• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.611-616
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• 2011

The impacts of ultrasonic pretreatment on the biodegradability of domestic sewage sludge were evaluated through a series of anaerobic digestion experiments in batch system. The gas and methane production from the sludge samples pretreated by an ultrasonic tool with different durations were measured with time. Although the biogas production increased with the extent of sludge solubilization and the period of ultrasonic pretreatment, the enhancement of sludge biodegradability was much more sensitive to the pretreatment for the relatively short periods. Most of the enhanced biodegradability by the pretreatment was appeared in the early stage of anaerobic digestion, less than 6 days. The maximum biogas production per day was observed between 4 to 6 days when the sludge was pretreated less than 10 minutes while it was obtained in the beginning for the sludge pretreated longer periods. The results suggest that the repeated alternation of low strength ultrasonic pretreatment and anaerobic digestion may be more effective than the combination of one time pretreatment for a relatively long period and following anaerobic digestion.

• Journal of Korean Society of Water and Wastewater
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• v.14 no.1
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• pp.117-126
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• 2000

Solubilization pretreatments were conducted to enhance the anaerobic digestion of the waste activated sludge. Four pretreatment techniques including heating, sonication freezing and thawing, and enzyme addition were employed to solubilize the waste activated sludge under various conditions. Thermal pretreatment by heating showed the highest efficiency compared with other methods, and freezing and thawing was confirmed as a feasible alternative of solubilization as well as the pretreatment of dewatering. There is a clear correlation between the solubilization efficiency of the waste activated sludge and the gas production. Batch digestion results showed the cumulative gas production as much as four times after thermal pretreatment as compared with that by the control sludge without pretreatment. As a result, hydrolysis or solubilization pretreatment might play a significant role in the high rate digestion of the waste activated sludge.

• Journal of Environmental Science International
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• v.16 no.2
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• pp.211-218
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• 2007

The objectives of this study have been carried out to investigate the solubilization of municipal sewage sludge by single and dual frequency ultrasonic pretreatment, and the methane production characteristics of pretreated sewage sludge by specific methanogenic activity test for sewage sludge reduction. The waste activated sludge was collected from thickened tank of Suyoung sewage treatment plant in Busan city, and its concentration was adjusted to 1.0% total solids. Ultrasonic frequency was varied 15, 20, 15+20 kHz, and acoustic density was used a maximum 176W/L. The dual frequency ultrasonic pretreatment was found to be more effective than single frequency ultrasonic in the solubilization rate and methane production. The $SCOD_{Cr}/TCOD_{Cr}$, rate were 15.2%, 13.9%, 17.0% with single frequency of 15 kH2, 20 kHz, dual frequency of 15+20 kHz, respectively. The application of dual frequency ultrasound for sewage sludge pretreatment can be interest for sewage treatment plants having problems in sludge treatment and disposal.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.6
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• pp.469-474
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• 2000

In order to enhance the degradation efficiency of waste activated sludge (WAS) by thermophilic aerobic digestion, an ultrasonic pretreatment was examined. It was observed that ultrasonic pretreatment increased the solubilization of organic matter in the WAS and that the solubilization ratio of the organics increased during the first 30 min but did not extensively increase thereafter. Therefore, a pretreatment time of 30 min was determined to be the economical pretreatment time from the experimental results. From the digestion experiments, which was conducted using the WAS collected from an oil refinery plant in Inchon, Korea, investigating the effects of an ultrasonic pretreatment on thermophilic aerobic digestion, it was confirmed that the proposed ultrasonic pretreatment was effective at enhancing the release of the cellular components in WAS and the degradation of released components in the thermophilic aerobic digestion.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.565-572
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• 2011

The effects of chemical pretreatments on the excess sludge production in the membrane-coupled bioreactor were investigated. In addition, their effects on membrane fouling were also evaluated. Two membrane bioreactors were operated. In one reactor, a part of the mixed liquor was t reated with NaOH and ozone gas consecutively and was returned to the reactor. T he f lowrate of the chemical pretreatment stream was 1.5% of the influent flowrate. During the 200days of operation, the MLSS level in the bioreactor with mixed liquor pretreatment was maintained relatively constant at the range of 8,000 ~ 10,000$mg/{\ell}$ while it increased steadily up to 26,000 $mg/{\ell}$ in the absence of the pretreatment. Each reactor was equipped with two laboratory membrane modules where the flux for each module was 20, and 30 ${\ell}/m^2{\cdot}h$, respectively. With pretreatment, almost constant transmembrane pressure(TMP) was observed throughout the operation at the flux of 20 ${\ell}/m^2{\cdot}h$. Without pretreatment the membrane module at the same flux could also be operated at relatively stable condition. However, as the MLSS increases up to 25,000 $mg/{\ell}$, a fast TMP increase was observed. In conclusion, a complete control of excess sludge production in the membrane-coupled bioreactor was possible without significant deterioration of the treated water quality. In addition, it was shown that stable operation in terms of TMP is possible with sludge pretreatment and recirculation.

