Vedat Uyak

Pamukkale University, Denisli, Denizli, Turkey

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Publications (14)31.2 Total impact

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    ABSTRACT: The objective of this study was to investigate powdered activated carbon (PAC) contribution to natural organic matter (NOM) removal by a submerged MF and UF hybrid systems. It was found that filtration of surface waters by a bare MF and UF membranes removed negligible TOC; by contrast, significant amounts of TOC were removed when daily added PAC particles were predeposited on the membrane surfaces. These results support the assumption that the membranes surface properties and PAC layer structure might have considerably influential factor on NOM removal. Moreover, it was concluded that the dominant removal mechanism of hybrid membrane system is adsorption of NOM within PAC layer rather than size exclusion of NOM by both of membrane pores. Transmembrane pressure (TMP) increases with PAC membrane systems support the view that PAC adsorption pretreatment will not prevent the development of membrane pressure; on the contrary, PAC particles themselves caused membrane fouling by blocking the entrance of pores of MF and UF membranes. Although all three source waters have similar HPI content, it appears that the PAC interaction with the entrance of membrane pores was responsible for offsetting the NOM fractional effects on membrane fouling for these source waters.
    The Scientific World Journal 01/2014; 2014:893203. · 1.73 Impact Factor
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    ABSTRACT: In this study, the changes in UV absorbance of water samples were characterized using defined differential UV spectroscopy (DUV), a novel spectroscopic technique. Chlorination experiments were conducted with water samples from Terkos Lake (TL) and Büyükçekmece Lake (BL) (Istanbul, Turkey). The maximum loss of UV absorbance for chlorinated TL and BL raw water samples was observed at a wavelength of 272 nm. Interestingly, differential absorbance at 272 nm (ΔUV272) was shown to be a good indicator of UV absorbing chromophores and the formation of trihalomethanes (THMs) resulting from chlorination. Furthermore, differential spectra of chlorinated TL waters were similar for given chlorination conditions, peaking at 272 nm. The correlations between THMs and ΔUV272 were quantified by linear equations with R (2) values >0.96. The concentration of THMs formed when natural organic matter is chlorinated increases with increasing time and pH levels. Among all THMs, CHCl3 was the dominant species forming as a result of the chlorination of TL and BL raw water samples. The highest chloroform (CHCl3), dichlorobromomethane (CHCl2Br), and dibromochloromethane (CHBr2Cl) concentration were released per unit loss of absorbance at 272 nm at pH 9 with a maximum reaction time of 168 hours and Cl2/dissolved organic carbon ratio of 3.2.
    The Scientific World Journal 01/2013; 2013:890854. · 1.73 Impact Factor
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    ABSTRACT: Arsenic occurs naturally in the ground and surface water and is not desired in the drinking water due to carcinogenic effect on human body. The common types of arsenic are arsenate (As V) and arsenite (As III). Although arsenate removal has been achieved by membranes, adsorption, ion exchange and coagulation, arsenite removal is diffi cult to decrease the concentration up to the standard level (below to 10 µg/L). In this study, nanofi ltration (NF) and adsorption techniques have been compared to remove arsenite from drinking water. In nanofi ltration study, different NF membranes and arsenite feed concentrations have been studied. Feed water was prepared synthetically and laboratory scale cross-fl ow mode fi ltration apparatus with a fl at-sheet membrane cell was used for NF experiments. In the adsorption experiments with granular iron hydroxide (GIH), all studies were performed in the free water flow and at the normal pH of tap water. It was concluded that arsenite concentration was lowered to below 10 µg/L with adsorption. These results showed that GIH adsorption can be used to remove arsenite concentration of 0.1 and 0.5 g/L from water supplies.
    Desalination and Water Treatment - DESALIN WATER TREAT. 01/2009; 9:149-154.
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    ABSTRACT: Chlorine reacts with the natural organic matter (NOM) in waters and forms disinfection by-products (DBP). Major of these by-products are trihalomethanes (THM) and haloacetic acids (HAA). They have been known to cause cancer and other toxic effects to human beings. This study determined the removal efficiencies of THM by nanofiltration (NF) techniques with NF200 and DS5 membrane. The rejection of this chlorination by-products was studied at various feed concentration by changing transmembrane pressure. Experimental results indicated that in general increasing operating pressure produces a higher flux but does not have a significant effect on THM rejection. On the other hand, increasing the feed concentration produces a little change in the overall flux and rejection capacity. NF200 membrane removed more THM than DS5 membrane. The higher removal efficiency of dibromochloromethane (DBCM) was attributed to brominating characteristics (higher molecular weight (MW) and molecular size). As a consequence, the results of this study suggest that the NF membrane process is one of the best available technologies for removing THM compounds.
    Journal of Hazardous Materials 05/2008; 152(2):789-94. · 3.93 Impact Factor
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    ABSTRACT: A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV(254)), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.
    Science of The Total Environment 03/2008; 390(2-3):417-24. · 3.26 Impact Factor
  • Vedat Uyak, Ismail Toroz
