• Journal of Environmental Science International
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• v.15 no.9
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• pp.897-905
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• 2006

This study has been conducted to investigate biodegradation characteristics and optimum mixing ratio for co-digestion with thermophilic acid-fermented food waste and sewage sludge using batch anaerobic digester. As the basis operating conditions for anaerobic digestion, the reaction temperature was controlled $35{\pm}1^{\circ}C$ and stirrer was set 70rpm. Thermophilic acid-fermented food waste and sewage sludge were mixed at the ratio of 10:0, 7:3, 5:5, 3:7, 0:10 and 5;5(food waste : sewage sludge) as the influent substrates. In results of co-digestion according to mixing ratio of thermophilic fermented food wastes and sewage sludge in batch mesophilic anaerobic digestion reactor, $385mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio was more than that of any other mixing ratios. Compared with $293mL\;CH_4/g\;VS_{added}$ of methane production rate at 1:1 mixing ratio of food wastes and sewage sludge, pretreatment of food wastes by thermophilic acid fermentation was more effective in co-digestion with sewage sludge.

• Journal of Korean Society on Water Environment
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• v.26 no.5
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• pp.810-815
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• 2010

Ultrasonic sludge pre-treatment has been studied to enhance the performance of anaerobic digestion by increasing sludge hydrolysis which is regarded as the rate-limiting-step of anaerobic digestion. In this study, the effect of ultrasonic pre-treatment on sludge hydrolysis (solubilization) and methane production was investigated. Sludge solubilization efficiency increased with ultrasonic energy input. However, it is uneconomical to apply more than 720 kJ/L as the solubilization efficiency per energy input declines afterwards. Volatile fatty acids concentration increased after the ultrasonic sludge hydrolysis. Anaerobic batch digestion showed that methane volume reached 64.7 and 84.5 mL after 18 days of incubation with the control sludge and ultrasonically hydrolyzed sludge, respectively. Methane production potential, maximum methane production rate, and the lag time of modified Gompertz equation were changed from 70 mL, 6.4 mL/day, and 1.2 days to 89 mL, 9.6 mL/day, and 0.5 day, respectively, after the ultrasonic sludge treatment. The results proved that ultrasonic pre-treatment contributed significantly not only for the methane production but also for the reduction of anaerobic digestion time which is critical for the performance of anaerobic sludge digestion.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.5
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• pp.763-770
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• 2006

The purpose of this study was to investigate the effects of mechanical(ball-mill) solubilization of excess sludge especially focused on the TSS(total suspended solid) reduction during the conventional aerobic digestion of sewage sludges including primary and/or excess sludge, HRT was examined at the 10 days and 20 days. According to the results of this study, TSS removal efficiency of solubilized excess sludge was almost two times higher than that of non-solubilized excess sludge. And as the proportion of the primary sludge increased, TSS removal efficiency became worse because primary sludge rarely contained microbial cells which could be easily solubilized physically. It was also proved that by the application of proper solubilization techniques to the excess sludge, HRT for the aerobic digestion could be lessened(above 50%) dramatically keeping the same or better digestion performance. The fact that between primary and excess sludges, only the excess sludge is quite effective in the sludge solubilization and in it's reduction says that excess sludge releasing sources are key-point in the sludge cake reduction field as a source control.

• Journal of Microbiology and Biotechnology
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• v.26 no.1
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• pp.110-119
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• 2016

High-solid anaerobic digestion of sewage sludge achieves highly efficient volatile solid reduction, and production of volatile fatty acid (VFA) and methane compared with conventional low-solid anaerobic digestion. In this study, the potential mechanisms of the better performance in high-solid anaerobic digestion of sewage sludge were investigated by using 454 high-throughput pyrosequencing and real-time PCR to analyze the microbial characteristics in sewage sludge fermentation reactors. The results obtained by 454 highthroughput pyrosequencing revealed that the phyla Chloroflexi, Bacteroidetes, and Firmicutes were the dominant functional microorganisms in high-solid and low-solid anaerobic systems. Meanwhile, the real-time PCR assays showed that high-solid anaerobic digestion significantly increased the number of total bacteria, which enhanced the hydrolysis and acidification of sewage sludge. Further study indicated that the number of total archaea (dominated by Methanosarcina) in a high-solid anaerobic fermentation reactor was also higher than that in a low-solid reactor, resulting in higher VFA consumption and methane production. Hence, the increased key bacteria and methanogenic archaea involved in sewage sludge hydrolysis, acidification, and methanogenesis resulted in the better performance of high-solid anaerobic sewage sludge fermentation.

