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Netherlands

E-proceedings of the 36th IAHR World Congress 28 June – 3 July, 2015, The Hague, the

EFFECTS OF TRIANGULAR MULTI-ORIFICE PLATES WITH VENTURI TUBE ON DEGRADATION OF HYDROPHILIC AND HYDROPHOBIC MIXING POLLUTANTS

(1) (2)

ZHIYONG DONG (1) & ZHEN ZHANG (2)

e-mail:

e-mail: zhejiangzhangzhen@126.com

, Hangzhou, China, , Hangzhou, China,

Hydraulic and Municipal Research Institute at

Zhejiang University of Technology

dongzy@zjut.edu.cn

ABSTRACT

Hydraulic and Municipal Research Institute at

Zhejiang University of Technology

Hydrodynamic cavitation is a novel technique that has been found to be substantially application in wastewater treatment, especially in degradation of refractory pollutants. Cavitation means phenomena of formation, growth and collapse of cavitatin bubbles. Microjets and shock waves due to collapse of cavitation bubbles can release high intensity energy, which generate strong oxidation conditions of chemical process such as hydroxyl radical (OH*) and hydrogen peroxide (H2O2). This paper experimentally studied effects of the hydrodynamic cavitation due to triangular multi-orifice plates with Venturi tube on degradation of hydrophilic and hydrophobic mixing pollutants. The different combinations of triangular multi-orifice plates with Venturi tube to generate hydrodynamic cavitation were carried out. A mixture of p- nitrophenol (PNP) and nitrobenzene was prepared for hydrophilic and hydrophobic mixing wastewater in the hydrodynamic cavitation reactor, and the degradation rates due to the hydrodynamic cavitation were analyzed by an ultraviolet spectrophotometer. Effects of different flow velocities, cavitation numbers, orifice numbers, orifice sizes, initial wastewater concentrations and wastewater circulation cycles (treatment time) through the cavitation reactor on degradation of the hydrophilic and hydrophobic mixture were experimentally investigated. The experimental results showed that the higher initial flow velocity is, the greater the rate of degradation reaches, and as the reaction progresses, effect of the initial velocity on the degradation rate is more apparent; with the increase in the circulation cycle, cavitation number of the mixture increases, reaching a certain cycle, the degradation rate tends to be stable; degradation rate is affected by the initial concentration, exhibiting a variation in increase first and then decrease, and an optimal initial concentration corresponding to the maximum degradation rate exists; under the condition of the same orifice size, the more orifice number is, the greater the degradation rate reaches; and at the same orifice number, the larger orifice size results in higher turbulence intensity and shear stress, thus causing more intense cavitation and greater degradation rate.

Keywords: hydrodynamic cavitation; triangular multi-orifice plates; Venturi tube; hydrophilic and hydrophobic mixing pollutants 1. INTRODUCTION

With the development of human civilization, the speeding up of urbanization and industrialization, the issues of water pollution and water shortage have become more and more serious, which has posed more and more severe threats to human survival and social development. Therefore, the use of advanced wastewater treatment technology to improve water environment and protect water resources is particularly important. Hydrodynamic cavitation technology, as a new wastewater treatment method, not only can effectively degrade complex organic compounds and biological refractory material, but also has simple operation, easy to implement and no secondary pollution etc. Hydrodynamic cavitation occurs when liquid undergoes a dynamic pressure reduction due to constriction devices like the Venturi tube, multi- orifice plate etc., which means that phenomena of formation, growth and collapse of cavitatin bubbles. Microjets and shock waves due to collapses of cavitation bubbles can release high intensity energy, which generate strong oxidation conditions of chemical process such as hydroxyl radical (OH*), hydrogen peroxide (H2O2). Under the extreme conditions, these powerful oxidants react with refractory organic pollutants, which can decompose organic lmacromolecules into inorganic small molecules.

Brown and Goodman (1965) early described liquid cavitation generated by ultrasonic wave, and high efficiency oxidant-- -hydroxyl radical produced by formation, growth and collapse due to cavitation bubbles, so that activated chemical reaction in liquid. Suslick (1989) gave ultrasonic cavitation activated reaction in water through action of sonochemistry, which generated high-effective strong oxidation free radicals, and the hydroxyl radical OH* is an extremely powerful oxidant and also the best initiating agent of chain reaction. Pandit and Joshi (1993) experimentally investigated fat hydrolysis by use of hydrodynamic cavitation early. Many researchers have utilized hydrodynamic cavitation to degrade

wastewater, and made a certain progress, but the hydrodynamic cavitation reactors did not reach the good effects. They have had to unite with the other advanced oxidation process (AOP), for example, Fenton oxidation, ferric ion catalysis and photocatalysis etc., to increase the treatment effect of hydrodynamic cavitation reactor (Chakinala, Gogate and

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