• Journal of Korean Society of Water and Wastewater
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• v.20 no.3
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• pp.451-460
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• 2006

While sludge settles down in a batch column, sludge concentration becomes high. Sludge concentration change is one of the most critical causes of the sludge settling velocity variation. Therefore, sludge concentration change causes sludge index to change. SVI is more sensitive than other sludge indexes to the change of sludge concentration. And if sludge-water interface has reached final height within 30minutes, SVI is not suitable for prediction of sludge settling characteristic, Therefore, SVIs of each sludge are, in some cases, different although each sludge has the same settling velocity. But SVI has been widely used to interpret sludge settling characteristic by a simple testing method. This work has two purposes. The first purpose is to predict sludge settling velocity by using sludge-water interface settling velocity. And the second purpose is to develop new sludge settling characteristic index to exactly interpret sludge settling characteristic by overcoming the limit of SVI.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.1
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• pp.156-163
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• 2006

While sludge is settling in batch column, sludge concentration becomes high. Because the characteristic of sludge settling changes in function of time due to the sludge concentration change, the sludge settling velocity changes too. Also, because the sludge settling characteristic is influenced by a physical characteristic of sludge and a column height etc, it is difficult to exactly measure the sludge settling characteristic. Although the sludge volume indexes, SVI, SSVI and $SSVI_{3.5}$, are used to predict sludge settling characteristic, these indexes are not reliable values. Because the previously established models for sludge settling velocity predict the sludge settling velocity only, it is difficult to predict sluge-water interface height by using those models. The purpose of this experiment is to establish the empirical model which predicts the sludge interface height change with respect to the sludge physical characteristic and the settling condition.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.1
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• pp.147-155
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• 2006

For the further study of the solids flux theory, several researchers have proposed models to predict sludge settling velocity for each different concentration by using sludge indexes, SVI, SSVI and $SSVI_{3.5}$. It is difficult to apply the above models to predict sludge-water interface height in a batch column because sludge settling velocity changes while sludge settle down. While sludge settle down in a batch column, sludge concentration becomes high. The sludge concentration change is one of the most critical causes of the change of sludge settling velocity. Also, sludge concentration change causes of sludge index to change. SVI is more sensitive than SSVI or $SSVI_{3.5}$ to the change of sludge concentration. Each sludge has physical characteristics of its own which makes the settling velocity for each sludge different. The purpose of this study is to establish the correction factors that are able to compensate the errors derived from each different sludge settling characteristic by using sludge indexes, therefore the correction factors are applicable to the model for the change of sludge-water interface height.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.6
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• pp.857-865
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• 2006

The submerged barrier, employed in a reactor, divided a reactor into sludge settling zone and mixing zone according to flow type. In spite of mixing in the mixing zone, the lower part of sludge settling zone than the top of barrier was in a steady flow due to the barrier, which prevented the turbulent flow, produced from the mixing zone, from being diffused into the sludge settling zone. Therefore, the sludges in the mixing zone flowed backward over the barrier into the upper part of the sludge settling zone by turbulent flow and settled down in the sludge settling zone by the force of gravity. When barrier/water level ratio was 0.5, most sludges almost did not settle down in tile sludge settling zone because the sludges were directly affected by the turbulent flow, generated from mixer in the mixing zone. At 0.63 of barrier/water level ratio, sludge in the middle part of sludge settling zone rocked from side to side weakly. And sludge in the lower part became piled up on the bottom over this ratio. After 10minutes of sludge settling, the lower part of sludge settling zone was over 5000mg/L of sludge concentration although intial sludge concentration was 2300mg/L. By using the submerged barrier and the flow types, it could transfer sludge from this to that.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.3
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• pp.443-450
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• 2006

For understanding sludge concentration profile as a function of time, sludge was sampled at each sampling port. When sludge concentration was 3g/L, the vertical sludge concentration distribution was similar to that of 2g/L of sludge concentration. During the early stage of sludge settling, sludge concentration increased remarkably as the sludge interface height in batch column became lower. The higher sludge concentration became, the worse sludge setteability became. Also, the type of sludge settling was influenced with sludge concentration gradient in batch column. In the same concentration, the greater sludge concentration gradient was, the faster sludge interface settled down. And the changing sludge concentrations in a batch settling or a continuous settling were simulated by using the equation of sludge interface height change model.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.2
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• pp.265-272
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• 2006

While sludge settles down in a column, sludge settling characteristic is influenced by effect parameters, interparticle force, wall effect etc. As the height of a column changes, the settling velocity of sludge-water interface changes, too. At lower sludge concentration, particular effect was not observed by the difference of column height, however it was observed that settleability of sludge was greatly influenced by column height when sludge settling was poor or sludge concentration was high. It is therefore required to consider the effect of column height when the power model for sludge interface settling is established. In the tests, there was hardly any $SVI_{ts}$(SVI after "t" minutes) difference in each column after 10min at $1.5kg/m^3$ of sludge concentration. When sludge concentration was at $2.5kg/m^3$, $SVI_{ts}$ tended to be constant after 20min. At $3.5kg/m^3$, $SVI_{ts}$ increased to 30minuets. The purpose of this work is to establish the correction factor that is able to compensate the errors derived from each different height of column.

