

The objective of this research is to evaluate various reclamation methods of sewage sludge cake after treating with microwave under optimum conditions. In this study the sewage sludge cakes used from S and N wastewater treatment plants in the P city. Microwave with an induced electricity heating way was employed for dehydration of sewage sludge cake. Microwave operation conditions is 2,450 MHz of frequency and the power with 1 to 4 kW. This sewage sludge cake had a moisture content of 70%. The moisture content of the sludge decreased notable up to 2%(wt) resulted in breaking of cell wall. When the treated sewage sludge cake mixed with soils could be applied to use midterm and last cover material soils. Moreover, the adsorption ability of heavy metals such as copper, lead, chromium and cadmium was greatly enhanced by treated sewage sludge cake. Within 30 minutes, 1ppm of copper, chromium and cadmium and 10ppm of lead with 1g of the treated sewage sludge cake in $100m{\ell}$ were below detection. It was possible to use the treated sewage sludge cake as an absorbent for absorption of toxic heavy metals. Results from this research indicated that using of microwave radiation was an effective method for treating sewage sludge cake economically and environmental. A point of view of reclamation, the treated sewage sludge cake appeared to be feasible with an adsorption of heavy metals in steady of using expensive yellow earth.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.5
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• pp.303-311
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• 2015

To determine the concentrations of selected 10 perfluorinated compounds (PFCs), a field study was conducted in the water body of Yeongsan River Water System. Raw water samples were collected in the spring and the fall, respectively, which included 18 sampling sites. Collected samples were equally mixed and then served as an analytical sample. The concentration of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) were in range of 20.80-92.0 ng/L and ND-28.40 ng/L respectively. Perfluorononanoate (PFNA) and perfluorohexanesulfonate (PFHxS) were ranged from ND to 42.20 ng/L and from ND to 11.47 ng/L. The detection frequencies of other PFCs selected in this study were very sparse at very low concentrations, except for PFOS, PFOA, PFNA and PFHxS. PFOS was higher detection frequency and concentration in both spring and fall, PFOA and PFNA were in spring, and PFHxS was in fall. As a result, the observed concentrations of PFCs in the downtown water area of Gwangju, located in the wastewater treatment plants, were relatively higher than other sampling points.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.3
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• pp.232-239
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• 2009

This research investigated the characteristics of antibiotic resistance of bacteria in microbial communities from municipal wastewater treatment plants (MWTPs), and monitored seasonal changes of antibiotic resistant bacteria (ARB) from MWTPs and Han river. When antibiotics were amended to either R2A agar (R2A) for general heterotrophs or MacConeky sorbitol agar (MSA) for coliform bacteria, all the MWTP samples exhibited multiple antibiotic resistance on the antibiotic-amended solid media. The antibiotic resistance appearing frequencies of ampicillin and sulfathiazole, respectively, were higher than reported data for other countries. The antibiotic resistance appearances differed depending upon the concentrations of primary substrate and nutrients and the types of cultivation media. The following 16S rRNA gene phylogenetic analysis showed that the identified multiple-antibiotic resistant microbes on R2A plates were more likely to be known human-pathogenic bacteria than the background heterotrophic bacteria were, suggesting a high risk of antibiotic resistance appearance to public health. In addition, according to our investigation of seasonal changes of ARB from urban MWTP and river samples, the frequency of ARB appearances was shown to correlate positively with temperature. This indicates a possibility that global warming result in increase in microbial risk to public health.

• Journal of Soil and Groundwater Environment
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• v.6 no.3
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• pp.73-91
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• 2001

compounds (VOCs) were selected for assessment of VOCs contamination in some urban runoff and groundwater samples in Seoul. They included 3 aromatic hydrocarbons, 13 alkyl benzenes, 1 ether, 26 halogenated alkanes, 10 halogenated alkenes, and 9 halogenated aromatics. The levels of VOCs in urban runoff and groundwater were measured for samples collected in March 2000, June 2000 and November 2000 in Seoul City. A total of 78 samples (44 run-off water, 27 groundwater, and 7 samples from 4 urban wastewater treatment plants in Seoul) were collected and analysed by GC-MS with purge and trap. After examination of the runoff, it was concluded that alkyl benzenes and aromatic hydrocarbons were organic compounds which were significantly impacted by traffic flows in Seoul. Of 62 VOCs, only 11 VOCs were not detected in runoff samples, while 14 VOCs were detected in 27 groundwater samples. The toluene content in the runoff was extremely variable from 0.1ppb to 29,310ppb, depending on the different sampling sites. The concentrations of xylene ranged between 0.07ppb and 2970ppb in the runoff. The concentrations ranged from 0.05ppb to 33.0ppb for benzene, 0.05ppb to 960ppb for ethylbenzene, 0.08ppb to 20ppb for trichloromethane (chloroform) , 0.03ppb to 4.30ppb for trichloroethylene(TCE) and 0.1ppb to 50ppb for 1,1,2-trichloroethane. From the preliminary study of groundwater from some wells in Seoul, the most frequently detected VOCs are djchlorornethane(methylene chloride), trichloromethane(chloroform) and toluene. Most of aromatic hydrocarbons, alkyl benzenes and other solvents generally lower than detection limits.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.451-455
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• 2006

Heterotrophic biomass yield coefficients, $Y_H$, for aerobic, anoxic and anaerobic reactors were successfully estimated for the two wastewater treatment plants, where one plant was operating in the $A^2/O$ process and the other was operating in the 4-stage BNR process. The estimation of $Y_H$ was undertaken by plotting the biomass COD concentrations versus the soluble COD concentrations in order to calculate the ${\Delta}biomass$ COD/ ${\Delta}soluble$ COD in each batch reactor. The batch reactors employed in this study were fed by filtered influent and mixed liquors in the ratio of 10:1, and operated in the aerobic, anoxic and anaerobic conditions, which represented the actual operating conditions for the $A^2/O$ and 4-stage BNR process. The average $Y_H$ values of the aerobic, anoxic and anaerobic reactor for the $A^2/O$ process were 0.52, 0.41 and 0.18 mg COD/mg COD, respectively, and those for the 4-stage BNR process were 0.58, 0.40 and 0.20 mg COD/mg COD, respectively. The average ratio of the $Y_H$ for aerobic reactors to those for the anoxic reactors were about 1:0.79 for the $A^2/O$ process, and about 1:0.69 for the 4-stage BNR process. The experimental method for anoxic and anaerobic $Y_H$ estimation shown in this study has turned out to be simple and efficient in its practical application.