Yazar "Ayyildiz, Onder" seçeneğine göre listele

Listeleniyor 1 - 10 / 10
  • [ X ]
    Öğe
    Activation of zinc particles with 3-(N-morpholino)propanesulfonic acid buffer and ultrasound for nitrite reduction
    (Desalination Publ, 2023) Bute, Duygu Nur; Ayyildiz, Onder
    Zinc (Zn0) is a potent zero-valent metal (ZVM) capable of promoting both oxidation and reduction reactions in water. Similar to other ZVMs, Zn0's reactivity is rapidly retarded in water. This study aims to improve the activation of zinc particles (Zn0) by ultrasound in aqueous solutions buffered with 3-(N-morpholino)propanesulfonic acid (MOPS). Nitrite (NO2-) was chosen as a model compound to evaluate the effectiveness of ultrasonic zinc-MOPS treatment (US/Zn0/MOPS). Under similar experimental conditions, the maximum percent nitrite removal by Zn0 (8 g/L) in MOPS buffered solutions was around 45%, but it increased above 99% when ultrasound was introduced at 220.5 W. Results obtained from scanning electron microscopy-energy-dispersive X-ray spectroscopy and X-ray diffraction measurements have suggested that during US/Zn0/MOPS treatment, nitrite was reduced to nitrogen gas (N2) while Zn0 was oxidized to Zn2+ and/or Zn(OH)2. The results also indicated that the high nitrite reduction achieved by the combined method was due to a joint effect of both catalysts on zinc activation.
  • [ X ]
    Öğe
    DENITRIFICATION OF NITRATE BY COMBINED ULTRASOUND AND ZERO VALENT MAGNESIUM AT pH CONTROLLED CONDITIONS
    (Yildiz Technical Univ, 2015) Ileri, Burcu; Apaydin, Omer; Ayyildiz, Onder
    In this study, ultrasound (US), zero-valent magnesium (Mg-0) and their simultaneous combination were tested at different Mg-0 doses (0.5, 1, 1.5, 2 ve 2.5 g/L), pH values (2, 4, 7 ve 9) and ultrasonic powers (30, 60 ve 90 W) for nitrate reduction. Ultrasound alone was found to be ineffective for nitrate removal at different pH values. Effect of ultrasonic power for pH controlled operation, nitrate reduction was increased with increasing dose of magnesium powder. Ultrasound induced profound effects on denitrification capacity of magnesium particles. For example, with controlling pH at 4, 95% of initial nitrate was reduced by 2.5 g/L of magnesium powder within 60 min, while keeping the applying combined US/Mg-0 for 30, 60, and 90 W ultrasonic powers at the same dose, required durations to achieve at the same nitrate removal efficiencies were determined to be approximately 30, 20 and 20 min, respectively. When pH was controlled at 7 and 9, up to 70% of nitrate was removed by 2.5 g Mg-0/L dose after 60 min, but in the same conditions with 90 W ultrasonic power a complete nitrate reduction was attained only within 30 min. Effect of ultrasonic on magnesium surface activation and nitrate removal was arised more clearly at alkaline conditions, when particle surface passivation was increased at increased pH. Nitrogen gas (N-2), nitrite (NO2-) and ammonium/ammonia (NH4+/NH3) were detected as the major denitrification by-products following US/Mg-0 treatment. As more ultrasonic power and magnesium dose were applied, the rate of conversion of nitrate to nitrogen gas increased significantly.
  • [ X ]
    Öğe
    Effect of ultrasonic pretreatment on chlorine dioxide disinfection efficiency
    (Elsevier, 2011) Ayyildiz, Onder; Sanik, Serdar; Ileri, Burcu
    Ultrasound (US) and chlorine dioxide (ClO2) were combined sequentially in an aim to improve wastewater disinfection. Results demonstrated that the combined effect of US and ClO2 on Escherichio coli (E. coli) and total coliform (TC) inactivation in raw wastewater was synergistic involving high removal of bacteria from the solution. A sequential combination of US (150 or 300 W/L) and ClO2 (2 mg/L) provided about 3.2-3.5 log reduction in the number E. coli and TC in raw wastewater, while the sum of log reductions by the individual treatments were 1.4-1.9. However, the measured inactivation rate with the combination of ultrasound and ClO2 in synthetic wastewater or secondary effluent was the same as the sum of the log inactivations with individual treatments. The enhancement attained by combined US and ClO2 disinfection methods was attributed to the presence of high concentration of particles in raw wastewater and their break up under shock sound waves. (C) 2010 Elsevier B.V. All rights reserved.