• 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.

• Journal of Korean Society of Water and Wastewater
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• v.16 no.6
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• pp.733-740
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• 2002

The effects on dewaterability and settlability of wastewater sludge according to acid and ultrasonic pretreatment which was expected to change ECP (exocellular polymers) compounds in the sludge and bulk solution was investigated. Though ECP which attached to the sludge could stimulate coagulation of sludge particles by bridging effect, but ECP in the bulk solution deteriorated dewaterability and settlability of the sludge on the contrary. That is as the pH of the solution was decreased to 3 gradually by acid treatment, proportionally ECP in the bulk solution was attached to the sludge flocs and resulted in improvement of dewaterability and settlability of the sludge. In case of ultrasonic pretreatment, with proportional to the intensity and duration of ultrasonic application, ECP was detached and extracted from sludge flocs and these phenomena deteriorated dewaterability and settlability. Also because of the increasement of minute sludge particles according to ultrasonic, dewaterability became so much the worse.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.4
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• pp.449-454
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• 2008

Some pretreatment methods have been proposed to enhance the biodegradability and to shorten the hydrolysis reaction time. By means of efficient pretreatment the suspended solids (SS) can be made of better accessible for the anaerobic bacteria. There are several ways how this can be accomplished, which include biological, mechanical, thermal, and chemical methods. For the sludge solubilization using the cavitation phenomenon, we have tried to develop a pretreatment process consisted of a reactor and pumps. The objectives of this study were to develop a advanced wastewater treatment consisted of IABR and the cavitation with PGA. The most effective removal for organic matter and nutrients were occured when both cavitation pretreatment and ${\gamma}$-PGA were applied at the IABR process. Only small portion of ${\gamma}$-PGA at a rate of 1.38mg/L, was enough to improve sedimentation ability, SS removal efficiencies, and sludge volume reduction. After the sludge solubilization by the cavitation, SCOD increased to 193% and SS decreased to 36%. The removal ratio of BOD was 94.5%, T-N removal ratio was 85.5% and T-P removal ratio was 84.9%. The combination process of the IABR with the cavitation and PGA addition seems to be very effective alternative wastewater treatment process.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.1
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• pp.25-32
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• 2014

In order to investigate the effective pretreatment methods in WAS(=waste activated sludge) solubilization, the values of SCOD yield per unit SS (SCOD/gSS.hr) were compared. After the hydrodynamic cavitation with pH of 12.5, SCOD increased to 7800 mg/L, SS decreased to 45 % and the solubilization rate was 29 %. Combination of alkality (pH 12.5) and the cavitation seems to be the optimal condition for sludge solubilization. After the cavitational pretreatment, efficiencies of anaerobic digestion of the unfiltered sludge(the control), raw sludge and pretreated sludge were evaluated with BMP(=biochemical methane potential) tests. For evaluation of the biodegradability characteristics of pretreated sewage sludge, the methane production has been measured for 6 months. The methane production of pretreated sludge increased 1.4 times than that of untreated sludge. The result indicates that the cavitationally pretreated sludge was a better biodegradability substrate in anaerobic condition compared to raw sludge. It is obvious that cavitational pretreatment could enhance not only solubilization but also biodegradability of WAS. In conclusion, cavitational pretreatment of WAS to convert the particulate into soluble portion was shown to be effective in enhancing the digestibility of the WAS.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.1
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• pp.90-96
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• 2008

In order to meet the stringent requirement of sludge disposal and to find ecological alternative, aerobic digestion coupled with alkaline pretreatment was studied. The treated sludge was tested for the potential of liquid fertilizer. In the aerobic digestion, it was obvious that the performance of digester B(fed with the sludge pretreated by NaOH) was better than that of digester A(fed with raw sludge) in terms of COD and SS removal. SS and VSS removal rates in digester B were 66% and 69%, respectively. At 5 days, TSS removal rate reached 47% in the digester B, which was 71% of final TSS removal rate. It revealed that the pretreatment process can shorten the retention time of aerobic digestion. 94.1% of TCOD in the raw sludge was reduced by alkaline pretreatment and aerobic digestion. Final SCOD was in the range of 220$\sim$230 mg/L implying the sludge was stabilized. Nitrification and pH drop were observed in the aerobic digestion. Final nitrate concentrations in digester A and B were 445.4 and 223.1 mg/L and final pH in digester B was 3.0. Biological assays reported that leaf size of cucumber seedling increased with nitrate concentration and sludge to soil ratio. The sludge treated by alkaline and aerobic digestion promoted the growth of seedling leaf and stem remarkably compared to raw sludge. In contrast, the aerobically digested sludge without pretreatment improved leaf growth and inhibited stem growth.