Hydrodynamic cavitation of p-nitrophenol: A theoretical and experimental insight

This paper presents a theoretical and experimental study of cavitation as an advanced oxidation process. The degradation rate of p-nitrophenol (PNP) was experimentally investigated and used as an estimator of the sonochemical effect in hydrodynamic cavitation. The PNP initial concentration was varied in the range 0.1-1 g L-1 and the pressure in the range 0.2-0.7 MPa, with a corresponding flow rate of 3.5-6.9 L min(-1). In terms of removal rate and energy efficiency, an optimal inlet pressure value was found close to 0.4 MPa and cavitation number of 0.25. The calculated first-order kinetic constant values show the existence of an optimal configuration: k = 1.13 x 10(-2) min(-1) at 0.45 MPa with a value for the electrical energy per order E-EO = 66.7 kWh m(-3). Moreover, the kinetic data was purged from the influence of the experimental apparatus configuration, allowing for the evaluation of an intrinsic kinetic constant. The physical-chemical behavior of hydrodynamic cavitation is discussed on the basis of single bubble dynamics. The numerical simulations, at different inlet pressures, provided a good explanation of the values observed. Furthermore, a simple energy balance on cavitating bubbles, taking into account for the actual production of cavitating events, gave a further confirmation of the experimental trends. (C) 2014 Elsevier B.V. All rights reserved.