  • [ X ]
    Öğe
    Flow injection analysis of sulphide based on its photoelectrocatalytic oxidation at poly-methylene blue modified glassy carbon electrode
    (Pergamon-Elsevier Science Ltd, 2012) Dilgin, Yusuf; Canarslan, Seda; Ayyildiz, Onder; Ertek, Bensu; Nisli, Gurel
    A new approach for photoelectrocatalytic determination of sulphide in a flow injection analysis (FIA) system was studied using a poly-methylene blue modified glassy carbon electrode (poly-MB/GCE). Results from electrochemical measurements have revealed that poly-MB/GCE is capable of signalling electrocatalytic and photoelectrocatalytic activity towards sulphide oxidation. When the surface of poly-MB/GCE was irradiated with a light source (250W Halogen lamp), the electrocatalytic current increased substantially. A homemade flow electrochemical cell with a suitable transparent window for the irradiation of the electrode surface was used to perform the photoelectrocatalytic determination of sulphide in FIA system. The currents obtained from the photoamperometric measurements in the FIA system at optimum conditions (carrier solution: pH 9.0 Britton Robinson buffer solution containing 0.1 M KCl; flow rate: 1.3 mL min(-1); transmission tubing length: 10 cm; injection volume: 100 mu L; and constant applied potential: +150 mV vs. Ag/AgCl/KClcat) were linearly correlated with the sulphide concentration. The calibration curves were obtained for sulphide concentrations in a range of 0.5-500 mu M. The detection limits were found to be 0.27 and 0.15 mu M for amperometric and photoamperometric methods, respectively. The proposed method was successfully applied to different wastewaters such as municipal sewage or tannery wastewater. Finally, results from the sulphide measurements by poly-MB/GCE were in good agreement with those attained using spectrophotometric method. Clown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
  • [ X ]
    Öğe
    Impacts of water organic load on chlorine dioxide disinfection efficacy
    (Elsevier, 2009) Ayyildiz, Onder; Ileri, Burcu; Sanik, Serdar
    This study has examined the bactericidal effect of chlorine dioxide in untreated artificial and domestic wastewaters and secondary effluent of various organic loads. Results indicated that the inactivation of Escherichia coli in artificial wastewater was similar with that in real municipal wastewater. Among three waters, the bactericidal effect of chlorine dioxide was lowest in secondary effluent. The bacteria log inactivation increased by up to threefold when the COD concentration of raw wastewater was decreased by half. An unfavorable COD effect was also observed for the disinfection of secondary effluent. To explain the COD effect on bacteria inactivation, chlorine dioxide residuals were measured with time through each disinfection process. Results from statistical analyses have revealed that, in comparison to the correlations using CT values, the inactivation data can be better correlated with the ratio of COD to ClO2 concentrations. The results of this study would be a useful guide for many municipalities and communities in determining chlorine dioxide dosages for water and wastewater disinfection systems. (C) 2009 Elsevier B.V. All rights reserved.
  • [ X ]
    Öğe
    Microbial Quality in Coastal Waters of Dardanelles in Relation to the Pollution Sources and Transport Pathways
    (Wiley, 2012) Turkmen, Cafer; Ayyildiz, Onder; Akbulut, Mehmet; Kaya, Hasan
    The coastal water quality of Canakkale Dardanelles (Turkey) was assessed based on bacteriological data and physicalchemical parameters. Total coliform (TC), fecal coliform (FC), and enterococci (ENT) bacteria along with physicochemical parameters were measured monthly up to a year at 12 different sampling sites located through both coastal lines of the strait. The fecal bacteria were abounded at several sampling sites such as B1, B3, G3, and G4 due to direct wastewater discharges and septic leakages or overloading. Storm water runoff and sediment resuspension were important pathways for the transport of coliform and ENT bacteria to the Dardanelles, as the region receives high precipitation and strong winds for most part of the year. The values of pH, temperature, and salinity were in typical ranges for the studied area. The microbiological and physicochemical data were correlated individually and in combination. The best fit correlations for bacterial data were attained between TC and FC or TC and ENT (R?=?0.67 or -0.68), while those for the combined data were obtained for TC with temperature (R?=?0.94) and TC with salinity (R?=?-?0.70).