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    ABSTRACT: Recent epidemiological studies reported that brominated DBPs may be more carcinogenic than their chlorinated analogs. Thus, this research was designed to investigate the role of bromide ion in the formation and speciation of disinfection by-products (DBPs) during chlorination of Buyukcekmece Lake Water (BLW) in Istanbul. Chlorination of BLW samples was carried out at pH 7.0 with 5 and 12 mg/l chlorine dosages. For each chlorine dosage, six bromide concentrations ranging from 0.05 to 4.0mg/l were added to form a 2 x 6 experimental matrix. In general, increasing bromide concentration gradually shifted trihalomethanes (THMs) and haloacetic acids (HAAs) speciation from chlorinated species to the mixed bromochloro species during chlorination. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be estimated through the use of probability theory. It was concluded that, in both halogen substitution for THM and dihalogenated HAA formation, HOBr was found to be 20 times more reactive than HOCl.
    Journal of Hazardous Materials 11/2007; 149(2):445-51. · 3.93 Impact Factor
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    ABSTRACT: Oxidation of raw water with chlorine results in formation of trihalomethanes (THM) and haloacetic acids (HAA). Factors affecting their concentrations have been found to be organic matter type and concentration, pH, temperature, chlorine dose, contact time and bromide concentration, but the mechanisms of their formation are still under investigation. Within this scope, chlorination experiments have been conducted with water reservoirs from Terkos, Buyukcekmece and Omerli lakes, Istanbul, with different water quality regarding bromide concentration and organic matter content. The factors studied were pH, contact time, chlorine dose, and specific ultraviolet absorbance (SUVA). The determination of disinfection by-products (DBP) was carried out by gas chromatography techniques. Statistical analysis of the results was focused on the development of multiple regression models for predicting the concentrations of total THM and total HAA based on the use of pH, contact time, chlorine dose, and SUVA. The developed models provided satisfactory estimations of the concentrations of the DBP and the model regression coefficients of THM and HAA are 0.88 and 0.61, respectively. Further, the Durbin-Watson values confirm the reliability of the two models. The results indicate that under these experimental conditions which indicate the variations of pH, chlorine dosages, contact time, and SUVA values, the formation of THM and HAA in water can be described by the multiple linear regression technique.
    Science of The Total Environment 07/2007; 378(3):269-80. · 3.26 Impact Factor
  • Vedat Uyak, Ismail Toroz
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    ABSTRACT: Coagulation process can be used to control natural organic matter (NOM) during drinking water production. The effectiveness of the coagulation process appeared to depend on the pH of coagulation rather than coagulant dosages. Jar tests conducted with depressed pH levels at different coagulation conditions removed more dissolved organic carbon (DOC) than those at moderate pH levels. For low DOC waters, like Omerli Lake Water (OLW), additional treatment would be necessary to achieve enhanced removal of NOM. In this study, three different coagulation techniques were used to remove disinfection by-products (DBP) precursors from three Istanbul surface water supplies. Jar test results indicate that optimize coagulation (OC) can enhance the removal of DBP precursors, and the removal of DOC could be improved from the current average of 15% to an average of 56% at the three sites tested. At lower pH, ferric coagulants generally performed better for removal of DBP precursors than did alum.
    Journal of Hazardous Materials 04/2007; 141(1):320-8. · 3.93 Impact Factor
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    ABSTRACT: Because of concerns over the health effects of disinfection by-products (DBPs), the removal of DBPs precursors from the Terkos Lake water (TLW) of the Istanbul City by enhanced coagulation and powdered activated carbon (PAC) adsorption was investigated. The results of this study clearly indicated that the effects of coagulation and PAC adsorption on the removal of dissolved organic carbon (DOC) and DBPs precursors from TLW were complementary. Maximum DOC removal efficiency of enhanced coagulation by ferric chloride was 45%, and this type of natural organic matter (NOM) is preferentially large organic molecules with negatively charged functional groups. However, supplementing enhanced coagulation with PAC adsorption increased the removal of DOC to 76%, and PAC adsorption removed mostly low molecular weight and uncharged NOM substances. This study shows that the combination of enhanced coagulation and PAC adsorption can be more effective than enhanced coagulation alone for meeting the Turkish trihalomethanes (THM) limit of 150 μg/L.
    Desalination. 01/2007; 216:334-344.
  • Vedat Uyak, Ismail Toroz
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    ABSTRACT: Because of increasing need to balance health risks for pathogen control and disinfection by-products (DBP) formation in drinking water supplies, water utilities are forced to closely examine and optimize their disinfection practices. This research was designed to investigate the effects of independent variables of dissolved organic carbon (DOC), ferric chloride dosage, chlorine dose, and reaction time on trihalomethanes (THMs) formation in Terkos Lake Water (TLW) of Istanbul City. A statistically-based empirical model was developed for predicting THM formation during enhanced coagulation. The R (2) and F value of model were 0.762 and 460, respectively. The model was found to be statistically significant for all four variables, and model predictions appear to be most accurate for this study. A multiple linear model exhibited the best fit of data. It was observed that THM formation depended primarily on DOC removal. Model calibration, testing and validation were accomplished by using independent data set.
    Environmental Monitoring and Assessment 11/2006; 121(1-3):503-17. · 1.59 Impact Factor
