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

Abstract

Abstract 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 × 10−2 min−1 at 0.45 MPa with a value for the electrical energy per order EEO = 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.