  • [ X ]
    Öğe
    Sonocatalytic Reduction of Hexavalent Chromium by Metallic Magnesium Particles
    (Springer International Publishing Ag, 2016) Ayyildiz, Onder; Acar, Ekrem; Ileri, Burcu
    The chemical reduction of hexavalent chromium (Cr(VI)) by combined zerovalent magnesium (ZVMg) and ultrasound (US) was studied under batch conditions. Results have demonstrated that the reduction of Cr(VI) mediated by ZVMg enhanced significantly with the ultrasonic effect. The percent reduction of Cr(VI) by ZVMg (5 g/L) was about 20 % after 60 min, but its complete reduction was attained within an hour when ultrasound was applied at a power of 100 W. The efficiency of Cr(VI) reduction increased with increasing ultrasonic power and magnesium dose. The synergy of the combined treatment has been attributed to the surface activation of ultrasonic treatment. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), atomic absorption spectrophotometer (AAS), pH, and X-ray diffraction (XRD) analyses have revealed that magnesium and chromium hydroxides and hydroxide ion were three major by-products during the reduction of Cr(VI) by US/ZVMg under pH-uncontrolled conditions. The proposed method does not require acid and buffer addition and has an advantage of removing Cr(VI) and its by-product (Cr(III)) simultaneously.
  • [ X ]
    Öğe
    Sonolytic degradation of halogenated organic compounds in groundwater: Mass transfer effects
    (Elsevier, 2007) Ayyildiz, Onder; Peters, Robert W.; Anderson, Paul R.
    Organic pollutants in liquid exposed to acoustic waves behave differently according to their physical and chemical properties. Laboratory batch experiments of sonication for the degradation of trichloroethylene (TCE) and ethylene dibromide (EDB) were carried out in groundwater at 20 kHz, and 12.5 and 35 W/cm(2). A theoretical model for the batch sonication system was derived to examine the mass transfer dependency of the ultrasonic degradation. Experimental results were supported with model predictions suggesting that both liquid phase diffusion coefficient and Henry's law constant are important parameters for the sonolytic degradation of the halogenated organic compounds in groundwater. When compared with the effect of the diffusion coefficient, Henry's constant exerts a greater influence on sonolytic degradation. When Henry's constant exceeds a value of I (volume/volume ratio), however, it no longer has much influence on the degradation process. The results also suggest that degradation is enhanced with an increase in ultrasonic power probably due to a greater bubble residence time and the formation of larger bubble at high-energy intensities. (C) 2006 Elsevier B.V. All rights reserved.
  • [ X ]
    Öğe
    Ultrasound-assisted activation of zero-valent magnesium for nitrate denitrification: Identification of reaction by-products and pathways
    (Elsevier Science Bv, 2015) Ileri, Burcu; Ayyildiz, Onder; Apaydin, Omer
    Zero-valent magnesium (Mg-0) was activated by ultrasound (US) in an aim to promote its potential use in water treatment without pH control. In this context, nitrate reduction was studied at batch conditions using various doses of magnesium powder and ultrasound power. While neither ultrasound nor zero-valent magnesium alone was effective for reducing nitrate in water, their combination removed up to 90% of 50 mg/L NO3-N within 60 min. The rate of nitrate reduction by US/Mg-0 enhanced with increasing ultrasonic power and magnesium dose. Nitrogen gas (N-2) and nitrite (NO2-) were detected as the major reduction by-products, while magnesium hydroxide Mg(OH)(2) and hydroxide ions (OH-) were identified as the main oxidation products. The results from SEM-EDS measurements revealed that the surface oxide level decreased significantly when the samples of Mg particles were exposed to ultrasonic treatment. The surface passivation of magnesium particles was successfully minimized by mechanical forces of ultrasound, which in turn paved the way to sustain the catalyst activity toward nitrate reduction. (C) 2015 Elsevier B.V. All rights reserved.
  • [ X ]
    Öğe
    Urban groundwater pollution in Turkey - A national review of urban groundwater quality issues
    (Springer, 2006) Baba, Alper; Ayyildiz, Onder
    Groundwater pollution in Turkey is examined. Important natural sources of groundwater pollution identified include seawater intrusion, discharges from contaminated lakes and streams, geothermal waters, and dissolution of minerals. The major sources of anthropogenic groundwater contamination identified are: agricultural pesticides and fertilizers; mining waste products; industrial waste; on-site septic tank systems; and pollution from poorly constructed wells. Although industrial waste and on-site septic tanks are important sources of anthropogenic pollution, because agricultural activities are very significant contributors to the Turkish economy, pollution from pesticides and fertilizers poses the larger threat.