  • Vedat Uyak
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    ABSTRACT: The lifetime cancer risk and the hazard index of trihalomethanes (THMs) through oral ingestion, dermal absorption, and inhalation exposure from tap water of 15 districts in Istanbul are estimated. The most dominant THM compounds are chloroform, bromodichloromethane (BDCM), and dibromochloromethane (DBCM) in Istanbul tap water. The results indicate that within three different pathways, Istanbul residents had a higher cancer risk through oral ingestion than through the other two pathways. The lifetime cancer risks of oral ingestion for total THMs was highest in Esenyurt district, while the lowest lifetime cancer risk for total THMs was in Basaksehir district. The lifetime cancer risks of chloroform, BDCM, and DBCM from tap water of all 15 districts were higher than 10(-6), the negligible risk level defined by the USEPA. Among the 15 districts, people living in Esenyurt have the highest risk of cancer due to the THM exposure through the multi-pathways, mainly because of the exposure to BDCM and DBCM. The total cancer risk analysis concluded that each year approximately 5 of the 8 million Istanbul residents could get cancer from the daily intake of tap water.
    Environment International 02/2006; 32(1):12-21. · 6.25 Impact Factor
  • V Uyak, I Toroz
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    ABSTRACT: During the chlorination of drinking water, chlorine reacts with natural organic matter (NOM) to produce disinfection by-products (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs), which are believed to be harmful to human health. Enhanced coagulation is a DBPs precursor treatment technique with the objective of removing total organic carbon (TOC) to control DBPs formation in water. Scientifically, the removal of organic matter by coagulation depends on the TOC concentration, the chemical nature of the NOM, coagulant type, coagulant dosage, and coagulation pH. Currently, water treatment plants are practicing enhanced coagulation to further increase DBPs precursor removal. The focus of this study was to investigate enhanced coagulation of Terkos Lake Water (TLW) of Istanbul City. In this study, jar test experiments were conducted on TLW source to determine the effectiveness of enhanced coagulation for removal of DBPs surrogate parameters of total organic carbon (TOC), ultraviolet absorbance (UV(254)), and THM formation potential (THMFP). Jar tests results indicated that enhanced coagulation can increase the removal of DBPs precursors. To evaluate the coagulation performances, two different coagulants, aluminum and iron salts were used at different pH values to determine optimal coagulation conditions for surrogate parameters removal quantity.
    Environmental Technology 04/2005; 26(3):261-6. · 1.61 Impact Factor
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    V Uyak, I Toroz, S Meriç
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    ABSTRACT: Because of increasing concern for both microbial control and disinfection by-products (DBPs) formation, water utilities are strictly examining and optimizing disinfection practices. In this study, modeling of trihalomethanes (THMs) formation at processed water of the Kagithane water treatment plant in Istanbul City was conducted. Data for THMs and other water quality and operational parameters were generated through a 12-month sampling program between January and December 2003. A multiple linear regression model was developed to predict THMs concentrations in processed water. Routinely measured parameters including total organic carbon (TOC), pH, temperature, and chlorine dose were used to develop the model for the prediction of THMs. Both pH (r = 0.963) and temperature (r = 0.921) were found to be the parameters of the highest statistical significance as predictors for THMs occurrence. The regression analysis resulted in a model that is directly applicable to the chlorination of raw waters. This indicated that the linear models developed could be used to estimate THMs concentration for different water quality and treatment processes with different operational conditions.
    Desalination. 01/2005; 176:91-101.
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    I. Toroz, V. Uyak
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    ABSTRACT: Seasonal variations of trihalomethane (THM) concentrations were investigated within distribution systems of the Buyukcekmece water treatment plant in Istanbul City (Turkey). The investigation was based on an intensive 30-week sampling program, undertaken during the spring, summer and fall of the year 2003. THMs and other water quality and operational parameters were monitored at points along the distribution system between the treatment plant and the system's extremity. The results showed that THM concentrations vary significantly between finished waters and water at the distribution network. When water temperature exceeds 24°C in summer, the THM levels are 1.2–1.8 times higher than finished water, while when water temperature is below 15°C in the spring and fall, the measured THM concentrations at the system's extremity were very rarely higher than 100 μg/L. Finally, THM levels were measured at sampling points representing progressively greater travel times from the plant to the extremity of the distribution system. Multiple regression analysis was also conducted in order to estimate THMs from total organic carbon, temperature, and chlorine dose parameters. The regression model resulted in a R2 value of 0.827.
    Desalination. 01/2005;

Publication Stats

158 Citations
4 Downloads
585 Views
31.20 Total Impact Points

Institutions

  • 2008–2009
    • Pamukkale University
      • Department of Environmental Engineering
      Denisli, Denizli, Turkey
  • 2005–2007
    • Istanbul Technical University
      • Department of Environmental Engineering
      İstanbul, Istanbul, Turkey
    • Università degli Studi di Salerno
      • Department of Civil Engineering (DICIV)
      Fisciano, Campania, Italy