Effect of pH on the sonochemical degradation of organic pollutants |
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Authors: | Zongsu Wei Richard Spinney Runhui Ke Zhihui Yang Ruiyang Xiao |
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Affiliation: | 1.Institute of Environmental Engineering, School of Metallurgy and Environment,Central South University,Changsha,China;2.Grand Water Research Institute-Rabin Desalination Laboratory, Wolfson Faculty of Chemical Engineering,Technion-Israel Institute of Technology,Technion City, Haifa,Israel;3.Department of Chemistry and Biochemistry,The Ohio State University,Columbus,USA;4.China National Research Institute of Food and Fermentation Industries,Beijing,China;5.Chinese National Engineering Research Center for Control and Treatment of Heavy Metal Pollution,Changsha,China |
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Abstract: | An increasing number of organic compounds are manufactured, consumed, and discarded every year. Incomplete destruction of these compounds in wastewater treatment plants leads to pollution of natural waters, posing great health and ecological concerns. Ultrasound, as an emerging advanced oxidation technology, can quickly and effectively degrade organic pollutants in waters. To improve removal efficiency of organic pollutants in an ultrasonic system, operational parameters, especially pH, have been frequently evaluated and optimized. This review show that pH-induced changes in volatility, hydrophobicity and Coulombic force between the target compound and cavitation bubbles leads to higher degradation at acidic pH for most compounds. In addition, pH also changes free radical formation and reactivity in water during sonication, thereby altering degradation kinetics of target compounds. However, the influence of pH is not always consistent for various organic pollutants covering a broad range of physicochemical properties and reactivities. A systematic investigation on the pH effect is necessary to elucidate how pH alters cavitation bubble dynamics and collapse, radical yield and reactivity, distribution of target compounds in the vicinity of cavitation bubbles, water matrices transformation, and ultimately the degradation kinetics of organic pollutants. This first systematic review provides valuable insight into the pH effects on organic pollutant sonolysis, helps to improve our mechanistic understanding of the sonochemical system, and sheds light on future application of ultrasound in water engineering. |
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