• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1285-1300
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• 2022

Turbidity, the measure of the cloudiness of water, is used as an important index for water quality management. The turbidity can vary greatly in small river systems, which affects water quality in national rivers. Therefore, the generation of high-resolution spatial information on turbidity is very important. In this study, a turbidity retrieval model using the Korea Multi-Purpose Satellite-3 and -3A (KOMPSAT-3/3A) images was developed for high-resolution turbidity mapping of Han River system based on eXtreme Gradient Boosting (XGBoost) algorithm. To this end, the top of atmosphere (TOA) spectral reflectance was calculated from a total of 24 KOMPSAT-3/3A images and 150 Landsat-8 images. The Landsat-8 TOA spectral reflectance was cross-calibrated to the KOMPSAT-3/3A bands. The turbidity measured by the National Water Quality Monitoring Network was used as a reference dataset, and as input variables, the TOA spectral reflectance at the locations of in situ turbidity measurement, the spectral indices (the normalized difference vegetation index, normalized difference water index, and normalized difference turbidity index), and the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived atmospheric products(the atmospheric optical thickness, water vapor, and ozone) were used. Furthermore, by analyzing the KOMPSAT-3/3A TOA spectral reflectance of different turbidities, a new spectral index, new normalized difference turbidity index (nNDTI), was proposed, and it was added as an input variable to the turbidity retrieval model. The XGBoost model showed excellent performance for the retrieval of turbidity with a root mean square error (RMSE) of 2.70 NTU and a normalized RMSE (NRMSE) of 14.70% compared to in situ turbidity, in which the nNDTI proposed in this study was used as the most important variable. The developed turbidity retrieval model was applied to the KOMPSAT-3/3A images to map high-resolution river turbidity, and it was possible to analyze the spatiotemporal variations of turbidity. Through this study, we could confirm that the KOMPSAT-3/3A images are very useful for retrieving high-resolution and accurate spatial information on the river turbidity.

• Analytical Science and Technology
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• v.24 no.5
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• pp.378-386
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• 2011

The goal of this study is to understand the influence of temperature on phosphorus release rate from soil into water. As the temperature increases, $PO_4$-P reaches equilibrium more quickly and the equilibrium concentration increases, and thus the $PO_4$-P concentration increases, and pH decreases. The $PO_4$-P concentration affects pH. $PO_4$-P released from turbidity is not adsorbed onto the turbidity. $PO_4$-P was independent on the turbidity and yet $PO_4$-P was steadily increasing. However, $PO_4$-P was dependent upon the turbidity concentration as the turbidity releases $PO_4$-P. The total phosphorous (T-P) and turbidity were directly linked because T-P changed with the turbidity. T-P includes the $PO_4$-P content of water and the phosphorus content of the turbidity. As the temperature decreases, density of water increases, and the precipitation of turbidity decreases, resulting in an increases in T-P concentration. As the temperature increases, the T-P concentration decreases, but the PO4-P release rate from turbidity increases. At the same time, even at different temperatures, the T-P concentrations of the samples were about the same. When the lake gets deepened, the water temperature decreases, hence, the phosphorus release rate from soil into water was decreased. This mechanism is of great interest because phosphorus is released from soil sediment into the lake water.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.4
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• pp.660-665
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• 1994

Treatment of rice-washing wastewater was considered under various pH levels and chitosan concentrations. Compared with the control test, addition of chitosan at the various concentrations did not noticeably enhanced turbidity reduction at pH 4 and 5 , but greatly enhanced at above pH 6. However, reduction of turbidity in the wastewater, irrespective of chitosan concentrations, was the greatest at pH 4 and became lower by increasing pH. Suspended solids in the wastewater were the most effectively recovered by pH adjustment of the wastewater to 4 followed by centrifugation, with over 99% reduction in turbidity . Different concentrations of suspended solids in the wastewater and various kinds of acids used for p/H adjustment did not affect turbidity reduction. Increasing storage periods of the wastewater resulted in lower reductions in turbidity.

