• Journal of Korean Society of Water and Wastewater
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• v.27 no.5
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• pp.561-570
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• 2013

There are two types of rectangular secondary clarifier at biological nutrient removal (BNR) facility to settle MLSS; conventional activated sludge secondary clarifier and Gould Type I clarifier. In this study, the performances of two types at respective biological nutrient removal facility are compared using weekly operational data. Surface Overflow Rate (SOR), Surface Loading Rate (SLR), Sludge Volume Index (SVI), secondary effluent SS concentration are studied. It has found that Gould Type I has 3.5 times less average secondary effluent SS concentration that is 2.4 mg/L than that of conventional activated sludge secondary clarifier. Both SOR and SLR have shown little effect on secondary effluent SS concentrations at Gould Type I clarifier in contrary that SOR affects the secondary effluent SS concentrations at conventional activated sludge rectangular secondary clarifier. From this study, it is recommended that Gould Type I must be considered for secondary clarifier when BNR plant is designed.

• Journal of the Korean Society of Combustion
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• v.7 no.3
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• pp.16-22
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• 2002

Combustion performance of an internally cycloned circulating fluidized bed for paper sludge was discussed through a series of batch type experiments. Operation parameters such as water content, feeding mass of sludge and secondary air injection rate were varied to find out the effect on the combustion performance, which was examined with carbon conversion rate and pollutant emission such as CO and NOx. A conventional solid fuel reaction was observed in the experiments of varying water content and feeding mass of the sludge, which is characterized with kinetic limited reaction zone, diffusion limited reaction zone and transition zone. Secondary air injection with swirl enhances the mixing of the gas phase as well as the solid phase, and improves combustion efficiency accompanied with higher carbon conversion rate and lower pollutant emission rate.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.5
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• pp.551-559
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• 2008

An experimental study was carried out to evaluate the potential of flotation process for the secondary clarifier of an activated sludge process. Flotation techniques, applied in this study, include electrofloation (EF) which generated fine bubbles smaller than $35{\mu}m$ in average and diffuser flotation (DF) which generated fine bubbles smaller than $55{\mu}m$ in average. The batch experiments were done with activated sludge displaying various characteristics. It was shown that the efficiency of solids/liquid separation was reduced as the diluted sludge volume index ($DSVI_{30}$) of activated sludge increased. The dependency, however, gradually decreased as the gas to solids (G/S) ratio increased. Thickening efficiency of EF was more than 2~10 times and DF process was more than 1.5~5 times as compared with gravity sedimentation (GS). Stable sludge blanket was maintained regardless of sludge settleability when the G/S ratio was 0.019 in the EF. On the other hand, Serious deterioration in the sludge blanket was observed in the DF depends on G/S ratio and sludge settleability. And For EF and DF, the suspended solids concentration of effluent was not nearly influenced on settleability of activated sludge and more clear than GS. A biological nutrient removal (BNR) process, combined with EF as a secondary clarifier was operated for three months. The mean MLSS (mixed liquid suspended solids) concentration in the reactor and mean solids concentration of return sludge were estimated to be 5,340 mg/L and 16,770 mg/L, respectively. The water quality of effluent was considerably stable and low value was accomplished, that was, standard suspended solids concentration $0.07{\pm}0.51mg/L$ and standard turbidity $1.44{\pm}0.56NTU$. The EF could be applicable for enhancement of efficiency of activated sludge system as well as improvement of the water quality of effluent.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.1130-1136
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• 2006

This work elucidates the effects of pretreatment of the sewage sludge from wastewater treatment plant by microwave irradiation on elutriated acid fermentation. These experiments typically fell into two process; pretreatment as microwave irradiation and elutriated acid fermentation for hydrolysis and acidification as main process of primary sludge. The results of maximum solubilization rate of B, D primary and secondary sludge were 0.042, 0.086 and 0.15 gSCODprod./gICODin and the optimum irradiation time of microwave on 2,450 MHz and 900 W were 5 min. for primary sludge and 7 min. for secondary sludge. From batch tests on elutriated acid fermentation that was used the pretreated primary sludge as microwave, the optimum pH and HRT (hydraulic retention time) were 7 and 5 days at $35^{\circ}C$ condition.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.204-211
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• 2002

Combustion experiments are carried out to obtain the fundamental data for application of a internally circulating fluidized bed combustor to the combustion of paper sludge wastes. Experimental parameters are identified as secondary air ratio, sludge weight and water contents. The secondary air ratio was varied from 0 to 20% and water content was 14%, 25%, 35%, 45%, 62% and sludge weight was 30g, 60g, 90g. As a result, carbon conversion ratio was higher than injection of primary air. Emission of CO and NOx reduced with an increase of secondary air injection.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.93-100
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• 2005

