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    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.
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    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.