• Journal of Environmental Science International
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• v.19 no.8
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• pp.931-940
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• 2010

The Raw water from Deer Creek (DC) reservoir and Little Cottonwood Creek (LCC) reservoir in the Utah, USA were collected for jar test experiments. This study examined the removal of arsenic and turbidity by means of coagulation and flocculation processes using of aluminum sulfate and ferric chloride as coagulants for 13 jar tests. The jar tests were performed to determine the optimal pH range, alum concentration, ferric chloride concentration and polymer concentration for arsenic and turbidity removal. The results showed that a comparison was made between alum and ferric chloride as coagulant. Removal efficiency of arsenic and turbidity for alum (16 mg/L) of up to 79.6% and 90.3% at pH 6.5 respectively were observed. Removal efficiency of arsenic and turbidity for ferric chloride (8 mg/L) of up to 59.5% at pH 8 and 90.6% at pH 8 respectively were observed. Optimum arsenic and turbidity removal for alum dosages were achieved with a 25 mg/L and 16 mg/L respectively. Optimum arsenic and turbidity removal for ferric chloride dosages were achieved with a 20 mg/Land 8 mg/L respectively. In terms of minimizing the arsenic and turbidity levels, the optimum pH ranges were 6.5 and 8for alum and ferric chloride respectively. When a dosage of 2 mg/L of potassium permanganate and 8 mg/L of ferric chloride were employed, potassium permanganate can improve arsenic removal, but not turbidity removal.

• Journal of Korean Society on Water Environment
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• v.26 no.2
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• pp.326-331
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• 2010

Montmorillonite is one of representative inorganic clay particles. As the characteristics of clay particulate matter in aqueous environment determine the efficiencies of wastewater treatment and some industrial operations, it is essential to understand its aquatic behavior in relation with turbidity. The change of electrokinetic potential of montmorillonite suspension shows that it tends to negatively increase as the pH of suspension increases. In addition, it is observed that its potential is around 0mV when the solution pH is ca. 5. The turbidity of suspension is shown to be very low when pH is lower than its isoelectric point. However, the turbidity gradually enhances according to beyond isoelectric point. These results reveal that the correlation between electrokinetic potential and turbidity for clay mineral suspension is peculiar which should be fundamentally considered for systematic treatment of wastewater.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.531-538
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• 2007

The effects of temperature, coagulants and pre-chlorination on the removal of turbidity and pathogenic protozoa by coagulation process were investigated using jar test of lab scale. In room temperature ($25^{\circ}C$), protozoa were removed over 1.0log at the proper concentration range of coagulants, and up to over 2log at the optimal concentration of coagulants. Considering the 1.5log target removal for Giardiain the processes of coagulation, sedimentation, and filtration, this results implies that the target could be satisfied. However, the removal of protozoa and turbidity was reduced, and optimal PAC concentration was narrowed in low turbidity and cold temperature ($5^{\circ}C$). These results suggest that the drop of coagulation efficiency may be occurred in winter if the conditions are not optimized. Despite the effect of water temperature, the relation of turbidity and protozoa removal appeared to be good. The various kinds of coagulants did not significantly affected for removals of turbidity and protozoa when the concentrations of $Al_2O_3$ were considered. Prechlorination did not increase or decrease the removal of turbidity and protozoa in optimum condition at room temperature, pH 7, 15mg/L of PAC concentration.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.1
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• pp.71-78
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• 2006

The removal of protozoa in the coagulation process was evaluated under the different pH and turbidity using the jar test after the addition of polyaluminium chloride (PAC) as a coagulant. Two well-known protozoa of Cryptosporidium parvum and Giardia lamblia were tested at the same time with turbidity, the critical water quality parameter of the water treatment process. Both protozoa were removed about 1log (and up to 2log) at the optimum injection of PAC. The source water turbidity and pH affected the removal of protozoa and turbidity. At neutral and alkaline pH, 1.3-1.7log removal of protozoa for low turbid water with 5NTU, and 1.6-2.3log removal for high turbid water with 30NTU were achieved. However, at acidic pH, maximum 0.8-1.0log and 1.1-1.2log were removed for low and high turbid water, respectively, at the optimum PAC injection of 15mg/L. The relation of protozoa and turbidity removals were expressed as the 1st order equation (significantly positive relation) in the most of the tested conditions. In addition, the relation of protozoan removals with residual turbidity were also expressed the 1st order equation (significantly negative relation), although the significance of the equations were reduced at acidic pH. Therefore, residual turbidity could be a good index of efficient protozoan removal in the coagulation process, probably except at the low pH condition.