• 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 Korean Society on Water Environment
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• v.25 no.6
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• pp.964-971
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• 2009

In this paper, activated sludge settling was characterized based on field trip and zone settling tests. Plants used for this study include 5 conventional activated sludge processes and 3 A2O type treatment processes. The treatment capacities are in the range from 12,000 to $250,000m^3$/day. Total number of zone settling tests were 188 set and SVI values representing settling characteristics were from 100 to 300 mL/g. It was found out that zone settling velocity of these examined plant sludges can be approximated by mean values calculated by Keinath and Daigger/Roper models. Based on these three models, solid flux analysis were carried out in order to compare design criteria ($3.96{\sim}6.04kg/m^2-hr$) recommended by Korea Sewage Facility Design Guideline with two models used in USA. The results show that design criteria are only applicable for normal condition in settling characteristics (below SVI 100 mL/g). Solid flux analysis of surveyed plants indicates that most of the plants are operated underload conditions except several plants experiencing poor sludge settling problem. Most of the plants are operated under high sludge blanket depths (SBD).

• Journal of Korean Society of Water and Wastewater
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• v.22 no.6
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• pp.627-632
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• 2008

It is necessary to investigate methods for improvement by diagnosing sludge settling characteristics on inflow of slurry to thickener. The results of the settling tests are correlated to determine zone settling velocities at the various sludge solids concentrations. Conditioning of WTP residuals is generally done by either chemical or physical treatment. The settling test was conducted with 1m columns dosing polymer to WTP residuals at various solids concentration. The estimated results for dosing to WTP residuals for a sludge of 2,100 ~ 16,012 mg/L solids concentration were the zone settling velocities of 48.38 ~ 6.8 m/day, supernatant solid concentration of 3.2 ~ 19 mg/L and solid flux of $101.6{\sim}317.61kg/m^3{\cdot}day$. The values for non-polymer treatment were the zone settling velocities of 28.37 ~ 0.12 m/day, supernatent solid concentration of 8.5 ~ 108 mg/L and solid flux of $59.58{\sim}1.92kg/m^2{\cdot}day$. The limiting solid flux value by Yoshioka methods was $4.0kg\;TS/m^3{\cdot}day$ for Non-polymer and $228.0kg\;TS/m^3{\cdot}day$ for dosing polymer. These results are to indicate a possibility of improvement on the thickening characteristics and the quality of supernatant as increasing the settling velocities by dosing polymer to WTP residuals.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.1
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• pp.151-159
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• 2006

In these days, the importance of sludge treatment is emerging due to the London Convention, so this study was conducted to propose the alternatives for the improved sludge treatment on the organic wastewater and sewage sludge with JAR test and settling column equipped with stirrer. The minimum coagulant dosage to earn the optimum sludge settling efficiency resulted from 200mg/l and each critical sludge settling interface showed no distinct difference when PAC was dosed over 200mg/l. Accordingly, Clarification Rate(CR) with 200mg/l dosage was calculated to CR=(Ho-Ht) / Ho=1-0.4=0.6 because the critical sludge settling height stopped at 0.4. The settling velocity of sludge interface was decreased with the increase of MLSS concentration but rather increased with MLSS concentration over 1,000mg/l. This resulted from positive effect of interacted coagulation for floc formation by transfer to the zone of compressed settling when MLSS concentration increased over 1,000mg/l. The settling velocity of sludge interface showed $28.66{\times}10^{-3}/min$ for average settling velocity of sewage sludge which is 6.7 times higher than $4.25{\times}10^{-3}/min$ for average settling velocity of organic wastewater sludge. The increasing rate of CR for organic wastewater activated sludge was higher than that of settling velocity under 200mg/l of PAC dosage but settling velocity was higher than CR over 200mg/l of PAC dosage. However, in case of sewage sludge, the differential rate of CR was low when PAC dosage was increased but the settling velocity was suddenly increased with over 200mg/l dosage. Therefore coagulation effect was more efficient to MLSS settling velocity rather than SS removal effect in the supernatant.