• Korean Chemical Engineering Research
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• v.48 no.1
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• pp.103-109
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• 2010

Anaerobic digestion has been widely used for the treatment of sludge, which is generated from the municipal and industrial wastewater treatment, for its volume reduction and methane production. Many researches on sludge pre-treatment have been carried out in order to enhance the performance of anaerobic digestion by increasing the hydrolysis of sludge which is the rate limiting step of anaerobic digestion. In this study, the effect of pre-treatment on sludge hydrolysis(solubilization), methane production and sludge reduction by anaerobic digestion after thermal, ultrasonic, and thermal-alkali sludge treatment were compared. Thermal-alkali treatment showed 67 and 70% solubilization with municipal and industrial wastewater sludge, respectively, while ultrasonic treatment and thermal treatment gave similar solubilization efficiency of 40% or more. Methane content of the anaerobic digestion gas reached 45~70% and pretreated sludge gave higher methane content than the control sludge. Methane production of thermal, ultrasonic, and thermal-alkali pre-treatment gave 2.6, 2.7, 3.5 times of municipal control sludge and 3.5, 4.1, 4.2 times of industrial control sludge, respectively. Sludge reduction of pre-treated sludge after anaerobic digestion gave 5~19% point higher than that of control sludge, and thermal-alkali treatment showed higher reduction efficiency than thermal and ultrasonic treatment. The results proved that pre-treatment contributed significantly not only for the methane production but also for the cost reduction of sludge treatment and disposal, and thermal-alkali treatment gave the best performance for the sludge treatment.

• Journal of Korea Society of Waste Management
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• v.35 no.8
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• pp.731-743
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• 2018

This study was performed to test the feasibility of thermophilic ($55^{\circ}$) co-digestion of municipal sewage sludge and food wastes. The management variables of co-digestion were the mixed ratios of municipal sewage sludge and food waste hydraulic retention times (HRTs). During the operation of thermophilic co-digestion, the reactor pH ranged from 7.0 to 7.5 and the reactor alkalinity remained above 3,200 to 4,000 mg/L as $CaCO_3$. The volatile fatty acids concentration increased as the HRT shortened from 20 days to 10 days and the mixture ratio increased to 1:4, but did not reach toxic levels for co-digestion of sewage sludge and food wastes. Methane productivity increased gradually as the organic loading rate increased. Maximum methane productivity reached 1.03v/v-d at an HRT of 10 days and at the mixture ratio of 1:4. The TVS removal efficiency decreased from 70.6% to 58.3% as the HRT shortened from 20 days to 10 days. TVS removal efficiency ranged from 57.0% to 77% during the entire operation. It is likely that thermophilic co-digestion of sewage sludge and food wastes is a very effective method both to environmentally treat food waste and to economically produce gas for energy.

• Journal of Environmental Health Sciences
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• v.30 no.3
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• pp.253-258
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• 2004

Synthetic organic polyelectrolytes can be used to condition sludges to enhance their dewaterability. Intermittent aerobic digestion is an useful digestion technology and has many advantages like neutral pH, low installation cost and easiness to operation. The objectives of this study were to investigate the dewaterability of intemittent aerobic digestion sludge and to find the relationship between dewaterability and particle size distribution change under the conditioning of intermittent aerobic digestion sludge by cationic polyelectrolyte. Digested sludge from intermittent aerobic digestion was used and cationic polyacrylamide polymer was added as a conditioner. CST(capillary suction time), TTF(time-to-filtration) were tested as a dewaterability index and the number of particle distribution was analyzed using particle size analyzer. The results indicate that cationic polyelectrolytes is useful to enhance dewaterability of intermittent aerobic digestion sludge. Mean particle diameter was increased as polymer dosage increased and its value was reached up to 100 mm on the condition of optimal cationic polymer dosage. CST and TTF are well correlated with mean particle diameter when the weighting order is 1.7. By the optimal conditioning with cationic polymer, particles in the filtrate are also reduced significantly and this means that conditioning is helpful to main stream by reducing SS loading from return flow.

• Journal of Environmental Science International
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• v.23 no.6
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• pp.1061-1066
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• 2014

This study has cross checked the change of internal sludge-recycle in Anaerobic-Digestion, and researched about not only the improvement of Bio-gas production from the digested sludge but also the efficient method of sludge minimization. Ultimate object of the study is to reduce the amount of sludge by the improved efficiency of contact with the organic-matter and the microbes in Anaerobic-Digestion. The sludge-recycle fluidized sludge layer and raised the activity of the sludge, the optimal sludge-recycle ratio, VS and COD removal ratio were 1,000%, 28.2% and 27.7%, respectively. Through these results of this study, it may be of use to treat waste sludge by the sludge-recycle ratio in terms of minimization and circulation of resources.

• 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.