• Journal of Environmental Science International
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• v.28 no.3
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• pp.291-301
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• 2019

This study was conducted to investigate the effect of salt concentration and turbidity on the inactivation of Artemia sp. by electrolysis, UV photolysis, electrolysis+UV process to treat ballast water in the presence of brackish water or muddy water caused by rainfall. The inactivation at different salt concentrations (30 g/L and 3 g/L) and turbidity levels (0, 156, 779 NTU) was compared. A decrease in salt concentration reduced RNO (OH radical generation index) degradation and TRO (Total Residual Oxidant) production, indicating that a longer electrolysis time is required to achieve a 100% inactivation rate in electrolysis process. In the UV process, the higher turbidity results in lower UV transmittance and lower inactivation efficiency of Artemia sp. Higher the turbidity resulted in lower ultraviolet transmittance in the UV process and lower inactivation efficiency of Artemia sp. A UV exposure time of over 30 seconds was required for 100% inactivation. Factors affecting inactivation efficiency of Artemia sp. in low salt concentration are in the order: electrolysis+UV > electrolysis > UV process. In the case of electrolysis+UV process, TRO is lower than the electrolysis process, but RNO is more decomposed, indicating that the OH radical has a greater effect on the inactivation effect. In low salt concentrations and high turbidity conditions, factors affecting Artemia sp. inactivation were in the order electrolysis > electrolysis+UV > UV process. When the salt concentration is low and the turbidity is high, the electrolysis process is affected by the salt concentration and the UV process is affected by turbidity. Therefore, the synergy due to the combination of the electrolysis process and the UV process was small, and the inactivation was lower than that of the single electrolysis process only affected by the salt concentration.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.6
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• pp.753-762
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• 2010

The objective of this study was to evaluate the backwashing frequency and method on the Granular Activated Carbon (GAC) in G WTP. A backwashing period was determined as 50 days and 60 days, respectively. Prior to Backwashing by head loss build, biomass concentration in effluent as constant and DO concentration was maintained more than 11.5 mg/L in GAC bed. Peak turbidity of backwashing water was 73.6~303 NTU. Mean turbidity of backwashing water at initial 9 minute of backwash operation was 50.7~82.8 NTU. After 30 minute backwashing operation, final turbidity reaches approximately 10 NTU. The frequency of backwashing and turbidity of backwashing water overtime were evaluated. At 20days of backwashing frequency, the peak turbidity was 73 NTU and 42 NTU respectively when 10% and 25% of expansion of GAC were applied. At 14 minute of backwashing time, it was observed that turbidity of 10% expansion of GAC was higher than that of 20% expansion.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.3
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• pp.359-366
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• 2007

Slow sand filtrations have been widely used for water treatment in small communities, however their capacity is often limited by high turbidity in the raw water. For this reason, several pre-treatment facilities were required for a slow sand filter. Turbidity removal from the highly turbid raw water was investigated in roughing filters as a pre-treatment process. The roughing filters followed by rapid mixing tank were operated in the form of a contact filtration. In several jar tests, the predetermined optimum aluminium sulfate (alum) doses for turbid water of 30 and 120NTU were 30 and 50mg/L, respectively. At the optimum alum dose, physically optimum parameters including G value of $220sec^{-1}$ and rapid mixing time of 3 minutes were applied to the contact filtration system. Without addition of alum, the filtrate turbidity from the roughing filters, packed respectively with different media such as sand, porous diatomite ball and gravel, was in the range of 5~30NTU at filtration velocities of 30 and 50m/day. However, the application of a contact filtration to roughing filters showed stably lower filtrate turbidity below 1.0NTU at filtration velocity of 30 m/day. Although the filtration velocity increased to 50m/day, filtrate turbidity was still below 1.0NTU in both single and double layer roughing filters. At influent turbidity of 120NTU, the filtrate turbidity was over 5 NTU in the triple layer roughing filter, which shortened the filter run time. The flocs larger than $10{\mu}m$, formed in the rapid mixing tank, were almost captured through the roughing filter bed, while the almost flocs smaller than $10{\mu}m$ remained in filtrate.