Comparative thickening and dewatering characteristics of municipal wastewater sludge were investigated in terms of separated and combined treatment of primary and secondary BNR sludge. Also, various conditioning methods such as cation polymer addition, steam and ultrasonication treatment were examined to improve dewaterability of sludge. The dewaterability was measured by using specific resistant test, wedge zone simulator and centrifuge. The result of the sludge thickening test revealed that separated thickening was better in terms of solids recovery and supernatant quality. Particularly, the thickening of primary sludge with high solids (about 3.5% TS) showed very poor solid separation. The addition of cation polymer showed better conditioning characteristic for dewatering and the optimal polymer dosage was 0.26% for primary sludge, 0.43% for secondary sludge and 0.38% for combined sludge. Contrary to the result of the thickening, the dewatering test revealed that dewatering of the combined sludge is better than that of separated sludge, representing better solids separation and filtrate quality. The polymer addition was essential to improve dewaterability in filter (belt) press type dewatering but it was inefficient for the dewatering of secondary sludge only. The centrifuge type dewatering showed better performance and the dewaterability was slightly improved when the polymer was added. Based on the results of this research a sustainable sludge treatment process, particularly in terms of the recycle water quality and solids recovery, was proposed.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.468-474
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• 2006

In the secondary settling tanks, three different types of settling phenomena occurs; i.e., zone settling for sludge thickening in the bottom part of settling tank, and discrete and flocculent settling for clarification in the upper part. In this paper, morphological parameters of the floc in sludge blanket layers along the length of a long rectangular tank were investigated. The plant used for this study had a serious bulking problem caused by Microthrix parvicella. Floc size decreased as the surface area of settling tank increases, which indicates that in the secondary settling tank where zone settling believed to be predominant, free or flocculent type of settling contributes to floc size distributions. Large floc particles deposit in the front zone of settling tank, but small and loose flocs mostly in the zone near its outlet. On the other hand, filament length contained in one gram of sludge blanket solid increases along the flow direction. Large flocs with less filaments settle faster, but small flocs having more filaments result in poor settling. These results support function of microorganism selection occurring in secondary settling tank. In addition, designing a long rectangluar settling tank with double hoppers might be one of the ways of bulking control, but this idea has to be verified with a further study.

• Journal of Environmental Science International
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• v.32 no.1
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• pp.47-55
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• 2023

This study evaluated the biochemical methane potential (BMP) of primary sludge, secondary sludge, and food waste in batch anaerobic mono-digestion tests, and investigated the effects of mixture ratio of those organic wastes on methane yield and production rate in batch anaerobic co-digestion tests, that were designed based on a simplex mixture design method. The BMP of primary sludge, secondary sludge and food waste were determined as 234.2, 172.7, and 379.1 mL CH₄/g COD, respectively. The relationships between the mixing ratio of those organic wastes with methane yield and methane production rate were successfully expressed in special cubic models. Both methane yield and methane production rate were estimated as higher when the mixture ratio of food waste was higher. At a mixing ratio of 0.5 and 0.5 for primary sludge and food waste, the methane yield of 297.9 mL CH₄/g COD was expected; this was 19.4% higher than that obtained at a mixing ratio of 0.3333, 0.3333 and 0.3333 for primary sludge, secondary sludge, and food waste (249.5 mL CH₄/g COD). These findings could be useful when designing field-scale anaerobic digersters for mono- and co-digestion of sewage sludges and food waste.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.238-244
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• 2005

This study performs the pilot-plant experiments to evaluate the effect of the oxygen enrichment on the co-incineration of municipal solid waste and organic sludge from a wastewater treatment facility. The design capacity of the stoker-type incinerator pilot-plant is 150 kg/h. Combustion chamber temperatures were measured as well as the stack gas concentrations, i.e., NOx, CO, and the residual oxygen. The maximum ratio of organic sludge waste to the total waste input is 30%. Also the oxygen-enriched air with 23% of oxygen in supplied air is used for stable combustion. As the co-incineration ratio of the sludge increased up to 30% of the total waste input, the primary and the secondary combustion chamber temperature was decreased $to900^{\circ}C$ (primary combustion chamber), $750^{\circ}C$(secondary combustion chamber), respectively, approximately $200^{\circ}C$ below the incineration temperature of the domestic waste only (primary: $1,100^{\circ}C$, secondary: $950^{\circ}C$). However, if the supplied air was enriched to 22% oxygen content in air, the incinerator temperature was high enough to burn the waste mixture with 30% sludge, which has the heating value of 1,600 kcal/kg.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.2043-2048
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• 2013

OPR-1000 CE Steam Generator, of which tube material is composed of Alloy-600 HTMA in nuclear power plant, secondary side is generated ODSCC(Outside Diameter Stress Corrosion Cracking) due to the accumulated sludge. ODSCC is centered around the tube sheet and is being affected depending on the height of the sludge. Chemical cleaning was carried out for a top-of-the-tube sheet(TTS) of Steam Generator in order to decrease corrosive condition of the secondary side of Steam Generator tubes and suppress the occurrence of stress corrosion cracking. The amount of sludge removal was 259.2kg. The height of the accumulated sludge was reduced from 0.71 to 0.34 inches. Corrosion rate as the maximum 2.34 mils was satisfied to within EPRI (Electric Power Research Institute) recommendation(10 mils).